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The Universe Is Far Bigger Than You Think · Boring Science

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  Speaker 1: Hello, and welcome to Boring Science to Sleep, a quiet
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  Speaker 1: place where science becomes slow, soft, and easy to drift through. Tonight,
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  Speaker 1: you're going to gently explore the true size, distance, and
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  Speaker 1: passage of time in the universe. Not to learn everything,
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  Speaker 1: and not to remember every number, but simply to notice
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  Speaker 1: how enormous the space around you really is. Humanity has
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  Speaker 1: been part of a universe evolving for more than 14
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  Speaker 1: billion years. And for most of your everyday life, you
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  Speaker 1: have no reason to think about distances measured in light
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  Speaker 1: years or spaces wide enough to hold entire galaxies. So tonight,
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  Speaker 1: there's nothing to figure out and nothing you need to remember.
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  Speaker 1: You are safe. There's nothing to do, just listen, breathe
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  Speaker 1: slowly and drift. If you enjoy these quiet journeys through
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  Speaker 1: interesting facts about science, you're welcome to like this video
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  Speaker 1: and subscribe. only if it feels right for you. And
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  Speaker 1: when you're ready, let me know in the comments where
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  Speaker 1: you're listening from, and what time it is right now.
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  Speaker 1: It's always a quiet joy to imagine how many different
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  Speaker 1: places and moments are gathered here together. Now, dim the lights,
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  Speaker 1: perhaps let a fan hum softly somewhere nearby, settle into
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  Speaker 1: whatever position feels comfortable, and let us slowly begin, very gently,
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  Speaker 1: with the place you already know. Earth. You do not
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  Speaker 1: need to travel anywhere tonight. You can remain exactly where
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  Speaker 1: you are, resting quietly on the surface of earth, while
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  Speaker 1: your imagination begins to move. Beneath you is the ground,
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  Speaker 1: solid and familiar. Around you is air, carrying the small
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  Speaker 1: sounds of the room, the distant movement of a city,
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  Speaker 1: perhaps the quiet hum of a fan, or the almost
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  Speaker 1: complete silence of the night. And above you, if you
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  Speaker 1: could see through the ceiling and through the atmosphere, there
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  Speaker 1: would be a darkness so deep that your ordinary sense
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  Speaker 1: of distance would slowly begin to lose its meaning. You
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  Speaker 1: are standing, or perhaps lying, on a world that feels enormous.
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  Speaker 1: Earth is enormous to you. You can spend hours travelling
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  Speaker 1: across a city, days travelling across a country, and many
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  Speaker 1: hours more crossing an ocean. Your mind understands these distances
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  Speaker 1: because your mind was shaped by them. You understand the
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  Speaker 1: distance from your bed to a window. You understand the
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  Speaker 1: distance across a room. You understand a road, a mountain,
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  Speaker 1: a coastline. But when the distances become astronomical, something strange happens.
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  Speaker 1: Your intuition becomes quiet. A million kilometres does not feel
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  Speaker 1: a million times farther than one kilometre. A billion kilometres...
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  Speaker 1: does not feel a thousand times farther than a million.
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  Speaker 1: The numbers become large, but the feeling does not grow
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  Speaker 1: in the same way. So instead of asking your mind
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  Speaker 1: to imagine enormous numbers, you can begin with something smaller.
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  Speaker 1: Imagine that Earth is no larger than a peppercorn, a
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  Speaker 1: tiny round grain resting between your fingertips. On this little
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  Speaker 1: peppercorn are oceans, mountains, forests, cities, deserts, clouds, birds, people, memories,
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  Speaker 1: and every ordinary thing you have ever known. The whole
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  Speaker 1: human world becomes almost impossibly small. And yet, even this
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  Speaker 1: tiny peppercorn is separated from the moon by a surprising
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  Speaker 1: amount of space. When you look at the moon from Earth,
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  Speaker 1: it seems close. It hangs above the horizon like a
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  Speaker 1: pale object that you could almost reach toward. But your
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  Speaker 1: eyes are not good at judging its distance. The moon
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  Speaker 1: gives you very little visual information about how far away
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  Speaker 1: it really is. This is where something wonderfully simple begins
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  Speaker 1: to happen. You can measure distance without touching the thing
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  Speaker 1: you are measuring. Imagine two people standing in different places
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  Speaker 1: on Earth at the same moment. One might be in France,
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  Speaker 1: the other might be in Greece. Both look toward the moon,
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  Speaker 1: and both look at the same distant background of stars.
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  Speaker 1: The moon itself is relatively close to Earth, So when
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  Speaker 1: you change your position, the moon appears to shift slightly
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  Speaker 1: against those distant stars. Not dramatically. Not enough for you
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  Speaker 1: to notice just by looking casually into the night. Just
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  Speaker 1: a small change in apparent position. And that small change
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  Speaker 1: contains information about distance. This is called parallax. You can
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  Speaker 1: experience the basic idea yourself without leaving your room. Hold
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  Speaker 1: one finger in front of your face. Close one eye.
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  Speaker 1: Then the other. your finger seems to move against the background.
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  Speaker 1: The distant wall does not move nearly as much. Nothing
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  Speaker 1: actually jumped across the room. You simply changed your point
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  Speaker 1: of view. The same quiet idea can be used on
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  Speaker 1: a much larger scale. For the moon, two observing positions
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  Speaker 1: on Earth provide two slightly different viewpoints. The stars far
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  Speaker 1: behind the moon act as a background. Because those stars
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  Speaker 1: are so extraordinarily far away, The light arriving from them
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  Speaker 1: can be treated, for this simple measurement, as travelling along
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  Speaker 1: almost parallel paths. You do not need to imagine the
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  Speaker 1: actual beams stretching through endless space. Just imagine two very
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  Speaker 1: straight lines arriving from the darkness, almost side by side,
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  Speaker 1: carrying the ancient light of the same distant stars. The
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  Speaker 1: moon sits somewhere in front of them. From one place
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  Speaker 1: on Earth, you see it in one position. From another place,
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  Speaker 1: you see it's slightly shifted. And that tiny shift allows
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  Speaker 1: geometry to enter quietly. Two positions on Earth, one distant moon,
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  Speaker 1: one background star, and a small triangle. That is enough
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  Speaker 1: to begin measuring the distance. You might imagine drawing the
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  Speaker 1: triangle gently on a piece of paper. One side represents
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  Speaker 1: the distance between the two observing positions on Earth. Another
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  Speaker 1: side stretches outward toward the moon. and the small angle
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  Speaker 1: between them tells you how the moon appeared to shift.
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  Speaker 1: If the triangle can be understood, the distance can be calculated.
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  Speaker 1: You do not need advanced mathematics. You do not need
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  Speaker 1: complicated equations. A simple right triangle, together with basic trigonometry,
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  Speaker 1: is enough to reveal something that your eyes alone could
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  Speaker 1: never tell you. The distance to the moon. There is
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  Speaker 1: something deeply calming about that. You do not have to
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  Speaker 1: travel to the moon to know how far away it is.
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  Speaker 1: You do not have to touch it. You do not
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  Speaker 1: even need a spacecraft. You can stand on Earth, look upward,
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  Speaker 1: compare two viewpoints, and allow geometry to quietly bridge the distance.
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  Speaker 1: And the same principle reaches much farther. When astronomers measure
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  Speaker 1: nearby stars, they can watch how a star seems to
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  Speaker 1: shift slightly against the much more distant background as Earth
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  Speaker 1: moves around the sun. Again, the movement is tiny, almost nothing.
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  Speaker 1: A small change in position, produced by a change in viewpoint.
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  Speaker 1: Yet that tiny change can reveal an enormous distance. It
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  Speaker 1: is almost as though the universe leaves its measurements hidden
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  Speaker 1: in plain sight. You only need to change where you
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  Speaker 1: are standing. And as you begin to appreciate this, the
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  Speaker 1: moon slowly becomes something different in your imagination. Not a
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  Speaker 1: small object hanging close above you, but another world, separated
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  Speaker 1: from your world by a vast region of space. Then
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  Speaker 1: the earth becomes smaller in your mind. The moon becomes
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  Speaker 1: smaller too, and beyond them the sun waits, far larger
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  Speaker 1: than earth, yet separated from earth by a distance so
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  Speaker 1: great that even light needs several quiet minutes to cross it.
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  Speaker 1: You do not need to rush toward it. There is
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  Speaker 1: no need to count the minutes. Just imagine a small
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  Speaker 1: pulse of sunlight leaving the surface of the sun. Travelling
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  Speaker 1: silently through the darkness, crossing the enormous space between the
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  Speaker 1: two worlds, and finally reaching the place where you are
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  Speaker 1: resting now. For a moment, you can simply remain here,
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  Speaker 1: on the tiny peppercorn of Earth, with the moon far away,
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  Speaker 1: with the sun farther still, and with the stars quietly
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  Speaker 1: fixed against the background, waiting for your viewpoint to change.
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  Speaker 1: The universe does not become larger because you imagine it,
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  Speaker 1: It was already this large. You are simply beginning to
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  Speaker 1: see its scale a little more clearly. And somewhere beyond
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  Speaker 1: the familiar distance of the moon and the sun, the
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  Speaker 1: spaces between worlds are about to become much larger, much quieter,
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  Speaker 1: and much harder for the human mind to picture. You
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  Speaker 1: can let that thought remain unfinished for now, resting softly
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  Speaker 1: in the darkness. There is nothing to solve. You are safe.
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  Speaker 1: Just listen and drift. You can remain here for a
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  Speaker 1: little longer, resting quietly on Earth, while the Moon and
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  Speaker 1: the Sun slowly become smaller in your imagination. There is
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  Speaker 1: no need to move quickly. In fact, if you were
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  Speaker 1: able to travel outward from Earth tonight, the most important
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  Speaker 1: thing you would notice would not be the planets themselves.
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  Speaker 1: It would be the space between them. From Earth, the
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  Speaker 1: solar system often looks rather crowded. You may have seen
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  Speaker 1: diagrams with the Sun in the middle, followed by Mercury, Venus, Earth, Mars, Jupiter, Saturn,
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  Speaker 1: Uranus and Neptune, all arranged neatly in a row. The
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  Speaker 1: planets look close together, almost as though they are neighbours
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  Speaker 1: living along the same quiet street. But those pictures are
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  Speaker 1: usually not drawn to scale. If they were, the planets
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  Speaker 1: would become so tiny, and the distances between them so enormous,
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  Speaker 1: that the page would hardly be useful at all. So tonight,
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  Speaker 1: instead of looking at the familiar picture, you can let
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  Speaker 1: it slowly dissolve. Imagine the Sun becoming a small glowing
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  Speaker 1: sphere behind you. Then imagine Earth becoming smaller, the Moon
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  Speaker 1: becomes smaller still, and as you move away, the planets
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  Speaker 1: do not gather together, they separate. Mercury is far from Venus.
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  Speaker 1: Venus is far from Earth. Earth is far from Mars,
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  Speaker 1: and beyond Mars, the spaces become wider and wider. Jupiter
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  Speaker 1: appears like a distant world, surrounded by a great region
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  Speaker 1: of darkness, then Saturn, then Uranus, then, much farther away, Neptune.
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  Speaker 1: You might expect Neptune to be almost at the edge
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  Speaker 1: of everything, but it is not. Neptune's orbit reaches roughly
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  Speaker 1: 30 times farther from the Sun than Earth's orbit does,
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  Speaker 1: and even that enormous distance represents only a small portion
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  Speaker 1: of the wider region still influenced by the Sun. The
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  Speaker 1: solar system continues outward into colder, quieter regions. There are
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  Speaker 1: distant bodies moving far beyond the familiar planets, small pieces
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  Speaker 1: of ice and rock travelling through darkness, and far beyond
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  Speaker 1: the known planets lies a vast region that astronomers believe
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  Speaker 1: may contain countless icy objects, forming what is called the
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  Speaker 1: Oort Cloud. You do not need to picture a sharp boundary.
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  Speaker 1: There is no glowing wall saying, Here the solar system ends. Instead,
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  Speaker 1: the sun's influence simply becomes weaker and weaker with distance.
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  Speaker 1: The gravitational connection fades gently into the background, and eventually,
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  Speaker 1: beyond the most distant regions, the space between our sun
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  Speaker 1: and the neighbouring stars becomes the dominant feature. This is
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  Speaker 1: where a small human spacecraft becomes a useful companion. New
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  Speaker 1: Horizons You may imagine it as a tiny machine moving
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  Speaker 1: through a darkness that has no road, no signposts, and
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  Speaker 1: no destination that can be reached within a human lifetime.
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  Speaker 1: It began its journey from Earth in 2006. It travelled
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  Speaker 1: past Jupiter, using the giant planet's gravity to help increase
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  Speaker 1: its speed, and continued outward toward Pluto. It reached Pluto
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  Speaker 1: in 2015. sending back the first close views of that
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  Speaker 1: distant world. But after Pluto, the journey did not simply end.
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  Speaker 1: New horizons continued onward into the Kuiper Belt, passing through
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  Speaker 1: a region populated by distant icy objects, and then continued
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  Speaker 1: farther into the darkness. The spacecraft has already travelled more
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  Speaker 1: than 50 astronomical units from the Sun. An astronomical unit
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  Speaker 1: is simply the average distance between Earth and the Sun.
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  Speaker 1: You can think of it as one familiar cosmic measuring stick,
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  Speaker 1: one Earth to Sun distance, then another, then another, and another,
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  Speaker 1: more than 50 of them. Yet even after travelling that far,
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  Speaker 1: New Horizons is still only beginning to leave the broader
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  Speaker 1: neighbourhood of the Sun. That is the strange thing about scale.
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  Speaker 1: A distance that seems unimaginably large to you can still
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  Speaker 1: be a small distance on the map of the solar system.
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  Speaker 1: and a distance that seems enormous within the solar system
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  Speaker 1: can become almost insignificant when compared with the space between stars.
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  Speaker 1: You can let that thought settle gently. A spacecraft can
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  Speaker 1: travel for years. It can cross the orbits of planets.
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  Speaker 1: It can pass worlds that humans once knew only as
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  Speaker 1: points of light. And still, the journey outward continues. There
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  Speaker 1: is a quiet lesson hidden here. Space is not difficult
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  Speaker 1: to cross. because there is something constantly blocking the way.
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  Speaker 1: Space is difficult to cross, because there is so much
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  Speaker 1: of it. The path itself is mostly empty. There are
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  Speaker 1: no walls, no mountains, no oceans, just distance, and the
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  Speaker 1: farther you travel from the sun, the weaker its light becomes.
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  Speaker 1: The warmth that feels so natural on earth slowly fades.
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  Speaker 1: The familiar brightness of daylight becomes a distant memory. Eventually
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  Speaker 1: the sun would appear not as the great glowing disk
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  Speaker 1: you know from Earth, but as a small and brilliant
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  Speaker 1: star among many others, and around you would be a
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  Speaker 1: kind of emptiness that is difficult to reproduce anywhere on Earth.
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  Speaker 1: Interstellar space is not perfectly empty. There are still atoms.
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  Speaker 1: There are tiny grains of dust, there are charged particles,
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  Speaker 1: magnetic fields, and very faint traces of gas, but these
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  Speaker 1: materials are spread incredibly thinly. You might imagine a vast
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  Speaker 1: room containing only a few grains of dust. Now imagine
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  Speaker 1: making the room larger, and larger, and larger still, until
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  Speaker 1: the grains are separated by distances that would make the
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  Speaker 1: original room seem microscopic. That is closer to the feeling
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  Speaker 1: of interstellar space. There is matter there, just very little
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  Speaker 1: of it. The spacecraft continues. The sun continues to shrink
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  Speaker 1: behind you. The planets are already far behind. and ahead
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  Speaker 1: nothing appears to be waiting, only darkness. Somewhere in that darkness, however,
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  Speaker 1: another star exists, then another, and another. The nearest stars
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  Speaker 1: are not separated from us by walls of darkness. They
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  Speaker 1: are connected to us by enormous stretches of space. Light
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  Speaker 1: crosses those stretches quietly. A beam leaves one star, travels
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  Speaker 1: for years, and eventually reaches another world. You can think
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  Speaker 1: of light as As the first traveller capable of crossing
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  Speaker 1: these distances within a human lifetime, a spacecraft is much slower.
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  Speaker 1: Even the fastest machines humans have built need enormous amounts
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  Speaker 1: of time to travel between the stars. That difference is
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  Speaker 1: difficult to feel when you are standing beneath the night sky.
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  Speaker 1: The stars look close because they are bright. Brightness hides distance.
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  Speaker 1: A star can look like a tiny point of light
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  Speaker 1: and still be several light years away, and a light
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  Speaker 1: year is not a measure of time, despite its name.
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  Speaker 1: It is a measure of distance, the distance that light
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  Speaker 1: can travel in one year. So when you hear that
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  Speaker 1: another star is four light years away, you can imagine
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  Speaker 1: a journey made by light itself, beginning more than four
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  Speaker 1: years ago, crossing the darkness continuously, until that faint ancient
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  Speaker 1: light finally reaches your eyes. For now, you do not
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  Speaker 1: need to follow it, You can simply watch the solar
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  Speaker 1: system disappear behind you. The sun becomes smaller, the planets
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  Speaker 1: become invisible. The familiar neighbourhood of Earth dissolves into darkness.
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  Speaker 1: And somewhere ahead, among the countless points of distant light,
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  Speaker 1: there are other suns, other worlds, and other quiet systems
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  Speaker 1: waiting in the vast spaces between them. The darkness is
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  Speaker 1: becoming larger, the stars are becoming farther apart. and the universe,
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  Speaker 1: very slowly, is beginning to reveal just how much of
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  Speaker 1: itself is made not of worlds, but of the silent
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  Speaker 1: distance between them. As the solar system slowly fades behind you,
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  Speaker 1: the sun becomes one point of light among many. The
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  Speaker 1: planets have disappeared into the darkness. Earth is no longer visible.
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  Speaker 1: The familiar warmth of sunlight has become something distant, something
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  Speaker 1: remembered rather than felt. and now, for a moment, you
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  Speaker 1: are simply floating between stars. There is no road here,
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  Speaker 1: no direction that feels naturally forward, no sign telling you
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  Speaker 1: where one place ends and another begins. There is only darkness,
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  Speaker 1: and scattered through that darkness, tiny points of light. The
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  Speaker 1: first of these distant lights belongs to a system called
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  Speaker 1: Alpha Centauri. From Earth, Alpha Centauri appears as a bright
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  Speaker 1: star in the southern sky, but it is actually a
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  Speaker 1: system containing more than one star. Two of its stars,
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  Speaker 1: Alpha Centauri A and Alpha Centauri B, are somewhat similar
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  Speaker 1: to our own sun. One is a little more massive
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  Speaker 1: and brighter. The other is somewhat smaller and cooler. And then,
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  Speaker 1: farther from those two, there is a much smaller companion,
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  Speaker 1: Proxima Centauri, Its name simply means the closest, and that
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  Speaker 1: small name carries an enormous distance. Proxima Centauri is our
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  Speaker 1: nearest stellar neighbour, yet its light still takes more than
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  Speaker 1: four years to cross the space between its star and Earth.
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  Speaker 1: Think about that gently. The light you see from Proxima
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  Speaker 1: Centauri tonight began its journey years before you saw it.
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  Speaker 1: It left the star. It travelled through darkness. It crossed
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  Speaker 1: an enormous emptiness, and eventually it arrived here. You can
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  Speaker 1: imagine that light as a quiet message that needed years
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  Speaker 1: just to reach you. And yet Proxima Centauri is considered
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  Speaker 1: our closest neighbouring star. This is one of the first
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  Speaker 1: places where the scale of the universe begins to feel
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  Speaker 1: almost strange. If the Earth were represented by a tiny peppercorn,
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  Speaker 1: the distance to another nearby star would no longer fit
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  Speaker 1: comfortably inside a room. The peppercorn could remain on your desk,
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  Speaker 1: but the other star would need to be many miles away.
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  Speaker 1: The objects themselves are not what makes the distance so enormous.
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  Speaker 1: It is the space between them. Proxima Centauri is a
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  Speaker 1: red dwarf. It is much smaller and dimmer than the Sun.
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  Speaker 1: If you could somehow place the two stars side by side,
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  Speaker 1: the Sun would appear dramatically larger and brighter, but size
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  Speaker 1: does not determine importance. A small star can still have worlds,
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  Speaker 1: and Proxima Centauri does. One of those worlds is called
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  Speaker 1: Proxima Centauri b. You do not need to picture it
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  Speaker 1: as another Earth. It may not be, But it is interesting,
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  Speaker 1: because its orbit places it in a region where temperatures might,
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  Speaker 1: under suitable conditions, allow liquid water to exist. Astronomers sometimes
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  Speaker 1: call this region the habitable zone. The name can sound
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  Speaker 1: more certain than it really is. It does not mean
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  Speaker 1: that a planet is inhabited. It does not mean that
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  Speaker 1: oceans are waiting there. It simply means that, at the
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  Speaker 1: right distance from its star, temperatures could potentially allow liquid
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  Speaker 1: water if the atmosphere and other conditions are suitable. Even
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  Speaker 1: this simple idea becomes more complicated when you remember what
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  Speaker 1: kind of star Proxima Centauri is. Red dwarfs can be active.
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  Speaker 1: They can release powerful bursts of energy. Their planets may
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  Speaker 1: experience radiation and stellar activity very different from what Earth
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  Speaker 1: experiences from the Sun. And Proxima Centauri b may also
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  Speaker 1: be tidally locked. That means the same side of the
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  Speaker 1: planet could remain facing its star, while the other side
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  Speaker 1: remains turned away. You can imagine a world where one
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  Speaker 1: hemisphere is always looking toward its little red sun, while
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  Speaker 1: the other hemisphere remains beneath a permanent night. It is
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  Speaker 1: a beautiful image, even though the real conditions may be
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  Speaker 1: far less gentle. The atmosphere, if one exists, could change everything.
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  Speaker 1: Air can move. Heat can travel. Warm regions can influence
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  Speaker 1: colder regions. So even a world with a permanent day
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  Speaker 1: side and night side might have a more complicated climate
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  Speaker 1: than the simple picture suggests. And this is where astronomers
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  Speaker 1: face an interesting problem. How do you learn about a
• 22:25
  Speaker 1: planet that you cannot see clearly? Sometimes, you do not
• 22:29
  Speaker 1: see the planet itself. Instead, you watch its star very carefully,
• 22:35
  Speaker 1: again and again. You measure the star's light. You wait.
• 22:40
  Speaker 1: You compare one observation with another. And eventually, a tiny
• 22:44
  Speaker 1: rhythm may appear. The star seems to move back and forth.
• 22:49
  Speaker 1: Only a very small amount. Almost nothing. But that small
• 22:53
  Speaker 1: movement can reveal the presence of a planet. The planet's
• 22:56
  Speaker 1: gravity gently pulls on its star. The star responds with
• 23:00
  Speaker 1: a tiny motion. It is almost like watching a person
• 23:04
  Speaker 1: standing on a quiet boat while a small object moves
• 23:08
  Speaker 1: around them. The boat shifts slightly, not enough to notice
• 23:12
  Speaker 1: from far away at first, but if you watch for
• 23:15
  Speaker 1: a long time, the movement begins to repeat. Astronomers call
• 23:19
  Speaker 1: this the radial velocity method. The name is technical. The
• 23:24
  Speaker 1: idea is surprisingly simple. A planet can reveal itself by
• 23:29
  Speaker 1: making its star move. And once again, something very small
• 23:33
  Speaker 1: can tell us something very large. you are still floating
• 23:36
  Speaker 1: in the darkness. The stars around you appear motionless, but
• 23:40
  Speaker 1: they are not. They are moving through the galaxy. Some
• 23:44
  Speaker 1: are moving toward us, some are moving away, some are
• 23:47
  Speaker 1: moving sideways across our view. The motions are usually too
• 23:51
  Speaker 1: slow for your eyes to notice. The sky looks still
• 23:55
  Speaker 1: because human life is short compared with the timescale of stars.
• 23:59
  Speaker 1: Barnard's star gives us a beautiful example. It is another
• 24:03
  Speaker 1: nearby red dwarf, only a few light-years farther away than
• 24:07
  Speaker 1: Proxima Centauri. It moves unusually quickly across our sky compared
• 24:12
  Speaker 1: with many other stars. Over the course of many human lifetimes,
• 24:17
  Speaker 1: its position changes enough to become measurable. The star is
• 24:21
  Speaker 1: also very dim. Even though it is relatively close, it
• 24:25
  Speaker 1: does not shine brightly like Sirius, one of the brightest
• 24:28
  Speaker 1: stars visible from Earth. And that contrast is worth noticing.
• 24:33
  Speaker 1: Distance and brightness are not the same thing. A nearby
• 24:37
  Speaker 1: star can be faint. A much more distant star can
• 24:40
  Speaker 1: appear bright. The night sky does not give you a
• 24:43
  Speaker 1: simple map of distance. It gives you light. You have
• 24:47
  Speaker 1: to learn how to read the light. Sirius is a
• 24:50
  Speaker 1: lovely example. From Earth it appears as one brilliant point.
• 24:55
  Speaker 1: But it is actually a binary system, containing two stars.
• 24:59
  Speaker 1: The brighter star is large, hot and luminous. Its companion
• 25:04
  Speaker 1: is a white dwarf, the dense remnant of a star
• 25:08
  Speaker 1: that has already passed through much of its life. So
• 25:11
  Speaker 1: even one point of light can hide more than one
• 25:14
  Speaker 1: world of information. And this is becoming a quiet pattern.
• 25:18
  Speaker 1: You look at a point. Then you look more carefully.
• 25:22
  Speaker 1: A point becomes a star. A star becomes a system.
• 25:26
  Speaker 1: A system may contain planets. A planet may have an atmosphere.
• 25:30
  Speaker 1: And an atmosphere may contain clues about a world you
• 25:33
  Speaker 1: may never visit. The deeper you look, the more the
• 25:36
  Speaker 1: simple points of light begin to unfold. But even now,
• 25:41
  Speaker 1: after meeting several nearby stars, the overwhelming impression remains the same.
• 25:46
  Speaker 1: There are not many stars around you, not compared with
• 25:49
  Speaker 1: the amount of space. Imagine standing somewhere in the darkness
• 25:54
  Speaker 1: between the sun and Proxima Centauri. You could look in
• 25:58
  Speaker 1: every direction and see almost nothing nearby. A star might
• 26:02
  Speaker 1: shine far ahead. Another might shine far behind. But most
• 26:07
  Speaker 1: of the space around you would remain empty. And that
• 26:10
  Speaker 1: emptiness is not a flaw in the map. It is
• 26:13
  Speaker 1: the map. The stars are the scattered lights. The darkness
• 26:18
  Speaker 1: is the distance that separates them. And as you drift
• 26:21
  Speaker 1: a little farther from our neighbouring stars... you begin to
• 26:24
  Speaker 1: sense that even this small stellar neighbourhood is only the beginning,
• 26:29
  Speaker 1: because beyond these nearby suns lies an enormous structure containing
• 26:33
  Speaker 1: hundreds of billions of stars, a great spiral of light, dust, gas,
• 26:38
  Speaker 1: planets and darkness, our galaxy, the Milky Way, and somewhere
• 26:44
  Speaker 1: within that immense river of stars, our small sun is
• 26:47
  Speaker 1: still quietly moving. The Milky Way is still far ahead,
• 26:54
  Speaker 1: but before you allow its enormous spiral to fill your imagination,
• 26:58
  Speaker 1: you can pause for a while among the stars that
• 27:01
  Speaker 1: are already around you. Because these stars are not simply
• 27:04
  Speaker 1: points of light. Many of them carry worlds. Some may
• 27:08
  Speaker 1: be rocky. Some may be covered in deep oceans. Some
• 27:12
  Speaker 1: may be wrapped in thick atmospheres. And some may be
• 27:15
  Speaker 1: so hot, so strange, and so unlike Earth that even
• 27:19
  Speaker 1: the word planet begins to feel less familiar. One of
• 27:23
  Speaker 1: these systems belongs to Wolf 1061. It is another small
• 27:28
  Speaker 1: red dwarf, quiet compared with some of the more active
• 27:31
  Speaker 1: stars you have already encountered, and it has several known
• 27:35
  Speaker 1: planets moving around it. One of them, Wolf 1061c, is
• 27:40
  Speaker 1: particularly interesting because its orbit lies within what astronomers call
• 27:44
  Speaker 1: the habitable zone. You have heard this phrase before. It
• 27:48
  Speaker 1: can sound almost magical. The habitable zone. A place where
• 27:53
  Speaker 1: life might live. But the idea is actually much quieter
• 27:58
  Speaker 1: than that. The habitable zone is simply a region around
• 28:01
  Speaker 1: a star where temperatures could, under suitable conditions, allow liquid
• 28:06
  Speaker 1: water to exist on a planet's surface. That is all.
• 28:10
  Speaker 1: It is not a promise. It is not evidence that
• 28:13
  Speaker 1: life is present. It is not another Earth waiting patiently
• 28:17
  Speaker 1: for someone to arrive. It is simply a distance from
• 28:20
  Speaker 1: a star where one particular ingredient of familiar life, liquid water,
• 28:26
  Speaker 1: might be possible. A planet can sit inside this region
• 28:31
  Speaker 1: and still be dry. It can have no suitable atmosphere.
• 28:35
  Speaker 1: It can receive intense radiation. It can be covered in clouds.
• 28:40
  Speaker 1: It can be frozen beneath the surface. Or it can
• 28:44
  Speaker 1: be something that Earth has never been. So you can
• 28:47
  Speaker 1: let the word habitable become softer in your mind. Not
• 28:51
  Speaker 1: a guarantee, just a possibility, a small opening in the darkness.
• 28:57
  Speaker 1: And this is where the variety of planets begins to
• 28:59
  Speaker 1: become interesting. Some worlds may be dominated by water, not
• 29:04
  Speaker 1: simply a blue ocean spread across familiar continents, but oceans
• 29:09
  Speaker 1: so deep that the pressure far below the surface changes
• 29:13
  Speaker 1: the behaviour of water itself. Imagine descending through an ocean
• 29:17
  Speaker 1: that never seems to end, The light from the star
• 29:20
  Speaker 1: disappears above you. The water becomes darker. The pressure grows,
• 29:25
  Speaker 1: and eventually, under conditions far beyond anything you experience in
• 29:30
  Speaker 1: an ordinary ocean on Earth, water can become solid in
• 29:34
  Speaker 1: forms very different from the ice in your freezer. The
• 29:37
  Speaker 1: molecules are squeezed together so strongly... that the material begins
• 29:41
  Speaker 1: to behave in unfamiliar ways. These are sometimes called high-pressure
• 29:46
  Speaker 1: forms of ice. It is still water, but the same
• 29:50
  Speaker 1: substance can take on a different structure when the pressure
• 29:53
  Speaker 1: becomes enormous. One example discussed by astronomers is GJ1214b a
• 30:00
  Speaker 1: planet that may contain a large amount of water or
• 30:03
  Speaker 1: other volatile material. Its true composition is still uncertain. That
• 30:08
  Speaker 1: uncertainty is important. When astronomers study a distant planet, they
• 30:13
  Speaker 1: often work with clues rather than complete pictures. They may
• 30:17
  Speaker 1: measure the planet's size. They may estimate its mass. They
• 30:21
  Speaker 1: may observe how starlight passes through its atmosphere. And from
• 30:25
  Speaker 1: these small pieces of information, they begin to build a picture.
• 30:29
  Speaker 1: not a photograph, more like a slowly assembled impression. You
• 30:34
  Speaker 1: can imagine someone describing a distant landscape only by feeling
• 30:38
  Speaker 1: its temperature, listening to the wind, and measuring the weight
• 30:42
  Speaker 1: of a stone. The landscape is still hidden, but little
• 30:45
  Speaker 1: by little, its nature begins to emerge, and then there
• 30:49
  Speaker 1: are worlds that are almost the opposite of these cold,
• 30:52
  Speaker 1: watery possibilities. Lava worlds. K2-141b is one of the more
• 30:59
  Speaker 1: extreme examples. It orbits extremely close to its star, so
• 31:04
  Speaker 1: close that its day side may be heated to temperatures
• 31:07
  Speaker 1: high enough for rock to melt. Imagine standing above a
• 31:11
  Speaker 1: dark world where the surface is no longer solid in
• 31:14
  Speaker 1: the familiar sense. Instead, enormous regions may glow with molten rock,
• 31:20
  Speaker 1: a world with an ocean, but not an ocean of water,
• 31:24
  Speaker 1: an ocean of lava. The atmosphere, if present, could participate
• 31:29
  Speaker 1: in a slow cycle. Rock on the hot side may vaporize.
• 31:33
  Speaker 1: That material could move through the atmosphere. As it travels
• 31:37
  Speaker 1: toward cooler regions, it may condense again. Then material could
• 31:42
  Speaker 1: return toward the hotter side. Heat, evaporation, movement, cooling, return.
• 31:49
  Speaker 1: A slow planetary cycle repeating over and over. You do
• 31:54
  Speaker 1: not need to imagine the process happening quickly. Even the
• 31:57
  Speaker 1: most extreme worlds are governed by physical processes that unfold
• 32:02
  Speaker 1: through time. The planet turns. Heat moves. Material changes form.
• 32:08
  Speaker 1: The atmosphere responds. And the cycle continues. There are also
• 32:13
  Speaker 1: planets that orbit so close to their stars that their
• 32:16
  Speaker 1: atmospheres can reach extraordinary temperatures. One of these is KELT-9b.
• 32:22
  Speaker 1: It is a gas giant, much larger than Earth, but
• 32:25
  Speaker 1: its closeness to its star makes its atmosphere intensely hot.
• 32:30
  Speaker 1: At such temperatures, familiar substances can behave in unfamiliar ways.
• 32:35
  Speaker 1: Some metals can exist in vapour form. The upper atmosphere
• 32:39
  Speaker 1: can gradually escape into space. The planet is slowly losing
• 32:43
  Speaker 1: material to its surrounding environment. Again, you can think of
• 32:47
  Speaker 1: this not as a dramatic event, but as a long process,
• 32:51
  Speaker 1: a planet spending its life very close to a star.
• 32:55
  Speaker 1: A star continuously pouring energy onto its atmosphere, particles receiving
• 33:00
  Speaker 1: enough energy to drift away, the loss happening slowly, almost invisibly.
• 33:06
  Speaker 1: And perhaps that is one of the most useful things
• 33:08
  Speaker 1: to remember when thinking about distant worlds. The universe rarely
• 33:13
  Speaker 1: gives us only one kind of planet. There is no
• 33:16
  Speaker 1: universal template. A planet does not need to have blue
• 33:20
  Speaker 1: oceans and green continents. It does not need a breathable atmosphere.
• 33:25
  Speaker 1: It does not need a comfortable temperature. It simply needs
• 33:28
  Speaker 1: to follow the laws of physics. Those laws allow enormous variety.
• 33:34
  Speaker 1: A small rocky planet can circle a faint red star.
• 33:37
  Speaker 1: A world can remain permanently turned toward its star. A
• 33:41
  Speaker 1: deep ocean can become strange ice under enormous pressure. A
• 33:46
  Speaker 1: rocky surface can melt into a global sea of lava.
• 33:49
  Speaker 1: A giant planet can become hot enough for metals to
• 33:52
  Speaker 1: exist as vapour. And all of these worlds can exist
• 33:56
  Speaker 1: while the space between them remains almost completely dark. That
• 34:00
  Speaker 1: contrast is beautiful. Worlds can be extraordinarily complicated. Space between
• 34:05
  Speaker 1: those worlds can be extraordinarily simple. Mostly emptiness. Mostly darkness.
• 34:11
  Speaker 1: Mostly distance. And perhaps this is why the universe can
• 34:15
  Speaker 1: feel so vast. Not because every corner is filled with something.
• 34:20
  Speaker 1: but because a remarkable variety of worlds can be scattered
• 34:23
  Speaker 1: across enormous regions where almost nothing is happening at all.
• 34:27
  Speaker 1: You remain suspended there for a moment, somewhere between these
• 34:31
  Speaker 1: distant systems. One faint star behind you, another ahead. A
• 34:37
  Speaker 1: planet too far away to see clearly. A world you
• 34:40
  Speaker 1: may never visit. A light that may have begun its
• 34:44
  Speaker 1: journey years ago. And while you are thinking about all
• 34:47
  Speaker 1: these distant worlds... the stars around you continue to drift
• 34:51
  Speaker 1: slowly through the Milky Way. The galaxy is becoming larger
• 34:56
  Speaker 1: in your imagination now. The individual stars are becoming countless,
• 35:00
  Speaker 1: and somewhere within that growing sea of light, there is
• 35:04
  Speaker 1: a place where stars gather into a great spiral structure,
• 35:08
  Speaker 1: with clouds of gas, lanes of dust, ancient stars, young stars,
• 35:14
  Speaker 1: and an enormous invisible mass surrounding it all. The Milky
• 35:18
  Speaker 1: Way is waiting quietly ahead. The stars around you are
• 35:25
  Speaker 1: beginning to lose their individuality. One star becomes many. Many
• 35:29
  Speaker 1: become hundreds. Hundreds become thousands. And as you slowly drift
• 35:34
  Speaker 1: farther away, the individual points of light begin to merge
• 35:38
  Speaker 1: into something larger. A faint river of stars. A broad
• 35:42
  Speaker 1: band of light stretching across the darkness. You are beginning
• 35:46
  Speaker 1: to see the Milky Way as a whole. From Earth,
• 35:49
  Speaker 1: the Milky Way can look like a pale, cloudy ribbon
• 35:52
  Speaker 1: across the night sky. For thousands of years, people looked
• 35:56
  Speaker 1: at that faint band without knowing exactly what it was.
• 36:00
  Speaker 1: Only gradually did we understand that the soft glow was
• 36:03
  Speaker 1: made from enormous numbers of individual stars, together with clouds
• 36:07
  Speaker 1: of gas and dust, all arranged within one enormous galaxy.
• 36:13
  Speaker 1: And even now, the Milky Way is difficult to picture
• 36:16
  Speaker 1: in its entirety. because you are inside it. Imagine standing
• 36:20
  Speaker 1: inside a forest and trying to understand the shape of
• 36:23
  Speaker 1: the entire forest. You can see trees. You can walk
• 36:27
  Speaker 1: between them. You can look toward distant hills. But you
• 36:31
  Speaker 1: cannot simply step outside and see the whole landscape. The
• 36:35
  Speaker 1: Milky Way is like that. You live inside the forest
• 36:39
  Speaker 1: of stars. The sun is one of them. The earth
• 36:42
  Speaker 1: is one small world circling one small star. and the
• 36:47
  Speaker 1: entire solar system moves quietly through one region of this
• 36:50
  Speaker 1: enormous structure. The Milky Way is a barred spiral galaxy.
• 36:56
  Speaker 1: That means its stars are spread through a broad, flattened disk,
• 37:00
  Speaker 1: with a dense central region and large curved arms extending outward.
• 37:05
  Speaker 1: At the centre is a long, bar-like structure made of stars.
• 37:10
  Speaker 1: From this central region, the spiral pattern reaches outward. Gas
• 37:14
  Speaker 1: and dust gather along parts of these arms. And where
• 37:18
  Speaker 1: gas becomes dense enough, gravity can slowly pull it together.
• 37:22
  Speaker 1: New stars are born. So the galaxy is not a
• 37:26
  Speaker 1: frozen picture. It is changing. Stars are forming. Stars are aging.
• 37:32
  Speaker 1: Stars are moving. Gas is gathering. Dust is drifting. And
• 37:37
  Speaker 1: some stars are eventually scattered away from the places where
• 37:40
  Speaker 1: they were born. You can imagine the galaxy as a
• 37:43
  Speaker 1: very slow river, not a river of water, but a
• 37:46
  Speaker 1: river of stars, clouds and gravity, flowing over distances so
• 37:51
  Speaker 1: immense that a human lifetime becomes almost invisible beside it.
• 37:56
  Speaker 1: The disk of the Milky Way stretches for roughly 100,000
• 38:01
  Speaker 1: light-years across, depending on exactly where its boundary is defined.
• 38:06
  Speaker 1: You do not need to imagine that number all at once. Instead,
• 38:10
  Speaker 1: remember what a light year means. It is the distance
• 38:14
  Speaker 1: light can travel in one year. Now imagine that distance
• 38:18
  Speaker 1: repeated tens of thousands of times. Then imagine that entire
• 38:22
  Speaker 1: width filled with stars. Some old, some young, some surrounded
• 38:28
  Speaker 1: by planets. Some alone, some gathered into clusters, some hidden
• 38:33
  Speaker 1: behind clouds of dust. And somewhere within this great spiral,
• 38:38
  Speaker 1: about 27,000 light-years from the centre, is our own solar system.
• 38:44
  Speaker 1: You can imagine yourself moving toward that centre now. The
• 38:48
  Speaker 1: stars gradually become more crowded. The darkness between them begins
• 38:52
  Speaker 1: to feel different. There are more stars, more clouds, more
• 38:57
  Speaker 1: ancient light. The central region of the galaxy is much
• 39:00
  Speaker 1: more densely populated than the quiet neighbourhood where the Sun lives.
• 39:05
  Speaker 1: But even here, the galaxy is not simply bright. dust
• 39:09
  Speaker 1: and gas hide much of what lies behind them. There
• 39:12
  Speaker 1: is one region, however, where the material is thinner, allowing
• 39:16
  Speaker 1: astronomers to look more deeply toward the galactic centre. Through
• 39:20
  Speaker 1: this clearer window they can study a remarkable object, Sagittarius A-star.
• 39:27
  Speaker 1: At the very heart of the Milky Way is a
• 39:29
  Speaker 1: supermassive black hole. Its mass is roughly four million times
• 39:34
  Speaker 1: that of our Sun, and yet, from our distance, it
• 39:38
  Speaker 1: is still only a tiny part of the enormous galaxy
• 39:41
  Speaker 1: surrounding it. You do not need to imagine a giant
• 39:44
  Speaker 1: dark sphere swallowing the entire Milky Way. A black hole
• 39:49
  Speaker 1: is does not behave like a cosmic vacuum cleaner. Instead,
• 39:54
  Speaker 1: imagine an extremely concentrated region of gravity. Stars can orbit
• 39:59
  Speaker 1: around it. Gas can move around it. Matter can pass
• 40:03
  Speaker 1: close to it. And when something approaches too closely, the
• 40:07
  Speaker 1: strength of gravity becomes extreme. The black hole itself does
• 40:11
  Speaker 1: not shine in the ordinary way. but the material around
• 40:14
  Speaker 1: it can become very bright as gas and dust move
• 40:18
  Speaker 1: through the intense gravitational environment. The stars near the centre
• 40:22
  Speaker 1: also reveal something important. They orbit. They move around an
• 40:27
  Speaker 1: unseen concentration of mass. And by carefully tracking those motions
• 40:31
  Speaker 1: over many years, astronomers can infer what is there. Again,
• 40:36
  Speaker 1: you do not need to see something directly to know
• 40:39
  Speaker 1: that it exists. Sometimes motion is enough. A star moves
• 40:44
  Speaker 1: one way, then another. Its orbit repeats. And from that
• 40:48
  Speaker 1: quiet pattern, the invisible centre begins to reveal itself. Farther
• 40:53
  Speaker 1: from the black hole, the central bulge of the galaxy
• 40:56
  Speaker 1: begins to open around you. This region contains enormous numbers
• 41:00
  Speaker 1: of stars. Many are old. Some formed more than 10
• 41:05
  Speaker 1: billion years ago, long before Earth existed in anything like
• 41:09
  Speaker 1: its present form. And yet … The galaxy is not
• 41:12
  Speaker 1: made only of ancient stars. Farther out, in the spiral arms,
• 41:18
  Speaker 1: new stars continue to form. Clouds of gas and dust
• 41:22
  Speaker 1: gather together. Gravity slowly draws material inward. The cloud becomes denser. Eventually,
• 41:29
  Speaker 1: a new star begins to shine. Some of these stellar
• 41:33
  Speaker 1: nurseries are enormous. Within them, many stars can be born together,
• 41:38
  Speaker 1: spending their earliest years near one another before gradually drifting apart.
• 41:44
  Speaker 1: You can imagine one such cloud as a quiet room
• 41:47
  Speaker 1: filled with mist. Inside the mist, tiny points of light
• 41:51
  Speaker 1: begin to appear. At first there are only a few,
• 41:55
  Speaker 1: then more, then many. And over immense stretches of time,
• 41:59
  Speaker 1: those young stars slowly move away from their birthplace. The
• 42:03
  Speaker 1: galaxy is always renewing itself. Some stars are almost as
• 42:08
  Speaker 1: old as the galaxy. Others are only beginning their lives.
• 42:12
  Speaker 1: Some will live quietly for billions of years. Others will
• 42:15
  Speaker 1: exist for much shorter periods before returning their material to space.
• 42:20
  Speaker 1: The Milky Way carries all of these histories together. Ancient stars.
• 42:25
  Speaker 1: Young stars. Cold dust. Warm gas. Planets. Remnants of stars
• 42:32
  Speaker 1: that died long ago. And something else that cannot be
• 42:35
  Speaker 1: seen directly. Dark matter. Astronomers infer its presence because stars
• 42:41
  Speaker 1: and gas move as though there is much more mass
• 42:44
  Speaker 1: in the galaxy than the visible material can account for.
• 42:47
  Speaker 1: It does not glow like a star. It does not
• 42:50
  Speaker 1: reflect ordinary light in the way dust or planets do.
• 42:54
  Speaker 1: Its presence is known mainly through gravity. So even the
• 42:57
  Speaker 1: Milky Way is partly invisible. What you see when you
• 43:01
  Speaker 1: look at the night sky is only the luminous portion.
• 43:04
  Speaker 1: Like the surface of a quiet ocean, It shows you
• 43:07
  Speaker 1: something beautiful, while much more exists beneath what your eyes
• 43:11
  Speaker 1: can see. And now, after moving through the centre, you
• 43:16
  Speaker 1: can slowly drift outward again, past the dense central stars,
• 43:21
  Speaker 1: past the great clouds of gas and dust, past the
• 43:24
  Speaker 1: bright spiral regions, back toward the quieter part of the galaxy,
• 43:30
  Speaker 1: toward the Orion Arm. This is where our solar system lives,
• 43:35
  Speaker 1: not at the centre. not at the edge, but somewhere
• 43:39
  Speaker 1: within the broad structure of the Milky Way, moving quietly
• 43:42
  Speaker 1: along with everything around it. The Sun is not special
• 43:46
  Speaker 1: because it sits at the centre. It does not. It
• 43:49
  Speaker 1: is not special because it is the largest star. It
• 43:53
  Speaker 1: is not. It is simply one ordinary star among an
• 43:57
  Speaker 1: enormous population. And around that ordinary star, one small planet
• 44:02
  Speaker 1: carries oceans, mountains, forests … cities, memories, and you. The
• 44:08
  Speaker 1: galaxy continues turning, stars continue drifting, light continues travelling, and
• 44:14
  Speaker 1: the great spiral continues to move through space. For a moment,
• 44:19
  Speaker 1: you can simply rest inside that thought. You are not
• 44:22
  Speaker 1: outside the Milky Way looking in. You are part of it.
• 44:26
  Speaker 1: A small world, circling a small star, moving quietly through
• 44:31
  Speaker 1: one small region of a galaxy that stretches across unimaginable distance.
• 44:36
  Speaker 1: And beyond the bright disk you have been travelling through,
• 44:39
  Speaker 1: something even more difficult to see is waiting. The galaxy
• 44:43
  Speaker 1: does not suddenly end, its visible stars simply become fewer.
• 44:48
  Speaker 1: The light becomes thinner, and beyond the familiar spiral arms
• 44:52
  Speaker 1: lies a much larger, quieter region surrounding the entire galaxy,
• 44:57
  Speaker 1: a place where ancient stars drift. where streams of former
• 45:01
  Speaker 1: galaxies remain, and where most of the mass may never
• 45:05
  Speaker 1: shine at all. The darkness around the Milky Way is
• 45:08
  Speaker 1: about to become part of the story. The bright spiral
• 45:14
  Speaker 1: of the Milky Way is slowly falling behind you. The
• 45:18
  Speaker 1: stars that once seemed countless are becoming more widely separated.
• 45:23
  Speaker 1: The great band of light that filled your imagination is
• 45:26
  Speaker 1: beginning to thin, and if you continue drifting outward, something
• 45:30
  Speaker 1: curious happens. The galaxy does not simply disappear. It becomes quieter.
• 45:37
  Speaker 1: The bright disk is only one part of the Milky Way.
• 45:39
  Speaker 1: Around it is a much larger region, far more diffuse
• 45:44
  Speaker 1: and difficult to see, extending outward into the surrounding darkness.
• 45:49
  Speaker 1: This is the galactic halo. You can imagine leaving a
• 45:52
  Speaker 1: brightly lit city at night. At first there are streets everywhere.
• 45:57
  Speaker 1: Windows glow. Cars pass. The world feels full. Then you
• 46:03
  Speaker 1: travel farther away. The lights become fewer. The roads become quieter. Eventually,
• 46:09
  Speaker 1: you can still see the glow of the city behind you,
• 46:12
  Speaker 1: but most of the landscape around you is dark. The
• 46:15
  Speaker 1: galactic halo is somewhat like that. There are still stars here,
• 46:20
  Speaker 1: but they are scattered much more thinly. Many of them
• 46:23
  Speaker 1: are very old. Some are gathered into enormous spherical groups
• 46:26
  Speaker 1: called globular clusters. Imagine hundreds of thousands of stars held
• 46:31
  Speaker 1: together by gravity, moving through the darkness as a single
• 46:35
  Speaker 1: ancient family. These stars can be among the oldest objects
• 46:39
  Speaker 1: in the galaxy. They were born long ago, when the
• 46:43
  Speaker 1: Milky Way looked very different from the galaxy you would
• 46:45
  Speaker 1: recognise today. And some of the stars surrounding the Milky
• 46:49
  Speaker 1: Way are not truly native to it. They may have
• 46:53
  Speaker 1: once belonged to smaller galaxies. Over immense stretches of time,
• 46:57
  Speaker 1: Gravity can draw smaller galaxies toward larger ones. The smaller
• 47:02
  Speaker 1: galaxy can be stretched, its stars can be pulled apart,
• 47:06
  Speaker 1: gas and dust can be scattered. Eventually, the original galaxy
• 47:11
  Speaker 1: may no longer remain recognisable as a separate structure, but
• 47:14
  Speaker 1: its stars do not simply vanish. They can continue moving
• 47:18
  Speaker 1: through the larger galaxy. Sometimes they form long, faint streams.
• 47:23
  Speaker 1: You can imagine a small cloud of stars being gently
• 47:26
  Speaker 1: pulled apart until it becomes a thin ribbon. The ribbon
• 47:30
  Speaker 1: may stretch for enormous distances. Individual stars may be separated
• 47:35
  Speaker 1: by vast amounts of space, yet their motions still reveal
• 47:39
  Speaker 1: that they once belonged together. One example comes from a
• 47:43
  Speaker 1: very ancient merger known as Gaia Enceladus. Long ago, the
• 47:48
  Speaker 1: young Milky Way encountered a smaller galaxy. Over time, gravity
• 47:53
  Speaker 1: drew the two systems together. The smaller galaxy was disrupted,
• 47:58
  Speaker 1: and many of its stars became part of the larger
• 48:01
  Speaker 1: Milky Way. Today, astronomers can find traces of that ancient
• 48:05
  Speaker 1: event by studying the movements and properties of stars. The
• 48:09
  Speaker 1: galaxy remembers, not through words, not through photographs, but through motion.
• 48:16
  Speaker 1: A star can carry a memory of where it came from.
• 48:19
  Speaker 1: Its movement through space can preserve a small trace of
• 48:23
  Speaker 1: an event that happened billions of years ago. And this
• 48:27
  Speaker 1: gives the Milky Way a strange quality. It is not
• 48:30
  Speaker 1: only a place, it is also a record. A record
• 48:34
  Speaker 1: written in the motions of stars. A record written in
• 48:37
  Speaker 1: ancient light. A record written in the faint streams left
• 48:41
  Speaker 1: behind by galaxies that no longer exist in their original form.
• 48:46
  Speaker 1: You can drift farther into the halo now, The bright
• 48:49
  Speaker 1: disk is becoming a distant plane of light. Around you,
• 48:53
  Speaker 1: stars are sparse. And beyond the visible stars, there is
• 48:58
  Speaker 1: another layer to the galaxy that cannot be seen directly.
• 49:01
  Speaker 1: Dark matter. The name can sound mysterious, but the basic
• 49:06
  Speaker 1: idea is gentle. Astronomers observe how stars and gas move.
• 49:12
  Speaker 1: They measure how galaxies rotate. They study how light bends
• 49:15
  Speaker 1: as it passes through large structures. and again and again,
• 49:19
  Speaker 1: the visible matter does not seem to provide enough gravity
• 49:23
  Speaker 1: to explain what is happening. Something unseen appears to be
• 49:27
  Speaker 1: contributing additional mass. We call that unseen material dark matter.
• 49:33
  Speaker 1: You cannot see it glowing. You cannot point a telescope
• 49:36
  Speaker 1: toward it and watch a dark cloud appear. Instead, you
• 49:40
  Speaker 1: notice what gravity is doing. It is like feeling the
• 49:44
  Speaker 1: presence of wind without seeing the air itself. A tree moves,
• 49:49
  Speaker 1: leaves tremble, branches bend. You know something is there because
• 49:54
  Speaker 1: of its effect. Dark matter is somewhat similar. Its gravitational
• 49:59
  Speaker 1: influence can be observed even though the material itself does
• 50:02
  Speaker 1: not shine in ordinary light. Around the Milky Way, This
• 50:06
  Speaker 1: invisible component appears to extend much farther than the bright
• 50:10
  Speaker 1: disk of stars. So the galaxy you can see is
• 50:14
  Speaker 1: not the whole galaxy. The luminous spiral is surrounded by
• 50:18
  Speaker 1: a much larger gravitational structure. And once again, the universe
• 50:22
  Speaker 1: quietly reminds you that what is visible is not necessarily
• 50:27
  Speaker 1: everything that exists. You can let that thought rest for
• 50:30
  Speaker 1: a moment. Most of the Milky Way cannot be seen
• 50:33
  Speaker 1: as a bright collection of stars. and even the visible
• 50:37
  Speaker 1: stars occupy only a small fraction of the space surrounding them.
• 50:41
  Speaker 1: The darkness is enormous. Now, instead of continuing farther away,
• 50:46
  Speaker 1: you can gently turn your attention back toward the solar system.
• 50:51
  Speaker 1: Not all the way to Earth, just toward our small neighbourhood.
• 50:55
  Speaker 1: The Sun is moving through a very thin cloud of
• 50:58
  Speaker 1: interstellar material, known as the Local Interstellar Cloud. It is
• 51:03
  Speaker 1: not a cloud like the clouds you see in Earth's sky.
• 51:06
  Speaker 1: There is no soft white shape, no visible edge, no rain.
• 51:12
  Speaker 1: It is an extremely thin mixture of gas and tiny
• 51:15
  Speaker 1: particles spread across space. The material is so sparse that
• 51:19
  Speaker 1: the emptiness between individual particles is almost beyond ordinary imagination.
• 51:24
  Speaker 1: You could imagine a vast hall containing only a few
• 51:27
  Speaker 1: grains of dust. Then imagine stretching the hall until those
• 51:31
  Speaker 1: grains are separated by enormous distances. That is closer to
• 51:36
  Speaker 1: the environment surrounding the solar system. Even here, in what
• 51:40
  Speaker 1: seems like the immediate neighbourhood of the sun, space is
• 51:44
  Speaker 1: overwhelmingly empty. There may be a particle moving nearby. Then another.
• 51:50
  Speaker 1: Then nothing for a long while. The sun continues through
• 51:53
  Speaker 1: this faint material. The planets continue their quiet orbits. Earth
• 51:58
  Speaker 1: continues turning, and above Earth, the stars continue shining. But
• 52:03
  Speaker 1: between the stars, almost nothing happens. This is one of
• 52:07
  Speaker 1: the deepest patterns you have encountered so far. The solar
• 52:11
  Speaker 1: system contains planets separated by large distances, the galaxy contains
• 52:16
  Speaker 1: stars separated by even larger distances, and the halo contains
• 52:21
  Speaker 1: stars scattered through an even wider darkness. The farther you travel,
• 52:26
  Speaker 1: the more the universe seems to become defined by the
• 52:28
  Speaker 1: spaces between things. The Milky Way itself begins to look
• 52:32
  Speaker 1: less like a solid object and more like a delicate
• 52:35
  Speaker 1: island of light surrounded by darkness. And now you can
• 52:39
  Speaker 1: slowly imagine moving even farther away. The entire galaxy begins
• 52:44
  Speaker 1: to shrink. Its spiral arms become less distinct. The central
• 52:49
  Speaker 1: bulge becomes a tiny glow. The solar system disappears completely.
• 52:54
  Speaker 1: The Milky Way becomes one galaxy among many. For a moment,
• 52:58
  Speaker 1: it may seem almost impossible that something so enormous could
• 53:02
  Speaker 1: become so small. But that is what happens when you
• 53:05
  Speaker 1: change scale. A planet becomes a point. A star becomes
• 53:10
  Speaker 1: a point. A galaxy becomes a point. And the process
• 53:14
  Speaker 1: can continue. Far beyond the halo of the Milky Way
• 53:18
  Speaker 1: are other galaxies. Some large. Some small. Some spiral. some
• 53:24
  Speaker 1: smooth and rounded, some irregular. They are scattered across distances
• 53:28
  Speaker 1: so large that the word neighbourhood begins to lose its meaning,
• 53:33
  Speaker 1: and among them is another great spiral galaxy, Andromeda. It
• 53:38
  Speaker 1: is more than two million light-years away. From Earth it
• 53:42
  Speaker 1: appears as a faint smudge in the night sky, but
• 53:45
  Speaker 1: from here, drifting beyond the Milky Way, it can begin
• 53:49
  Speaker 1: to feel less like a distant smudge and more like
• 53:53
  Speaker 1: another island of stars, another galaxy, another enormous collection of worlds,
• 53:59
  Speaker 1: another place where light has been travelling for millions of years.
• 54:03
  Speaker 1: And as the Milky Way continues shrinking behind you, Andromeda
• 54:07
  Speaker 1: slowly becomes the next landmark in this quiet journey. The
• 54:11
  Speaker 1: darkness between the two galaxies is vast, almost entirely empty,
• 54:17
  Speaker 1: and yet, somehow, the two galaxies belong to the same
• 54:21
  Speaker 1: larger neighbourhood, A small gathering of galaxies held together by gravity.
• 54:26
  Speaker 1: A place called the Local Group. You can simply remain
• 54:29
  Speaker 1: here for a moment, floating between two enormous galaxies, with
• 54:34
  Speaker 1: millions of light-years of quiet space stretching around you. The
• 54:38
  Speaker 1: Milky Way is behind you. Andromeda is ahead. And between them,
• 54:44
  Speaker 1: there is mostly darkness. The Milky Way is behind you now.
• 54:50
  Speaker 1: It has become a distant island of light, its spiral
• 54:54
  Speaker 1: structure slowly fading into the darkness. And ahead of you
• 54:58
  Speaker 1: is another island, Andromeda. From Earth, Andromeda appears as a faint,
• 55:04
  Speaker 1: soft patch of light in the night sky. It does
• 55:07
  Speaker 1: not look enormous. It does not look like a galaxy
• 55:10
  Speaker 1: containing hundreds of billions of stars. It simply looks like
• 55:14
  Speaker 1: a small glow. But the reason it looks small is
• 55:17
  Speaker 1: not because it is small, it is because it is
• 55:20
  Speaker 1: very far away. Andromeda lies roughly two and a half
• 55:24
  Speaker 1: million light years from us. So the light reaching Earth
• 55:28
  Speaker 1: tonight began its journey long before modern human civilization existed.
• 55:34
  Speaker 1: It crossed the darkness for more than two million years,
• 55:37
  Speaker 1: carrying a picture of Andromeda from a distant moment in
• 55:41
  Speaker 1: the past. you can let that idea become gentle rather
• 55:45
  Speaker 1: than enormous. When you look toward Andromeda, you are not
• 55:49
  Speaker 1: seeing it as it is right now. You are seeing
• 55:52
  Speaker 1: ancient light, a message that has been travelling through space
• 55:55
  Speaker 1: for an almost unimaginable length of time. Andromeda itself is
• 56:00
  Speaker 1: another great spiral galaxy. It has its own stars, its
• 56:05
  Speaker 1: own clouds of gas and dust, its own ancient stellar populations,
• 56:10
  Speaker 1: its own younger stars. and its own smaller companion galaxies.
• 56:15
  Speaker 1: Around Andromeda are many satellite galaxies, smaller systems held by
• 56:19
  Speaker 1: its gravity. Some are faint dwarf galaxies, containing far fewer
• 56:24
  Speaker 1: stars than the Milky Way. Others are more substantial. Together,
• 56:30
  Speaker 1: they form a small neighbourhood around Andromeda, and this gives
• 56:33
  Speaker 1: you a new way to think about the word distance.
• 56:37
  Speaker 1: A galaxy is not always alone. Galaxies can travel together.
• 56:42
  Speaker 1: They can orbit one another. They can interact. They can
• 56:45
  Speaker 1: slowly change one another through gravity. And sometimes they can
• 56:50
  Speaker 1: become part of the same larger structure. Andromeda and the
• 56:54
  Speaker 1: Milky Way belong to such a structure, the Local Group.
• 56:58
  Speaker 1: The name sounds almost ordinary, local, as though you could
• 57:02
  Speaker 1: walk across it. But the Local Group is enormous. It
• 57:06
  Speaker 1: contains the Milky Way, Andromeda, the Triangulum Galaxy, and many
• 57:11
  Speaker 1: smaller galaxies scattered across a region of space measured in
• 57:15
  Speaker 1: millions of light years. The galaxies are not packed together.
• 57:19
  Speaker 1: They are separated by immense darkness. Yet gravity connects them.
• 57:24
  Speaker 1: You can imagine several islands spread across a very calm ocean.
• 57:29
  Speaker 1: The islands are separated by great distances, but they still
• 57:32
  Speaker 1: belong to the same archipelago. The ocean between them is
• 57:36
  Speaker 1: much larger than the islands themselves. The local group is
• 57:40
  Speaker 1: something like that. The galaxies are the islands, the space
• 57:44
  Speaker 1: between them is the ocean, and the invisible connection is gravity.
• 57:49
  Speaker 1: For a long time, human beings had no way to
• 57:51
  Speaker 1: appreciate how enormous this neighbourhood really was. The stars seemed
• 57:56
  Speaker 1: like points, the Milky Way seemed like a cloudy band,
• 58:00
  Speaker 1: and Andromeda seemed like a faint smudge. Only as telescopes
• 58:05
  Speaker 1: became more powerful did the smudge become a galaxy. And
• 58:09
  Speaker 1: once galaxies could be identified as separate systems, the scale
• 58:13
  Speaker 1: of the universe opened again. You could begin to compare
• 58:17
  Speaker 1: one galaxy with another. You could begin to measure how
• 58:20
  Speaker 1: quickly they were moving. And this brings another quiet clue
• 58:24
  Speaker 1: into the story. Light itself can change as space and
• 58:29
  Speaker 1: motion affect what we observe. When a distant galaxy is
• 58:33
  Speaker 1: moving away from us, its light can be shifted toward
• 58:36
  Speaker 1: the redder part of the spectrum. Astronomers call this redshift.
• 58:41
  Speaker 1: It is one of the ways they study enormous cosmic
• 58:44
  Speaker 1: distances and the motions of galaxies. You do not need
• 58:49
  Speaker 1: to imagine the colours changing dramatically. Think instead of a
• 58:53
  Speaker 1: wave being gently stretched as it travels. The light arrives
• 58:57
  Speaker 1: carrying information about the journey it has made. And in
• 59:01
  Speaker 1: that stretched light, astronomers can find clues about motion and distance.
• 59:07
  Speaker 1: Some galaxies, depending on their local motion, can instead appear
• 59:11
  Speaker 1: shifted toward the blue. So even a galaxy millions of
• 59:15
  Speaker 1: light years away can leave behind a small signature in
• 59:19
  Speaker 1: its light. Again, you do not need to touch the galaxy.
• 59:23
  Speaker 1: You do not need to travel there. You simply receive
• 59:26
  Speaker 1: its light and listen to what that light has to say.
• 59:30
  Speaker 1: Andromeda is especially interesting because its motion is influenced by
• 59:34
  Speaker 1: the gravitational environment around it. The Milky Way and Andromeda
• 59:39
  Speaker 1: are moving toward one another. The motion is slow by
• 59:43
  Speaker 1: human standards, but across millions and billions of years, gravity
• 59:48
  Speaker 1: has plenty of time to shape the future. The galaxies
• 59:51
  Speaker 1: do not need to rush. The universe itself is patient.
• 59:55
  Speaker 1: You can imagine the two great spiral galaxies drifting through darkness,
• 1:00:00
  Speaker 1: each surrounded by countless stars, each carrying its own history,
• 1:00:05
  Speaker 1: each moving through the same broad gravitational neighbourhood. And beyond
• 1:00:09
  Speaker 1: the Local Group, the scale grows again. The Local Group
• 1:00:13
  Speaker 1: is not an isolated island. It belongs to a larger,
• 1:00:17
  Speaker 1: flattened arrangement of galaxies, known as the Local Sheet. Hundreds
• 1:00:22
  Speaker 1: of galaxies can be found within this broader structure. The
• 1:00:26
  Speaker 1: name is gentle, a sheet, and that is useful to imagine.
• 1:00:30
  Speaker 1: Instead of galaxies filling space evenly in every direction, picture
• 1:00:35
  Speaker 1: them gathered along a vast, thin arrangement, like tiny points
• 1:00:39
  Speaker 1: sprinkled across a sheet that stretches far beyond anything you
• 1:00:43
  Speaker 1: could see at once. The local sheet itself is part
• 1:00:47
  Speaker 1: of an even larger structure traditionally associated with the Virgo supercluster.
• 1:00:53
  Speaker 1: Now the word supercluster begins to sound appropriate. You are
• 1:00:57
  Speaker 1: no longer thinking about one galaxy. You are thinking about
• 1:01:00
  Speaker 1: groups of galaxies, then groups of groups, then immense regions
• 1:01:05
  Speaker 1: containing thousands or many thousands of galaxies. The numbers begin
• 1:01:10
  Speaker 1: to lose their emotional meaning, so you can return to
• 1:01:13
  Speaker 1: the image. One galaxy, then another, then a group, then
• 1:01:19
  Speaker 1: a sheet, then a supercluster. The pattern keeps expanding, and eventually,
• 1:01:25
  Speaker 1: even the supercluster is only one part of something larger, Laniakea,
• 1:01:30
  Speaker 1: a vast region of cosmic structure containing multiple supercluster regions,
• 1:01:36
  Speaker 1: including the larger environment associated with our own galaxy. From
• 1:01:41
  Speaker 1: this distance, the Milky Way is no longer a world.
• 1:01:45
  Speaker 1: It is not even a point that you can easily
• 1:01:47
  Speaker 1: separate from the surrounding galaxies. It becomes one small light
• 1:01:51
  Speaker 1: among many. And then the individual galaxies begin to disappear
• 1:01:55
  Speaker 1: as well. You pull farther away. The galaxies become points.
• 1:02:00
  Speaker 1: The points begin to gather into lines. The lines gather
• 1:02:04
  Speaker 1: into broad threads. And the threads begin to form a pattern.
• 1:02:09
  Speaker 1: This is where the universe begins to look less like
• 1:02:11
  Speaker 1: a collection of separate objects and more like a great structure.
• 1:02:16
  Speaker 1: Galaxies gather along enormous filaments. They collect into sheets and clusters,
• 1:02:22
  Speaker 1: and between these structures are vast regions containing far fewer galaxies.
• 1:02:27
  Speaker 1: The spaces are beginning to become as important as the
• 1:02:30
  Speaker 1: things inside them. You can almost imagine a delicate web
• 1:02:34
  Speaker 1: suspended in darkness. The bright threads are galaxies. The knots
• 1:02:39
  Speaker 1: are clusters. The broad empty spaces between them are enormous
• 1:02:43
  Speaker 1: cosmic voids. And now... As you continue drifting outward, the
• 1:02:48
  Speaker 1: Milky Way, Andromeda, the local group, and even the larger
• 1:02:52
  Speaker 1: structures around them, begin to feel like tiny details within
• 1:02:56
  Speaker 1: a much greater pattern. There is no sudden boundary, no edge,
• 1:03:01
  Speaker 1: only another widening of perspective. The universe keeps unfolding, and
• 1:03:06
  Speaker 1: somewhere ahead, beyond the bright threads of galaxies, the spaces
• 1:03:11
  Speaker 1: between those threads become so enormous that that the word
• 1:03:14
  Speaker 1: empty begins to take on a completely different meaning. The
• 1:03:20
  Speaker 1: galaxies around you have become very small now. The Milky
• 1:03:24
  Speaker 1: Way is no longer a great spiral filling your imagination.
• 1:03:28
  Speaker 1: Andromeda is only another distant point. The local group has
• 1:03:33
  Speaker 1: become a tiny gathering of lights, and around these lights
• 1:03:37
  Speaker 1: the darkness continues. You can drift farther. There is no
• 1:03:41
  Speaker 1: wall to cross. No sudden boundary. Only more space. And
• 1:03:46
  Speaker 1: as you move outward, you begin to notice that the
• 1:03:49
  Speaker 1: galaxies are not spread evenly through the universe. They gather.
• 1:03:54
  Speaker 1: They form long threads. They collect into broad sheets. They
• 1:03:58
  Speaker 1: gather into dense knots and clusters. And between those structures
• 1:04:03
  Speaker 1: are enormous regions where galaxies become much less common. These
• 1:04:07
  Speaker 1: are cosmic voids. The word void can sound as though
• 1:04:10
  Speaker 1: it means absolute nothing. But a cosmic void is not
• 1:04:14
  Speaker 1: perfectly empty. There can still be galaxies. There can still
• 1:04:18
  Speaker 1: be thin gas. There can still be faint matter and
• 1:04:21
  Speaker 1: radiation moving through the darkness. A void simply contains much
• 1:04:26
  Speaker 1: less matter than the regions around it. Imagine a very
• 1:04:30
  Speaker 1: quiet field. In one part of the field, thousands of
• 1:04:34
  Speaker 1: small lights gather together. Then you look farther away. The
• 1:04:38
  Speaker 1: lights become fewer. Farther still, There may be only one
• 1:04:42
  Speaker 1: or two, and beyond them, a broad darkness stretches for
• 1:04:46
  Speaker 1: an enormous distance. That is closer to the idea of
• 1:04:50
  Speaker 1: a cosmic void. One of the nearest large examples is
• 1:04:54
  Speaker 1: the local void. It lies beside the local sheet, the
• 1:04:58
  Speaker 1: larger arrangement of galaxies that includes our own local group.
• 1:05:03
  Speaker 1: From our perspective, the local void is not unimaginably far away.
• 1:05:08
  Speaker 1: Its nearest regions begin only a few million light-years from Earth,
• 1:05:12
  Speaker 1: yet its full scale is enormous. Its diameter is measured
• 1:05:16
  Speaker 1: in hundreds of millions of light-years, so even something called
• 1:05:20
  Speaker 1: local can be almost impossible to hold inside the human imagination.
• 1:05:25
  Speaker 1: You can let the Milky Way become smaller behind you,
• 1:05:29
  Speaker 1: then the local group, then the local sheet, and ahead,
• 1:05:33
  Speaker 1: the galaxies become increasingly sparse. Perhaps you notice a single
• 1:05:37
  Speaker 1: small galaxy floating in the darkness. Its name is NGC 6503.
• 1:05:43
  Speaker 1: It is a dwarf spiral galaxy located within the region
• 1:05:49
  Speaker 1: associated with the local void. From Earth it is extremely distant,
• 1:05:54
  Speaker 1: but in this imagined journey it can become a small
• 1:05:57
  Speaker 1: point of light inside an enormous emptiness. Its spiral arms
• 1:06:02
  Speaker 1: contain regions of glowing gas and young stars. There are
• 1:06:07
  Speaker 1: bright clouds where stars are being born. There are darker
• 1:06:11
  Speaker 1: regions filled with cooler gas and dust. So even inside
• 1:06:15
  Speaker 1: a great void, the universe is not completely silent. A
• 1:06:19
  Speaker 1: galaxy can still glow, stars can still form, light can
• 1:06:24
  Speaker 1: still travel, and yet the surrounding space remains almost empty.
• 1:06:28
  Speaker 1: This is one of the most beautiful contrasts in the
• 1:06:31
  Speaker 1: large-scale universe. A single galaxy can contain billions of stars.
• 1:06:37
  Speaker 1: And around that galaxy there can be millions of light-years
• 1:06:40
  Speaker 1: of sparse space. The emptiness is not outside the universe,
• 1:06:44
  Speaker 1: it is part of the universe. And astronomers believe that
• 1:06:48
  Speaker 1: these vast differences in density began very early. The young
• 1:06:53
  Speaker 1: universe was not perfectly smooth. There were tiny differences in
• 1:06:57
  Speaker 1: how matter and energy were distributed. Some regions were slightly denser,
• 1:07:02
  Speaker 1: others were slightly less dense. Gravity slowly amplified those differences.
• 1:07:08
  Speaker 1: Matter gathered into the denser regions. Gas and dark matter
• 1:07:12
  Speaker 1: became concentrated. Galaxies began to form. Groups of galaxies gathered,
• 1:07:19
  Speaker 1: filaments and sheets developed, and the regions with less matter
• 1:07:23
  Speaker 1: gradually became even more empty by comparison. The universe, over
• 1:07:28
  Speaker 1: immense stretches of time, slowly drew itself into a pattern.
• 1:07:33
  Speaker 1: Dense regions became brighter. Sparse regions became darker. The contrast grew.
• 1:07:39
  Speaker 1: You can imagine a slow river dividing into streams. Water
• 1:07:43
  Speaker 1: gathers into the channels. The spaces between the channels become quieter.
• 1:07:48
  Speaker 1: Nothing needs to push the water away from the empty regions.
• 1:07:51
  Speaker 1: The flow simply gathers where gravity and the shape of
• 1:07:54
  Speaker 1: the landscape guide it. On cosmic scales, gravity plays a
• 1:07:59
  Speaker 1: similar role. The pattern takes billions of years to develop.
• 1:08:03
  Speaker 1: And because the universe is so old, there has been
• 1:08:06
  Speaker 1: plenty of time for tiny differences to become enormous structures.
• 1:08:11
  Speaker 1: You can drift farther now. The local void becomes only
• 1:08:15
  Speaker 1: one small part of a much larger arrangement. The Virgo
• 1:08:19
  Speaker 1: region stretches across a vast area. The surrounding structures contain
• 1:08:24
  Speaker 1: enormous numbers of galaxies, and beyond them lies an even
• 1:08:27
  Speaker 1: greater network. The cosmic web continues. Filaments, sheets, clusters, voids.
• 1:08:36
  Speaker 1: Again and again, light and darkness, matter and emptiness. Structure
• 1:08:42
  Speaker 1: and space. The source material also describes a much larger
• 1:08:47
  Speaker 1: region surrounding our local cosmic environment, known as the KBC supervoid.
• 1:08:53
  Speaker 1: It is presented as an enormous, roughly spherical underdense region,
• 1:08:59
  Speaker 1: potentially extending across more than a billion light years. The
• 1:09:03
  Speaker 1: idea is remarkable because our own galactic neighbourhood may lie
• 1:09:06
  Speaker 1: within such a broad region of relatively low density. You
• 1:09:10
  Speaker 1: do not need to imagine a perfect bubble with a
• 1:09:12
  Speaker 1: sharp surface. Space does not usually work that way. Instead,
• 1:09:18
  Speaker 1: imagine a gradual change. Fewer galaxies here, a little more there,
• 1:09:23
  Speaker 1: a long transition between denser and thinner regions. The universe
• 1:09:28
  Speaker 1: rarely draws its boundaries with a straight line. It prefers gradients,
• 1:09:34
  Speaker 1: soft changes, slow differences. And this matters when astronomers measure
• 1:09:39
  Speaker 1: the expansion of space. The farther away a galaxy is,
• 1:09:43
  Speaker 1: the more its light carries information about the changing universe
• 1:09:47
  Speaker 1: through which it has travelled. Distant galaxies generally appear to
• 1:09:51
  Speaker 1: be moving away from us as space expands, and because
• 1:09:55
  Speaker 1: light takes time to cross these distances, looking farther away
• 1:10:00
  Speaker 1: also means looking further into the past. This is one
• 1:10:04
  Speaker 1: of the quietest ideas in astronomy. Distance becomes time. A
• 1:10:09
  Speaker 1: nearby galaxy shows you something relatively recent. A galaxy millions
• 1:10:13
  Speaker 1: of light-years away shows you a much older moment, And
• 1:10:17
  Speaker 1: galaxies billions of light years away show you an even
• 1:10:21
  Speaker 1: earlier universe. So when you look outward, you are also
• 1:10:25
  Speaker 1: looking backward. The farther you travel through space, the deeper
• 1:10:30
  Speaker 1: you travel through time. Eventually, the light reaching us comes
• 1:10:34
  Speaker 1: from a universe so young that galaxies were only beginning
• 1:10:38
  Speaker 1: to form. And even beyond the most distant galaxies we
• 1:10:42
  Speaker 1: can observe, there is ancient light left over from the
• 1:10:45
  Speaker 1: early universe. The cosmic microwave background, a faint afterglow spread
• 1:10:51
  Speaker 1: across the sky. It is not the light of a star.
• 1:10:54
  Speaker 1: It is not the light of a galaxy. It is
• 1:10:57
  Speaker 1: a much older signal, arriving from an era when the
• 1:11:01
  Speaker 1: universe was still very young. You can imagine it as
• 1:11:04
  Speaker 1: a soft background glow surrounding everything you have seen. The stars,
• 1:11:10
  Speaker 1: the galaxies, the filaments, the voids, all of them are
• 1:11:13
  Speaker 1: part of a universe that once looked very different. And
• 1:11:17
  Speaker 1: when astronomers study this ancient background, they can find tiny
• 1:11:21
  Speaker 1: variations within it, small differences in temperature, small differences in density,
• 1:11:27
  Speaker 1: tiny traces of the uneven beginning from which today's enormous
• 1:11:31
  Speaker 1: structures eventually grew. Even after travelling outward through galaxies and voids,
• 1:11:36
  Speaker 1: you have not reached an edge. You have reached only
• 1:11:39
  Speaker 1: the limit of what light has had enough time to
• 1:11:42
  Speaker 1: show us. The observable universe is enormous. Its diameter is
• 1:11:47
  Speaker 1: roughly 93 billion light years in the source material. And yet,
• 1:11:52
  Speaker 1: the observable universe may not be the whole universe. There
• 1:11:56
  Speaker 1: may be regions beyond what we can currently observe, not
• 1:12:00
  Speaker 1: because there is a physical wall there, but because light
• 1:12:03
  Speaker 1: from those regions has not had enough time to reach us.
• 1:12:08
  Speaker 1: That is a very different kind of boundary. It is
• 1:12:10
  Speaker 1: not an edge in space. It is an edge in knowledge.
• 1:12:14
  Speaker 1: And perhaps this is where the journey can become quiet again.
• 1:12:17
  Speaker 1: You began on Earth, a tiny world beneath your body.
• 1:12:21
  Speaker 1: You moved to the Moon, then to the Sun, past
• 1:12:25
  Speaker 1: the planets, through the outer solar system, between the stars,
• 1:12:30
  Speaker 1: toward Proxima Centauri, across the Milky Way, beyond its halo,
• 1:12:36
  Speaker 1: toward Andromeda, through the local group, across the cosmic web,
• 1:12:41
  Speaker 1: and finally into the great spaces between its threads. At
• 1:12:45
  Speaker 1: every stage, the objects became smaller, but the spaces became larger.
• 1:12:51
  Speaker 1: And now, from this impossible distance, even the largest structures
• 1:12:55
  Speaker 1: you have imagined begin to fade. The galaxies become points,
• 1:13:00
  Speaker 1: the points become patterns, the patterns become faint traces of
• 1:13:04
  Speaker 1: ancient light, and the darkness between them remains. Perhaps this
• 1:13:09
  Speaker 1: is the deepest perspective that scale can offer. The universe
• 1:13:13
  Speaker 1: is not only a collection of stars and planets, it
• 1:13:17
  Speaker 1: is also the enormous distance between them. It is the
• 1:13:21
  Speaker 1: quiet space between galaxies, the darkness between filaments, the long
• 1:13:26
  Speaker 1: stretches in which almost nothing happens, and somehow, inside one
• 1:13:32
  Speaker 1: of those small bright regions, on one small planet, you
• 1:13:36
  Speaker 1: are here. You do not need to become smaller than
• 1:13:39
  Speaker 1: you are. You do not need to feel insignificant. You
• 1:13:43
  Speaker 1: can simply feel connected. Because the same universe that contains
• 1:13:47
  Speaker 1: enormous voids also contains the small world beneath you. The
• 1:13:52
  Speaker 1: same laws that shaped galaxies shaped stars. The same stars
• 1:13:56
  Speaker 1: produced the elements that became planets. And on one quiet planet,
• 1:14:01
  Speaker 1: those elements eventually became oceans, forests, living things, and you.
• 1:14:08
  Speaker 1: So for now, you can stop travelling. Let the cosmic
• 1:14:12
  Speaker 1: web fade. Let the galaxies become distant lights. Let the
• 1:14:17
  Speaker 1: enormous voids become quiet darkness. And slowly, gently, let your
• 1:14:23
  Speaker 1: attention return toward Earth. Back toward the small blue world.
• 1:14:28
  Speaker 1: Back toward the air around you. Back toward the place
• 1:14:32
  Speaker 1: where you are resting. The universe can remain enormous without
• 1:14:35
  Speaker 1: you having to hold all of it in your mind.
• 1:14:38
  Speaker 1: There is nothing more you need to measure, nothing more
• 1:14:41
  Speaker 1: you need to understand. The stars can continue moving. The
• 1:14:46
  Speaker 1: galaxies can continue drifting. Light can continue crossing distances that
• 1:14:51
  Speaker 1: take millions and billions of years. And you can simply
• 1:14:54
  Speaker 1: rest beneath it all, safe, still, here. The great emptiness
• 1:15:00
  Speaker 1: continues around you. And for tonight, it is quiet enough.
• 1:15:04
  Speaker 1: And so, our journey drifts quietly to its end, You
• 1:15:08
  Speaker 1: began close to home, beneath the familiar sky of Earth,
• 1:15:12
  Speaker 1: and slowly travelled outward, past the moon, past the sun,
• 1:15:17
  Speaker 1: beyond the planets, through the quiet space between stars, and
• 1:15:21
  Speaker 1: into the enormous structure of the Milky Way. You watched
• 1:15:25
  Speaker 1: nearby stars become distant lights. You watched the Milky Way
• 1:15:29
  Speaker 1: become one galaxy among many. You watched galaxies gather into groups, sheets,
• 1:15:35
  Speaker 1: and filaments. And eventually... You reach the vast spaces between them,
• 1:15:41
  Speaker 1: where almost nothing can be seen. Yet even there, the
• 1:15:45
  Speaker 1: universe was never truly empty. There was always something moving
• 1:15:49
  Speaker 1: quietly through the darkness. A faint particle. An ancient photon.
• 1:15:55
  Speaker 1: A distant galaxy. A trace of matter. A little light
• 1:15:59
  Speaker 1: from a very old time. And now you can let
• 1:16:02
  Speaker 1: all of it drift away. You do not need to
• 1:16:04
  Speaker 1: remember the distances. You do not need to remember the names.
• 1:16:09
  Speaker 1: You do not need to hold the scale of the
• 1:16:11
  Speaker 1: universe inside your thoughts. Just remember the feeling. A small world,
• 1:16:16
  Speaker 1: a quiet planet, a sky filled with distant light, and
• 1:16:20
  Speaker 1: an enormous universe surrounding you. Whether you are still listening
• 1:16:24
  Speaker 1: beneath the glow of your screen, or already floating somewhere
• 1:16:28
  Speaker 1: between dreams and distant stars, thank you for travelling here tonight.
• 1:16:33
  Speaker 1: If this wandering brought you a little calm, you are
• 1:16:35
  Speaker 1: welcome to subscribe or share it with someone who could
• 1:16:38
  Speaker 1: use a gentler night beneath the cosmos. For now, rest well.
• 1:16:43
  Speaker 1: The stars will keep shining, the planets will keep turning,
• 1:16:48
  Speaker 1: the galaxies will keep drifting, and the universe will carry
• 1:16:51
  Speaker 1: on softly around you while you sleep.