Latest / Boring Science / Whats Really at the Edge of the Universe_ _ Boring Science for Sleep

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Whats Really at the Edge of the Universe_ _ Boring Science for Sleep · Boring Science

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  Speaker 1: Hello and welcome. If you're settling in for the night
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  Speaker 1: or just taking a quiet moment to relax and unwind,
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  Speaker 1: I'm glad you've chosen to spend this time pondering some
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  Speaker 1: of the deepest mysteries of our universe. As you get comfortable,
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  Speaker 1: I invite you to share in the comments where in
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  Speaker 1: the world you're listening from and what time of day
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  Speaker 1: it is for you. It's always a joy to know
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  Speaker 1: that these words are reaching curious minds like yours all
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  Speaker 1: across the globe at all hours. If you find yourself
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  Speaker 1: enjoying this kind of calm, thoughtful exploration, I encourage you
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  Speaker 1: to subscribe. There's so much more to discover together, but
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  Speaker 1: for now, let's allow ourselves to drift to the very
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  Speaker 1: edge of the known cosmos and imagine what lies beyond.
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  Speaker 1: Out there in the vast expanse, beyond the reach of
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  Speaker 1: even our most powerful telescopes and brilliant minds, the universe continues,
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  Speaker 1: an endless frontier waiting to be explored, if only in
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  Speaker 1: our dreams and imaginations. It's a question that has captivated
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  Speaker 1: humans for as long as we've turned our eyes to
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  Speaker 1: the stars. What wonders and mysteries might we find? out
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  Speaker 1: there in the uncharted reaches of space and time. Though
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  Speaker 1: the furthest depths of the cosmos are hidden from our view,
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  Speaker 1: that hasn't stopped the curious from peering into the void
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  Speaker 1: and imagining what might be. Ancient astronomers like Ptolemy and
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  Speaker 1: Aristotle gazed up at the night sky and saw it
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  Speaker 1: as a finite sphere, with the Earth at the very centre.
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  Speaker 1: But as technology and human knowledge advanced, so too did
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  Speaker 1: our understanding of the true scale and structure of the universe.
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  Speaker 1: It was Edwin Hubble, in the early 20th century, who
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  Speaker 1: first began to grasp just how expansive the cosmos truly is.
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  Speaker 1: As he studied distant galaxies, he noticed something peculiar. The
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  Speaker 1: light coming from them was shifted toward the red end
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  Speaker 1: of the spectrum. The more distant the galaxy, the more
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  Speaker 1: extreme this redshift appeared to be. Hubble realised that this
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  Speaker 1: could only mean one thing. Those galaxies were moving away
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  Speaker 1: from us, and the further away they were, the faster
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  Speaker 1: they were receding. This revelation shook the very foundations of cosmology.
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  Speaker 1: The universe, Hubble showed, was not a static and unchanging place,
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  Speaker 1: as many had long believed. Instead, it was something dynamic
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  Speaker 1: and ever-expanding, with galaxies being carried away from each other
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  Speaker 1: by the very stretching of space itself. It was as
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  Speaker 1: if they were raisins in a loaf of rising bread dough,
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  Speaker 1: being pushed apart as the dough expanded. Hubble's groundbreaking discovery
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  Speaker 1: painted a whole new picture of the cosmos, one that
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  Speaker 1: was full of motion and change on the grandest of scales.
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  Speaker 1: As he peered deeper into space with his telescopes, he
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  Speaker 1: could see that this expansion was happening in all directions,
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  Speaker 1: everywhere he looked. The universe wasn't just vast in size,
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  Speaker 1: it was also growing larger with each passing moment. This
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  Speaker 1: brought up a profound and somewhat melancholy realisation, that as
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  Speaker 1: the universe expands, galaxies are steadily carried away from us
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  Speaker 1: by the stretching of space. And at a certain distance,
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  Speaker 1: known as the Cosmic Horizon, This expansion is happening so
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  Speaker 1: quickly that it outpaces the speed of light itself. Once
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  Speaker 1: a galaxy crosses that horizon, the very space it occupies
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  Speaker 1: is stretching away faster than its light can travel back
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  Speaker 1: to us. It means that galaxy, and all the stars
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  Speaker 1: and worlds it contains, are lost to us forever, never
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  Speaker 1: to be seen again from our cosmic vantage point. Even now,
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  Speaker 1: as you listen to these words, innumerable galaxies are slipping
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  Speaker 1: across that horizon, drawn by the relentless expansion of the universe.
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  Speaker 1: With each passing second, more and more of the cosmos
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  Speaker 1: is receding from view, carried off into realms unknown. It's
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  Speaker 1: a poignant reminder of how much of the universe has
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  Speaker 1: already passed beyond our ability to explore, fading into the
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  Speaker 1: mists of cosmic history. But though these distant reaches may
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  Speaker 1: be forever hidden from us, that doesn't stop us from
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  Speaker 1: imagining what lies beyond the boundaries of the observable universe.
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  Speaker 1: After all, the cosmos had already been expanding for eons
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  Speaker 1: before we humans ever looked up and began to wonder
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  Speaker 1: about its true extent. To really understand what the universe
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  Speaker 1: is like beyond our field of view, we need to
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  Speaker 1: rewind the clock, to journey back in time to the
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  Speaker 1: very birth of the cosmos itself. According to our best
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  Speaker 1: theories and observations, the story of our universe began some 13.8
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  Speaker 1: billion years ago, in an event we call the Big Bang.
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  Speaker 1: But despite its name, the Big Bang wasn't an explosion
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  Speaker 1: in the usual sense. with matter and energy being flung
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  Speaker 1: violently outward from a central point. Instead, it marked the
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  Speaker 1: beginning of space and time themselves, with all the matter
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  Speaker 1: and energy of the observable universe emerging from an infinitesimally small,
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  Speaker 1: incredibly dense, and unimaginably hot state. In those first few
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  Speaker 1: moments after the Big Bang, the universe was a seething
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  Speaker 1: cauldron of energy, so hot that the fundamental forces of
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  Speaker 1: nature were unified into a single, all-encompassing force. As the
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  Speaker 1: newborn cosmos expanded and cooled in the tiniest fractions of
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  Speaker 1: a second, it underwent a series of incredible transformations. Quarks
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  Speaker 1: combined to form protons and neutrons, the building blocks of
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  Speaker 1: atomic nuclei. After just a few minutes, these particles began
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  Speaker 1: to fuse together, forming the first light elements like hydrogen
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  Speaker 1: and helium, and bathing the universe in a scorching plasma.
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  Speaker 1: It would take another 380,000 years for the universe to
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  Speaker 1: cool enough for electrons to bind with atomic nuclei, forming
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  Speaker 1: stable neutral atoms. In that moment, the cosmos became transparent
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  Speaker 1: for the first time, allowing light to stream freely through space.
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  Speaker 1: That ancient light, stretched and red-shifted to microwave wavelengths by
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  Speaker 1: billions of years of cosmic expansion, is still detectable today
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  Speaker 1: as the Cosmic Microwave Background Radiation. a distant echo and
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  Speaker 1: snapshot of the infant universe. One of the first to
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  Speaker 1: grasp the true implications of this primordial radiation was a
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  Speaker 1: Belgian physicist and priest named Georges Lemaître. In the late 1920s,
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  Speaker 1: years before Hubble's revelation of the expanding universe, Lemaître proposed
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  Speaker 1: that the cosmos had originated from what he called the
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  Speaker 1: primeval atom, a single point that had contained all the
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  Speaker 1: matter of the universe before expanding to its current size.
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  Speaker 1: It was a revolutionary idea, one that upended the conventional
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  Speaker 1: wisdom of an eternal and unchanging cosmos. LeMaitre's model of
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  Speaker 1: a universe born in a distant past, expanding and evolving
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  Speaker 1: over eons, laid the groundwork for what we now know
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  Speaker 1: as Big Bang cosmology. He recognised that by running the
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  Speaker 1: clock backwards, by reversing the expansion that Hubble had observed,
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  Speaker 1: one would ultimately come to a moment of origin, a
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  Speaker 1: cosmic birth from which the entire known universe had sprung.
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  Speaker 1: it's a staggering thought to contemplate, that everything we see
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  Speaker 1: from the ground beneath our feet to the stars shining
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  Speaker 1: down from above was once compressed into a speck smaller
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  Speaker 1: than a single atom. And yet, from that humble beginning,
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  Speaker 1: a cosmos of astonishing scale and complexity has emerged, a
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  Speaker 1: universe filled with a hundred billion galaxies, each brimming with
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  Speaker 1: billions upon billions of stars, worlds, and perhaps even fellow
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  Speaker 1: wanderers peering up into the same shared sky. But even
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  Speaker 1: the observable portion of our universe, as incomprehensibly vast as
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  Speaker 1: it is, is only a small slice of a much
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  Speaker 1: larger cosmos. Most of the volume of space was likely
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  Speaker 1: pushed far beyond our view in the first instant after
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  Speaker 1: the Big Bang, driven by a process called cosmic inflation.
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  Speaker 1: This is the idea, first proposed by physicist Alan Guth
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  Speaker 1: in 1980, that the newborn universe underwent a brief but
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  Speaker 1: incredible period of exponential expansion doubling in size every tiny
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  Speaker 1: fraction of a second. During this inflationary epoch, space itself
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  Speaker 1: expanded faster than the speed of light, a cosmic growth
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  Speaker 1: spurt that took a microscopic volume and enlarged it to
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  Speaker 1: astronomical proportions. This rapid ballooning stretched out the tiny quantum
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  Speaker 1: fluctuations present in the early universe, magnifying them to cosmological
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  Speaker 1: scales and sowing the seeds of cosmic structure. Without inflation,
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  Speaker 1: It's hard to explain the incredible smoothness and flatness of
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  Speaker 1: space we observe today, or the subtle variations in density
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  Speaker 1: that would eventually give rise to galaxies, stars and planets.
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  Speaker 1: Inflation also provides a possible answer to the question of
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  Speaker 1: what lies beyond our cosmic horizon. If the theory is correct,
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  Speaker 1: the observable universe is just a small bubble in an
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  Speaker 1: enormously larger space, one that was inflated far beyond our
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  Speaker 1: view in that first fraction of a second. Most of
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  Speaker 1: the true volume of the universe, in this picture, is
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  Speaker 1: forever inaccessible to us, pushed away by the expansion of
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  Speaker 1: space itself. But the implications of inflation go even further.
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  Speaker 1: Some versions of the theory suggest that our universe is
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  Speaker 1: just one of countless bubble universes, each one sprouting from
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  Speaker 1: an eternally expanding multiverse. In this view, the process of
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  Speaker 1: inflation never truly ends. It continues forever in some regions
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  Speaker 1: of space. spinning off new bubble universes all the time.
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  Speaker 1: Each of these universes may have its own unique properties,
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  Speaker 1: its own set of physical laws and constants, born out
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  Speaker 1: of the quantum fluctuations that were stretched and frozen in
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  Speaker 1: by inflation. If this picture is correct, it means our
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  Speaker 1: universe is just one island in an unimaginably vast cosmic archipelago,
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  Speaker 1: a single bubble adrift in an eternally inflating sea. the
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  Speaker 1: true extent of reality would be far greater than what
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  Speaker 1: we see within our observable slice. A multiverse of astonishing
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  Speaker 1: scale and variety, one in which our entire cosmos is
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  Speaker 1: but a tiny fragment. It's a concept that pushes the
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  Speaker 1: boundaries of human imagination to zoom out in our mind's
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  Speaker 1: eye and try to envision this grander cosmic context. An
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  Speaker 1: eternal expanse, forever giving birth to new and diverse universes,
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  Speaker 1: each one a self-contained experiment in the possibilities of physics
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  Speaker 1: and complexity. In this view, everything we know, all the
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  Speaker 1: stars and galaxies, all the beauty and structure within our
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  Speaker 1: observable bubble, is just one tiny corner of an endlessly
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  Speaker 1: rich and varied multiverse. The idea of the multiverse remains speculative,
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  Speaker 1: a tantalising possibility that follows from our theories but has
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  Speaker 1: yet to be confirmed observationally. But it's a reminder that
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  Speaker 1: even the most basic facts of our existence, the particles
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  Speaker 1: and forces that shape our world, the constants of nature
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  Speaker 1: that allow complexity to arise, may not be the only
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  Speaker 1: ways a universe can be, that perhaps we live in
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  Speaker 1: a cosmos that is not only stranger than we imagine,
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  Speaker 1: but stranger than we can imagine from our limited vantage point.
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  Speaker 1: As we ponder these questions of what lies beyond, both
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  Speaker 1: in space and in possibility, it's hard not to feel
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  Speaker 1: a sense of awe and humility, to recognise that for
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  Speaker 1: all our knowledge and achievement, we've still only glimpsed the
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  Speaker 1: tiniest slice of a much larger and perhaps endlessly varied reality.
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  Speaker 1: And yet, that glimpse is enough to fill us with wonder,
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  Speaker 1: to ignite the spark of curiosity that has carried us
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  Speaker 1: from the first campfires to the frontiers of cosmic understanding.
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  Speaker 1: But there is another dimension to consider, beyond the spatial
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  Speaker 1: scope of the universe, and that is time, the great
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  Speaker 1: unfurling of moments that carries us from past to future.
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  Speaker 1: having explored the far reaches of space and the earliest
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  Speaker 1: eras of cosmic history, let us now turn our gaze
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  Speaker 1: in the other direction, to the unwritten chapters that await
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  Speaker 1: our universe in the eons to come. From our vantage
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  Speaker 1: point in the present, the future seems wide open, full
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  Speaker 1: of possibility and promise. But just as the expansion of
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  Speaker 1: the universe has carried galaxies beyond our view, so too
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  Speaker 1: will it continue to shape the cosmos on the grandest
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  Speaker 1: scales of space and time. As the eons unfold, gravity
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  Speaker 1: will continue to pull galaxies together into ever larger structures,
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  Speaker 1: great walls and filaments spanning billions of light-years surrounding vast
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  Speaker 1: cosmic voids. On the scale of individual galaxies, this process
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  Speaker 1: of structure formation will play out as a majestic dance
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  Speaker 1: of collision and merger. Over the next few billion years,
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  Speaker 1: our own Milky Way will be drawn into an intimate
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  Speaker 1: gravitational embrace with the neighbouring Andromeda Galaxy. The two great
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  Speaker 1: spiral arms each home to hundreds of billions of stars,
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  Speaker 1: will intertwine and distort as their mutual gravity tugs at gas,
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  Speaker 1: dust and starlight. In a process taking hundreds of millions
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  Speaker 1: of years, the galaxies will pass through each other again
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  Speaker 1: and again, their stars sliding past one another without colliding,
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  Speaker 1: until the two distinct structures merge into a single, grand,
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  Speaker 1: elliptical galaxy. It's a future that's at once breathtaking and melancholy.
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  Speaker 1: The end of our cosmic island is a separate entity,
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  Speaker 1: but the birth of something even more vast and ancient,
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  Speaker 1: a realm of starlight that will endure for countless ages.
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  Speaker 1: But even as galaxies come together under the pull of
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  Speaker 1: their own gravity, the expansion of the universe continues unabated,
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  Speaker 1: driven by the mysterious repulsive force we call dark energy.
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  Speaker 1: In a hundred billion years, give or take, this expansion
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  Speaker 1: will have carried all but the closest galaxies beyond our
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  Speaker 1: cosmic horizons. leaving our merged Milky Way Andromeda galaxy as
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  Speaker 1: an island universe in an increasingly empty sea of space.
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  Speaker 1: From that distant future vantage point, the cosmos will appear
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  Speaker 1: very different than it does today. The grand ballet of
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  Speaker 1: the galaxies, the great structures woven by gravity over billions
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  Speaker 1: of years, will have receded from view. An observer in
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  Speaker 1: that far future universe, looking out into the void, might
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  Speaker 1: see little more than our lonely merged galaxy. floating in
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  Speaker 1: a vast and seemingly unchanging expanse. And yet, even that
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  Speaker 1: island universe will not endure forever. On the scale of
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  Speaker 1: trillions of years, the last stars will flicker out one
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  Speaker 1: by one, their fuel exhausted, leaving behind only dim stellar
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  Speaker 1: embers and the slumbering remnants of once bright suns. Even
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  Speaker 1: the grand forges of creation, the great molecular clouds that
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  Speaker 1: gave birth to whole generations of stars, will be depleted
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  Speaker 1: and dispersed. In that far distant era, The universe will
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  Speaker 1: be a much darker and more diffuse place, with the
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  Speaker 1: galaxy's starlight all but extinguished. The great engines of energy
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  Speaker 1: and complexity that fill the cosmos with light and life
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  Speaker 1: for eons will have wound down, leaving only darkness in
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  Speaker 1: their wake. It's a prospect at once chilling and poetic,
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  Speaker 1: a universe fading into a long, cold night. But even
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  Speaker 1: that night will not be eternal. Over unimaginable gulfs of time,
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  Speaker 1: spanning perhaps ten to the power of one hundred years
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  Speaker 1: or more, Even the black holes that once anchored the
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  Speaker 1: hearts of galaxies will slowly evaporate, leaking their mass and
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  Speaker 1: energy back into the void through the drip, drip, drip
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  Speaker 1: of Hawking radiation. Matter itself will decay, with protons and
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  Speaker 1: neutrons dissolving into a thin gruel of lonely particles drifting
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  Speaker 1: through ever-expanding space. This is the fate that awaits our
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  Speaker 1: universe in the far distant future, according to our current understanding.
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  Speaker 1: A slow, inexorable slide into a state of maximum entropy.
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  Speaker 1: with all structure and complexity eroded by the ceaseless march
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  Speaker 1: of time. It's a cosmic story that ends not with
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  Speaker 1: a bang, but with a whimper, an inky void, growing
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  Speaker 1: ever colder and more diffuse as the eons unfold. This
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  Speaker 1: ultimate fate, sometimes called the heat death of the universe,
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  Speaker 1: has a certain poetic melancholy to it. To picture all
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  Speaker 1: the richness and grandeur of the cosmos, all the starlight
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  Speaker 1: and beauty and possibility slowly winding down into darkness and silence.
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  Speaker 1: There is a sombre inevitability to it, the knowledge that
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  Speaker 1: even a universe as vast and ancient as ours must
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  Speaker 1: someday fade away. And yet, even in that far future darkness,
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  Speaker 1: there is a strange and subtle beauty, the idea that
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  Speaker 1: the cosmos, having flowered into astonishing complexity, will settle into
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  Speaker 1: a peaceful quiescence, like a ripple fading on the surface
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  Speaker 1: of a still pond. That the story of the universe,
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  Speaker 1: grand and sprawling as it is, will someday reach a
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  Speaker 1: quiet denouement, with all its plot threads resolved into a
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  Speaker 1: tranquil equilibrium. From our vantage point, living on a pale
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  Speaker 1: blue dot orbiting a middle-aged star, that ending is almost
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  Speaker 1: unimaginably remote. The universe we inhabit is still vibrant and dynamic,
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  Speaker 1: filled with the light of countless suns and the vast
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  Speaker 1: churning structures of the cosmic web. We are fortunate to
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  Speaker 1: be here now, able to trace the grand story of
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  Speaker 1: the cosmos from its fiery birth to the majestic tapestry
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  Speaker 1: of galaxies we see today. and we are doubly fortunate
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  Speaker 1: as conscious beings to be able to contemplate that story,
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  Speaker 1: to follow the trail of evidence and inference that leads
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  Speaker 1: us back to the Big Bang and forward to the
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  Speaker 1: ultimate fate of the universe. We are, as Carl Sagan
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  Speaker 1: so beautifully put it, a way for the cosmos to
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  Speaker 1: know itself. The universe, after eons of unconscious evolution, has
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  Speaker 1: awoken to its own existence through us. That is a
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  Speaker 1: profound and humbling thought. that we, for all our flaws
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  Speaker 1: and limitations, carry the spark of cosmic self-awareness. That our
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  Speaker 1: drive to explore, to discover, to understand, is the universe
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  Speaker 1: looking back on itself with wonder. We are stardust pondering
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  Speaker 1: the stars, matter marvelling at the depths of space and
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  Speaker 1: time from which it emerged. And though much of that
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  Speaker 1: space and time may lie forever beyond our reach, hidden
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  Speaker 1: behind cosmic horizons or the veil of the far future,
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  Speaker 1: that doesn't diminish the grandeur of what we can know
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  Speaker 1: and imagine. The observable universe, the slice of space and
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  Speaker 1: time that we can explore, is a cosmos unto itself,
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  Speaker 1: filled with enough beauty and mystery to occupy our minds
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  Speaker 1: for countless generations. In the centuries since Hubble and Lemaître
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  Speaker 1: peered into the depths and caught a glimpse of our
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  Speaker 1: universe's origin and expansion, we have traced the story of
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  Speaker 1: the cosmos in astonishing detail. From the fluctuations of the
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  Speaker 1: primordial plasma to the birth of the first stars and galaxies,
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  Speaker 1: from the forging of heavy elements in stellar furnaces to
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  Speaker 1: the slow dance of worlds around newly formed suns, the
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  Speaker 1: grand arc of cosmic evolution has unfolded before our eyes.
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  Speaker 1: We have learned to read the subtle echoes of the
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  Speaker 1: Big Bang in the cosmic microwave background, seeing in its
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  Speaker 1: gentle ripples the seeds of all the structure we see today.
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  Speaker 1: We have probed the hearts of stars and the edges
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  Speaker 1: of black holes. witnessed the collision of neutron stars and
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  Speaker 1: the birth of space-time itself. And we have looked back
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  Speaker 1: to the cosmic dawn, seeing the first luminous objects flicker
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  Speaker 1: on in the aftermath of the Big Bang. Each of
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  Speaker 1: these discoveries is a testament to the power of the
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  Speaker 1: curious mind, the ability of mere matter to rise up
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  Speaker 1: and comprehend the cosmos from which it sprang. And each
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  Speaker 1: one spurs us onward, inviting us to probe further and deeper.
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  Speaker 1: As we ponder the incredible timeline of our universe, from
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  Speaker 1: its fiery birth in the Big Bang to its eventual
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  Speaker 1: descent into darkness eons from now, it's hard not to
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  Speaker 1: feel a profound sense of awe. The sheer scale of
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  Speaker 1: the cosmos in both space and time is almost incomprehensible
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  Speaker 1: to our human minds. And yet, throughout history, there have
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  Speaker 1: been visionaries who dared to study this immense universe we
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  Speaker 1: find ourselves in, to ask the deep questions and follow
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  Speaker 1: the evidence wherever it leads. One such visionary was the
• 19:18
  Speaker 1: Belgian Catholic priest and astronomer Georges Lemaitre. In the 1920s,
• 19:24
  Speaker 1: at a time when most scientists believed the universe was
• 19:26
  Speaker 1: static and eternal, Lemaître proposed a radical idea, that the
• 19:31
  Speaker 1: universe had a beginning. Digging into Albert Einstein's groundbreaking theory
• 19:36
  Speaker 1: of general relativity, Lemaître realised something astonishing, that space itself
• 19:41
  Speaker 1: could expand. If space could expand, Lemaître reasoned, then it
• 19:46
  Speaker 1: must have been smaller in the past. Winding the clock back,
• 19:50
  Speaker 1: he imagined all the matter and energy of the universe
• 19:52
  Speaker 1: compressed into an incredibly dense point, a primeval atom, as
• 19:57
  Speaker 1: he called it. This atom was highly unstable, and around 13.8
• 20:02
  Speaker 1: billion years ago, it exploded in a tremendous burst of
• 20:05
  Speaker 1: expansion that gave birth to space and time themselves. Though
• 20:10
  Speaker 1: he didn't know it at the time, Lemaitre had just
• 20:12
  Speaker 1: envisioned the Big Bang. It's amazing to think about, that
• 20:16
  Speaker 1: everything we see around us, from the ground beneath our
• 20:19
  Speaker 1: feet to the most distant galaxies, all came from an
• 20:22
  Speaker 1: infinitesimal point in the far reaches of the past. In
• 20:25
  Speaker 1: those first few moments after the Big Bang, the universe
• 20:28
  Speaker 1: was inconceivably hot and dense. As it expanded and cooled,
• 20:32
  Speaker 1: it underwent incredible transformations. In the first billionth of a second,
• 20:37
  Speaker 1: the fundamental forces of nature, gravity, electromagnetism and the strong
• 20:42
  Speaker 1: and weak nuclear forces froze out of the searing maelstrom.
• 20:46
  Speaker 1: Subatomic particles called quarks combined to form protons and neutrons.
• 20:52
  Speaker 1: After a few minutes, these particles fused to create the
• 20:54
  Speaker 1: first light elements, mostly hydrogen and helium, with a sprinkle
• 20:58
  Speaker 1: of lithium. For hundreds of thousands of years, the infant
• 21:01
  Speaker 1: universe was a sea of scorching plasma, with light and
• 21:05
  Speaker 1: matter coupled together in an opaque fog. But as space
• 21:09
  Speaker 1: continued to expand and cool, something remarkable happened. Around 380,000
• 21:14
  Speaker 1: years after the Big Bang, the universe had diluted and
• 21:17
  Speaker 1: cooled enough for electrons to join with atomic nuclei, forming
• 21:21
  Speaker 1: the first neutral atoms. Light was finally able to decouple
• 21:25
  Speaker 1: from matter and stream freely through space. This ancient light,
• 21:29
  Speaker 1: called the cosmic microwave background, still fills the universe today.
• 21:34
  Speaker 1: It's the oldest light we can see. a snapshot of
• 21:36
  Speaker 1: the universe as it was in its infancy. When it
• 21:39
  Speaker 1: first shone, the universe was a fiery 3,000 degrees Kelvin.
• 21:44
  Speaker 1: But as space expanded over eons, stretching this primordial light
• 21:47
  Speaker 1: to longer and cooler wavelengths, it faded to the faint
• 21:51
  Speaker 1: microwave glow we detect today, just 2.7 degrees above absolute zero.
• 21:56
  Speaker 1: It's humbling to realise that every photon of this ancient
• 21:59
  Speaker 1: light has been travelling for over 13 billion years to
• 22:02
  Speaker 1: reach us. In a sense, When we look at the
• 22:04
  Speaker 1: cosmic microwave background, we're seeing the ultimate baby picture of
• 22:08
  Speaker 1: the universe. It's a visual echo of the Big Bang itself,
• 22:12
  Speaker 1: and a reminder of how far the cosmos has come
• 22:15
  Speaker 1: in the eons since. But the early universe wasn't done
• 22:18
  Speaker 1: transforming yet. In fact, the period of expansion right after
• 22:21
  Speaker 1: the Big Bang may have been even more dramatic than
• 22:24
  Speaker 1: the Big Bang itself. In the 1980s, a young physicist
• 22:29
  Speaker 1: named Alan Guth proposed a remarkable idea called cosmic inflation.
• 22:33
  Speaker 1: brief burst of exponential expansion in the first fraction of
• 22:36
  Speaker 1: a second of the universe's existence. According to inflation theory,
• 22:40
  Speaker 1: in the tiniest sliver of time after the universe was born,
• 22:44
  Speaker 1: space underwent a growth spurt like no other. It doubled
• 22:47
  Speaker 1: in size every 10 to the negative 34 seconds, expanding
• 22:51
  Speaker 1: faster than the speed of light. In an eye blink,
• 22:54
  Speaker 1: the observable universe went from smaller than a proton to
• 22:57
  Speaker 1: macroscopic size. This might sound impossible, but After all, nothing
• 23:01
  Speaker 1: can move through space faster than light. But inflation wasn't
• 23:05
  Speaker 1: about moving through space. It was space itself expanding. There's
• 23:09
  Speaker 1: no speed limit on the expansion of the universe itself.
• 23:13
  Speaker 1: In fact, even today, there are distant galaxies being carried
• 23:16
  Speaker 1: away from us by the expansion of space faster than
• 23:19
  Speaker 1: the speed of light. Their light will never reach us.
• 23:22
  Speaker 1: They've crossed the cosmic horizon, the ultimate boundary between the
• 23:26
  Speaker 1: observable and unobservable universe. Inflation was so dramatic that it
• 23:30
  Speaker 1: pushed most of the universe, in fact most of reality
• 23:33
  Speaker 1: as we know it, forever beyond our view. If inflation
• 23:37
  Speaker 1: is correct, our observable universe is just a tiny island
• 23:41
  Speaker 1: in an unimaginably vast sea of space, most of it
• 23:44
  Speaker 1: permanently out of our reach. It's a bit like a
• 23:47
  Speaker 1: ship on the ocean. We can only see to the horizon,
• 23:50
  Speaker 1: but we know there's much more ocean beyond our view.
• 23:53
  Speaker 1: In the case of the universe... Inflation has pushed most
• 23:56
  Speaker 1: of that ocean far beyond the cosmic horizon. But why
• 24:00
  Speaker 1: did the universe inflate so dramatically? What drove this incredible
• 24:04
  Speaker 1: burst of expansion? That's still a mystery. But inflation does
• 24:08
  Speaker 1: seem to solve some long-standing cosmic conundrums. For example, when
• 24:12
  Speaker 1: we look out into space on the larger scales, we
• 24:15
  Speaker 1: see something remarkable. The universe is almost perfectly smooth. On average,
• 24:20
  Speaker 1: one region of the observable universe has roughly the same
• 24:23
  Speaker 1: density and composition as any other region This is quite puzzling.
• 24:27
  Speaker 1: How did these vastly distant regions, which are now out
• 24:29
  Speaker 1: of contact with each other, manage to coordinate their properties?
• 24:33
  Speaker 1: Inflation offers an answer. Before inflation, the observable universe was
• 24:38
  Speaker 1: microscopically small, allowing every region to mingle and equilibrate. As
• 24:42
  Speaker 1: inflation kicked in, and these regions were flung far apart
• 24:46
  Speaker 1: faster than light, they carried the echo of their primordial
• 24:49
  Speaker 1: connection with them. A smoothness established in the infant universe
• 24:53
  Speaker 1: became locked in, as inflation catapulted these regions beyond the
• 24:57
  Speaker 1: cosmic horizon. Inflation also explains another strange property of the universe,
• 25:02
  Speaker 1: its flatness. When we measure the geometry of space on
• 25:06
  Speaker 1: the larger scales, it appears to be perfectly flat. Parallel
• 25:09
  Speaker 1: lines remain parallel forever. They never curve together or apart.
• 25:14
  Speaker 1: But this flatness is very unstable, like a pencil balanced
• 25:17
  Speaker 1: precariously on its tip. Any deviation from perfect flatness in
• 25:21
  Speaker 1: the early universe should have grown over billions of years,
• 25:24
  Speaker 1: resulting in a highly curved universe today. But that's not
• 25:27
  Speaker 1: what we see. Space is still uncannily flat. How can
• 25:31
  Speaker 1: this be? Once again, inflation provides a solution. The rapid
• 25:36
  Speaker 1: stretching of space during inflation would have diluted any curvature,
• 25:40
  Speaker 1: flattening the universe out like pulling on a wrinkled sheet.
• 25:44
  Speaker 1: What we're left with is a cosmos that's almost perfectly
• 25:47
  Speaker 1: geometrically flat. a legacy of that early inflationary episode. Inflation
• 25:52
  Speaker 1: even planted the seeds for everything we see in the
• 25:54
  Speaker 1: universe today, from galaxies and stars to planets and people.
• 25:59
  Speaker 1: According to quantum physics, even empty space is never truly empty.
• 26:04
  Speaker 1: It's always flickering with tiny energy fluctuations, popping particles in
• 26:08
  Speaker 1: and out of existence. During inflation, these quantum ripples were
• 26:12
  Speaker 1: stretched to macroscopic scales, becoming subtle density variations spread throughout space.
• 26:17
  Speaker 1: Over eons, these primordial density variations grew under gravity, with
• 26:22
  Speaker 1: slightly denser regions attracting more and more matter. Eventually, some
• 26:26
  Speaker 1: regions reached a critical density and collapsed to form the
• 26:29
  Speaker 1: first stars and galaxies, lighting up the cosmos. In a
• 26:33
  Speaker 1: very real sense, the large-scale structure of the universe, with
• 26:37
  Speaker 1: its sprawling cosmic web of galaxies and vast voids, all
• 26:41
  Speaker 1: grew from quantum seeds stretched by inflation. It's incredible to
• 26:45
  Speaker 1: think about, that the largest structures in the universe, spanning
• 26:48
  Speaker 1: hundreds of millions of light years, all came from subatomic
• 26:51
  Speaker 1: quantum flickers, blown up by the rapid expansion of space.
• 26:55
  Speaker 1: We are, each of us, the product of these primordial
• 26:59
  Speaker 1: quantum fluctuations. Every atom in our bodies can trace its
• 27:03
  Speaker 1: history back to those first moments after the Big Bang.
• 27:06
  Speaker 1: But as mind-boggling as inflation is, it pales in comparison
• 27:10
  Speaker 1: to the idea it gave rise to, the multiverse. You see,
• 27:14
  Speaker 1: most versions of inflation theory suggest that inflation never truly ends,
• 27:18
  Speaker 1: that even as our observable universe grew from an inflating
• 27:21
  Speaker 1: patch of space, other patches were doing the same, sprouting
• 27:25
  Speaker 1: like bubbles in a sea of eternally inflating spacetime. Each
• 27:29
  Speaker 1: of these patches could become a universe in its own right,
• 27:32
  Speaker 1: with its own physical properties. Some might have more dimensions
• 27:36
  Speaker 1: than ours. Others might have different types of particles or forces.
• 27:40
  Speaker 1: In this view, Our universe is just one island in
• 27:43
  Speaker 1: an archipelago of universes, a cosmic bubble bath of unimaginable proportions.
• 27:48
  Speaker 1: This idea, called the multiverse, is still highly speculative. But
• 27:53
  Speaker 1: if it's correct, it has profound implications for our understanding
• 27:56
  Speaker 1: of reality. It would mean that everything we've ever known,
• 28:00
  Speaker 1: all the stars and galaxies in our observable universe, is
• 28:03
  Speaker 1: just a tiny sliver of a much vaster multiverse. Our
• 28:07
  Speaker 1: universe would be one grain of sand on an endless beach.
• 28:11
  Speaker 1: one bubble in an eternal foam. The philosophical implications are staggering.
• 28:16
  Speaker 1: Is there a copy of you reading this in another
• 28:18
  Speaker 1: universe right now? Are there universes where life never took hold?
• 28:22
  Speaker 1: Or where the laws of physics are so different that
• 28:24
  Speaker 1: stars and galaxies could never form? The multiverse opens up
• 28:28
  Speaker 1: a dizzying array of possibilities. Of course, we have to
• 28:31
  Speaker 1: be careful not to let our imaginations run too wild.
• 28:35
  Speaker 1: The multiverse is still a highly speculative idea, and we
• 28:38
  Speaker 1: may never have direct evidence for other universes, By definition,
• 28:42
  Speaker 1: they would be causally disconnected from us, meaning no light
• 28:46
  Speaker 1: or information could ever pass between them and us. For now,
• 28:49
  Speaker 1: the multiverse remains firmly in the realm of theory. But
• 28:53
  Speaker 1: even if we restrict ourselves to the observable universe, the
• 28:56
  Speaker 1: one patch of spacetime we can actually see, there are
• 28:59
  Speaker 1: still so many wonders to explore, from the birth and
• 29:02
  Speaker 1: death of stars to the colliding of galaxies and the
• 29:05
  Speaker 1: warping of spacetime by black holes. And as we peer
• 29:08
  Speaker 1: further back in time to the earliest moments of the
• 29:11
  Speaker 1: Big Bang, we're pushing the boundaries of known physics, probing
• 29:15
  Speaker 1: realms of energy and density we can barely imagine. It's
• 29:18
  Speaker 1: amazing to think about how far we've come in our
• 29:20
  Speaker 1: understanding of the universe. Just a century ago, we thought
• 29:24
  Speaker 1: the Milky Way was the entire universe. Now we know
• 29:27
  Speaker 1: it's one of trillions of galaxies in an expanding cosmos
• 29:31
  Speaker 1: that's been evolving for nearly 14 billion years. We've traced
• 29:35
  Speaker 1: the history of the universe back to the first seconds
• 29:37
  Speaker 1: after the Big Bang, and we're starting to piece together
• 29:39
  Speaker 1: clues about what came before. But there's still so much
• 29:43
  Speaker 1: we don't know. So many mysteries waiting to be unlocked.
• 29:47
  Speaker 1: What exactly happened at the moment of the Big Bang?
• 29:50
  Speaker 1: What drove inflation, and did it give rise to a multiverse?
• 29:54
  Speaker 1: What is the nature of dark matter and dark energy?
• 29:57
  Speaker 1: the invisible stuff that seems to dominate the cosmos? And
• 30:00
  Speaker 1: perhaps most profoundly, why is there something rather than nothing?
• 30:05
  Speaker 1: Why does the universe exist at all? These are the
• 30:08
  Speaker 1: questions that keep cosmologists up at night. They're the questions
• 30:12
  Speaker 1: that have driven thinkers like Georges Lemaître and Alan Guth
• 30:15
  Speaker 1: to devote their lives to studying the universe. And they're
• 30:18
  Speaker 1: the questions that will continue to inspire and perplex us
• 30:21
  Speaker 1: as we push the boundaries of cosmic knowledge. But for now,
• 30:24
  Speaker 1: as we drift off to sleep under the canopy of
• 30:26
  Speaker 1: the night sky, we can take a moment to marvel
• 30:29
  Speaker 1: at the universe we find ourselves in. We can trace
• 30:32
  Speaker 1: the graceful arc of the Milky Way across the sky
• 30:35
  Speaker 1: and know that we're seeing the light of a hundred
• 30:37
  Speaker 1: billion stars. We can think about the countless galaxies pinwheeling
• 30:41
  Speaker 1: through the inky depths of space, each one an island
• 30:45
  Speaker 1: universe unto itself. And we can ponder the deep mysteries
• 30:49
  Speaker 1: that still await us, the secrets hidden in the far
• 30:51
  Speaker 1: reaches of space and time. In a very real sense,
• 30:55
  Speaker 1: to study the universe is to study ourselves. We are,
• 30:58
  Speaker 1: after all, creatures of the cosmos, our atoms forged in
• 31:01
  Speaker 1: the crucibles of long-dead stars. When we gaze up at
• 31:05
  Speaker 1: the night sky, we're not separate from the universe. We're
• 31:08
  Speaker 1: part of its grand, unfolding story. So as we close
• 31:12
  Speaker 1: our eyes and surrender to sleep, we can carry that
• 31:14
  Speaker 1: cosmic perspective with us. We can remember that even in
• 31:17
  Speaker 1: our dreams, we're still children of the stars, forever linked
• 31:21
  Speaker 1: to the vast and wondrous universe that gave us birth
• 31:24
  Speaker 1: And perhaps as we drift off, we can smile at
• 31:26
  Speaker 1: the thought that somewhere out there, the universe is dreaming too,
• 31:30
  Speaker 1: dreaming through us and through all the living things that
• 31:33
  Speaker 1: call it home. Good night, and may your dreams be
• 31:36
  Speaker 1: as vast and wondrous as the cosmos itself. As we
• 31:40
  Speaker 1: ponder the vast expanses beyond our cosmic horizon, it's humbling
• 31:44
  Speaker 1: to realise that our observable universe is but a small
• 31:48
  Speaker 1: island in an unimaginably large cosmos. The expansion of space
• 31:53
  Speaker 1: itself ensures that much of the universe will remain forever
• 31:56
  Speaker 1: beyond our reach, receding faster than the speed of light.
• 31:59
  Speaker 1: It's a poignant reminder of our tiny place in the
• 32:02
  Speaker 1: grand scheme of things. But even within our observable universe,
• 32:05
  Speaker 1: there's still so much to explore and discover. As we
• 32:08
  Speaker 1: gaze out into the night sky, we're looking back in time,
• 32:12
  Speaker 1: seeing distant galaxies as they were billions of years ago,
• 32:15
  Speaker 1: their ancient light traversing the vast gulfs of space to
• 32:18
  Speaker 1: reach our eyes. It's a breathtaking thought, that we can
• 32:21
  Speaker 1: directly observe the universe's past, all the way back to
• 32:25
  Speaker 1: the afterglow of the Big Bang itself. That afterglow, the
• 32:28
  Speaker 1: cosmic microwave background, is a treasure trove of information about
• 32:32
  Speaker 1: the early universe. Encoded in its faint glow are the
• 32:35
  Speaker 1: seeds of cosmic structure, the tiny density variations that would
• 32:40
  Speaker 1: eventually give rise to galaxies, stars and planets. It's amazing
• 32:44
  Speaker 1: to think that everything we see around us, including our
• 32:47
  Speaker 1: own Earth and our own bodies, can trace its origins
• 32:49
  Speaker 1: back to quantum fluctuations in the universe's infancy. And if
• 32:53
  Speaker 1: the theory of cosmic inflation is correct, those quantum fluctuations
• 32:57
  Speaker 1: were stretched to cosmological scales by the universe's incredible exponential
• 33:02
  Speaker 1: expansion in its first fraction of a second. Inflation is
• 33:07
  Speaker 1: a mind-bending idea that the universe could have expanded faster
• 33:11
  Speaker 1: than the speed of light, pushing most of its volume
• 33:14
  Speaker 1: forever beyond our view. It's a humbling thought, to realise
• 33:18
  Speaker 1: that our entire observable universe may be just a tiny
• 33:22
  Speaker 1: bubble in an eternally inflating multiverse. The multiverse is a
• 33:26
  Speaker 1: concept that stretches the limits of our imagination. To think
• 33:30
  Speaker 1: that our universe, with its hundreds of billions of galaxies
• 33:33
  Speaker 1: and unimaginable vastness, could be just one of countless bubble
• 33:37
  Speaker 1: universes sprouting from the quantum foam of a greater multiverse.
• 33:41
  Speaker 1: It's almost too much to wrap our minds around. But
• 33:44
  Speaker 1: it's a possibility that some of the greatest thinkers of
• 33:46
  Speaker 1: our time are seriously considering One of those thinkers was
• 33:49
  Speaker 1: Andrei Lind, a Russian-American theoretical physicist who made groundbreaking contributions
• 33:55
  Speaker 1: to the theory of cosmic inflation and the multiverse. Born
• 33:58
  Speaker 1: in Moscow in 1948, Linda fell in love with physics
• 34:01
  Speaker 1: at an early age and excelled in his studies, earning
• 34:04
  Speaker 1: a PhD from the Lebedev Physical Institute in 1975. His
• 34:08
  Speaker 1: early work focused on particle physics and quantum field theory,
• 34:12
  Speaker 1: but he soon became fascinated by cosmology and the big
• 34:15
  Speaker 1: questions about the origin and evolution of the universe. In
• 34:18
  Speaker 1: the early 1980s, Linder began developing his ideas about inflation
• 34:22
  Speaker 1: and the multiverse. Building on the work of Alan Guth
• 34:25
  Speaker 1: and others, Linder proposed that inflation could be an eternal process,
• 34:29
  Speaker 1: with quantum fluctuations causing new bubble universes to continuously sprout
• 34:33
  Speaker 1: from the inflating spacetime. Each of these bubble universes could
• 34:37
  Speaker 1: have different physical properties and constants, giving rise to a
• 34:40
  Speaker 1: vast and diverse multiverse. Linder's ideas were revolutionary, and not
• 34:45
  Speaker 1: everyone in the physics community was ready to accept them.
• 34:49
  Speaker 1: The concept of a multiverse seemed like science fiction to some,
• 34:52
  Speaker 1: untestable and untethered from reality. But Linder persisted, refining his
• 34:57
  Speaker 1: theories and arguing persuasively for their merits. His 1986 paper,
• 35:02
  Speaker 1: Eternally Existing, Self-Reproducing, Chaotic Inflationary Universe, became a seminal work
• 35:08
  Speaker 1: in the field. Over the decades, Linder continued to be
• 35:11
  Speaker 1: a leading voice in the study of inflation and the multiverse.
• 35:14
  Speaker 1: His ideas have influenced a generation of cosmologists and sparked
• 35:18
  Speaker 1: countless hours of debate and discussion. Today, the theory of
• 35:21
  Speaker 1: eternal inflation and the multiverse, while still speculative, is taken
• 35:25
  Speaker 1: seriously by many of the world's top physicists. Looking back
• 35:29
  Speaker 1: on Linda's career, it's inspiring to see the impact that
• 35:32
  Speaker 1: one curious and creative mind can have. By daring to
• 35:35
  Speaker 1: ask the big questions and follow the math wherever it led,
• 35:38
  Speaker 1: Linda helped us to expand our understanding of the universe
• 35:41
  Speaker 1: and our place within it. His work reminds us that
• 35:44
  Speaker 1: even the most far-out ideas, if grounded in solid science,
• 35:49
  Speaker 1: can lead to incredible breakthroughs. As we continue to explore
• 35:53
  Speaker 1: the mysteries of the cosmos, it's good to keep an
• 35:55
  Speaker 1: open mind and a sense of wonder. The universe is
• 35:58
  Speaker 1: often stranger and more amazing than we can imagine, and
• 36:01
  Speaker 1: the theories we cling to today may one day be
• 36:04
  Speaker 1: superseded by even more astonishing ideas. The eternal inflation and
• 36:08
  Speaker 1: multiverse theory may be one such idea, a mind-blowing concept that,
• 36:12
  Speaker 1: if true, would mean our universe is just one humble
• 36:15
  Speaker 1: bubble among an infinity of others. But even if we
• 36:18
  Speaker 1: are alone in our bubble, our universe is still an
• 36:21
  Speaker 1: incredible place. As we look to the far future, we
• 36:24
  Speaker 1: can imagine the cosmos continuing to evolve and change in
• 36:28
  Speaker 1: ways we can scarcely imagine. Galaxy clusters will merge and
• 36:32
  Speaker 1: grow under the relentless pull of gravity, while dark energy
• 36:35
  Speaker 1: pushes the space between them ever wider. The expansion of
• 36:39
  Speaker 1: the universe will accelerate causing distant galaxies to recede beyond
• 36:43
  Speaker 1: our cosmic horizon until only our local supercluster remains visible.
• 36:48
  Speaker 1: On even longer timescales, the universe will continue to cool
• 36:51
  Speaker 1: and dim as the last stars exhaust their fuel and
• 36:54
  Speaker 1: wink out one by one. Eventually, only darkness will remain,
• 36:58
  Speaker 1: a void dotted with black holes and the fading embers
• 37:01
  Speaker 1: of stellar remnants. And in the unimaginably distant future, even
• 37:05
  Speaker 1: black holes will evaporate, their energy slowly dissipating into the
• 37:09
  Speaker 1: void until the universe reaches a state of maximum entropy,
• 37:13
  Speaker 1: the heat-death scenario. It's a poetic and melancholy vision, the
• 37:17
  Speaker 1: universe winding down to a cold, dark and quiescent state
• 37:20
  Speaker 1: over eons beyond imagining. But there's a strange beauty in
• 37:25
  Speaker 1: that long, slow fade into darkness. It's the beauty of
• 37:28
  Speaker 1: a universe that has run its course, that has given
• 37:31
  Speaker 1: rise to an incredible flowering of complexity and consciousness before
• 37:35
  Speaker 1: gently subsiding into eternal rest. And who knows? Perhaps in
• 37:40
  Speaker 1: that unimaginably distant future, long after our own universe has
• 37:44
  Speaker 1: gone dark, new universes will be born from the quantum foam.
• 37:48
  Speaker 1: Each one a new experiment in cosmic evolution, each one
• 37:51
  Speaker 1: a new canvas upon which the fundamental forces can paint
• 37:54
  Speaker 1: their masterpieces. The multiverse may be eternal and infinite, an
• 37:58
  Speaker 1: endless cycle of birth, growth and decay playing out over
• 38:02
  Speaker 1: vast scales of space and time. These are the thoughts
• 38:05
  Speaker 1: that fill our minds as we gaze up at the
• 38:07
  Speaker 1: night sky. marvelling at the beauty and mystery of the cosmos.
• 38:12
  Speaker 1: We are the universe becoming aware of itself, contemplating its
• 38:16
  Speaker 1: own existence through the unlikely medium of conscious matter. It's
• 38:20
  Speaker 1: a profound and humbling realisation, one that puts our own
• 38:24
  Speaker 1: lives and concerns into perspective. So as you drift off
• 38:27
  Speaker 1: to sleep, let your mind wander to the farthest reaches
• 38:30
  Speaker 1: of space and time. Ponder the incredible journey of discovery
• 38:34
  Speaker 1: that has brought us to this point. and the amazing
• 38:37
  Speaker 1: insights of thinkers like Andre Linder who have helped to
• 38:40
  Speaker 1: expand our cosmic horizons. Remember that even in an eternally
• 38:44
  Speaker 1: inflating multiverse, filled with countless bubble universes beyond our reach,
• 38:48
  Speaker 1: our own universe is still a wondrous and precious place.
• 38:52
  Speaker 1: And most of all, never lose that sense of curiosity
• 38:55
  Speaker 1: and wonder that draws us to the big questions. Keep dreaming,
• 38:59
  Speaker 1: keep exploring, and keep reaching for the stars. Because in
• 39:03
  Speaker 1: a universe as vast and mysterious as ours, there will
• 39:06
  Speaker 1: always be new frontiers to explore, new mysteries to unlock,
• 39:09
  Speaker 1: and new beauty to behold. Good night, and may your
• 39:13
  Speaker 1: dreams be as boundless as the cosmos itself. As we
• 39:16
  Speaker 1: ponder the vast expanse beyond our cosmic horizon, it's humbling
• 39:20
  Speaker 1: to consider the groundbreaking thinkers who first glimpsed the true
• 39:24
  Speaker 1: scale of our universe. In the early 20th century, an
• 39:28
  Speaker 1: astronomer named Henrietta Swan Leavitt made a discovery that would
• 39:31
  Speaker 1: change our perspective forever. Leavitt was born in 1868 in Massachusetts,
• 39:36
  Speaker 1: at a time when women were often discouraged from pursuing
• 39:39
  Speaker 1: scientific careers. Despite this, she developed a deep fascination with
• 39:43
  Speaker 1: the stars from a young age. After graduating from Radcliffe College,
• 39:47
  Speaker 1: she began work at the Harvard College Observatory as a computer,
• 39:51
  Speaker 1: one of several women hired to perform complex mathematical calculations.
• 39:55
  Speaker 1: It was tedious work, but Levitt had a keen eye
• 39:58
  Speaker 1: and a brilliant mind. While studying photographic plates of the
• 40:01
  Speaker 1: Magellanic clouds, two nearby dwarf galaxies, she noticed something peculiar
• 40:06
  Speaker 1: about the stars known as Zepheid variables. These stars pulsate
• 40:10
  Speaker 1: in a regular rhythm, growing brighter and dimmer over the
• 40:13
  Speaker 1: course of days or weeks. As Levitt carefully catalogued the
• 40:17
  Speaker 1: brightness and pulsation periods of these stars, a remarkable pattern emerged.
• 40:22
  Speaker 1: She realised that the slower Cepheid variable pulsed, the brighter
• 40:25
  Speaker 1: it was. This meant that by measuring a seafeed's pulsation period,
• 40:30
  Speaker 1: one could deduce its intrinsic brightness. If you then compared
• 40:34
  Speaker 1: this to its apparent brightness in the sky, you could
• 40:36
  Speaker 1: calculate its distance from Earth. It was a breakthrough that
• 40:40
  Speaker 1: would become known as the period-luminosity relationship, or Levitt's Law.
• 40:44
  Speaker 1: but its true power wouldn't be recognised until a decade later,
• 40:48
  Speaker 1: when Edwin Hubble used Cepheid variables as standard candles to
• 40:51
  Speaker 1: measure the distances to faraway galaxies. By doing so, he
• 40:55
  Speaker 1: discovered that our universe was far larger than previously imagined,
• 40:59
  Speaker 1: and forever shattered the notion of a small static cosmos.
• 41:03
  Speaker 1: Leavitt's discovery provided astronomers with a crucial tool for measuring
• 41:07
  Speaker 1: the scale of the universe, paving the way for Hubble's
• 41:10
  Speaker 1: groundbreaking work. Her story is a testament to the power
• 41:13
  Speaker 1: of curiosity, dedication and meticulous observation. Despite working in relative
• 41:19
  Speaker 1: obscurity and receiving little recognition in her lifetime, Levitt's contributions
• 41:23
  Speaker 1: laid the foundation for modern cosmology. As we drift further
• 41:27
  Speaker 1: out in space and time, it's easy to feel small
• 41:30
  Speaker 1: and insignificant against the vastness of the cosmos. But Levitt's
• 41:34
  Speaker 1: work reminds us that even seemingly minor discoveries can have
• 41:37
  Speaker 1: an outsized impact on our understanding of the universe. Her
• 41:41
  Speaker 1: story invites us to look at the world with fresh eyes,
• 41:44
  Speaker 1: to seek out patterns and connections that others might overlook.
• 41:48
  Speaker 1: One can imagine Levitt late at night, poring over photographic
• 41:52
  Speaker 1: plates by candlelight, her tireless work fuelled by a deep
• 41:56
  Speaker 1: sense of wonder. Did she have any inkling of the
• 41:59
  Speaker 1: revolution her discovery would spark? Could she ever have imagined
• 42:03
  Speaker 1: that her careful cataloguing of variable stars would one day
• 42:05
  Speaker 1: help us map the cosmos on the grandest of scales?
• 42:09
  Speaker 1: Like the Cepheid variables she studied, Levitt's legacy pulsates through
• 42:13
  Speaker 1: the history of astronomy, growing brighter with each passing year.
• 42:18
  Speaker 1: Her work reminds us that the universe reveals its secrets
• 42:21
  Speaker 1: not only in grand, sweeping gestures, but also in the quiet,
• 42:25
  Speaker 1: dedicated efforts of those who seek to understand its workings.
• 42:29
  Speaker 1: As we continue our journey to the edge of the
• 42:31
  Speaker 1: observable universe and beyond, let us carry with us the
• 42:34
  Speaker 1: spirit of Henrietta Levitt, a spirit of curiosity, perseverance, and
• 42:39
  Speaker 1: a deep reverence for the mysteries of the cosmos. For
• 42:42
  Speaker 1: even as we strain to see beyond our cosmic horizon,
• 42:46
  Speaker 1: we stand on the shoulders of giants whose insights light
• 42:49
  Speaker 1: the way forward, and so, as we drift off to sleep,
• 42:52
  Speaker 1: let us dream of the countless wonders that await us
• 42:55
  Speaker 1: in the vast expanse of space and time. May we
• 42:59
  Speaker 1: approach the universe with the same sense of awe and
• 43:02
  Speaker 1: determination that guided Levitt's work, knowing that even the smallest
• 43:06
  Speaker 1: steps can lead to the greatest of discoveries. In the
• 43:10
  Speaker 1: grand tapestry of the cosmos, we are but a tiny thread,
• 43:14
  Speaker 1: but oh, what a glorious and intricate pattern we are
• 43:16
  Speaker 1: woven into. As we contemplate the edge of our observable
• 43:20
  Speaker 1: universe and the infinite possibilities that lie beyond, let us
• 43:24
  Speaker 1: find comfort in the knowledge that we are part of
• 43:27
  Speaker 1: an endlessly fascinating and beautiful whole. So let your mind
• 43:31
  Speaker 1: wander to the farthest reaches of space, to the very
• 43:34
  Speaker 1: beginning and end of time. Let the gentle pulsations of
• 43:37
  Speaker 1: distant stars lull you into a peaceful slumber, secure in
• 43:42
  Speaker 1: the knowledge that you are an integral part of this
• 43:44
  Speaker 1: vast and wondrous universe. And as you drift off to sleep,
• 43:48
  Speaker 1: carry with you the spirit of all those who have
• 43:51
  Speaker 1: dedicated their lives to unravelling its mysteries, a spirit of wonder, perseverance,
• 43:57
  Speaker 1: and an unshakable faith in the power of human curiosity.
• 44:01
  Speaker 1: Sweet dreams, dear listener, and may your cosmic horizons be ever-expanding.
• 44:06
  Speaker 1: The work of Henrietta Swan Leavitt and other early astronomers
• 44:10
  Speaker 1: laid the groundwork for our modern understanding of the universe's
• 44:13
  Speaker 1: true extent. But as we've seen, there's still so much
• 44:16
  Speaker 1: we don't know about what lies beyond the edge of
• 44:18
  Speaker 1: our observable bubble. Could there be other universes out there,
• 44:22
  Speaker 1: forever hidden from our view? It's a question that continues
• 44:26
  Speaker 1: to captivate some of today's most brilliant minds. In the 1980s,
• 44:31
  Speaker 1: a young physicist named Andre Linder began to develop a
• 44:34
  Speaker 1: radical new theory about the origin and nature of our universe.
• 44:38
  Speaker 1: Born in Moscow in 1948, Linda was a precocious child
• 44:42
  Speaker 1: who excelled in mathematics and physics. His prodigious talent earned
• 44:46
  Speaker 1: him a place at Moscow State University, where he studied
• 44:49
  Speaker 1: under the renowned Soviet physicist Vitaly Ginzburg. It was a
• 44:53
  Speaker 1: time of great excitement and discovery in cosmology. Just a
• 44:57
  Speaker 1: few years earlier, physicists had detected the Cosmic Microwave Background Radiation,
• 45:03
  Speaker 1: the afterglow of the Big Bang that had been predicted
• 45:05
  Speaker 1: by George Gamow and others. This discovery had confirmed that
• 45:09
  Speaker 1: our universe had a beginning, and sent theorists scrambling to
• 45:12
  Speaker 1: understand the details of how it all began. Lind was
• 45:16
  Speaker 1: particularly intrigued by the idea of cosmic inflation, which had
• 45:19
  Speaker 1: been proposed by Alan Guth in 1980. Guth's theory suggested
• 45:24
  Speaker 1: that in the first fraction of a second after the
• 45:26
  Speaker 1: Big Bang, the universe underwent a period of exponential expansion.
• 45:30
  Speaker 1: doubling in size every 10 to the negative 34 seconds.
• 45:33
  Speaker 1: This rapid expansion could explain many of the universe's observed properties,
• 45:38
  Speaker 1: such as its smoothness and flatness. But as Linder studied
• 45:41
  Speaker 1: the equations of inflation, he began to suspect that the
• 45:45
  Speaker 1: story was even more bizarre and wonderful than Guth had imagined.
• 45:49
  Speaker 1: In a series of groundbreaking papers in the 1980s, Linder
• 45:53
  Speaker 1: proposed a new model called Eternal Chaotic Inflation. According to
• 45:57
  Speaker 1: this theory, Inflation wasn't just a one-time event in our
• 46:01
  Speaker 1: universe's history. It was a never-ending process that continuously spawned
• 46:05
  Speaker 1: new bubble universes. The implications were staggering. If Linda was right,
• 46:11
  Speaker 1: our universe was just one of countless bubbles floating in
• 46:14
  Speaker 1: an eternally inflating sea, a vast multiverse of unimaginable proportions.
• 46:21
  Speaker 1: Each bubble could have its own unique properties, governed by
• 46:24
  Speaker 1: different physical laws and constants. Some might be teeming with
• 46:28
  Speaker 1: complex structures and life, while others might be barren and inhospitable.
• 46:33
  Speaker 1: It was a vision of reality that challenged our most
• 46:35
  Speaker 1: fundamental assumptions about the nature of the cosmos. But Linder's
• 46:39
  Speaker 1: ideas weren't just wild speculation. They were grounded in rigorous
• 46:43
  Speaker 1: mathematical analysis and consistent with the laws of quantum mechanics.
• 46:48
  Speaker 1: His work helped to launch a new era of cosmological theorising.
• 46:52
  Speaker 1: as physicists grappled with the possibility of a multiverse that
• 46:55
  Speaker 1: dwarfed even our wildest imaginings. Today, the idea of the
• 46:59
  Speaker 1: multiverse remains controversial and unproven, but it continues to captivate
• 47:03
  Speaker 1: the imaginations of scientists and laypeople alike. There's something both
• 47:07
  Speaker 1: humbling and exhilarating about the notion that our universe might
• 47:10
  Speaker 1: be just one tiny bubble among infinitely many, a cosmic
• 47:14
  Speaker 1: grain of sand on an endless beach of possibilities. As
• 47:18
  Speaker 1: we lie here in the darkness... our minds adrift in
• 47:21
  Speaker 1: the vastness of space and time, it's easy to feel
• 47:24
  Speaker 1: small and insignificant in the face of such immensity. But
• 47:28
  Speaker 1: perhaps there's a strange sort of comfort in that smallness,
• 47:32
  Speaker 1: a reminder that we are part of something much grander
• 47:34
  Speaker 1: and more mysterious than we can ever fully comprehend. And so,
• 47:39
  Speaker 1: as we ponder the edge of our own cosmic bubble
• 47:41
  Speaker 1: and the infinite realms that may lie beyond, let us
• 47:44
  Speaker 1: embrace the sense of wonder and possibility that Linda's vision evokes.
• 47:49
  Speaker 1: Let us dream of the strange and marvellous universes that
• 47:52
  Speaker 1: may be lurking just out of view, each one a
• 47:55
  Speaker 1: testament to the breathtaking creativity and diversity of nature. In
• 47:59
  Speaker 1: the end, perhaps it doesn't matter whether we can ever
• 48:01
  Speaker 1: directly observe these other realms. What matters is the way
• 48:05
  Speaker 1: they stretch our imaginations and challenge us to think beyond
• 48:08
  Speaker 1: our everyday experience. They remind us that the universe is
• 48:11
  Speaker 1: always vaster, stranger and more beautiful than we can possibly imagine.
• 48:16
  Speaker 1: and that the quest to understand it is an endless
• 48:18
  Speaker 1: source of wonder and delight. So let your mind drift
• 48:22
  Speaker 1: to the farthest reaches of the multiverse, dear listener. Let
• 48:25
  Speaker 1: Linda's vision of an endlessly bubbling cosmos be the backdrop
• 48:29
  Speaker 1: for your dreams. And know that wherever your journeys take you,
• 48:33
  Speaker 1: in this universe or any other, you are part of
• 48:35
  Speaker 1: a grand and glorious unfolding that surpasses our wildest imaginings.
• 48:40
  Speaker 1: Good night, and may your dreams be as vast and
• 48:43
  Speaker 1: wondrous as the cosmos itself. As we ponder the vast
• 48:46
  Speaker 1: expanse beyond our cosmic horizon, it's humbling to think about
• 48:50
  Speaker 1: how much of the universe remains hidden from our view.
• 48:53
  Speaker 1: Our observable bubble is but a tiny island in the
• 48:56
  Speaker 1: grand cosmic ocean, a mere 46 billion light-years across. And yet,
• 49:01
  Speaker 1: even within this limited sphere, the sheer scope and majesty
• 49:04
  Speaker 1: of the cosmos is enough to inspire wonder and curiosity
• 49:07
  Speaker 1: that can last a lifetime. Just think, the light reaching
• 49:11
  Speaker 1: us from the most distant galaxies we can see has
• 49:14
  Speaker 1: been travelling for billions of years, a journey that began
• 49:17
  Speaker 1: long before Earth even existed. Those ancient photons have borne
• 49:21
  Speaker 1: silent witness to the birth and death of countless stars,
• 49:25
  Speaker 1: the formation and evolution of whole galaxies as they streamed
• 49:28
  Speaker 1: across the ever-expanding fabric of space. And still, they are
• 49:32
  Speaker 1: merely the forerunners, the vanguard of an even grander procession
• 49:35
  Speaker 1: of light that we may never glimpse. It's a staggering thought,
• 49:39
  Speaker 1: one that astronomers like Edwin Hubble could scarcely have imagined
• 49:42
  Speaker 1: when they first turned their telescopes to the night sky
• 49:45
  Speaker 1: in the early 20th century. Hubble, a brilliant yet unassuming man,
• 49:50
  Speaker 1: had already lived a full life by the time he
• 49:52
  Speaker 1: made his groundbreaking discoveries. Born in Missouri in 1889, he
• 49:57
  Speaker 1: was a gifted athlete and scholar, excelling in track and field, physics,
• 50:01
  Speaker 1: and even literature and law, but it was in astronomy
• 50:04
  Speaker 1: that he found his true calling. Working at the Mount
• 50:07
  Speaker 1: Wilson Observatory in California, Hubble had access to the most
• 50:10
  Speaker 1: powerful telescope of his day, the 100-inch Hooker Reflector. Night
• 50:14
  Speaker 1: after night, he trained this enormous eye on the heavens,
• 50:18
  Speaker 1: meticulously cataloguing and classifying the fuzzy nebulae he observed. At
• 50:23
  Speaker 1: the time, most astronomers believed these nebulae were relatively nearby
• 50:26
  Speaker 1: clouds of gas and dust within our own Milky Way galaxy.
• 50:31
  Speaker 1: But Hubble's keen observations would soon shatter that assumption. In 1923,
• 50:36
  Speaker 1: Hubble identified a special type of pulsating star called a
• 50:39
  Speaker 1: Cepheid variable in one of these nebulae, the Andromeda Nebula.
• 50:44
  Speaker 1: Cepheids are invaluable cosmic beacons. Their pulsation rate is directly
• 50:48
  Speaker 1: related to their intrinsic brightness. So by timing their light variations,
• 50:52
  Speaker 1: astronomers can deduce their true luminosity. Comparing this to their
• 50:56
  Speaker 1: apparent brightness allows their distance to be calculated. When Hubble
• 51:01
  Speaker 1: did this for the Cepheids in Andromeda, the result was staggering.
• 51:05
  Speaker 1: The nebula was nearly a million light-years away, far beyond
• 51:09
  Speaker 1: the bounds of the Milky Way. Andromeda wasn't a nebula
• 51:12
  Speaker 1: at all, but a whole other galaxy, what we now
• 51:15
  Speaker 1: call the Andromeda Galaxy. This discovery forever changed our conception
• 51:19
  Speaker 1: of the universe. No longer was our galaxy the entirety
• 51:23
  Speaker 1: of creation. Instead, it was just one island universe, among
• 51:27
  Speaker 1: countless others floating in the vast cosmic sea. But Hubble
• 51:31
  Speaker 1: wasn't finished. Continuing to measure the distances to dozens of
• 51:35
  Speaker 1: other galaxies, he made an even more astonishing finding. The
• 51:39
  Speaker 1: farther away a galaxy was, the faster it appeared to
• 51:41
  Speaker 1: be moving away from us. The light from these distant
• 51:44
  Speaker 1: galaxies was shifted towards the red end of the spectrum,
• 51:47
  Speaker 1: a telltale sign of recession. This relationship between distance and
• 51:52
  Speaker 1: recession speed became known as Hubble's Law, and pointed to
• 51:55
  Speaker 1: a remarkable conclusion. The universe itself was expanding. The space
• 52:00
  Speaker 1: between galaxies was stretching. carrying them apart like raisins in
• 52:04
  Speaker 1: a rising loaf of bread. It was an insight of
• 52:07
  Speaker 1: tremendous significance, one that would later be woven into the
• 52:11
  Speaker 1: tapestry of cosmic history as we came to understand the
• 52:14
  Speaker 1: universe's origin and evolution. But beyond the realm of scientific discovery,
• 52:20
  Speaker 1: Hubble's findings also evoked a deep sense of loneliness, of
• 52:24
  Speaker 1: poignant isolation. If the universe is expanding and and the
• 52:28
  Speaker 1: farther things are, the faster they recede, then doesn't that
• 52:31
  Speaker 1: imply that distant regions will eventually be carried away faster
• 52:34
  Speaker 1: than the speed of light? That as the eons unfold,
• 52:38
  Speaker 1: more and more of the cosmos will slip beyond our view,
• 52:41
  Speaker 1: vanishing across the cosmic horizon, never to be seen again
• 52:44
  Speaker 1: by us or our descendants? It's a melancholy thought, one
• 52:48
  Speaker 1: that Hubble himself may have contemplated in his later years.
• 52:52
  Speaker 1: After a lifetime of peering into the depths of space
• 52:55
  Speaker 1: and time, of charting the grandest structures of the cosmos,
• 52:59
  Speaker 1: perhaps he felt the weight of all those vanishing stars
• 53:01
  Speaker 1: and galaxies, all that unreachable majesty. One can imagine him
• 53:06
  Speaker 1: looking up at the night sky, knowing that even as
• 53:09
  Speaker 1: he watched, innumerable worlds were slipping away, their light and
• 53:13
  Speaker 1: beauty forever lost to human eyes. As you lie in bed,
• 53:17
  Speaker 1: your mind adrift in the currents of cosmic reverie, it's
• 53:20
  Speaker 1: hard not to feel a similar sense of poignant wonder.
• 53:23
  Speaker 1: The universe is so inconceivably vast. so much of it
• 53:26
  Speaker 1: already lost to our view, and yet we are here,
• 53:29
  Speaker 1: conscious and curious, able to trace its history and ponder
• 53:33
  Speaker 1: its mysteries. In the darkness behind your eyelids, you can
• 53:37
  Speaker 1: almost picture all those distant galaxies, their brilliant stars and
• 53:41
  Speaker 1: swirling nebulae, all the alien worlds and civilizations they might contain,
• 53:45
  Speaker 1: rushing away into the inky depths. How many trillions of
• 53:49
  Speaker 1: sunsets have those unseen planets witnessed? How many stories have
• 53:53
  Speaker 1: unfolded beneath those foreign stars? all those sagas of struggle
• 53:56
  Speaker 1: and triumph, love and loss, playing out across eons on
• 54:00
  Speaker 1: worlds we may never know. And yet, even as the
• 54:03
  Speaker 1: cosmos expands and the light of distant suns fades from view,
• 54:07
  Speaker 1: we are not alone. We have the legacy of thinkers
• 54:10
  Speaker 1: like Edwin Hubble to keep us company, the fruits of
• 54:13
  Speaker 1: their curiosity and brilliance to light our way. And we
• 54:16
  Speaker 1: have the knowledge that we are a part of this
• 54:18
  Speaker 1: vast and venerable universe, our atoms forged in the crucibles
• 54:22
  Speaker 1: of ancient stars and our consciousness a way for the
• 54:25
  Speaker 1: cosmos to know itself. As sleep begins to soften the
• 54:30
  Speaker 1: edges of your thoughts, let your mind drift out beyond
• 54:33
  Speaker 1: the cosmic horizon, to the farthest reaches of space and time,
• 54:37
  Speaker 1: and know that you are part of the grandest story
• 54:39
  Speaker 1: ever told, a story that will continue to unfold long
• 54:42
  Speaker 1: after we are gone, in realms and realities we can
• 54:45
  Speaker 1: scarcely imagine. But for now, let the lull of the
• 54:49
  Speaker 1: expanding universe carry you into the waiting embrace of dreams,
• 54:53
  Speaker 1: Let your waking mind release its hold on the here
• 54:56
  Speaker 1: and now and set your imagination adrift in the currents
• 54:59
  Speaker 1: of infinity. There will be time enough to ponder the
• 55:01
  Speaker 1: mysteries that remain, to chase the light of distant stars
• 55:05
  Speaker 1: and galaxies as they recede into the vast and venerable night.
• 55:09
  Speaker 1: For now it is enough to know that we are here,
• 55:13
  Speaker 1: alive and awake in this brief and shimmering moment, our
• 55:16
  Speaker 1: hearts filled with wonder at the scale and splendour of
• 55:19
  Speaker 1: it all. Rest now. and dream of the journeys yet
• 55:24
  Speaker 1: to come, the secrets yet to be revealed, in the glorious,
• 55:28
  Speaker 1: ever-unfolding story of our universe. As we prepare to venture
• 55:32
  Speaker 1: even deeper into the cosmos and its history, to explore
• 55:35
  Speaker 1: the earliest eras of the universe's existence, it's worth pausing
• 55:39
  Speaker 1: for a moment to appreciate how far our understanding has come.
• 55:43
  Speaker 1: For most of human history, the true nature and scale
• 55:45
  Speaker 1: of the universe were shrouded in mystery, the subject of
• 55:48
  Speaker 1: myth and speculation. Her ancestors looked up at the night
• 55:52
  Speaker 1: sky and saw a fixed eternal realm, a celestial sphere
• 55:56
  Speaker 1: that revolved around the Earth, which they believed to be
• 55:59
  Speaker 1: the centre of all creation. It was only through centuries
• 56:02
  Speaker 1: of careful observation, mathematical calculation and intellectual daring that this
• 56:07
  Speaker 1: parochial view began to crumble. Visionaries like Copernicus and Galileo
• 56:12
  Speaker 1: showed that the Earth was not the centre, but rather
• 56:14
  Speaker 1: orbited the Sun along with the other planets. Later thinkers
• 56:18
  Speaker 1: like Newton and Laplace established the physical laws that governed
• 56:22
  Speaker 1: the motions of celestial bodies, revealing a cosmos of astonishing
• 56:26
  Speaker 1: regularity and precision. And with the advent of ever more
• 56:29
  Speaker 1: powerful telescopes, the true depth and diversity of the universe
• 56:33
  Speaker 1: began to come into focus. A universe filled with countless stars,
• 56:37
  Speaker 1: nebulae and galaxies extending in all directions to unimaginable distances.
• 56:42
  Speaker 1: But even as our view of the cosmos expanded, the
• 56:44
  Speaker 1: question of its origin remained. How did this vast and
• 56:48
  Speaker 1: intricate universe come to be? Was it eternal and unchanging,
• 56:52
  Speaker 1: as many philosophers had long believed? Or did it have
• 56:55
  Speaker 1: a beginning, a moment of creation? It was a question
• 56:59
  Speaker 1: that would occupy some of the 20th century's greatest scientific minds,
• 57:03
  Speaker 1: and ultimately lead to a radical reimagining of the universe
• 57:07
  Speaker 1: and our place within it. At the forefront of this
• 57:10
  Speaker 1: revolution was a brilliant and unassuming Belgian priest named Georges Lemaître.
• 57:14
  Speaker 1: Born in 1894, Lemaître was a man of many talents,
• 57:18
  Speaker 1: a gifted mathematician, a skilled astronomer, and a deeply spiritual
• 57:22
  Speaker 1: thinker who saw no conflict between his scientific pursuits and
• 57:26
  Speaker 1: his religious faith. In fact, he believed that the study
• 57:30
  Speaker 1: of the universe was a way to glimpse the mind
• 57:32
  Speaker 1: of the creator, to marvel at the intricacy and beauty
• 57:35
  Speaker 1: of the cosmic design. Lemaître' s groundbreaking work began in the 1920s,
• 57:41
  Speaker 1: when he was a young graduate student studying physics and astronomy.
• 57:45
  Speaker 1: At the time, the prevailing view among scientists was that
• 57:48
  Speaker 1: the universe was static and eternal, a vast and unchanging
• 57:51
  Speaker 1: arena in which celestial bodies moved according to fixed, immutable laws.
• 57:56
  Speaker 1: But Lemaître, with his keen mathematical mind and his deep
• 57:59
  Speaker 1: intuition for the workings of nature, saw something different. Delving
• 58:04
  Speaker 1: into Einstein's recently published theory of general relativity, which described
• 58:08
  Speaker 1: gravity as a curvature in the fabric of spacetime, Lemaitre
• 58:12
  Speaker 1: realised that the equations allowed for a universe that was
• 58:14
  Speaker 1: not static but dynamic and evolving. In fact, as he
• 58:18
  Speaker 1: worked through the mathematics, he found that the universe could
• 58:21
  Speaker 1: not be static at all. It had to be either
• 58:23
  Speaker 1: expanding or contracting. This was a startling conclusion, one that
• 58:28
  Speaker 1: flew in the face of centuries of scientific and philosophical tradition.
• 58:33
  Speaker 1: But Lemaitre was convinced he was onto something. In 1927,
• 58:36
  Speaker 1: he published a paper titled a homogeneous universe of constant
• 58:41
  Speaker 1: mass and increasing radius, accounting for the radial velocity of
• 58:44
  Speaker 1: extragalactic nebulae, a mouthful of a title that would come
• 58:48
  Speaker 1: to be recognised as one of the seminal works of
• 58:50
  Speaker 1: modern cosmology. In this paper, Lemaître proposed a model of
• 58:54
  Speaker 1: the universe that began as a single point, what he
• 58:57
  Speaker 1: called the primeval atom, and then expanded and evolved over time.
• 59:01
  Speaker 1: He showed how this model could account for the observed
• 59:04
  Speaker 1: recession of distant galaxies, which had recently been discovered by
• 59:07
  Speaker 1: Edwin Hubble, and he even derived a mathematical relationship between
• 59:11
  Speaker 1: a galaxy's distance and its recession speed that was remarkably
• 59:15
  Speaker 1: similar to what Hubble would later establish. It was a
• 59:18
  Speaker 1: bold and visionary idea, one that required a leap of
• 59:21
  Speaker 1: imagination and a willingness to challenge long-held assumptions. But for Lemaître,
• 59:26
  Speaker 1: it was also a deeply satisfying convergence of his scientific
• 59:30
  Speaker 1: and spiritual convictions. In the primeval atom, he saw echoes
• 59:34
  Speaker 1: of the biblical creation story, a moment of divine origin
• 59:38
  Speaker 1: from which the universe unfolded in all its complexity and grandeur.
• 59:42
  Speaker 1: And in the ongoing expansion of the cosmos, he saw
• 59:45
  Speaker 1: evidence of a dynamic and purposeful creation, a universe imbued
• 59:49
  Speaker 1: with meaning and direction. Of course, not everyone was convinced
• 59:53
  Speaker 1: by Lemaitre's ideas. Many of his contemporaries, including Einstein himself,
• 59:58
  Speaker 1: were initially sceptical of the notion of an expanding universe,
• 1:00:02
  Speaker 1: preferring to believe in a cosmos that was eternal and unchanging.
• 1:00:06
  Speaker 1: But as evidence continued to mount, from Hubble's observations of
• 1:00:09
  Speaker 1: galactic recession to the discovery of the cosmic microwave background radiation,
• 1:00:15
  Speaker 1: the idea of a dynamic, evolving universe gradually gained acceptance. Today,
• 1:00:19
  Speaker 1: we know that Lemaître' s intuition was correct. The universe did
• 1:00:23
  Speaker 1: have a beginning. a moment of creation that we now
• 1:00:25
  Speaker 1: call the Big Bang. And in the decades since Lemaître' s
• 1:00:29
  Speaker 1: pioneering work, we have traced the evolution of the cosmos
• 1:00:32
  Speaker 1: back to its earliest moments, to the forging of the
• 1:00:35
  Speaker 1: first atoms and the seeds of cosmic structure. But as
• 1:00:38
  Speaker 1: we lie here in the darkness, our minds adrift in
• 1:00:41
  Speaker 1: the currents of cosmic history, it's worth reflecting on the
• 1:00:44
  Speaker 1: deeper significance of Lemaître' s vision. In a universe that began
• 1:00:48
  Speaker 1: as a single point and has been expanding and evolving
• 1:00:52
  Speaker 1: ever since, We are all, in a sense, the products
• 1:00:55
  Speaker 1: of that primeval atom. The atoms that make up our bodies,
• 1:00:59
  Speaker 1: the stars and planets that fill our skies, the very
• 1:01:02
  Speaker 1: fabric of space-time itself, all of it can be traced
• 1:01:05
  Speaker 1: back to that initial moment of creation. And yet, even
• 1:01:09
  Speaker 1: as we marvel at the grandeur and complexity of the universe,
• 1:01:12
  Speaker 1: we are also reminded of our own smallness, our own
• 1:01:15
  Speaker 1: fleeting existence in the vast sweep of cosmic time. Lemaître himself,
• 1:01:20
  Speaker 1: for all his brilliance and insight, lived a relatively brief life,
• 1:01:24
  Speaker 1: passing away in 1966 at the age of 71. But
• 1:01:28
  Speaker 1: his ideas, his vision of a dynamic and purposeful universe,
• 1:01:32
  Speaker 1: live on, inspiring new generations of thinkers and explorers to
• 1:01:36
  Speaker 1: probe the mysteries of the cosmos. As you drift off
• 1:01:39
  Speaker 1: to sleep, let your mind wander back to that primeval atom,
• 1:01:42
  Speaker 1: to the birth of space and time and all the
• 1:01:44
  Speaker 1: wonders that would unfold from it. And remember that you
• 1:01:48
  Speaker 1: too are a part of that grand cosmic story. a
• 1:01:51
  Speaker 1: child of the stars and the Big Bang, a conscious
• 1:01:53
  Speaker 1: witness to the awesome majesty of the universe, rest now
• 1:01:57
  Speaker 1: and dream of the mysteries yet to be revealed, the
• 1:02:00
  Speaker 1: secrets of the cosmos that await our discovery. For in
• 1:02:04
  Speaker 1: the end, the story of the universe is also the
• 1:02:06
  Speaker 1: story of us, of our endless quest to understand our
• 1:02:09
  Speaker 1: place in the grand scheme of things and to marvel
• 1:02:12
  Speaker 1: at the beauty and complexity of the world we inhabit.
• 1:02:16
  Speaker 1: Having explored the universe's distant past and the possibility of
• 1:02:19
  Speaker 1: a greater multiverse, let's turn our gaze to the far future.
• 1:02:24
  Speaker 1: The universe we inhabit today, filled with hundreds of billions
• 1:02:27
  Speaker 1: of galaxies, each shining with the light of countless stars,
• 1:02:30
  Speaker 1: feels eternal and unchanging. But like a cosmic clock ticking
• 1:02:35
  Speaker 1: on nearly unimaginable timescales, the future of our universe is
• 1:02:39
  Speaker 1: one of gradual yet profound transformation. In the coming eons,
• 1:02:43
  Speaker 1: gravity will continue its patient work, drawing galaxies together into
• 1:02:47
  Speaker 1: ever-larger structures. Our own Milky Way is destined for a
• 1:02:51
  Speaker 1: collision with our nearest neighbour, the Andromeda Galaxy, in about
• 1:02:54
  Speaker 1: 4 billion years. The two spiral galaxies will dance around
• 1:02:59
  Speaker 1: each other in a majestic swirl of starlight, their individual
• 1:03:02
  Speaker 1: stars far enough apart to avoid collision, until they eventually
• 1:03:06
  Speaker 1: merge into a single, larger elliptical galaxy. On even greater scales,
• 1:03:11
  Speaker 1: galaxy clusters will continue to grow, as smaller groups and
• 1:03:14
  Speaker 1: individual galaxies fall inwards and merge with these titanic structures.
• 1:03:19
  Speaker 1: The Virgo supercluster, of which our local group is a part,
• 1:03:23
  Speaker 1: will eventually combine with other nearby superclusters like Hydra Centaurus
• 1:03:27
  Speaker 1: and Pavo Indus to form a structure spanning nearly a
• 1:03:31
  Speaker 1: billion light years. But even as gravity draws these vast
• 1:03:35
  Speaker 1: cosmic archipelagos together, another force is at work on the
• 1:03:39
  Speaker 1: grander scales. Dark energy, the mysterious force that makes up
• 1:03:43
  Speaker 1: about 68% of the universe's total energy and matter content,
• 1:03:47
  Speaker 1: is causing the expansion of the universe to accelerate. Like
• 1:03:51
  Speaker 1: a cosmic anti-gravity, dark energy pushes space itself apart from within.
• 1:03:56
  Speaker 1: As the universe continues to expand and dark energy continues
• 1:04:00
  Speaker 1: to push ever harder, an increasing fraction of galaxies will
• 1:04:03
  Speaker 1: begin to recede from us faster than the speed of light.
• 1:04:06
  Speaker 1: The light from these distant structures will become increasingly redshifted,
• 1:04:10
  Speaker 1: eventually sliding out of the visible spectrum and into the infrared,
• 1:04:14
  Speaker 1: microwave and radio bands as they cross our cosmic horizon
• 1:04:17
  Speaker 1: and disappear from view forever. Eventually, in 100 billion years
• 1:04:22
  Speaker 1: or more, the persistent push of dark energy will leave
• 1:04:25
  Speaker 1: only local clusters of galaxies gravitationally bound, like lonely islands
• 1:04:30
  Speaker 1: in a vast and ever-widening cosmic ocean. The rest of
• 1:04:34
  Speaker 1: the universe will be carried beyond our view, even galaxies
• 1:04:37
  Speaker 1: we can see now, their light and existence erased and
• 1:04:40
  Speaker 1: inaccessible to us, orphaned by the relentless expansion of space itself.
• 1:04:46
  Speaker 1: This idea of an island universe, a cluster of galaxies
• 1:04:50
  Speaker 1: isolated by cosmic expansion, was first proposed by American astronomer
• 1:04:54
  Speaker 1: Harlow Shapley in the early 20th century. At the time,
• 1:04:59
  Speaker 1: the true scale of the universe was a mystery, and
• 1:05:01
  Speaker 1: the concept of island universes was a contentious topic of debate.
• 1:05:06
  Speaker 1: Shapley himself argued against the idea, believing that the Milky
• 1:05:10
  Speaker 1: Way was the entirety of the universe. It wasn't until
• 1:05:13
  Speaker 1: the 1920s with Edwin Hubble's observations of distant galaxies, that
• 1:05:17
  Speaker 1: the island universe theory was confirmed and our conception of
• 1:05:21
  Speaker 1: the cosmos expanded once again. Shapley's contributions to astronomy extended
• 1:05:26
  Speaker 1: far beyond the island universe debate. His research on globular
• 1:05:30
  Speaker 1: clusters and his calibration of the period-luminosity relationship of Cepheid
• 1:05:34
  Speaker 1: variable stars allowed him to make the first reliable estimates
• 1:05:37
  Speaker 1: of the size of the Milky Way and our sun's
• 1:05:39
  Speaker 1: position within it. In the famous Great Debate of 1920
• 1:05:42
  Speaker 1: with Heber Curtis... Shapley argued correctly for the vast size
• 1:05:46
  Speaker 1: of our galaxy, but failed to anticipate the existence of
• 1:05:49
  Speaker 1: countless other galaxies beyond our own. Nevertheless, his work helped
• 1:05:54
  Speaker 1: pave the way for our modern understanding of the scale
• 1:05:56
  Speaker 1: and structure of the cosmos. As the universe continues to
• 1:06:00
  Speaker 1: expand and cool over countless eons, the formation of new
• 1:06:03
  Speaker 1: stars will gradually taper off. In galaxies like our own,
• 1:06:08
  Speaker 1: star formation will decrease, as the interstellar medium becomes increasingly
• 1:06:12
  Speaker 1: enriched with heavy elements from earlier stellar generations. These elements
• 1:06:16
  Speaker 1: allow gas clouds to cool and fragment more efficiently, producing smaller,
• 1:06:20
  Speaker 1: lower-mass stars. Eventually, in the far future of the universe,
• 1:06:25
  Speaker 1: only these small, dim, long-lived stars will remain, steadily consuming
• 1:06:29
  Speaker 1: their meagre hydrogen reserves over trillions of years. But even
• 1:06:33
  Speaker 1: these ancient stellar embers will eventually fade. On timescales of
• 1:06:37
  Speaker 1: 1 to 100 trillion years, The last stars will exhaust
• 1:06:41
  Speaker 1: their fuel, collapsing into faint white dwarfs or exploding as supernovae,
• 1:06:46
  Speaker 1: leaving behind neutron stars and black holes. The universe will
• 1:06:51
  Speaker 1: enter a period known as the Degenerate Era, where no
• 1:06:54
  Speaker 1: new stars are born to replace those that have died.
• 1:06:57
  Speaker 1: Galaxies will become dark and quiescent, increasingly dominated by dark
• 1:07:02
  Speaker 1: matter and the remnants of long-dead stars. Yet even this
• 1:07:06
  Speaker 1: is not the end. In the far future of the
• 1:07:08
  Speaker 1: Degenerate Era... On timescales of 10 to the power of
• 1:07:11
  Speaker 1: 15 to 10 to the power of 37 years, even
• 1:07:15
  Speaker 1: the stellar remnants will begin to fade. White dwarfs will
• 1:07:18
  Speaker 1: cool and crystallise, their nuclear fires exhausted, becoming black dwarfs
• 1:07:23
  Speaker 1: invisible against the void of space. Neutron stars will collide
• 1:07:26
  Speaker 1: and merge, or decay into protons and electrons, and even
• 1:07:30
  Speaker 1: the supermassive black holes at the centres of galaxies will
• 1:07:33
  Speaker 1: slowly evaporate through the process of Hawking radiation. a quantum
• 1:07:37
  Speaker 1: mechanical effect first proposed by Stephen Hawking in 1974. Hawking's
• 1:07:42
  Speaker 1: groundbreaking work on black hole thermodynamics upended our understanding of
• 1:07:46
  Speaker 1: these enigmatic objects. According to his calculations, black holes are
• 1:07:51
  Speaker 1: not entirely black. They emit a faint stream of thermal
• 1:07:54
  Speaker 1: radiation generated by quantum effects at their event horizons. For
• 1:07:59
  Speaker 1: stellar mass black holes, this radiation is minuscule. and the
• 1:08:03
  Speaker 1: evaporation process would take some 10 to the power of
• 1:08:05
  Speaker 1: 67 years, vastly longer than the current age of the universe.
• 1:08:10
  Speaker 1: But for microscopic primordial black holes thought to have formed
• 1:08:13
  Speaker 1: in the early universe, Hawking radiation could cause them to
• 1:08:17
  Speaker 1: evaporate explosively, providing a potential window into exotic gravitational phenomena.
• 1:08:23
  Speaker 1: As the eons tick by and the universe continues to
• 1:08:26
  Speaker 1: expand and cool, even the black holes will gradually decay
• 1:08:29
  Speaker 1: into a thin soup of photons, neutrinos, electrons and positrons.
• 1:08:34
  Speaker 1: Matter itself will begin to break down, as protons and
• 1:08:37
  Speaker 1: neutrons decay into their constituent quarks, and then into leptons
• 1:08:41
  Speaker 1: and radiation. In this epoch, known as the Dark Era,
• 1:08:45
  Speaker 1: the universe will be a dilute, ever-expanding sea of fundamental
• 1:08:49
  Speaker 1: particles and low-energy radiation, with no trace of the rich
• 1:08:53
  Speaker 1: cosmic structures that once filled the cosmos. This bleak, far-future
• 1:08:57
  Speaker 1: scenario is known as the Heat Death of the universe,
• 1:09:00
  Speaker 1: a state of maximum entropy where no useful energy remains
• 1:09:04
  Speaker 1: to sustain motion or life. It is a poetic and
• 1:09:07
  Speaker 1: melancholy notion, the idea that the universe will eventually exhaust
• 1:09:11
  Speaker 1: its reserves of order and energy, decaying into a featureless
• 1:09:14
  Speaker 1: void for all eternity. But there is a strange beauty
• 1:09:18
  Speaker 1: in this ultimate fate. a reminder of the preciousness and
• 1:09:22
  Speaker 1: fragility of the present moment and the structures in life
• 1:09:24
  Speaker 1: the universe has managed to create and sustain. But even
• 1:09:28
  Speaker 1: the heat death may not be the end. Some theories
• 1:09:31
  Speaker 1: propose that random quantum fluctuations, occurring over vast timescales of
• 1:09:35
  Speaker 1: 10 to the power of 10 to the power of
• 1:09:37
  Speaker 1: 120 years, could trigger a new Big Bang, giving birth
• 1:09:42
  Speaker 1: to a new universe rising phoenix-like from the ashes of
• 1:09:44
  Speaker 1: the old. This notion of a cyclic or oscillating universe,
• 1:09:49
  Speaker 1: where each cosmic cycle lasts a near eternity before giving
• 1:09:52
  Speaker 1: way to the next, has ancient roots, appearing in Hindu
• 1:09:56
  Speaker 1: cosmology as the days and nights of Brahma. In the
• 1:10:01
  Speaker 1: 1920s and 30s, Richard Tolman and others explored the cyclic
• 1:10:04
  Speaker 1: model through the lens of general relativity, but found that
• 1:10:07
  Speaker 1: with each cycle, entropy would increase, resulting in longer and
• 1:10:11
  Speaker 1: longer cycles until the universe reached a final heat-death state.
• 1:10:16
  Speaker 1: More recently, Paul Steinhardt and Neil Turok proposed a cyclic
• 1:10:20
  Speaker 1: model based on string theory and the collision of higher
• 1:10:23
  Speaker 1: dimensional brains, but the ultimate fate of our universe remains
• 1:10:27
  Speaker 1: an open question. As we ponder the far future, we're
• 1:10:31
  Speaker 1: confronted with the immensity of time that our universe has
• 1:10:34
  Speaker 1: before it. The current age of 13.8 billion years is
• 1:10:38
  Speaker 1: but an eye-blink compared to the trillions, quadrillions and unimaginable
• 1:10:43
  Speaker 1: eons that cosmic evolution will continue. It is a humbling
• 1:10:47
  Speaker 1: and awe-inspiring realisation, one that puts our fleeting human existence
• 1:10:52
  Speaker 1: into a truly cosmic perspective. And yet, we are the
• 1:10:56
  Speaker 1: universe becoming aware of itself. These speculations and discoveries are
• 1:11:00
  Speaker 1: the products of the same cosmic evolution that will carry
• 1:11:03
  Speaker 1: the universe into its far future. We are the matter
• 1:11:06
  Speaker 1: of the cosmos, arranged into living, thinking beings capable of
• 1:11:10
  Speaker 1: contemplating our origins, our destiny, and our place in the
• 1:11:13
  Speaker 1: grand sweep of cosmic time. In that sense, we are
• 1:11:17
  Speaker 1: the universe's way of knowing itself, a cosmic self-awareness that
• 1:11:21
  Speaker 1: is both fleeting and precious. So as we drift off
• 1:11:24
  Speaker 1: to sleep, let us hold that thought in our minds,
• 1:11:28
  Speaker 1: that we are part of a grand cosmic story, a
• 1:11:31
  Speaker 1: tale of evolution and discovery that stretches from the birth
• 1:11:35
  Speaker 1: of the universe to its ultimate fate. The dreamers and
• 1:11:39
  Speaker 1: thinkers that came before us, from ancient astronomers to Hubble,
• 1:11:43
  Speaker 1: Hawking and beyond, have guided us to this present understanding,
• 1:11:47
  Speaker 1: sketching the outlines of the cosmos in ever greater detail.
• 1:11:52
  Speaker 1: But the story is far from over. As we slumber,
• 1:11:55
  Speaker 1: new discoveries are waiting to be made, new chapters to
• 1:11:58
  Speaker 1: be written in the epic of cosmic exploration. We may
• 1:12:01
  Speaker 1: be separated from the far future by unfathomable gulfs of time,
• 1:12:05
  Speaker 1: but we are connected to it by the unbroken chain
• 1:12:07
  Speaker 1: of cause and effect, the cosmic heritage of a universe
• 1:12:10
  Speaker 1: unfolding according to the laws of nature. And so... As
• 1:12:14
  Speaker 1: we let sleep overtake us, let us dream of the
• 1:12:17
  Speaker 1: wonders yet to be discovered, the secrets yet to be
• 1:12:20
  Speaker 1: unlocked in the grand cosmic drama of our universe. Let
• 1:12:24
  Speaker 1: us be inspired by the thinkers and dreamers who came
• 1:12:26
  Speaker 1: before us, and let us add our own verse to
• 1:12:28
  Speaker 1: the great poem of the cosmos. For though the universe
• 1:12:32
  Speaker 1: may be vast and our time within it fleeting, we
• 1:12:35
  Speaker 1: are an essential part of its unfolding story, and that
• 1:12:38
  Speaker 1: is a profound and beautiful thing. Good night. And may
• 1:12:41
  Speaker 1: your dreams be filled with the wonders of the cosmos
• 1:12:44
  Speaker 1: as we drift off to sleep beneath the canopy of
• 1:12:46
  Speaker 1: our vast, mysterious and endlessly fascinating universe. The universe continues
• 1:12:52
  Speaker 1: far beyond the limits of what we can see. As
• 1:12:54
  Speaker 1: we gaze up at the night sky, we're only glimpsing
• 1:12:57
  Speaker 1: the tiniest sliver of the vast cosmic expanse. The observable
• 1:13:01
  Speaker 1: universe stretches out some 46 billion light years in every direction,
• 1:13:06
  Speaker 1: containing hundreds of billions of galaxies, trillions of stars and
• 1:13:10
  Speaker 1: countless worlds. but this impressively large sphere is still just
• 1:13:14
  Speaker 1: a small portion of the entire universe. The reason we
• 1:13:17
  Speaker 1: can only see a limited distance is that the universe
• 1:13:19
  Speaker 1: has a finite age. It began in the Big Bang
• 1:13:22
  Speaker 1: about 13.8 billion years ago. In that time, light has
• 1:13:26
  Speaker 1: only been able to travel a certain distance, roughly 46
• 1:13:30
  Speaker 1: billion light years, accounting for the expansion of space. This
• 1:13:34
  Speaker 1: sets a boundary on our observations, like a circular horizon
• 1:13:37
  Speaker 1: centred on the Earth. Beyond that horizon, The universe continues,
• 1:13:41
  Speaker 1: perhaps infinitely. We just can't see those distant reaches because
• 1:13:45
  Speaker 1: their light hasn't had time to get to us. It's
• 1:13:48
  Speaker 1: a staggering thought. The observable universe, as incomprehensibly huge as
• 1:13:53
  Speaker 1: it is, is just an island in the vast cosmic ocean.
• 1:13:57
  Speaker 1: Imagine standing on the shore, looking out at the waves
• 1:14:00
  Speaker 1: extending to the horizon, knowing the ocean continues far beyond
• 1:14:04
  Speaker 1: what the eye can see. The entire Earth, in all
• 1:14:07
  Speaker 1: its diversity and scale, is like a grain of sand
• 1:14:11
  Speaker 1: on that beach. That's the observable universe, a speck in
• 1:14:14
  Speaker 1: the wider cosmos. This idea began to take shape about
• 1:14:18
  Speaker 1: a century ago thanks to the tireless work of American
• 1:14:21
  Speaker 1: astronomer Edwin Hubble. In the 1920s, while working at the
• 1:14:25
  Speaker 1: Mount Wilson Observatory in California, Hubble began using the largest
• 1:14:29
  Speaker 1: telescope in the world at the time, the Hooker 100-inch
• 1:14:32
  Speaker 1: reflector to peer at distant nebulae, or clouds in space.
• 1:14:37
  Speaker 1: Some of these nebulae, like the Andromeda Nebulae, had been
• 1:14:40
  Speaker 1: observed by astronomers for centuries, but they were generally thought
• 1:14:43
  Speaker 1: to be clouds of gas and dust within our own galaxy,
• 1:14:46
  Speaker 1: the Milky Way. Hubble, however, noticed something peculiar about them.
• 1:14:51
  Speaker 1: Using a special type of pulsating star called a Cepheid variable,
• 1:14:55
  Speaker 1: Hubble was able to estimate the distances to these nebulae.
• 1:14:59
  Speaker 1: To his surprise, they were incredibly far away, much farther
• 1:15:02
  Speaker 1: than the size of the Milky Way. Hubble realised that
• 1:15:05
  Speaker 1: these weren't nebulae within our galaxy at all. They were
• 1:15:08
  Speaker 1: entire galaxies in their own right, each containing billions of stars.
• 1:15:13
  Speaker 1: This was a transformative discovery. The universe was far bigger
• 1:15:17
  Speaker 1: than anyone had imagined. Our Milky Way galaxy, once thought
• 1:15:21
  Speaker 1: to be the entire universe, was just one of countless
• 1:15:24
  Speaker 1: island universes dotting the cosmic sea. But Hubble's groundbreaking discoveries
• 1:15:28
  Speaker 1: didn't stop there. As he studied the light from these
• 1:15:31
  Speaker 1: distant galaxies, he noticed another peculiar thing. Their light was
• 1:15:36
  Speaker 1: shifted toward the red end of the spectrum, like the
• 1:15:38
  Speaker 1: pitch of a receding train's whistle drops as it moves
• 1:15:40
  Speaker 1: away from you. This red shift was greater for more
• 1:15:43
  Speaker 1: distant galaxies. Hubble realised this was evidence that the galaxies
• 1:15:47
  Speaker 1: were moving away from us. And not just that. The
• 1:15:50
  Speaker 1: farther away a galaxy was, the faster it was receding.
• 1:15:53
  Speaker 1: The universe wasn't static, but expanding. This revolutionary finding overturned
• 1:15:59
  Speaker 1: the conventional wisdom of the time. The prevailing view was
• 1:16:02
  Speaker 1: that the universe was eternal and unchanging. the steady state model.
• 1:16:07
  Speaker 1: But Hubble's data clearly showed that the universe was in
• 1:16:09
  Speaker 1: fact dynamic and evolving. Hubble's observations led him to a
• 1:16:13
  Speaker 1: profound conclusion, now known as Hubble's Law. The universe is
• 1:16:18
  Speaker 1: uniformly expanding, with galaxies moving away from each other like
• 1:16:22
  Speaker 1: raisins in a rising loaf of bread. The greater the
• 1:16:25
  Speaker 1: distance between any two galaxies, the faster they recede from
• 1:16:29
  Speaker 1: one another. It was a stunning realisation. The universe wasn't
• 1:16:32
  Speaker 1: just unimaginably vast in space, it was also changing over time.
• 1:16:37
  Speaker 1: And if you rewind the cosmic clock playing the expansion
• 1:16:39
  Speaker 1: in reverse, everything converges to a single point or singularity
• 1:16:43
  Speaker 1: in the finite past. The implication was clear, though controversial
• 1:16:47
  Speaker 1: at the time, the universe had a beginning. The idea
• 1:16:51
  Speaker 1: of a universe with a finite age, born in a
• 1:16:53
  Speaker 1: cosmic birth or Big Bang, represented a seismic shift in
• 1:16:57
  Speaker 1: our understanding of the cosmos. It was a radical departure
• 1:17:00
  Speaker 1: from the steady-state view, Though initially met with scepticism, the
• 1:17:04
  Speaker 1: evidence mounted over the 20th century. The discovery of the
• 1:17:08
  Speaker 1: cosmic microwave background in the 1960s, the leftover heat of
• 1:17:12
  Speaker 1: the Big Bang, was a major confirmation of the theory.
• 1:17:15
  Speaker 1: The static universe gave way to the idea of cosmic evolution,
• 1:17:19
  Speaker 1: of a universe with a history unfolding over eons. As
• 1:17:22
  Speaker 1: we'll explore, that evolutionary story has taken the universe from
• 1:17:26
  Speaker 1: an infinitesimal speck to the vast expanse we see today.
• 1:17:30
  Speaker 1: and carried much of its volume forever beyond our view.
• 1:17:34
  Speaker 1: The Big Bang set cosmic expansion in motion, and in
• 1:17:37
  Speaker 1: doing so, it ensured that the observable universe would only
• 1:17:40
  Speaker 1: ever be a small portion of the grander whole. But
• 1:17:44
  Speaker 1: let's not get ahead of ourselves. To truly appreciate why
• 1:17:47
  Speaker 1: we can only see a slice of the universe, we
• 1:17:49
  Speaker 1: have to go back to the beginning, to the primordial
• 1:17:52
  Speaker 1: fireball of the Big Bang itself, 13.8 billion years ago.
• 1:17:57
  Speaker 1: Imagine the entire observable universe compressed into a volume smaller
• 1:18:01
  Speaker 1: than an atom. That's the state of the cosmos in
• 1:18:04
  Speaker 1: its first fraction of a second. Everything is squeezed into
• 1:18:07
  Speaker 1: an infinitesimally small, searing, hot, densely compressed point. At this moment,
• 1:18:14
  Speaker 1: the four fundamental forces that govern the universe, gravity, electromagnetism,
• 1:18:19
  Speaker 1: and the strong and weak nuclear forces, are unified as
• 1:18:22
  Speaker 1: a single, immensely powerful force. The stuff of the universe
• 1:18:27
  Speaker 1: is a seething, turbulent froth of energy, so hot that
• 1:18:30
  Speaker 1: not even atoms can form. This is where the story
• 1:18:33
  Speaker 1: of our universe begins, but the idea that the universe
• 1:18:36
  Speaker 1: had a beginning was a radical one until the early
• 1:18:38
  Speaker 1: 20th century. Scientists largely believed in an eternal and unchanging
• 1:18:43
  Speaker 1: steady-state cosmos with no beginning or end. It took the
• 1:18:47
  Speaker 1: insights of astronomer and physicist Georges Lemaître to begin challenging
• 1:18:50
  Speaker 1: that notion. Born in 1894 in Belgium, Lemaître was both
• 1:18:54
  Speaker 1: a devout Catholic priest and a brilliant scientist. In the
• 1:18:58
  Speaker 1: late 1920s, he derived what became known as Hubble's Law,
• 1:19:01
  Speaker 1: from Einstein's equations of general relativity, before Hubble did so observationally,
• 1:19:06
  Speaker 1: showing that the universe must be expanding. Moreover, Lemaître took
• 1:19:11
  Speaker 1: this idea to its logical conclusion. If the universe is expanding,
• 1:19:15
  Speaker 1: then it must have been smaller in the past. And
• 1:19:18
  Speaker 1: if you rewind far enough, the entire universe would have
• 1:19:21
  Speaker 1: been compressed into what he called the primeval atom, a
• 1:19:24
  Speaker 1: single point from which the cosmos burst forth. It was
• 1:19:27
  Speaker 1: a revolutionary idea. Lemaître envisioned the birth of space and
• 1:19:31
  Speaker 1: time in a now without yesterday, as he poetically put it.
• 1:19:34
  Speaker 1: His primeval atom represented a physical beginning to the universe,
• 1:19:38
  Speaker 1: a day without yesterday. Though Lemaître' s idea, which became known
• 1:19:42
  Speaker 1: as the Big Bang theory, was initially met with scepticism,
• 1:19:45
  Speaker 1: it gradually gained traction as evidence mounted. The discovery of
• 1:19:49
  Speaker 1: the cosmic microwave background radiation in the 1960s was a
• 1:19:53
  Speaker 1: major milestone, confirming a key prediction of the theory. Lemaître' s
• 1:19:58
  Speaker 1: insights paved the way for the modern understanding of cosmic evolution.
• 1:20:02
  Speaker 1: The universe began in an incredibly hot, dense state around 13.8
• 1:20:06
  Speaker 1: billion years ago and has been expanding and cooling ever since.
• 1:20:10
  Speaker 1: The fundamental forces decoupled, particles formed, light elements coalesced, matter
• 1:20:16
  Speaker 1: clumped into galaxies and stars, stars forged heavier elements, planets
• 1:20:21
  Speaker 1: formed around second-generation stars, and on at least one such planet,
• 1:20:25
  Speaker 1: life took root and eventually began to ponder its cosmic origins.
• 1:20:29
  Speaker 1: It's a mind-expanding story, and one we'll explore in more depth,
• 1:20:33
  Speaker 1: but the key point is that the universe has a history.
• 1:20:37
  Speaker 1: It has evolved profoundly over eons. carrying the observable portion
• 1:20:41
  Speaker 1: of the cosmos along with it as it expands. And
• 1:20:44
  Speaker 1: most relevant to our question, the Big Bang means that
• 1:20:46
  Speaker 1: the universe has a finite age. The cosmos may or
• 1:20:50
  Speaker 1: may not be spatially infinite, but it is temporarily finite.
• 1:20:53
  Speaker 1: It had a beginning in time. And that means that
• 1:20:56
  Speaker 1: light has only had a certain amount of time to travel.
• 1:20:59
  Speaker 1: Light is the fastest thing in the universe, zipping along
• 1:21:02
  Speaker 1: at about 300,000 kilometers per second. But even at that
• 1:21:06
  Speaker 1: incredible speed, it still takes time to get from one
• 1:21:10
  Speaker 1: place to another. The light from the Sun takes about
• 1:21:12
  Speaker 1: 8 minutes to reach Earth. The light from Proxima Centauri,
• 1:21:16
  Speaker 1: the nearest star beyond the Sun, takes 4.2 years to
• 1:21:19
  Speaker 1: bridge the gap. On cosmic scales, the travel time for
• 1:21:23
  Speaker 1: light is even more noticeable. The Andromeda Galaxy, our nearest
• 1:21:26
  Speaker 1: major galactic neighbour, is about 2.5 million light-years away, meaning
• 1:21:31
  Speaker 1: the light we see from it tonight left Andromeda 2.5
• 1:21:34
  Speaker 1: million years ago, when early hominins were just beginning to
• 1:21:37
  Speaker 1: walk the plains of Africa. The most distant observable galaxies
• 1:21:41
  Speaker 1: are billions of light years away. Their light has journeyed
• 1:21:44
  Speaker 1: for billions of years across expanding space to reach us.
• 1:21:48
  Speaker 1: The light of the cosmic microwave background has been travelling
• 1:21:50
  Speaker 1: for 13.8 billion years since shortly after the Big Bang,
• 1:21:55
  Speaker 1: before stars and galaxies had even formed. But there's a
• 1:21:58
  Speaker 1: limit to how far we can see. Because the universe
• 1:22:01
  Speaker 1: is 13.8 billion years old, light has only had 13.8
• 1:22:02
  Speaker 1: billion years to travel. There is a cosmic horizon, a
• 1:22:10
  Speaker 1: boundary in space, beyond which we cannot see. Not because
• 1:22:14
  Speaker 1: there's nothing there, but because the light from those regions
• 1:22:17
  Speaker 1: hasn't had time to reach us yet. As far as
• 1:22:20
  Speaker 1: we know, the universe continues on past that horizon. We
• 1:22:23
  Speaker 1: have no reason to believe space just stops, but we
• 1:22:26
  Speaker 1: can't directly observe those faraway reaches. They're cut off from
• 1:22:30
  Speaker 1: our view, hidden beyond a veil of time and distance.
• 1:22:34
  Speaker 1: When we gaze at the night sky, we're seeing a
• 1:22:36
  Speaker 1: cosmic cross-section, a slice of the universe that's 13.8 billion
• 1:22:40
  Speaker 1: years old in every direction. Telescopically, we can see back
• 1:22:45
  Speaker 1: to about 400,000 years after the Big Bang, when the
• 1:22:48
  Speaker 1: universe cooled enough for light to travel freely. Everything we
• 1:22:51
  Speaker 1: see in the sky, from stars to galaxies to the
• 1:22:54
  Speaker 1: cosmic microwave background, lies within our cosmic horizon. But the
• 1:22:59
  Speaker 1: key thing to remember is that this horizon isn't fixed
• 1:23:02
  Speaker 1: in space. It's fixed in time. The observable universe is
• 1:23:07
  Speaker 1: the part of the universe that light has had time
• 1:23:09
  Speaker 1: to reach us from since the Big Bang. As time
• 1:23:12
  Speaker 1: goes on, the horizon expands, slowly unveiling regions that were
• 1:23:15
  Speaker 1: previously too far for light to have reached us. In
• 1:23:18
  Speaker 1: a sense, we're like archaeologists gradually uncovering a buried city.
• 1:23:23
  Speaker 1: Each passing year, cosmic expansion lays bare a new layer
• 1:23:26
  Speaker 1: of the universe that was previously beyond our view. The
• 1:23:30
  Speaker 1: light from more distant regions finally completes its journey to
• 1:23:33
  Speaker 1: our telescopes, but it's a slow process, The observable universe
• 1:23:37
  Speaker 1: grows by one light year per year, as light from
• 1:23:40
  Speaker 1: slightly farther out finally reaches us. In a hundred years,
• 1:23:44
  Speaker 1: the radius of the observable universe will be 100 light
• 1:23:47
  Speaker 1: years larger. In a million years, it will be a
• 1:23:50
  Speaker 1: million light years larger. Still, there will always be a
• 1:23:53
  Speaker 1: limit to what we can see, a cosmic horizon beyond
• 1:23:57
  Speaker 1: which the universe continues unexplored. The Big Bang set the
• 1:24:02
  Speaker 1: clock ticking, and even at the speed of light, There's
• 1:24:05
  Speaker 1: only so far the universe's age lets us see. It's
• 1:24:08
  Speaker 1: a poignant thought. The observable universe is staggeringly vast, but
• 1:24:12
  Speaker 1: it's still just a glimpse of a larger whole, most
• 1:24:15
  Speaker 1: of it carried beyond our view by the arrow of
• 1:24:17
  Speaker 1: time and the expansion of space. We're like castaways on
• 1:24:20
  Speaker 1: an island, gazing out at an ocean that extends past
• 1:24:24
  Speaker 1: the horizon, knowing there are distant lands we cannot see
• 1:24:27
  Speaker 1: and may never visit. Edwin Hubble's groundbreaking observations in the
• 1:24:32
  Speaker 1: 1920s not only revealed the existence of distant galaxies and
• 1:24:36
  Speaker 1: the expansion of the universe, they also hinted at something
• 1:24:40
  Speaker 1: even more profound, regions of the universe that are forever
• 1:24:43
  Speaker 1: beyond our cosmic horizon. As Hubble studied the redshifts of
• 1:24:47
  Speaker 1: distant galaxies, the signature of cosmic expansion stretching their light,
• 1:24:52
  Speaker 1: he realised something remarkable. The farther away a galaxy is,
• 1:24:56
  Speaker 1: the faster it's receding from us. This wasn't just an
• 1:24:59
  Speaker 1: odd quirk, it was a fundamental feature of the universe.
• 1:25:03
  Speaker 1: It became known as Hubble's Law. Cosmic expansion carries galaxies
• 1:25:07
  Speaker 1: away from each other, with more distant galaxies receding faster.
• 1:25:11
  Speaker 1: At first glance, this seems to violate a cardinal rule
• 1:25:14
  Speaker 1: of physics, that nothing can travel faster than the speed
• 1:25:17
  Speaker 1: of light. How can distant galaxies possibly recede faster than
• 1:25:21
  Speaker 1: this cosmic speed limit? The key is that the galaxies
• 1:25:24
  Speaker 1: themselves aren't breaking the light barrier. Instead, it's the space
• 1:25:28
  Speaker 1: between them that's expanding. The galaxies are like raisins in
• 1:25:32
  Speaker 1: a rising loaf of bread. They're not zooming through space,
• 1:25:35
  Speaker 1: but being carried along as the space they inhabit stretches out.
• 1:25:39
  Speaker 1: And here's the thing. There's no limit to how far
• 1:25:42
  Speaker 1: space itself can expand. While matter and energy are constrained
• 1:25:45
  Speaker 1: by the speed of light, space itself can stretch faster
• 1:25:49
  Speaker 1: than light. It's not bound by the same rules. This
• 1:25:52
  Speaker 1: means that beyond a certain distance, space is carrying galaxies
• 1:25:55
  Speaker 1: away from us faster than the speed of light. From
• 1:25:58
  Speaker 1: our perspective... Those galaxies are receding so quickly that their
• 1:26:02
  Speaker 1: light can never catch up to us. They've crossed a
• 1:26:04
  Speaker 1: point of no return known as the cosmic event horizon.
• 1:26:08
  Speaker 1: It's a mind-bending concept. There are regions of the universe
• 1:26:11
  Speaker 1: that we can never see, not because they're too far away,
• 1:26:15
  Speaker 1: but because they're being swept away from us too quickly
• 1:26:18
  Speaker 1: for their light to ever close the gap. Even if
• 1:26:21
  Speaker 1: we left today on a journey to one of these
• 1:26:22
  Speaker 1: galaxies at the speed of light, we would never reach them.
• 1:26:25
  Speaker 1: Space would be expanding ahead of us faster than we
• 1:26:28
  Speaker 1: could travel through it. These galaxies are effectively lost to us,
• 1:26:32
  Speaker 1: cut off by the relentless expansion of the universe. Their
• 1:26:36
  Speaker 1: light is like a runner on a racetrack that keeps
• 1:26:38
  Speaker 1: getting longer. The finish line recedes faster than the runner
• 1:26:41
  Speaker 1: can sprint. For the most distant galaxies we can currently see,
• 1:26:45
  Speaker 1: this cosmic event horizon is already just 5 billion light
• 1:26:48
  Speaker 1: years away. A distance that sounds immense, but is a
• 1:26:52
  Speaker 1: mere stone's throw on cosmic scales. It's a poignant thought.
• 1:26:56
  Speaker 1: As we look out into the universe, we're not just
• 1:26:58
  Speaker 1: seeing distant galaxies. We're watching them slip away. And for
• 1:27:02
  Speaker 1: the most distant reaches, that farewell is forever. The light
• 1:27:05
  Speaker 1: from those galaxies will never reach us, even given an
• 1:27:08
  Speaker 1: eternity to travel. They're sailing over the cosmic horizon, never
• 1:27:12
  Speaker 1: to be glimpsed again from our shores. It's a natural
• 1:27:15
  Speaker 1: consequence of living in an expanding universe that's a finite age.
• 1:27:20
  Speaker 1: If the cosmos had no beginning, and galaxies were eternally receding,
• 1:27:24
  Speaker 1: everything beyond our local group would already be forever lost
• 1:27:27
  Speaker 1: from view. It's only because cosmic expansion has a starting
• 1:27:31
  Speaker 1: point in the Big Bang that we can see as
• 1:27:33
  Speaker 1: much as we do. But even that view is temporary.
• 1:27:36
  Speaker 1: As the eons unfold, more and more of the universe
• 1:27:39
  Speaker 1: will slip across the event horizon, winking out like receding
• 1:27:42
  Speaker 1: ships sailing over the Earth's curvature. A hundred billion years
• 1:27:47
  Speaker 1: from now, all galaxies beyond our local group will have
• 1:27:49
  Speaker 1: forever disappeared. The secrets of their stars, their worlds, Their
• 1:27:53
  Speaker 1: potential for life will be sealed away, carried off by
• 1:27:57
  Speaker 1: the incessant tide of expanding space. It's a melancholy thought.
• 1:28:02
  Speaker 1: We're afforded a brief glimpse of the cosmos, a fleeting
• 1:28:05
  Speaker 1: window in which to drink in the majesty of the
• 1:28:08
  Speaker 1: universe in its youth. But as time goes on, that
• 1:28:11
  Speaker 1: view will narrow, the horizons will close in, and the
• 1:28:14
  Speaker 1: rest of the universe will pass silently into the night,
• 1:28:17
  Speaker 1: lost to us except as a fading memory. In this sense,
• 1:28:21
  Speaker 1: we're profoundly fortunate. We've arisen as a species at a
• 1:28:24
  Speaker 1: time when the observable universe is gloriously vast, with billions
• 1:28:29
  Speaker 1: of galaxies strewn across billions of light-years still within our view.
• 1:28:34
  Speaker 1: Future civilizations will survey an emptier, lonelier cosmos, with most
• 1:28:38
  Speaker 1: of the universe's grandeur already stolen away by the ceaseless
• 1:28:41
  Speaker 1: expansion of space. So as we ponder what lies beyond
• 1:28:45
  Speaker 1: the edge of the universe, it's worth appreciating the slice
• 1:28:48
  Speaker 1: of it that we can see. That cosmic horizon represents
• 1:28:51
  Speaker 1: a poignant boundary. The limit of all we can ever
• 1:28:55
  Speaker 1: know through direct observation is a reminder of how fleetingly
• 1:28:58
  Speaker 1: we swim in the vast cosmic ocean. But it's also
• 1:29:01
  Speaker 1: an invitation to wonder. In our mind's eye, we can
• 1:29:05
  Speaker 1: voyage past that horizon, imagining the unseen vistas that lie beyond.
• 1:29:10
  Speaker 1: The observable universe may be our entire world, but it's
• 1:29:13
  Speaker 1: far from all there is. Our cosmic horizon is not
• 1:29:16
  Speaker 1: a physical boundary, but rather the limit of how far
• 1:29:19
  Speaker 1: light has travelled since the universe's fiery birth. As we
• 1:29:23
  Speaker 1: peer across billions of light years to the edge of
• 1:29:26
  Speaker 1: the observable universe, we're looking back through time, seeing ancient
• 1:29:30
  Speaker 1: light that set out eons ago and is only now
• 1:29:32
  Speaker 1: reaching our telescopes. The nature of light itself sets this
• 1:29:36
  Speaker 1: limit on our cosmic view. Though often described as the
• 1:29:39
  Speaker 1: fastest thing in the universe, even light speed is not infinite.
• 1:29:43
  Speaker 1: In the vastness of the cosmos, it can only travel
• 1:29:46
  Speaker 1: so far over the universe's 13.8 billion year history. The
• 1:29:50
  Speaker 1: most distant light we can see coming to us from
• 1:29:53
  Speaker 1: every direction, delineates a spherical boundary centred on Earth that
• 1:29:57
  Speaker 1: we call the observable universe. But make no mistake, the
• 1:30:01
  Speaker 1: observable universe is not all there is. Far from it.
• 1:30:04
  Speaker 1: Beyond that boundary, the universe continues indefinitely, perhaps even infinitely.
• 1:30:10
  Speaker 1: There are countless stars, galaxies and wonders that we cannot see,
• 1:30:14
  Speaker 1: not because they don't exist, but because their light has
• 1:30:17
  Speaker 1: not yet had time to reach us. The observable universe
• 1:30:21
  Speaker 1: is just our local patch, a finite sphere of space
• 1:30:24
  Speaker 1: and time embedded in a far grander cosmos. It can
• 1:30:27
  Speaker 1: be hard to wrap our minds around this cosmic horizon.
• 1:30:30
  Speaker 1: When we look out into the night sky, it feels
• 1:30:33
  Speaker 1: like we're seeing everything. But the truth is far more humbling.
• 1:30:37
  Speaker 1: Imagine you're swimming in the middle of a vast, misty ocean,
• 1:30:41
  Speaker 1: with a visibility of 100 metres in every direction. Beyond
• 1:30:44
  Speaker 1: your little sphere of clarity, the ocean continues unabated, but
• 1:30:49
  Speaker 1: you can't see it, Even if you had supremely acute vision,
• 1:30:52
  Speaker 1: you couldn't see further than 100 metres through the mist.
• 1:30:56
  Speaker 1: So your observable ocean is a sphere 200 metres across,
• 1:31:00
  Speaker 1: centred on you. No matter where you swim, this sphere
• 1:31:03
  Speaker 1: of visibility comes with you. But the vaster ocean is
• 1:31:06
  Speaker 1: always there beyond it. Our observable universe is a bit
• 1:31:09
  Speaker 1: like that, but on a grandly cosmic scale. The 46
• 1:31:14
  Speaker 1: billion light-year radius... marks the distance that light could have
• 1:31:17
  Speaker 1: travelled in the 13.8 billion years since the Big Bang.
• 1:31:21
  Speaker 1: As the universe ages and light keeps propagating, we can
• 1:31:24
  Speaker 1: see further and further. But there will always be a
• 1:31:27
  Speaker 1: cosmic horizon, a frontier of the unknown, with uncharted realms beyond.
• 1:31:32
  Speaker 1: The existence of this horizon speaks to how special light is.
• 1:31:36
  Speaker 1: In our universe, nothing can outrun a light beam. You
• 1:31:39
  Speaker 1: could race a photon across the cosmos with the fastest
• 1:31:42
  Speaker 1: rocket ship imaginable, and you would still lose. Light is
• 1:31:46
  Speaker 1: the ultimate speed limit, the velocity that sets the very
• 1:31:49
  Speaker 1: rhythm and scale of causality and change in the cosmos.
• 1:31:52
  Speaker 1: It's why the night sky is not a tapestry woven
• 1:31:54
  Speaker 1: all at once, but a cascade of nested snapshots from
• 1:31:57
  Speaker 1: across the eons. So in the darkness behind your closed eyes,
• 1:32:01
  Speaker 1: as you drift towards sleep, ponder the peculiar fact that
• 1:32:04
  Speaker 1: the observable universe is not static, but ever-growing as light
• 1:32:08
  Speaker 1: from distant realms finally reaches us after its long cosmic journey.
• 1:32:13
  Speaker 1: With every passing second, photons that have been in flight
• 1:32:16
  Speaker 1: for billions of years are plinking into telescopes and onto
• 1:32:19
  Speaker 1: the retinas of wide-eyed stargazers. The boundary of the known
• 1:32:23
  Speaker 1: is creeping ever outwards, bringing glimmers of new cosmic vistas
• 1:32:27
  Speaker 1: into view. But it's not just astronomers and their instruments
• 1:32:30
  Speaker 1: capturing this ancient light. When you look up at the
• 1:32:33
  Speaker 1: stars blinking through the darkness, some of those photons have
• 1:32:37
  Speaker 1: been crossing the cosmos since the time of the dinosaurs.
• 1:32:40
  Speaker 1: They've passed through the depths of intergalactic space, shimmied through
• 1:32:44
  Speaker 1: shimmering veils of dust and gas, and finally alighted in
• 1:32:47
  Speaker 1: your eye after a journey of millions or billions of years.
• 1:32:51
  Speaker 1: In a very real sense, stargazing is time travel, sipping
• 1:32:54
  Speaker 1: from the deep cosmic past. But even this grand revelation,
• 1:32:58
  Speaker 1: that we are always peering into the universe's history, has
• 1:33:01
  Speaker 1: a curious coda. Because the cosmos is expanding, there are
• 1:33:05
  Speaker 1: stars whose ancient light will just barely reach us, their
• 1:33:08
  Speaker 1: photons skirting across the observable universe like pebbles gliding along
• 1:33:12
  Speaker 1: the surface of a pond. And there are other stars,
• 1:33:15
  Speaker 1: perhaps innumerable, whose light has already missed the boat, destined
• 1:33:19
  Speaker 1: to traverse an ever-widening cosmic gulf that will always outpace
• 1:33:23
  Speaker 1: its velocity. In a strange and poetic way, the expansion
• 1:33:27
  Speaker 1: of the universe is like a receding tide, steadily carrying
• 1:33:30
  Speaker 1: away stars and galaxies in its ethereal currents. Over countless eons,
• 1:33:35
  Speaker 1: more and more of the universe will slip over the
• 1:33:37
  Speaker 1: cosmic horizon never to be seen again from our vantage point.
• 1:33:42
  Speaker 1: As space itself stretches between us and these distant realms,
• 1:33:46
  Speaker 1: it will eventually be stretching faster than light, causing these
• 1:33:49
  Speaker 1: luminous specks to flicker out of our observable domain like
• 1:33:53
  Speaker 1: fireflies winking into the night. There's a profound loneliness to
• 1:33:57
  Speaker 1: this picture, a cosmos where even the stars we hold
• 1:34:00
  Speaker 1: dear will eventually recede into unseeable realms, their ancient light
• 1:34:04
  Speaker 1: reaching into an empty sky. But there's also... a breathtaking grandeur,
• 1:34:10
  Speaker 1: a universe grander and more expansive than we can ever
• 1:34:14
  Speaker 1: directly know, with our little oasis of stars hurtling through
• 1:34:18
  Speaker 1: uncharted depths of space and time. In this view, even
• 1:34:23
  Speaker 1: the darkness of night takes on a new meaning, not
• 1:34:26
  Speaker 1: an empty void, but a frontier, rippling with the energy
• 1:34:30
  Speaker 1: of an expanding universe that's carrying the most distant lights
• 1:34:33
  Speaker 1: beyond our view. And so, as you settle deeper into
• 1:34:37
  Speaker 1: your pillows, Let your mind wander out to the edge
• 1:34:39
  Speaker 1: of the observable universe and beyond. Picture the glittering tapestry
• 1:34:44
  Speaker 1: of stars splayed out across the cosmos, some forever observable,
• 1:34:48
  Speaker 1: some destined to slip away. Marvel at the fact that,
• 1:34:52
  Speaker 1: even now, the most ancient light is still arriving, traversing
• 1:34:56
  Speaker 1: those vast gulfs of space and time to paint our skies.
• 1:34:59
  Speaker 1: And as your breathing deepens and sleep gathers around you
• 1:35:02
  Speaker 1: like a warm cosmic blanket, Take comfort in knowing that
• 1:35:05
  Speaker 1: though the universe may be grander and more inscrutable than
• 1:35:08
  Speaker 1: we can imagine, we are yet an integral part of
• 1:35:11
  Speaker 1: its story. For our minds, our dreams, our ceaseless quest
• 1:35:15
  Speaker 1: for knowledge, these too are expressions of the cosmos, as
• 1:35:19
  Speaker 1: surely as stars and galaxies. So let the soft darkness
• 1:35:23
  Speaker 1: cradle you, and dream of ancient starlight dancing across oceans
• 1:35:27
  Speaker 1: of space and time, whispering the secrets of a universe
• 1:35:30
  Speaker 1: vaster and more wondrous than we may ever know. The
• 1:35:33
  Speaker 1: work of Edwin Hubble in the 1920s marked a turning
• 1:35:35
  Speaker 1: point in our understanding of the cosmos. Hubble, born in
• 1:35:39
  Speaker 1: Missouri in 1889, was an American astronomer whose groundbreaking observations
• 1:35:44
  Speaker 1: would forever change our perception of the universe and our
• 1:35:46
  Speaker 1: place within it. As a young man, Hubble studied math,
• 1:35:50
  Speaker 1: astronomy and philosophy, nurturing a lifelong passion for unravelling the
• 1:35:54
  Speaker 1: mysteries of the heavens. He served in World War I
• 1:35:57
  Speaker 1: before completing his doctorate and beginning his career at the
• 1:35:59
  Speaker 1: Mount Wilson Observatory in California. There, he had access to
• 1:36:04
  Speaker 1: the most powerful telescope of its day, the 100-inch Hooker Reflector.
• 1:36:09
  Speaker 1: Night after night, Hubble would aim this mighty instrument at
• 1:36:11
  Speaker 1: the sky, meticulously cataloguing and studying the faint, fuzzy nebulae
• 1:36:17
  Speaker 1: that astronomers had puzzled over for centuries. Many believed these
• 1:36:20
  Speaker 1: nebulae were relatively close clouds of gas and dust within
• 1:36:23
  Speaker 1: our own Milky Way galaxy, but Hubble was about to
• 1:36:26
  Speaker 1: make a discovery that would shatter that assumption and reveal
• 1:36:29
  Speaker 1: the true immensity of the universe. Using the Hooker telescope,
• 1:36:33
  Speaker 1: Hubble was able to resolve individual stars within several of
• 1:36:36
  Speaker 1: these spiral nebulae, including the majestic Andromeda Nebula. To his surprise,
• 1:36:42
  Speaker 1: he identified a type of pulsating star called a Cepheid variable,
• 1:36:46
  Speaker 1: a standard candle whose intrinsic brightness could be determined based
• 1:36:49
  Speaker 1: on its pulsation rate. By comparing the apparent brightness of
• 1:36:53
  Speaker 1: these stars to their known luminosity, Hubble could calculate their distance.
• 1:36:57
  Speaker 1: The results were staggering. The seafeed variables, and thus the
• 1:37:01
  Speaker 1: nebulae that contained them, were far too distant to be
• 1:37:04
  Speaker 1: part of our Milky Way. Andromeda, Hubble determined, was a
• 1:37:09
  Speaker 1: separate galaxy in its own right, one of many island
• 1:37:12
  Speaker 1: universes populating the cosmos at inconceivable distances. The universe, it seemed,
• 1:37:18
  Speaker 1: was vaster than anyone had dared to imagine. But Hubble's
• 1:37:21
  Speaker 1: most profound discovery was yet to come, as he studied
• 1:37:24
  Speaker 1: the spectra of light from dozens of distant galaxies, he
• 1:37:28
  Speaker 1: noticed a curious pattern. The spectral lines of known elements
• 1:37:33
  Speaker 1: were consistently shifted toward the red end of the spectrum,
• 1:37:36
  Speaker 1: and this redshift was larger for fainter, more distant galaxies.
• 1:37:41
  Speaker 1: It was as if the galaxies were universally rushing away
• 1:37:44
  Speaker 1: from us, with more distant ones receding faster. The explanation
• 1:37:49
  Speaker 1: for this lay in the work of Georges Lemaître, a
• 1:37:51
  Speaker 1: Belgian physicist and Catholic priest, who had proposed that the
• 1:37:55
  Speaker 1: universe began in a primordial cosmic egg. and had been
• 1:37:59
  Speaker 1: expanding ever since. Hubble's observations provided the first empirical evidence
• 1:38:04
  Speaker 1: for this idea. The redshifts he observed were due to
• 1:38:07
  Speaker 1: the stretching of light waves by the expansion of space itself.
• 1:38:12
  Speaker 1: Hubble went on to plot the velocities of galaxies against
• 1:38:14
  Speaker 1: their distances, finding a striking linear relationship that became known
• 1:38:18
  Speaker 1: as Hubble's law. The farther a galaxy was, the faster
• 1:38:23
  Speaker 1: it appeared to be receding from us. This was not
• 1:38:26
  Speaker 1: due to the galaxies themselves moving through space, but the
• 1:38:29
  Speaker 1: expansion of the space between them. The universe, Hubble showed,
• 1:38:33
  Speaker 1: was not static, but dynamic, constantly growing larger. The implications
• 1:38:37
  Speaker 1: were profound. If the universe was expanding, then winding the
• 1:38:42
  Speaker 1: clock backwards would imply a beginning. A definite moment when
• 1:38:45
  Speaker 1: all matter and energy were compressed into an infinitesimal volume
• 1:38:48
  Speaker 1: before rapidly dilating. The Big Bang theory, as it would
• 1:38:52
  Speaker 1: come to be known, had found its first observational support. Moreover,
• 1:38:57
  Speaker 1: the expansion of the universe carried a poignant implication. At
• 1:39:01
  Speaker 1: immense distances, the stretching of space would be so extreme
• 1:39:04
  Speaker 1: that it would carry galaxies away from us faster than
• 1:39:07
  Speaker 1: the speed of light. There would come a point where
• 1:39:10
  Speaker 1: the light from these distant galaxies would never reach us,
• 1:39:13
  Speaker 1: as the space it needed to traverse was expanding too rapidly.
• 1:39:18
  Speaker 1: This boundary, known as the Cosmic Horizon, represented the ultimate
• 1:39:22
  Speaker 1: limit of our view, a spherical shell of space, centred
• 1:39:25
  Speaker 1: on us, roughly 46 billion light-years in radius. Light from
• 1:39:31
  Speaker 1: beyond this shell, emitted in the distant past, was destined
• 1:39:34
  Speaker 1: to remain forever out of sight, its source galaxies swept
• 1:39:38
  Speaker 1: away by the relentless tide of expanding space. Hubble's discoveries
• 1:39:42
  Speaker 1: painted a picture of a universe far grander and more
• 1:39:45
  Speaker 1: expansive than we had ever conceived. an eternal stretching fabric
• 1:39:50
  Speaker 1: of space-time, dotted with innumerable island galaxies. But they also
• 1:39:55
  Speaker 1: revealed how much of that universe is destined to pass
• 1:39:58
  Speaker 1: out of our view, carried by the same cosmic expansion
• 1:40:01
  Speaker 1: that brought it into being. It's a poignant realisation that
• 1:40:05
  Speaker 1: the light from countless billions of galaxies emitted eons ago
• 1:40:09
  Speaker 1: is fated to recede forever beyond the boundary of our
• 1:40:12
  Speaker 1: observable universe, never to meet the eyes of any terrestrial astronomer.
• 1:40:17
  Speaker 1: The secrets they hold, the cosmic stories they could tell,
• 1:40:21
  Speaker 1: remain untold, a reminder of the tantalising vastness forever beyond
• 1:40:25
  Speaker 1: our reach. As we contemplate this, we might feel a
• 1:40:29
  Speaker 1: sense of melancholy, perhaps even loneliness. To know that so
• 1:40:33
  Speaker 1: much of the cosmos is slipping continuously out of our
• 1:40:36
  Speaker 1: view can make the darkness of the night sky seem
• 1:40:38
  Speaker 1: a little emptier. The observable universe, vast as it is,
• 1:40:43
  Speaker 1: is but a diminishing island in the uncharted oceans. of
• 1:40:46
  Speaker 1: an ever-expanding cosmos. But I think there is beauty and
• 1:40:50
  Speaker 1: poetry to be found here too. The expansion of the
• 1:40:53
  Speaker 1: universe is, after all, a key part of the story
• 1:40:55
  Speaker 1: of us. Without it, the raw material spat forth in
• 1:40:59
  Speaker 1: the Big Bang may never have coalesced into galaxies, stars, planets,
• 1:41:04
  Speaker 1: and thinking beings like ourselves. We are, each of us,
• 1:41:08
  Speaker 1: children of the cosmos, our atoms forged in the hearts
• 1:41:11
  Speaker 1: of long-dead stars and gathered together on this pale blue
• 1:41:14
  Speaker 1: dot we call home. And though much of the universe
• 1:41:17
  Speaker 1: may be forever hidden from us, we can still marvel
• 1:41:20
  Speaker 1: at the ingenuity and dedication of thinkers like Edwin Hubble,
• 1:41:24
  Speaker 1: who peered deeper into the universe than anyone before him
• 1:41:27
  Speaker 1: and revealed just how immense and majestic our cosmos truly is.
• 1:41:31
  Speaker 1: His work is a testament to the power of human curiosity,
• 1:41:34
  Speaker 1: a ceaseless drive to explore, question and understand. As we
• 1:41:39
  Speaker 1: drift off to sleep, let us hold on to that
• 1:41:41
  Speaker 1: sense of wonder, secure in the knowledge that we are
• 1:41:44
  Speaker 1: part of an amazingly grand complex and mysterious universe. The
• 1:41:49
  Speaker 1: cosmic horizon may limit how much of it we see,
• 1:41:51
  Speaker 1: but it can never constrain our capacity to imagine, to dream,
• 1:41:55
  Speaker 1: and to revel in the magic of the cosmos. In
• 1:41:58
  Speaker 1: that sense, the universe within us is every bit as
• 1:42:00
  Speaker 1: vast and limitless as the universe without. Perhaps, as we
• 1:42:04
  Speaker 1: slip into our dreams, we can take a moment to
• 1:42:06
  Speaker 1: whisper a quiet thank you to Edwin Hubble, and to
• 1:42:09
  Speaker 1: all the scientists and thinkers who have dedicated their lives
• 1:42:12
  Speaker 1: to uncovering the secrets of the cosmos. Their work has
• 1:42:15
  Speaker 1: gifted us a universe far grander and more inspiring than
• 1:42:18
  Speaker 1: our ancestors ever dared to imagine. And while much of
• 1:42:21
  Speaker 1: it may lie beyond our reach, the bit we can see,
• 1:42:24
  Speaker 1: filled with billions of galaxies, trillions of stars and endless
• 1:42:28
  Speaker 1: potential for wonder, is more than enough to fuel our
• 1:42:31
  Speaker 1: curiosity and awe for generations to come. So let us
• 1:42:35
  Speaker 1: embrace the mystery and the majesty of the cosmos as
• 1:42:37
  Speaker 1: we drift off to sleep, comforted by the knowledge that
• 1:42:41
  Speaker 1: we are part of a grand universe. endlessly fascinating universe.
• 1:42:45
  Speaker 1: Our dreams may take us to the farthest reaches of
• 1:42:48
  Speaker 1: space and time, but always with the secure anchor of
• 1:42:51
  Speaker 1: our cosmic home, this delicate, life-bearing world adrift in the
• 1:42:55
  Speaker 1: immensity of space. Good night, and may your dreams be
• 1:42:59
  Speaker 1: as vast and wondrous as the universe itself. The universe,
• 1:43:03
  Speaker 1: as revealed by Edwin Hubble, George LeMaitre, and generations of
• 1:43:06
  Speaker 1: astronomers and cosmologists since, is a place of unimaginable scale, complexity,
• 1:43:12
  Speaker 1: and and mystery. Its story spans billions of years and
• 1:43:16
  Speaker 1: billions of light-years, from the quantum fluctuations of the infant
• 1:43:20
  Speaker 1: cosmos to the majestic dance of galaxies across the eons.
• 1:43:25
  Speaker 1: And yet, for all its vastness, the universe is also
• 1:43:27
  Speaker 1: deeply connected to us. The calcium in our bones, the
• 1:43:31
  Speaker 1: iron in our blood, the oxygen we breathe, all were
• 1:43:34
  Speaker 1: forged in the furnaces of ancient stars. We are, in
• 1:43:38
  Speaker 1: the most profound sense, children of the cosmos. our story
• 1:43:42
  Speaker 1: interwoven with the story of the universe itself. Perhaps that
• 1:43:45
  Speaker 1: is why the question of what lies beyond the cosmic
• 1:43:48
  Speaker 1: horizon holds such enduring fascination. It's not just a matter
• 1:43:51
  Speaker 1: of astronomical curiosity, but a deeper yearning to understand our
• 1:43:55
  Speaker 1: place in the grand tapestry of existence. When we gaze
• 1:43:59
  Speaker 1: up at the night sky, we are looking not just outward,
• 1:44:02
  Speaker 1: but inward, confronting the mysteries of our own origins and destiny.
• 1:44:06
  Speaker 1: The idea that much of the universe is forever hidden
• 1:44:09
  Speaker 1: from us can evoke a sense of cosmic loneliness, a
• 1:44:12
  Speaker 1: melancholy at the thought of all the wonders we will
• 1:44:14
  Speaker 1: never see. But it can also inspire a deep sense
• 1:44:17
  Speaker 1: of connection and gratitude for the patch of the cosmos
• 1:44:20
  Speaker 1: we call home. Our observable universe, vast as it is,
• 1:44:25
  Speaker 1: is a rare and precious oasis of light amid the vast,
• 1:44:28
  Speaker 1: dark expanses of the unknown. And within this oasis, on
• 1:44:32
  Speaker 1: a small, rocky world orbiting an ordinary star, the universe
• 1:44:36
  Speaker 1: has given rise to beings capable of studying and marvelling
• 1:44:39
  Speaker 1: at its grandeur. Through the work of Hubble and so
• 1:44:43
  Speaker 1: many others, we have come to see the cosmos in
• 1:44:45
  Speaker 1: a new light, not as a static backdrop, but as
• 1:44:48
  Speaker 1: a dynamic, evolving entity of which we are an integral part.
• 1:44:53
  Speaker 1: So as we contemplate the edge of the observable universe,
• 1:44:56
  Speaker 1: let's remember that the greatest frontier lies not out there,
• 1:44:59
  Speaker 1: but within us, in our capacity for wonder, discovery and understanding.
• 1:45:05
  Speaker 1: Every time we pursue a question, every time we peer
• 1:45:08
  Speaker 1: through a telescope or ponder an equation, we are participating
• 1:45:11
  Speaker 1: in the universe's journey of self-discovery. And though our individual
• 1:45:15
  Speaker 1: lives may be fleeting compared to the eons of cosmic history,
• 1:45:19
  Speaker 1: we each have a role to play in this grand story.
• 1:45:22
  Speaker 1: By seeking to understand the universe, we add our voices
• 1:45:26
  Speaker 1: to the chorus of generations who have gazed at the
• 1:45:28
  Speaker 1: stars and dared to dream of what lies beyond. As
• 1:45:31
  Speaker 1: we prepare to sleep, let's carry that sense of wonder
• 1:45:33
  Speaker 1: and connection with us. Let's dream not just of distant
• 1:45:37
  Speaker 1: galaxies and cosmic horizons, but of the boundless potential within
• 1:45:41
  Speaker 1: each of us to explore, to discover, and to make
• 1:45:44
  Speaker 1: our own small but meaningful contribution to the great cosmic story.
• 1:45:48
  Speaker 1: And let's hold fast to the knowledge that, though the
• 1:45:51
  Speaker 1: universe may be vast and much of it hidden from
• 1:45:53
  Speaker 1: our view, we are nevertheless an integral part of its
• 1:45:56
  Speaker 1: intricate web. In the words of Carl Sagan, We are
• 1:46:01
  Speaker 1: a way for the cosmos to know itself. That is
• 1:46:04
  Speaker 1: a profound and humbling truth, and one that can guide
• 1:46:07
  Speaker 1: and inspire us as we navigate our own brief but
• 1:46:10
  Speaker 1: momentous journeys through space and time. So good night, and
• 1:46:14
  Speaker 1: may your dreams be filled with the wonder and mystery
• 1:46:16
  Speaker 1: of the cosmos. Remember, the universe is not just out there,
• 1:46:20
  Speaker 1: it's also within you, a part of you, just as
• 1:46:23
  Speaker 1: you are a part of it. Embrace that connection, and
• 1:46:26
  Speaker 1: let it be a source of comfort, inspiration and endless fascination,
• 1:46:30
  Speaker 1: tonight and always. The story of the cosmos is still
• 1:46:34
  Speaker 1: being written, and each of us has a verse to contribute.
• 1:46:38
  Speaker 1: Make yours one of curiosity, compassion and ceaseless wonder at
• 1:46:41
  Speaker 1: the majesty of it all. As we ponder the far future,
• 1:46:45
  Speaker 1: our minds may drift to the great thinkers who have
• 1:46:47
  Speaker 1: shaped our understanding of the cosmos and its ultimate fate.
• 1:46:51
  Speaker 1: One such visionary was the physicist Freeman Dyson, who in
• 1:46:55
  Speaker 1: the 1970s imagined how intelligent life might harness the energy
• 1:46:58
  Speaker 1: of an entire star to power a thriving civilisation. Dyson
• 1:47:02
  Speaker 1: proposed that advanced beings could construct a vast, spherical shell
• 1:47:07
  Speaker 1: around a star, capturing its light to provide a nearly
• 1:47:10
  Speaker 1: limitless energy supply. These hypothetical megastructures became known as Dyson spheres.
• 1:47:16
  Speaker 1: A Dyson sphere would be the ultimate feat of astroengineering.
• 1:47:20
  Speaker 1: A shell of solar collectors encircling a star at a
• 1:47:22
  Speaker 1: distance of perhaps one astronomical unit, about the distance of
• 1:47:26
  Speaker 1: Earth's orbit. Building a complete Dyson sphere would require disassembling
• 1:47:31
  Speaker 1: entire planets, to harvest their raw materials. The interior of
• 1:47:35
  Speaker 1: the sphere would provide a staggering amount of living space,
• 1:47:38
  Speaker 1: equivalent to trillions of Earths. Dyson even imagined that a
• 1:47:41
  Speaker 1: sufficiently advanced civilization might use the sphere's interior as a
• 1:47:45
  Speaker 1: substrate for immensely powerful computation, a cosmic supercomputer with the
• 1:47:51
  Speaker 1: processing power of an entire star. Of course, Dyson's spheres
• 1:47:55
  Speaker 1: remain firmly in the realm of speculation. No evidence of
• 1:47:59
  Speaker 1: such structures has ever been found, the idea highlights the
• 1:48:03
  Speaker 1: incredible potential of harnessing the power of the stars themselves.
• 1:48:07
  Speaker 1: In our universe's distant future, when the expansion of space
• 1:48:10
  Speaker 1: has carried the galaxies beyond each other's horizons, a Dyson
• 1:48:14
  Speaker 1: sphere might allow a civilization to thrive for eons in
• 1:48:17
  Speaker 1: the darkness. As the eons tick by and the universe
• 1:48:21
  Speaker 1: continues to expand and cool, even a star-encircling civilization may
• 1:48:25
  Speaker 1: find its days numbered. On nearly unimaginable timescales of ten
• 1:48:30
  Speaker 1: to the power of one hundred years, an era so
• 1:48:33
  Speaker 1: vast it's been dubbed the Deep Time by some thinkers,
• 1:48:36
  Speaker 1: Even the largest black holes will evaporate into radiation via
• 1:48:39
  Speaker 1: the process Stephen Hawking described in the 1970s. Hawking realised
• 1:48:44
  Speaker 1: that the intense gravity at the edge of a black hole,
• 1:48:46
  Speaker 1: the region known as the event horizon, can cause pairs
• 1:48:49
  Speaker 1: of virtual particles to pop into existence. Normally, these pairs
• 1:48:53
  Speaker 1: quickly annihilate each other. But if a pair appears right
• 1:48:57
  Speaker 1: at the horizon, one particle may fall in while the
• 1:48:59
  Speaker 1: other escapes as radiation. To a distant observer, it would
• 1:49:03
  Speaker 1: appear that the black hole was slowly evaporating. Given enough time,
• 1:49:08
  Speaker 1: even the most massive black holes will dwindle away, gradually
• 1:49:11
  Speaker 1: radiating their mass back into the ever-expanding void. What an
• 1:49:16
  Speaker 1: almost unfathomable scene to imagine. A cosmos utterly dark and diffuse,
• 1:49:21
  Speaker 1: with the last vestiges of its once grand structures and
• 1:49:24
  Speaker 1: cataclysmic engines, finally giving way to an eerily peaceful sea
• 1:49:28
  Speaker 1: of radiation. Some thinkers, like the physicist Roger Penrose, have
• 1:49:33
  Speaker 1: even speculated that this cold, diffuse universe infinitely expanding state
• 1:49:37
  Speaker 1: could set the stage for a new cosmic cycle. The
• 1:49:40
  Speaker 1: vast distances between the decaying particles would render the very
• 1:49:44
  Speaker 1: concepts of space and time nearly meaningless. Quantum effects might
• 1:49:48
  Speaker 1: therefore predominate again, as they likely did in the universe's
• 1:49:51
  Speaker 1: earliest moments. Could this fade into entropy then somehow spark
• 1:49:55
  Speaker 1: the birth of a new universe? The notion is highly speculative,
• 1:49:59
  Speaker 1: but it's a captivating idea. One universe's bleak end sowing
• 1:50:04
  Speaker 1: the seeds of another's vibrant rebirth. As we contemplate these
• 1:50:09
  Speaker 1: mind-bending vistas, from Dyson's spheres harnessing the power of the
• 1:50:13
  Speaker 1: stars to a possible endless cycle of cosmic deaths and rebirths,
• 1:50:17
  Speaker 1: it's hard not to feel a profound sense of awe,
• 1:50:20
  Speaker 1: tinged perhaps with a bittersweet melancholy. The universe is grander
• 1:50:24
  Speaker 1: and more mysterious than we can fathom, and yet we've
• 1:50:27
  Speaker 1: been gifted the ability to ponder its workings, to trace
• 1:50:30
  Speaker 1: its history and imagine its future, to tell its story.
• 1:50:34
  Speaker 1: The great thinkers and explorers we've encountered in our journey,
• 1:50:38
  Speaker 1: from Edwin Hubble probing the distant galaxies to Andre Lind
• 1:50:41
  Speaker 1: imagining an eternal multiverse, all shared this priceless gift, the
• 1:50:45
  Speaker 1: ability to ask profound questions about the cosmos and our
• 1:50:48
  Speaker 1: place within it. Each one of them, through their brilliant
• 1:50:52
  Speaker 1: insights and courageous ideas, shone a light into the vast unknown.
• 1:50:56
  Speaker 1: So as we drift towards sleep, let's hold on to
• 1:50:59
  Speaker 1: that light. Let's celebrate the incredible human capacity for wonder,
• 1:51:04
  Speaker 1: and discovery that's carried us to the very edge of
• 1:51:07
  Speaker 1: the universe. And though much may lie beyond our view,
• 1:51:10
  Speaker 1: cloaked tantalisingly behind a cosmic horizon, let's treasure the slice
• 1:51:15
  Speaker 1: of space and time we call home, this breathtaking corner
• 1:51:18
  Speaker 1: of the cosmos that, for a brief flicker, we have
• 1:51:21
  Speaker 1: the privilege to explore. Our search for understanding may never
• 1:51:25
  Speaker 1: be complete. There may always be another horizon to chase,
• 1:51:28
  Speaker 1: another mystery waiting just out of view. But therein lies
• 1:51:32
  Speaker 1: the beauty. The pursuit of knowledge is an eternal voyage,
• 1:51:36
  Speaker 1: a continuing legacy passed down from the visionaries of the
• 1:51:39
  Speaker 1: past to the explorers of the future. It's a flame
• 1:51:42
  Speaker 1: carried by all those who dare to dream beyond the
• 1:51:44
  Speaker 1: edge of the known. So as you settle into the
• 1:51:47
  Speaker 1: embrace of sleep, let your mind wander freely through the
• 1:51:49
  Speaker 1: grand cosmic expanse. Follow in the footsteps of Hubble and Hawking,
• 1:51:54
  Speaker 1: Lemaitre and Lind, and all the other great thinkers who've
• 1:51:57
  Speaker 1: guided us on this journey, and know that you too
• 1:52:00
  Speaker 1: are part of this great story. a participant in the
• 1:52:03
  Speaker 1: universe's profound unfolding. The darkness beyond the edge of the
• 1:52:07
  Speaker 1: universe may always beckon, an eternal mystery, but the light
• 1:52:11
  Speaker 1: of human understanding shines brightly, illuminating our way to the
• 1:52:15
  Speaker 1: farthest reaches of space and time. So keep that flame
• 1:52:19
  Speaker 1: of curiosity burning, even in the quietest, most restful moments,
• 1:52:23
  Speaker 1: for it's in our dreams and ponderings that the universe
• 1:52:26
  Speaker 1: truly comes alive. As the last glimmers of wakefulness give
• 1:52:30
  Speaker 1: way to the restful hush of sleep, know that you
• 1:52:32
  Speaker 1: are forever connected to the cosmos, an integral part of
• 1:52:35
  Speaker 1: its grand tapestry. You are stardust pondering the stars, a
• 1:52:39
  Speaker 1: universe learning about itself, and that is a profound and
• 1:52:43
  Speaker 1: beautiful thing. So rest well, my fellow explorer. May your
• 1:52:47
  Speaker 1: dreams be filled with the wonders of the cosmos, and
• 1:52:49
  Speaker 1: may your curiosity forever light the way through the vast
• 1:52:52
  Speaker 1: and awe-inspiring universe we call home. Good night, and sweet dreams.
• 1:52:58
  Speaker 1: Here is part five, continuing the story from the previous sections.
• 1:53:03
  Speaker 1: As we drift along the cosmic currents, marvelling at the
• 1:53:06
  Speaker 1: majesty and mystery of all that came before, our curiosity
• 1:53:10
  Speaker 1: calls us to peer even further ahead, into the farthest
• 1:53:13
  Speaker 1: reaches of the future. What ultimate fate awaits our universe
• 1:53:17
  Speaker 1: in the eons to come? The cosmos is not static.
• 1:53:21
  Speaker 1: It is an ever-unfolding story, dynamic and evolving on the
• 1:53:25
  Speaker 1: grandest of scales. And one of the key players in
• 1:53:28
  Speaker 1: this saga is dark energy. that enigmatic force that is
• 1:53:31
  Speaker 1: causing the very fabric of space to stretch and expand
• 1:53:35
  Speaker 1: at an ever-increasing rate. In the coming eons, as the
• 1:53:38
  Speaker 1: universe continues to grow under the relentless influence of dark energy,
• 1:53:42
  Speaker 1: cosmic structures will be reshuffled and reshaped. Galaxy clusters, those
• 1:53:47
  Speaker 1: majestic metropolises of the cosmos, each home to hundreds or
• 1:53:51
  Speaker 1: thousands of galaxies, will merge and coalesce under the inexorable
• 1:53:54
  Speaker 1: pull of gravity. Cosmic collisions and cannibalism will give rise
• 1:53:58
  Speaker 1: to ever more magnificent galactic assemblages. Yet at the same time,
• 1:54:02
  Speaker 1: dark energy will be pushing space itself apart from within,
• 1:54:06
  Speaker 1: counteracting gravity's pull. In about 100 billion years, galaxy clusters
• 1:54:12
  Speaker 1: beyond our local group will have been carried beyond our
• 1:54:14
  Speaker 1: cosmic horizon by the expansion of space, never to be
• 1:54:18
  Speaker 1: seen by us again. These distant denizens of the universe
• 1:54:22
  Speaker 1: will become isolated island universes, marooned in an ever-widening sea
• 1:54:26
  Speaker 1: of space-time. Even within these galactic archipelagos, the passage of
• 1:54:30
  Speaker 1: deep time will bring profound transformations. The hearts of galaxies,
• 1:54:35
  Speaker 1: those brilliant beacons of light where new stars are born
• 1:54:38
  Speaker 1: in resplendent stellar nurseries, will gradually grow dim and still.
• 1:54:42
  Speaker 1: Star formation will sputter out as gas and dust are
• 1:54:45
  Speaker 1: depleted or too diffuse to condense into shining new suns.
• 1:54:49
  Speaker 1: The last generation of stars will burn through their fuel,
• 1:54:52
  Speaker 1: blazing defiantly against the encroaching darkness, before exhausting themselves and
• 1:54:57
  Speaker 1: fading out. One by one, these nuclear furnaces will wink out,
• 1:55:02
  Speaker 1: leaving behind only cooling embers, black holes, neutron stars, and
• 1:55:06
  Speaker 1: cold white dwarfs. In time, perhaps after hundreds of billions
• 1:55:11
  Speaker 1: of years, galaxies themselves will fade from view, their stellifiers extinguished,
• 1:55:16
  Speaker 1: reduced to shadowy collections of darkened remnants. Only the feeble
• 1:55:21
  Speaker 1: glow of ever-cooling stellar cinders will remain, a ghost light
• 1:55:25
  Speaker 1: echoing the luminous glory of eons past. But even these
• 1:55:29
  Speaker 1: remnants are not eternal. Over timescales that defy imagination, exceeding
• 1:55:33
  Speaker 1: trillions of years, the inexorable drumbeat of thermodynamics will see
• 1:55:37
  Speaker 1: black holes slowly evaporate and vanish, yielding their mass back
• 1:55:41
  Speaker 1: to the void via the whisper-thin trickle of Hawking radiation.
• 1:55:45
  Speaker 1: Matter itself will decay into a tenuous gruel of fundamental particles.
• 1:55:49
  Speaker 1: a thin mist permeating the ever-expanding void. And so we
• 1:55:54
  Speaker 1: come to contemplate the heat death of the universe, its
• 1:55:58
  Speaker 1: final state of maximum entropy, where the cosmos has reached
• 1:56:02
  Speaker 1: thermodynamic equilibrium. The temperature and density will asymptotically approach absolute
• 1:56:08
  Speaker 1: zero as space expands and cools forever. In this darkened
• 1:56:12
  Speaker 1: realm at the end of time, where all coherent structure
• 1:56:15
  Speaker 1: has been erased and dissolved, we can imagine only a
• 1:56:18
  Speaker 1: still and silent void, an endless expanse of near-nothingness, where
• 1:56:23
  Speaker 1: the possibility of change or complexity has been quenched by
• 1:56:26
  Speaker 1: the march of entropy to its inexorable conclusion. It is
• 1:56:29
  Speaker 1: a profound and poignant thing to envision the cosmos winding
• 1:56:33
  Speaker 1: down to a cold, quiescent state on the nearly infinite
• 1:56:36
  Speaker 1: horizon of deep time. There is a melancholy beauty in
• 1:56:40
  Speaker 1: pondering this ultimate fate, this inevitable denouement in the cosmic drama.
• 1:56:45
  Speaker 1: We are stirred to deeper appreciation for the light and
• 1:56:47
  Speaker 1: life of the present era, knowing they are precious and
• 1:56:50
  Speaker 1: fleeting gifts in an incomprehensibly vast universe. Even as we
• 1:56:55
  Speaker 1: contemplate this far future of gathering darkness and silence, we
• 1:56:59
  Speaker 1: must remember these are realms and possibilities that exist only
• 1:57:03
  Speaker 1: in our minds, in the speculative reaches of cosmological theory
• 1:57:07
  Speaker 1: and the extrapolations of physical laws. We are peering through
• 1:57:10
  Speaker 1: a glass darkly, straining to glimpse the ultimate fate of
• 1:57:14
  Speaker 1: all that is, And so, as we let this vision
• 1:57:17
  Speaker 1: of a winding down universe carry us towards the shores
• 1:57:20
  Speaker 1: of sleep, let us hold fast to a vital truth.
• 1:57:23
  Speaker 1: There is still so much light to witness, so much
• 1:57:26
  Speaker 1: discovery awaiting us in the here and now. We are
• 1:57:29
  Speaker 1: living in a truly wondrous era, when the universe has
• 1:57:32
  Speaker 1: opened itself to our questing minds, inviting us to unravel
• 1:57:35
  Speaker 1: its manifold mysteries. Though the far future may trend toward
• 1:57:40
  Speaker 1: a kind of beautiful bleakness, we need not hasten our
• 1:57:43
  Speaker 1: thoughts to that distant prospect. There are still countless cosmic
• 1:57:47
  Speaker 1: wonders to behold in the heavens above us, star clusters
• 1:57:51
  Speaker 1: and nebulae, pulses and supernovae, galaxies and quasars in their
• 1:57:55
  Speaker 1: untold billions and trillions. The same laws that will eventually
• 1:58:00
  Speaker 1: lead to the heat death also gave rise to us.
• 1:58:02
  Speaker 1: This improbable flowering of consciousness and curiosity, capable of deciphering
• 1:58:07
  Speaker 1: nature's code and delighting in its many splendours, We are
• 1:58:10
  Speaker 1: the universe awakening to its own majesty, however briefly, and
• 1:58:14
  Speaker 1: that is a profoundly beautiful thing. So as sleep's warm
• 1:58:18
  Speaker 1: embrace beckons, let us fill our minds not with visions
• 1:58:21
  Speaker 1: of a darkened end, but rather with vibrant images of
• 1:58:24
  Speaker 1: the cosmos in its glory. A symphony of form and light,
• 1:58:29
  Speaker 1: from the delicate tracery of interstellar dust to the grand
• 1:58:32
  Speaker 1: swirl of galaxies dancing across the firmament. We are part
• 1:58:36
  Speaker 1: of this grand story, connected to the greater universe in
• 1:58:38
  Speaker 1: ways both humbling and uplifting. Every atom in our bodies
• 1:58:42
  Speaker 1: was forged in the crucibles of long-dead stars. We are
• 1:58:45
  Speaker 1: quite literally stardust come alive, a way for the cosmos
• 1:58:48
  Speaker 1: to know itself. Even as we drift off to our
• 1:58:51
  Speaker 1: own ephemeral dreams, the universe continues to dream the great dream,
• 1:58:56
  Speaker 1: the cosmic dance of gravity and light, energy and matter,
• 1:58:59
  Speaker 1: space and time in their trillion-trillion-fold permutations. And though the
• 1:59:03
  Speaker 1: music may someday fade, though the dancers may eventually disperse
• 1:59:07
  Speaker 1: into the endless night, we're here now, awake, aware, and
• 1:59:12
  Speaker 1: exquisitely tuned to the rhythm and rhyme of this grand
• 1:59:15
  Speaker 1: cosmic ballet. In our fleeting moment under the stars, let
• 1:59:18
  Speaker 1: us marvel and wonder and drink deeply of the light.
• 1:59:22
  Speaker 1: Sleep well, dear dreamer, cradled in the arms of a
• 1:59:24
  Speaker 1: universe so vast and so very, very beautiful. For this
• 1:59:28
  Speaker 1: eternal instant all is illuminated. As we ponder the possibility
• 1:59:32
  Speaker 1: of innumerable bubble universes sprouting from the quantum foam of
• 1:59:36
  Speaker 1: an eternally inflating multiverse, it's natural to feel a sense
• 1:59:40
  Speaker 1: of awe and perhaps even a tinge of insignificance. If
• 1:59:44
  Speaker 1: our entire cosmos is but one humble bubble among countless others,
• 1:59:48
  Speaker 1: each potentially harbouring its own unique physical laws and properties,
• 1:59:51
  Speaker 1: what does that mean for our place in the grand
• 1:59:53
  Speaker 1: scheme of things? It's a question that has captivated some
• 1:59:57
  Speaker 1: of the greatest minds in modern cosmology. In the 1980s,
• 2:00:00
  Speaker 1: physicists like Andrei Linde began to seriously explore the idea
• 2:00:04
  Speaker 1: of eternal inflation and the multiverse. Linde, a Russian-American theoretical physicist,
• 2:00:10
  Speaker 1: made pioneering contributions to the theory of cosmic inflation and
• 2:00:13
  Speaker 1: became one of its most prominent advocates. Born in Moscow
• 2:00:17
  Speaker 1: in 1948, Linde showed an early aptitude for physics and mathematics.
• 2:00:22
  Speaker 1: He earned his PhD from the Lebedev Physical Institute in Moscow,
• 2:00:25
  Speaker 1: and later worked at CERN, the European Organization for Nuclear Research,
• 2:00:30
  Speaker 1: before settling at Stanford University in the United States. It
• 2:00:33
  Speaker 1: was there, in the early 1980s, that Lind began to
• 2:00:36
  Speaker 1: develop his groundbreaking ideas about inflation and the multiverse. Lind's
• 2:00:42
  Speaker 1: work built upon the earlier theories of Alan Guth and others,
• 2:00:45
  Speaker 1: who had proposed that the universe underwent an incredible exponential expansion,
• 2:00:49
  Speaker 1: called inflation in its first fraction of a second. This
• 2:00:53
  Speaker 1: rapid expansion could explain many of the observed features of
• 2:00:56
  Speaker 1: our cosmos, like its smoothness and flatness on large scales.
• 2:01:00
  Speaker 1: But Linde took the idea a step further. In Linde's
• 2:01:04
  Speaker 1: eternal inflation model, inflation never completely ends. Instead, quantum fluctuations
• 2:01:09
  Speaker 1: cause different regions of the inflating space to randomly stop
• 2:01:13
  Speaker 1: inflating and form bubble universes, while inflation continues elsewhere. This
• 2:01:18
  Speaker 1: process goes on forever. endlessly sprouting new and diverse bubble
• 2:01:22
  Speaker 1: universes in a vast, ever-expanding multiverse. It's a mind-bending concept
• 2:01:28
  Speaker 1: to wrap one's head around. In this view, our entire
• 2:01:31
  Speaker 1: observable universe, with its billions of galaxies and trillions of stars,
• 2:01:35
  Speaker 1: is just one humble bubble in an inconceivably vast sea
• 2:01:39
  Speaker 1: of bubble universes. Each of these universes may have its
• 2:01:42
  Speaker 1: own distinct set of physical constants and properties, determined by
• 2:01:46
  Speaker 1: the random quantum fluctuations that gave birth to it. Some
• 2:01:50
  Speaker 1: universes may be vastly different from ours, with wildly altered
• 2:01:53
  Speaker 1: strengths of forces like gravity and electromagnetism. Others may be
• 2:01:57
  Speaker 1: more subtly varied, perhaps with a slightly different ratio of
• 2:02:01
  Speaker 1: matter to antimatter, or a different mass for the electron.
• 2:02:05
  Speaker 1: In some universes, complex structures and even life may be possible,
• 2:02:08
  Speaker 1: while others may be too chaotic or fleeting for anything
• 2:02:11
  Speaker 1: interesting to form. It's a vision of reality that is
• 2:02:14
  Speaker 1: both humbling and awe-inspiring. A universe, grand and majestic as
• 2:02:18
  Speaker 1: it appears to us, may be just one facet of
• 2:02:21
  Speaker 1: an unimaginably greater whole. And if inflation is truly eternal,
• 2:02:26
  Speaker 1: then the multiverse is not only spatially infinite, but temporally
• 2:02:31
  Speaker 1: infinite as well. It had no beginning, and it will
• 2:02:34
  Speaker 1: have no end. A never-ending story of creation and possibility.
• 2:02:40
  Speaker 1: Of course, the idea of the multiverse is still speculative
• 2:02:43
  Speaker 1: and controversial among physicists. While eternal inflation is a leading
• 2:02:48
  Speaker 1: theory of cosmology, it's difficult to directly test or observe
• 2:02:52
  Speaker 1: other bubble universes. Some argue that the multiverse is more
• 2:02:55
  Speaker 1: of a philosophical concept than a scientific one, an unfalsifiable
• 2:02:59
  Speaker 1: hypothesis that lies beyond the realm of empirical science. But
• 2:03:03
  Speaker 1: for Linder and other proponents, the multiverse is a natural
• 2:03:06
  Speaker 1: consequence of our best theories of the early universe. It
• 2:03:09
  Speaker 1: arises almost inevitably from the marriage of cosmic inflation and
• 2:03:13
  Speaker 1: quantum mechanics. And even if we can't directly observe other
• 2:03:16
  Speaker 1: bubble universes, The theory makes certain predictions about the properties
• 2:03:21
  Speaker 1: of our own cosmos that we can test, such as
• 2:03:23
  Speaker 1: the distribution of galaxies on the larger scales. As you
• 2:03:27
  Speaker 1: lie in bed, letting your mind drift through these heady
• 2:03:31
  Speaker 1: cosmic thoughts, it's okay to feel a sense of smallness
• 2:03:35
  Speaker 1: and even a tinge of existential vertigo. Contemplating the vastness
• 2:03:39
  Speaker 1: of the multiverse and our place within it can be
• 2:03:41
  Speaker 1: both exhilarating and unsettling. but it's also a testament to
• 2:03:45
  Speaker 1: the incredible power of the human mind to ponder such
• 2:03:48
  Speaker 1: profound questions and to reach so far beyond our earthly
• 2:03:52
  Speaker 1: origins with the tools of science and mathematics. In a way,
• 2:03:55
  Speaker 1: the multiverse is the ultimate expression of nature's creativity and diversity.
• 2:04:00
  Speaker 1: Just as the biological evolution of life on Earth has
• 2:04:02
  Speaker 1: produced an astonishing variety of forms and adaptations, the evolution
• 2:04:06
  Speaker 1: of universes in the multiverse may have generated a kaleidoscopic
• 2:04:10
  Speaker 1: array of physical realities, each unique and precious in its
• 2:04:13
  Speaker 1: own way. and while we may never be able to
• 2:04:16
  Speaker 1: visit or even observe these other universes, we can still
• 2:04:19
  Speaker 1: appreciate the fact that we are part of something much
• 2:04:21
  Speaker 1: grander than ourselves. Our universe may be just one island
• 2:04:25
  Speaker 1: in an archipelago of universes, but it is our island,
• 2:04:29
  Speaker 1: and it is endlessly fascinating in its own right. As
• 2:04:32
  Speaker 1: you start to feel sleep gently beckoning, take a moment
• 2:04:35
  Speaker 1: to marvel at the sheer audacity of the human intellect,
• 2:04:38
  Speaker 1: to have risen from the African savannah to contemplate the
• 2:04:41
  Speaker 1: multiverse in just a few million years. we are the
• 2:04:45
  Speaker 1: universe becoming aware of itself, gazing out into the cosmic
• 2:04:49
  Speaker 1: ocean with eyes wide with wonder. And while our individual
• 2:04:53
  Speaker 1: lives may be brief and our corner of the cosmos
• 2:04:55
  Speaker 1: may be small, we are still an integral part of
• 2:04:58
  Speaker 1: the grand cosmic story. The atoms in our bodies were
• 2:05:02
  Speaker 1: forged in the hearts of ancient stars and the light
• 2:05:04
  Speaker 1: in our eyes is a reflection of the first light
• 2:05:07
  Speaker 1: that ever shone. We are stardust pondering the stars, a
• 2:05:11
  Speaker 1: fitting testament to the universe's capacity for beauty complexity and self-discovery.
• 2:05:17
  Speaker 1: As you finally drift off to sleep, let your mind
• 2:05:19
  Speaker 1: wander through the multiverse one last time. Picture the endless
• 2:05:23
  Speaker 1: cascade of bubble universes, each a unique expression of nature's
• 2:05:27
  Speaker 1: infinite potential. And know that somewhere out there, perhaps in
• 2:05:31
  Speaker 1: a universe with physical laws not too different from our own,
• 2:05:34
  Speaker 1: other conscious beings may be pondering the same profound questions
• 2:05:38
  Speaker 1: and marvelling at the same cosmic grandeur. It's a strangely
• 2:05:42
  Speaker 1: comforting thought, that even in an infinite multiverse we are
• 2:05:46
  Speaker 1: not alone in our pursuit of understanding and our capacity
• 2:05:49
  Speaker 1: for wonder. So dream well, dear listener, and may your
• 2:05:52
  Speaker 1: voyages through the cosmic ocean of your imagination be filled
• 2:05:55
  Speaker 1: with beauty, insight and the joy of discovery. And when
• 2:05:59
  Speaker 1: you awake, remember that the same universe that dreamed up
• 2:06:03
  Speaker 1: the multiverse also dreamed up you, a conscious, curious being
• 2:06:07
  Speaker 1: capable of pondering its own existence. That in itself is
• 2:06:11
  Speaker 1: a truly marvellous thing. And if you enjoyed this journey
• 2:06:13
  Speaker 1: to the edges of the cosmos and the frontiers of
• 2:06:15
  Speaker 1: human thought, please consider liking this video and subscribing to
• 2:06:19
  Speaker 1: the channel. Your support helps to keep the spirit of
• 2:06:22
  Speaker 1: curiosity and discovery alive, and ensures that we can continue
• 2:06:25
  Speaker 1: to explore the biggest and most profound questions in science together.
• 2:06:29
  Speaker 1: Because in a universe as vast and mysterious as ours,
• 2:06:33
  Speaker 1: there's always more to learn and more to marvel at.
• 2:06:35
  Speaker 1: The story of the cosmos is still being written, and
• 2:06:38
  Speaker 1: we all have a part to play in unravelling its secrets.
• 2:06:41
  Speaker 1: So stay curious, keep exploring, and never stop dreaming of
• 2:06:44
  Speaker 1: what lies beyond the horizon. The universe is waiting for us,
• 2:06:48
  Speaker 1: and the best is yet to come. Thanks for listening,
• 2:06:51
  Speaker 1: and until next time, good night and sweet dreams.