Latest / Boring Science / 100 Sleepy Facts About Cosmic Voids _ The Quietest Places in the Universe

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100 Sleepy Facts About Cosmic Voids _ The Quietest Places in the Universe · Boring Science

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Speaker 1: Good evening, and welcome back to Boring Science for Sleep. Tonight,
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we're going to drift somewhere very unusual. Not to a
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bright galaxy full of stars. Not to a glowing nebula.
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And not even to the crowded neighbourhoods of the cosmos
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where thousands of galaxies swirl together. Instead, we're going somewhere quieter.
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Much quieter. Tonight, we're travelling to the emptiest places in
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the universe. Before we begin though, I'd love to know something.
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Where in the world are you listening from tonight? And
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what time is it there? Some of you might be
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watching just before bed. Others may already be under blankets
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with the lights dimmed. And somewhere on earth right now,
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someone else is just beginning their night beneath the same sky.
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So if you feel like it, let us know in
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the comments. Where are you watching from? And what time
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is it where you are? Then settle in, relax, and
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let your mind drift gently into space. When most of
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us imagine the universe, we tend to picture it as
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something full, full of stars, full of glowing galaxies, full
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of swirling clouds of gas and dust. And in a way,
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that picture is true. The night sky above us sparkles
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with thousands of stars, and powerful telescopes reveal billions of
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galaxies scattered throughout the cosmos. But there is something strange
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about the universe that astronomers discovered only relatively recently. When
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they began mapping the positions of galaxies across vast distances,
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they noticed something unexpected. The galaxies were not spread evenly
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through space. Instead, they gathered together. Clusters of galaxies formed
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enormous chains and filaments stretching across the universe. These filaments
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connected massive galaxy clusters, creating a vast cosmic network. Astronomers
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sometimes call it the cosmic web, a structure so enormous
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that it stretches across billions of light years. But between
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those glowing threads of galaxies, something else appeared. Something very different.
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immense regions where almost nothing exists at all, vast expanses
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of space where galaxies are incredibly rare, places where the
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universe becomes almost empty. These regions are known as cosmic voids,
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and they are not small. Some cosmic voids span hundreds
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of millions of light years across, distances so vast that
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light itself takes millions of years just to cross them.
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Inside these voids, the universe becomes strangely quiet. No bright
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galaxy clusters. No crowded cosmic neighborhoods. Just enormous volumes of
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dark space. If you could travel into the center of
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one of these cosmic voids, the sky around you would
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look very different from the one we see on Earth.
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Here on Earth, our night sky is rich with stars.
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But in the deep center of a cosmic void, galaxies
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would be incredibly distant. The nearest galaxy might lie tens
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of millions of light years away. The sky might appear
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darker than anything we have ever seen. A vast, silent
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ocean of space, with only faint islands of light scattered
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along the horizon of the universe. In some ways, cosmic
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voids are like the great oceans of the cosmos. Imagine
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the galaxies as islands and continents. Between them stretch enormous
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cosmic seas. Empty, dark and unimaginably vast. Most of the
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universe is not made of galaxies. Most of it is
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this quiet emptiness. And yet these cosmic voids are not
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meaningless gaps. They are part of the grand architecture of
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the universe. The empty spaces that shape the cosmic web,
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the quiet regions that allow galaxies to gather along glowing filaments,
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Without voids, the large-scale structure of the universe would look
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completely different. The emptiness itself is part of the design. Tonight,
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we will slowly explore 100 sleepy facts about cosmic voids.
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We will drift through the vast cosmic web, visit the
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largest empty regions ever discovered. Imagine what it might feel
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like to travel through these silent spaces between galaxies. and
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reflect on what these enormous voids reveal about the nature
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of the universe. So dim the lights, get comfortable, and
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allow your thoughts to float gently into the quietest places
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in existence. Far beyond our galaxy, beyond the bright clusters
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of stars, there are regions where the universe grows incredibly still.
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Vast oceans of darkness between the islands of galaxies, the
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cosmic voids. And tonight, we're going to drift slowly through
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them together. As we gently continue our journey through the
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universe tonight, let us begin with a quiet realisation about
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the cosmos, one that took astronomers many years to fully understand.
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At first glance, it might seem reasonable to imagine that
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the universe is filled evenly with galaxies. After all, when
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we look up at the night sky, stars appear scattered everywhere.
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And when telescopes peer into the deep cosmos, they reveal
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countless galaxies, spiral galaxies, elliptical galaxies, glowing clusters of stars
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stretching out in every direction. It would be natural to
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assume that these galaxies are sprinkled through space like grains
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of sand across an endless beach. But the universe does
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not arrange itself so simply. When astronomers began carefully mapping
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the positions of galaxies across the sky, something surprising began
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to emerge. Galaxies were not spread smoothly throughout space. Instead,
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they gathered together. Some regions of the universe contained large
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numbers of galaxies clustered closely together. Other regions appeared strangely empty.
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At first, this pattern was subtle, but as telescopes improved
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and surveys expanded, the pattern became clearer. Galaxies were forming
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large cosmic structures, connected together in vast formations stretching across
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unimaginable distances. One of the most common structures in the
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universe is known as a galaxy cluster. A galaxy cluster
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is exactly what its name suggests, a large group of
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galaxies bound together by gravity. Instead of drifting alone through space,
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many galaxies exist within these gravitational communities. Some clusters contain
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a few dozen galaxies, others contain hundreds. The largest clusters
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may contain thousands of galaxies moving slowly around a shared
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center of gravity. From afar these clusters appear like glowing
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cities of light scattered through the darkness of space. Our
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own galaxy the Milky Way is not alone either. It
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belongs to a small group of galaxies called the Local Group.
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Within this group the Milky Way is accompanied by several
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neighboring galaxies including the Large Spiral Galaxy Andromeda and dozens
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of smaller dwarf galaxies. These galaxies interact through gravity, slowly
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orbiting one another across millions of years. Even this modest
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group represents a small example of the way galaxies tend
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to gather together, rather than remain isolated. But clusters themselves
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are only the beginning. When astronomers widened their view and
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began mapping galaxies across enormous regions of the universe, They
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noticed that clusters were also connected to one another. Clusters
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form chains. Long bridges of galaxies stretch between them. These
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bridges are known as cosmic filaments. Imagine strands of glowing
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threads stretching across the darkness of space. Along these threads,
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galaxies form long rivers of light. Thousands of galaxies may
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lie along a single filament, all slowly moving through the
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gravitational pull of the surrounding structure. When seen on the
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largest scales, these filaments form a gigantic network. Clusters of
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galaxies sit at the intersections, filaments connect them across vast distances,
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and between the filaments, enormous empty regions appear. Astronomers often
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describe this structure as the cosmic web, because when the
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positions of galaxies are mapped in three dimensions, the universe
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begins to resemble a vast web or foam-like pattern. Bright
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threads of galaxies woven across an immense cosmic tapestry. Yet
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what makes this structure so fascinating is not only the
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galaxies themselves, it is also the spaces between them. Between
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the glowing filaments lie regions where galaxies become incredibly rare.
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Places where the universe grows quiet. These regions are the
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cosmic voids we began discussing earlier. But to understand those voids,
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we must first appreciate the structure surrounding them. Because voids
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are not random holes. They are the natural result of
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the way matter gathered together during the early history of
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the universe. Long ago, shortly after the universe began expanding,
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matter was distributed almost evenly throughout space. But not perfectly evenly.
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Tiny differences in density existed slightly denser regions and slightly
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emptier ones. Over billions of years, gravity slowly amplified these
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tiny differences. Regions with slightly more matter attracted additional matter.
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Galaxies formed. Clusters grew larger. Filaments stretched between them. Meanwhile,
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regions with less matter gradually lost what little material they had.
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Matter drifted away toward the growing clusters and filaments, leaving
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behind vast areas of increasingly empty space. The result is
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the large-scale structure we see today. A universe shaped not
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like a uniform cloud, but like a vast network of matter.
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Galaxies gathering along filaments. clusters forming at their intersections, an
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enormous void stretching between them. In some ways, it resembles
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the structure of foam, or bubbles in a vast cosmic sea.
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The galaxies trace the edges. The voids occupy the interior spaces.
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From our position inside the Milky Way, we are already
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part of this structure. Our galaxy lies along one of
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these cosmic filaments. Nearby clusters and galaxies form part of
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the same network of matter. And far beyond our local region,
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the cosmic web stretches across billions of light years. A
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structure so vast that even light takes immense spans of
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time to cross it. So when we look up into
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the night sky and see stars scattered above us, we
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are witnessing only a tiny piece of this enormous cosmic pattern.
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Beyond the stars visible to our eyes lie galaxies. Beyond
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those galaxies lie clusters. Beyond those clusters lie filaments connecting
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vast regions of the universe. And between them all lie
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the quiet spaces we are slowly approaching. The cosmic voids.
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Places where the universe becomes almost unimaginably empty. In the
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next part of our journey tonight, we will explore how
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astronomers first began to notice these enormous empty regions and
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how mapping the universe revealed the hidden architecture of the
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cosmos itself. As we continue drifting gently through the structure
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of the universe tonight, we arrive at a fascinating moment
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in the history of astronomy. The moment when scientists first
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began to realize that the universe was not simply filled
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with galaxies, but also with enormous regions of emptiness. For
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much of human history, the universe appeared simple, When we
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looked up at the night sky with our eyes alone,
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the stars seemed scattered randomly across the heavens. Ancient observers
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could see patterns among those stars, constellations and familiar shapes.
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But beyond that, the sky seemed like a vast field
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of lights. Even when early telescopes revealed distant galaxies, astronomers
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initially assumed that these galaxies were distributed fairly evenly through space.
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It seemed reasonable to imagine the cosmos as a kind
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of grand star field. But as technology improved during the
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20th century, astronomers began to ask deeper questions. Where exactly
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are galaxies located in space? And how are they arranged
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across the universe? To answer these questions, scientists began conducting
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galaxy surveys. A galaxy survey is essentially a detailed map
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of the universe. Astronomers observe thousands or even millions of
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galaxies and measure their positions and distances. By combining these measurements,
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they can reconstruct a three-dimensional map showing where galaxies are
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located across vast cosmic volumes. In the early days of astronomy,
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this task was extremely difficult. Galaxies are incredibly distant objects.
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Even the closest ones lie millions of light-years away. But
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as telescopes became more powerful and photographic techniques improved, astronomers
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gradually began collecting the data needed to build these maps.
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One of the earliest pioneers in mapping the distribution of
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galaxies was the American astronomer Harlow Shapley in the early
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20th century. Shapley studied large clusters of galaxies and noticed
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that they were not evenly scattered across the sky. Instead,
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they appeared to form large groups and concentrations. This observation
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hinted that the universe might possess a larger structure beyond
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individual galaxies. But at that time, the available data was
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still limited. The true shape of the universe remained largely hidden.
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Decades later, new observations began revealing more of the cosmic picture.
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In the 1970s, astronomers started conducting more systematic surveys of
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galaxy positions. They measured not only where galaxies appeared on
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the sky, but also their redshift, a measure of how
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fast galaxies are moving away from us due to the
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expansion of the universe. Redshift allowed astronomers to estimate the
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distance to each galaxy. By combining position and distance measurements,
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scientists could begin mapping the universe in three dimensions. For
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the first time, the large-scale structure of the cosmos began
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to emerge. and what they discovered was unexpected. When the
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data was plotted on these early cosmic maps, galaxies did
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not appear randomly scattered. Instead, they seemed to form long
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chains and clusters. Even more surprising, between these chains of
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galaxies were large empty spaces, regions where very few galaxies
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appeared at all. At first, astronomers wondered whether these gaps
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might simply be caused by incomplete data. Perhaps the surveys
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had not yet observed enough galaxies. But as the surveys
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expanded and more galaxies were mapped, the pattern remained. The
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empty regions were real. They were enormous. And they were everywhere.
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One of the most famous early visualisations of this structure
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came from a study conducted in 1986 by astronomers Margaret
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Geller and John Hushra. they created a map of thousands
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of galaxies within a slice of the nearby universe. When
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they plotted the galaxies on their map, the result looked astonishing.
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Instead of filling space evenly, the galaxies traced delicate, interconnected patterns.
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Clusters linked by thin filaments, curving arcs of galaxies forming
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enormous walls, and between those structures, vast, empty regions The
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pattern resembled something surprisingly familiar. It looked like soap bubbles,
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or foam. Galaxies form the thin edges of bubbles, while
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the interior spaces remain mostly empty. This discovery gave rise
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to one of the most poetic descriptions of the universe's structure.
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Astronomers began calling it the cosmic foam, or cosmic web.
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Imagine a gigantic three-dimensional foam stretching across the universe. The
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thin edges of each bubble contain galaxies. The interior spaces
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are mostly empty. Those empty spaces are what we now
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call cosmic voids. Some voids span tens of millions of
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light years. Others are even larger. They're among the largest
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structures known in the universe. Not because they contain so
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much matter, but because they contain so little. One of
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the first cosmic voids to attract major attention was discovered
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in the early 1980s. It became known as the Boötes Void.
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This enormous region lies roughly 700 million light years away
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in the direction of the constellation Boötes. The Boötes Void
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is so vast that it measures roughly 250 million light
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years across. To put that into perspective, Our entire Milky
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Way galaxy is only about 100,000 light-years wide. The boat
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as void is therefore more than 2,000 times larger than
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our galaxy. Yet inside that enormous volume of space, astronomers
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have found very few galaxies. Only a handful appear scattered
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within its vast interior. For a region so immense, the
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emptiness is astonishing. When the Boötes Void was first discovered,
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some astronomers jokingly referred to it as the Great Nothing.
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The nickname reflected both its enormous size and its remarkable
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lack of galaxies. Yet despite its emptiness, the Boötes Void
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quickly became an important subject of study. By examining the
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edges of the void, astronomers could better understand how galaxies
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gather along filaments and clusters. The void itself helped reveal
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the large-scale architecture of the universe. Over time, additional galaxy
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surveys confirmed that the Boete's void was not unique. In fact,
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the universe appears to contain many cosmic voids. Some are small.
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Others are enormous. Together, they form a network of empty
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regions between the filaments and clusters of galaxies. These surveys
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eventually exposed to include millions of galaxies. Projects like the
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Sloan Digital Sky Survey produced detailed three-dimensional maps of the
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universe across billions of light years. When astronomers examined these maps,
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the cosmic web became unmistakable. Galaxies tracing glowing filaments. clusters
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forming massive intersections, and between them all, vast cosmic voids
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stretching across unimaginable distances. Today, astronomers understand that cosmic voids
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are a natural part of how the universe evolved. They
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are not mysterious gaps or missing matter. Instead, they formed
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gradually over billions of years as gravity pulled matter toward
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denser regions. As matter flowed toward galaxy clusters and filaments,
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the emptier regions became even emptier, like valleys deepening between
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rising mountain ridges. The result is the extraordinary structure we
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see today, a universe woven from filaments of galaxies surrounding
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enormous cosmic voids. And in many ways, these voids are
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just as important as the galaxies themselves. Without them, the
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universe would look completely different. The cosmic web, the great
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structure of the universe, would not exist. Voids help define
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the shape of the cosmos. They reveal how matter moved
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and gathered over billions of years. They allow astronomers to
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test theories about dark matter, gravity and the expansion of space.
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Even emptiness has a story to tell. So as we
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drift further into our exploration tonight, remember that the universe
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is not simply a collection of galaxies scattered through space.
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It is a grand structure, a cosmic web stretching across
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billions of light-years, clusters shining like cities of stars, filaments
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forming luminous bridges between them. And between those glowing threads
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lie the great, silent oceans of the cosmos, the cosmic voids.
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In the next part of our journey, we will take
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a closer look at what exactly defines a cosmic void
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and how astronomers measure and understand these enormous empty regions
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of space. As we continue drifting deeper into the quiet
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architecture of the universe tonight, we arrive at a simple
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but fascinating question. What exactly is a cosmic void? The
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name itself sounds mysterious. It suggests an emptiness so complete
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that nothing exists within it But like many ideas in astronomy,
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the reality is a little more subtle, and perhaps even
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more beautiful. A cosmic void is not a perfect vacuum.
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It is not a region where absolutely nothing exists. Instead,
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a cosmic void is an enormous region of space where
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galaxies are extremely rare. Compared with the crowded filaments and
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clusters of the cosmic web, voids contain very little matter.
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They are the quiet spaces between the great structures of
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the universe. To understand this more clearly, imagine looking down
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at a giant three-dimensional map of the cosmos. Across that
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map you would see long glowing strands of galaxies. These
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strands form the filaments of the cosmic web. Where several
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filaments meet, large clusters of galaxies gather together. These clusters
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shine brightly with the combined light of hundreds or thousands
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of galaxies. But between those filaments and clusters lie enormous gaps.
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Regions where the density of galaxies drops dramatically. Those regions
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are the cosmic voids. They are the dark spaces between
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the luminous threads of the universe. What makes cosmic voids
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so remarkable is their immense size. Even the smallest voids
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are enormous compared to familiar cosmic structures. Some voids measure
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tens of millions of light years across. Others are far larger.
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The largest known voids can stretch for hundreds of millions
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of light years from one side to the other. To
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appreciate how vast this truly is, consider the size of
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our own galaxy. The Milky Way spans about 100,000 light
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years in diameter. A large cosmic void can therefore be
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thousands of times wider than our entire galaxy. Inside such
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a region, you could travel for millions of years at
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the speed of light and still remain within the same
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enormous empty space. Within these voids, galaxies are not completely absent.
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A few isolated galaxies can still be found drifting through
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the darkness, but they are incredibly rare. While a dense
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galaxy cluster may contain thousands of galaxies packed together, a
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cosmic void might contain only a handful scattered across vast distances.
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The difference is dramatic. It is like comparing a crowded
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city to a remote desert. In the city, lights fill
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every street. In the desert, you may travel for miles
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before seeing another person. Cosmic voids are the deserts of
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the universe. Quiet, open, and almost empty. Astronomers sometimes describe
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cosmic voids as regions with very low matter density. In
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the crowded filaments of the cosmic web, matter, both visible
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matter and dark matter, collects together through gravity. But inside voids,
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the density of matter is far lower than the cosmic average.
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Over billions of years, gravity has slowly pulled matter away
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from these regions and toward the filaments and clusters surrounding them.
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The result is a universe where matter flows outward from
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voids and gathers along the edges. In this way, voids
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are not simply empty spaces. They are dynamic regions shaped
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by the movement of matter over cosmic time. The boundaries
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of cosmic voids are defined by the filaments of the
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cosmic web. These filaments act like the walls of enormous bubbles.
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Along these walls, galaxies gather in long chains and clusters.
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Inside the bubble the space remains mostly empty. When astronomers
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map the universe in three dimensions, this pattern becomes strikingly clear.
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The galaxies trace a delicate network of glowing threads, and
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between those threads lie vast, hollow spaces. Together, they form
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the extraordinary architecture of the cosmic web. Another remarkable feature
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of cosmic voids is their smoothness. Because they contain so
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little matter, there are fewer gravitational disturbances inside them. In
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galaxy clusters, gravity pulls galaxies in many directions. Collisions and
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interactions are common. But inside a void, galaxies are widely separated.
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Interactions between them are rare. The environment is quiet and
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relatively undisturbed. This makes voids fascinating laboratories for astronomers. By
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studying galaxies that live within voids, Scientists can learn how
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galaxies evolve in isolation far from the crowded influences of
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clusters and filaments. Cosmic voids also continue to change over time.
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As the universe expands, matter continues drifting toward the denser
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regions of the cosmic web. This process gradually makes voids
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larger and emptier. In effect, the voids slowly grow as
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matter flows away from them. Over billions of years, neighbouring
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voids can even merge together, creating even larger empty regions.
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In this way, the structure of the universe continues evolving
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on enormous timescales. If you could somehow travel to the
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centre of a cosmic void, the experience would be extraordinary.
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The nearest galaxies might lie tens of millions of light-years away.
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From your vantage point, the sky would appear very different
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from the one we see on Earth. Instead of a
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rich tapestry of nearby stars and galaxies, the heavens would
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feel distant and sparse. Most galaxies would appear as faint,
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isolated points far away along the edges of the void.
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The darkness between them would stretch across unimaginable distances. It
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would be one of the quietest places in the universe.
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Yet even in that immense emptiness, the universe would still
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be present. Invisible dark matter would still thread through space.
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Faint background radiation from the early universe would still glow
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softly across the cosmos. And gravity would continue shaping the
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slow movement of matter across billions of years. Even emptiness
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has its own subtle structure. So when astronomers speak of
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cosmic voids, they are not describing simple holes in space.
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They are describing the vast regions between the luminous structures
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of the cosmic web. Enormous cosmic bubbles, places where galaxies
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are few, distances are immense, and the universe becomes almost silent.
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These quiet regions occupy a huge portion of the cosmos.
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In fact, most of the universe's volume is made up
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of these enormous voids. The galaxies themselves occupy only the
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thin threads surrounding them. in the next part of our
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journey tonight, we will explore those threads more closely. Because
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the cosmic voids cannot exist alone. They are part of
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something even larger, the magnificent structure known as the cosmic web,
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where filaments of galaxies stretch across billions of light-years, weaving
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the grand design of the universe. As we continue our
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quiet journey through the structure of the universe tonight, we
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now arrive at one of the most beautiful and astonishing
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ideas in modern cosmology. The universe, when seen on its
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largest scales, is not random. It is not a chaotic
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scattering of galaxies across empty space. Instead, the cosmos forms
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a vast and delicate structure. A structure so enormous that
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it stretches across billions of light years. Astronomers call it
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the cosmic web. And once you understand it, the universe
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begins to look less like a random field of galaxies
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and more like a magnificent cosmic network. Imagine, for a moment,
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a giant, three-dimensional spider web stretching across the darkness of space.
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Along the thin strands of that web, countless galaxies gather.
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At the intersections of the strands, Enormous clusters of galaxies
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form bright cosmic hubs, and between the strands lie the
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vast empty bubbles we explored earlier, the cosmic voids. Together,
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these elements, filaments, clusters, and voids create the large-scale structure
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of the universe, a structure so immense that it can
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only be seen when astronomers map millions of galaxies across
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huge cosmic distances. The long strands of this network are
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known as cosmic filaments. Filaments are enormous rivers of galaxies.
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Instead of existing alone, galaxies tend to gather along these
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immense gravitational pathways. Each filament can stretch across hundreds of
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millions of light years. Along them, thousands of galaxies may
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drift slowly through space. From afar, a filament looks like
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a glowing thread woven through the darkness. but when examined
31:56
more closely it becomes a vast region containing countless galaxies,
32:01
clouds of gas and invisible dark matter. The galaxies within
32:05
a filament are not stationary. They move slowly under the
32:09
influence of gravity, drifting toward denser regions where clusters are forming.
32:14
Where several filaments intersect, something remarkable occurs. These intersections become
32:21
galaxy clusters. Clusters are the densest environments in the universe.
32:27
Hundreds or even thousands of galaxies gather there, bound together
32:31
by gravity. From a distance, a cluster appears like a
32:35
brilliant city of stars glowing within the cosmic darkness. Within clusters,
32:41
galaxies interact more frequently. Gravity pulls them toward the center.
32:46
Sometimes galaxies even collide or merge with one another. Over
32:50
billions of years, These clusters grow larger and more massive,
32:55
as matter continues flowing along the filaments into their centres.
32:59
But the cosmic web is not only made of visible galaxies.
33:03
Much of its structure is actually shaped by something invisible.
33:07
Dark matter. Dark matter does not emit light, so we
33:11
cannot see it directly. Yet its gravity influences the motion
33:15
of galaxies and gas across the universe. In fact, Scientists
33:20
believe that dark matter forms the underlying framework of the
33:24
cosmic web. Long before galaxies formed, dark matter gathered into
33:29
vast filaments and halos. Ordinary matter, gas, dust, and eventually
33:35
stars then followed those gravitational pathways. Over time, galaxies formed
33:41
along the dark matter filaments, tracing the hidden structure beneath.
33:46
In this way, the cosmic web we observe today reflects
33:50
the invisible architecture of dark matter across the universe. When
33:54
astronomers simulate the formation of the universe using powerful supercomputers,
33:59
the results are extraordinary. Starting from the tiny density variations
34:04
present shortly after the Big Bang, the simulations show matter
34:08
gradually gathering together under gravity. Small clumps grow larger. Filaments
34:14
stretch across space. Clusters emerge where those filaments intersect. And
34:19
between them, enormous voids open up. When these simulations are visualized,
34:25
the resulting structure looks astonishingly similar to the maps of
34:29
real galaxies observed by telescopes. A vast cosmic web stretching
34:34
across the universe. From a distance, the cosmic web resembles
34:38
something strangely organic. Some astronomers have compared it to the
34:43
structure of foam or soap bubbles. Others have noticed that
34:46
it resembles certain biological networks. In fact, when scientists compare
34:52
maps of the cosmic web to images of neural networks
34:56
in the human brain, the similarities can appear surprisingly striking.
35:01
Both contain interconnected filaments and nodes, forming complex networks. Of course,
35:08
the processes behind these structures are very different. Yet the
35:12
resemblance reminds us that the universe often forms patterns that
35:16
repeat across many scales. Within the cosmic web, Matter is
35:21
constantly in motion. Galaxies slowly drift along filaments toward clusters.
35:27
Gas flows through the web, feeding the growth of galaxies. Meanwhile,
35:32
the voids between the filaments gradually expand. Over billions of years,
35:38
this slow movement reshapes the structure of the universe. Filaments
35:42
become more defined. Clusters grow more massive. And voids become
35:48
even emptier. The cosmic web evolves slowly, but continuously. Our
35:55
own galaxy is part of this enormous structure. The Milky
35:59
Way resides within a filament of galaxies known as part
36:02
of the Laniakea Supercluster, an immense region containing thousands of galaxies.
36:09
Within this supercluster, galaxies flow slowly toward massive gravitational centers.
36:15
Our local region of the universe is therefore only a
36:19
tiny portion of the vast cosmic web. Beyond it lie
36:23
countless other filaments, clusters and voids stretching across the observable universe.
36:29
When astronomers step back and view the cosmos on the
36:31
largest scales, they see something extraordinary. The universe is not
36:37
just a collection of galaxies scattered randomly across space. It
36:41
is a grand structure. Woven from threads of matter across
36:46
billions of light years, filaments of galaxies glowing softly in
36:50
the darkness, clusters shining at the intersections, and between them all,
36:56
the silent cosmic voids we have been exploring. The cosmic
37:01
web is the universe's great design, a structure shaped by gravity,
37:06
dark matter, and the slow evolution of cosmic time. And
37:10
as we continue drifting through this quiet exploration tonight, we
37:14
will soon move closer to some of the largest empty
37:17
regions ever discovered. Because among the many voids scattered across
37:21
the universe, a few stand out as truly immense. Vast
37:26
cosmic cavities where galaxies are incredibly rare. In the next
37:30
part of our journey, we will visit some of the
37:32
largest cosmic voids known, including one of the most mysterious
37:37
regions of emptiness ever found in the universe. As we
37:42
continue drifting through the vast architecture of the cosmos tonight,
37:46
we now arrive at some of the most extraordinary structures
37:49
ever discovered. Not the largest galaxies, not the brightest clusters,
37:55
but the largest empty regions in the universe. Cosmic voids
38:00
that stretch across distances so immense that they challenge our imagination.
38:06
Among these enormous spaces, One void in particular captured the
38:10
attention of astronomers when it was first discovered. It is
38:14
known as the Boötes Void. And for a time, it
38:18
became famous for what it lacked. Almost everything. The Boötes
38:23
Void lies roughly 700 million light years away from Earth,
38:28
in the direction of the constellation Boötes. When astronomers first
38:32
mapped this region in the early 1980s, they noticed something remarkable.
38:37
In a section of space where many galaxies should have
38:40
been present, almost none appeared. The region seemed strangely empty.
38:47
At first, scientists suspected that the observations might be incomplete.
38:52
Perhaps the telescopes had simply not detected faint galaxies within
38:56
the area. But as more data was collected, the mystery deepened.
39:01
The emptiness remained, and the scale of that emptiness turned
39:05
out to be astonishing. The boat's void measures roughly 250
39:11
million light years across. To grasp the enormity of that distance,
39:16
it helps to compare it with something familiar. Our entire
39:20
Milky Way galaxy is about 100,000 light years wide. That
39:25
means you could line up 2,000, 500 Milky Way galaxies
39:30
side by side and still not span the full width
39:33
of the boat as void. It is one of the
39:36
largest known regions of space where galaxies are extremely rare.
39:41
Inside such an immense cosmic cavity, the universe becomes almost silent.
39:47
When the void was first discovered, astronomers found only a
39:51
few dozen galaxies within its enormous volume. Later, observations revealed
39:56
a few more scattered throughout the region. But compared with
40:00
the surrounding areas of the cosmic web, the density of
40:04
galaxies remains extraordinarily low. Imagine standing inside a city and
40:10
looking out at thousands of glowing lights across the skyline.
40:14
Now imagine travelling far into the desert, where those lights
40:18
disappear and the horizon becomes empty. Cosmic voids are like
40:22
those deserts of the universe, except instead of miles of emptiness,
40:28
they stretch across hundreds of millions of light years. The
40:32
discovery of the Boötes void raised fascinating questions. Why would
40:37
such an enormous region contain so few galaxies? Did something
40:42
unusual happen during the early formation of the universe? Or
40:46
was this simply a natural result of the cosmic web
40:49
evolving over billions of years? Over time, astronomers began to
40:54
understand that the Beuter's void was not an isolated oddity.
40:59
It was part of a larger pattern. Many voids exist
41:03
across the universe. Some smaller. Some even larger. Together, they
41:09
form the vast, empty spaces between the filaments and clusters
41:13
of the cosmic web. When scientists map the distribution of
41:17
galaxies across the observable universe, they find that voids occupy
41:21
a surprisingly large portion of cosmic space. In fact, most
41:26
of the volume of the universe lies inside these enormous
41:30
empty regions. The galaxies themselves occupy only the thin filaments
41:35
and clusters along the edges. In other words, the universe
41:39
is not primarily made of galaxies. It is primarily made
41:43
of space between galaxies. The luminous islands of matter form
41:48
only a delicate framework surrounding enormous cosmic voids. Although voids
41:54
contain very little matter, they are not completely empty. A
41:58
few isolated galaxies still drift through their interiors. These galaxies
42:03
often live very different lives compared with galaxies inside clusters.
42:08
Because they are so far from their neighbors, they experience
42:12
far fewer gravitational interactions. Collisions between galaxies are rare. Mergers
42:18
are uncommon. These galaxies evolve quietly, isolated in the immense
42:24
stillness of the void. Astronomers sometimes refer to them as
42:28
void galaxies, and studying them helps scientists understand how galaxies
42:33
behave when they grow without the disturbances common in crowded regions.
42:38
Voids are also constantly changing, As gravity pulls matter toward
42:43
the filaments and clusters of the cosmic web, the interior
42:46
of voids gradually becomes even emptier. Matter slowly flows outward
42:51
toward the edges. This process causes voids to expand over time.
42:57
Neighboring voids may even merge together, creating even larger empty
43:01
regions across the universe. In this way, the structure of
43:06
the cosmos evolves slowly, shaped by gravity across billions of years.
43:12
If you could somehow travel to the centre of a
43:14
massive void like the Boötes Void, the view would be
43:18
unlike anything we experience here on Earth. The nearest galaxies
43:22
might lie tens of millions of light-years away. Instead of
43:26
the rich cosmic neighbourhoods we see in telescope images, the
43:30
sky would appear sparse. A few distant galaxies might glow
43:35
faintly along the far horizon of the void, but most
43:39
of the sky would be dark. A quiet ocean of
43:42
space stretching across unimaginable distances. Yet even in this immense emptiness,
43:49
the universe continues its silent work. Gravity still shapes the
43:54
motion of matter. Dark energy continues to drive the expansion
43:58
of the cosmos. And faint radiation left over from the
44:02
early universe still fills the background of space. Even the
44:06
emptiest regions of the cosmos remain part of the universe's
44:10
grand story. As we continue our peaceful journey tonight, we
44:14
will soon look more closely at what life might be
44:17
like for galaxies living inside these quiet regions. Because although
44:21
voids may appear empty from afar, a few galaxies still
44:25
inhabit them. And these isolated galaxies evolve in ways very
44:29
different from those living inside crowded clusters. In the next
44:33
part of our exploration, we will step into those silent
44:37
environments and discover what it means for a galaxy to
44:40
live inside a cosmic void. As our journey continues tonight,
44:46
we now leave the crowded intersections of the cosmic web
44:50
and drift into one of the quietest environments the universe
44:53
can offer, the interior of a cosmic void. From a distance,
44:58
these enormous regions appear almost empty. But almost is the
45:03
important word. Because even in the vast silence of a void,
45:08
a few galaxies still exist. They drift slowly through the darkness,
45:14
separated from one another by enormous distances. These are known
45:18
as void galaxies, and they live very different lives compared
45:23
with galaxies found inside dense clusters. To understand this difference,
45:28
imagine two cities. One is crowded, vibrant, and constantly busy.
45:35
People move through the streets. Buildings grow close together. Interactions
45:40
happen everywhere. The other city lies far out in a
45:44
quiet desert. Only a few houses stand scattered across the landscape.
45:50
The streets are calm. Life moves slowly. The difference between
45:55
cluster galaxies and void galaxies is somewhat similar. In crowded
45:59
regions of the universe, galaxies interact frequently. Gravity pulls them together.
46:06
Some galaxies collide and merge with one another. These encounters
46:11
can trigger bursts of star formation or distort the shapes
46:15
of galaxies entirely. Clusters are dynamic places where gravity constantly
46:20
reshapes the cosmic landscape. Inside a void, however, things are
46:26
very different. Galaxies living within these regions are incredibly isolated.
46:32
Their nearest neighbors may lie millions of light years away.
46:35
Encounters between galaxies become extremely rare. And because of this isolation,
46:41
the galaxies inside voids evolve in a much quieter and
46:45
slower way. They live calmer cosmic lives. Astronomers studying void
46:50
galaxies have noticed several interesting characteristics. Many void galaxies appear
46:56
smaller and less massive than galaxies found in dense clusters.
47:01
They often contain fewer stars, and their structures can be simpler.
47:06
Some are delicate spiral galaxies with thin arms winding gently
47:10
around their centers. Others appear irregular, shaped by slow internal
47:16
processes rather than dramatic collisions. Without frequent gravitational disturbances from
47:22
nearby galaxies, these systems have more time to evolve quietly.
47:27
Another intriguing feature of many void galaxies is their continued
47:31
star formation. In crowded galaxy clusters, star formation sometimes slows
47:37
down as galaxies lose gas through interactions with their neighbors
47:41
or with the hot gas that fills the cluster environment.
47:44
But in void galaxies, the situation can be different. Because
47:49
they remain isolated, they often retain more of their original gas.
47:54
This gas can continue collapsing into new stars over long
47:58
periods of time As a result, some void galaxies still
48:02
produce young, blue stars, even when many galaxies in denser
48:07
environments have already slowed their stellar production. From a visual perspective,
48:12
a galaxy living inside a void might experience an extraordinary
48:16
night sky. If there were observers on a planet within
48:20
such a galaxy, their cosmic neighborhood would appear remarkably empty.
48:25
Nearby galaxies, the bright spirals and glowing clusters we see
48:29
in many telescope images would be extremely distant. The nearest
48:33
galaxy might lie tens of millions of light years away.
48:37
In comparison, the Andromeda Galaxy, our closest large neighbor, is
48:43
only about 2.5 million light years from Earth. In a
48:47
cosmic void, distances between galaxies are often far greater. The
48:52
sky between them would feel vast and silent. Yet despite
48:56
this isolation, void galaxies are not completely disconnected from the
49:01
rest of the universe. They still reside within the larger
49:05
framework of the cosmic web. Gravitational forces from distant filaments
49:10
and clusters still influence their motion. Over billions of years,
49:15
some void galaxies may slowly drift toward the edges of
49:18
the void where the cosmic web becomes denser. Eventually they
49:22
might even join the larger filaments of galaxies, but this
49:26
process unfolds over enormous time scales. For now, many void
49:31
galaxies continue their quiet journeys through the vast empty interiors
49:36
of these cosmic bubbles. Studying void galaxies provides astronomers with
49:41
valuable insights. Because these galaxies evolve with fewer external influences,
49:47
they can reveal how galaxies grow under more natural conditions.
49:51
Without the frequent collisions and disturbances found in clusters, astronomers
49:56
can observe how internal processes like star formation, gas dynamics,
50:01
and dark matter halos shape galaxies over time. In this sense,
50:06
Void galaxies act like cosmic laboratories. They allow scientists to
50:11
study galaxy evolution in some of the simplest environments the
50:14
universe offers. Another fascinating aspect of cosmic voids is how
50:19
matter flows around them. Because voids contain so little matter,
50:24
gravity pulls material outward toward the surrounding filaments. Galaxies near
50:29
the edges of voids gradually drift toward the denser structures
50:32
of the cosmic web. This movement slowly reshapes the boundaries
50:37
of the void. Over billions of years, voids can expand
50:42
and change shape as matter continues migrating toward the filaments.
50:47
Even emptiness participates in the slow evolution of the universe.
50:51
If you could somehow travel to the center of a
50:53
cosmic void and look out across the universe, the view
50:57
might feel both peaceful and humbling. Instead of a crowded
51:02
cosmic skyline filled with galaxies, the sky would appear mostly dark.
51:07
Only a few faint galaxies might glow far away near
51:10
the edges of the void. Their light would be soft
51:14
and distant. Between them, the darkness of space would stretch
51:18
across unimaginable distances. It would be one of the quietest
51:23
places in existence. Yet even there, in that immense silence,
51:29
The universe would still be alive with motion. Galaxies drifting
51:34
slowly through space. Gravity shaping the flow of matter. Dark
51:39
energy gently expanding the fabric of the cosmos. Life inside
51:44
a void may appear quiet, but it remains part of
51:47
the great cosmic story. And as we continue drifting through
51:51
that story tonight, we will soon explore something even more intriguing.
51:57
Because cosmic voids are not static regions, they are slowly
52:01
changing over time, expanding, evolving and reshaping the cosmic web itself.
52:09
In the next part of our journey, we will discover
52:12
how the expansion of empty space plays a surprising role
52:15
in the growth of cosmic voids across the universe. As
52:20
we continue drifting through the silent architecture of the universe tonight,
52:24
We now arrive at a fascinating idea, one that reveals
52:28
something subtle but powerful about cosmic voids. These enormous empty
52:33
regions are not simply sitting still. They are growing. Slowly. Quietly.
52:40
But steadily. The emptiness itself is expanding. To understand why
52:45
this happens, we must remember something important about the universe.
52:50
The universe itself is expanding. This idea was first discovered
52:54
in the early 20th century, when astronomers observed that distant
52:58
galaxies are moving away from us. The farther a galaxy
53:02
lies from Earth, the faster it appears to be receding.
53:06
This motion is not because galaxies are flying outward from
53:09
a central explosion. Instead, it is because space itself is stretching.
53:16
The fabric of the universe is expanding. Galaxies are simply
53:20
carried along with that expansion. like raisins drifting apart in
53:25
a loaf of bread as the dough rises.
53:27
Speaker 2: In the oven.
53:28
Speaker 1: But the expansion of the universe does not affect all
53:31
regions of space equally. In areas where matter is dense,
53:35
such as galaxy clusters, gravity works to pull matter together.
53:39
Clusters of galaxies remain gravitationally bound. Even though space expands,
53:45
gravity keeps these systems relatively stable. But in regions where
53:50
matter is scarce, Things behave differently. In cosmic voids, there
53:55
is very little gravity pulling matter inward. With so little
54:00
mass present, nothing strongly resists the expansion of space. As
54:05
a result, the expansion of the universe can stretch these
54:08
empty regions even more easily. Void interiors gradually grow larger.
54:14
Imagine a cosmic bubble floating inside a vast ocean. If
54:19
the surrounding matter slowly drifts away from the center, the
54:23
bubble expands. This is similar to what happens inside cosmic voids.
54:28
Matter slowly flows outward toward the denser filaments of the
54:32
cosmic web. As this process continues, the interior of the
54:36
void becomes even emptier, and the boundaries of the void
54:40
gradually move outward. Over billions of years, neighboring voids can
54:44
even merge together. forming larger and larger regions of emptiness.
54:50
This process is sometimes described as void expansion, but it
54:54
is not expansion in the sense of something pushing outward. Instead,
54:59
it is more like the universe slowly redistributing its matter.
55:03
Gravity pulls galaxies and dark matter toward the dense filaments
55:07
and clusters. Meanwhile, the under-dense regions, the voids, lose material.
55:13
As the matter leaves, the void grows. It is a
55:17
gentle reshaping of the cosmic web, a slow rearrangement unfolding
55:22
over billions of years. Another mysterious force also plays an
55:27
important role in this process, a force that scientists still
55:31
do not fully understand. It is known as dark energy.
55:36
Dark energy appears to be a property of space itself.
55:40
It acts like a kind of cosmic pressure that pushes
55:42
the universe to expand faster and faster over time. Although
55:46
dark energy is invisible and difficult to detect directly, its
55:50
effects can be measured through the motion of distant galaxies.
55:54
Observations show that the expansion of the universe is not
55:58
slowing down. It is accelerating. And dark energy appears to
56:03
be the reason why. In cosmic voids, the influence of
56:07
dark energy becomes especially noticeable. Because voids contain so little matter,
56:14
gravity provides less resistance against the expansion driven by dark energy.
56:19
This allows the emptiest regions of the universe to expand
56:23
even more freely. Over immense time scales, voids become larger.
56:28
Their interiors become emptier. The cosmic web gradually stretches and thins.
56:34
Clusters remain connected by filaments, but the distances between them
56:38
slowly increase. This means that the universe we see today
56:43
is not the same universe that existed billions of years ago.
56:48
In the distant past, cosmic voids were smaller. Galaxies were
56:52
closer together. The cosmic web was more compact. But as
56:57
the universe expanded, the voids grew. They stretched outward, pushing
57:02
the filaments of galaxies farther apart. Even today, this process continues.
57:08
The universe is still evolving. Still stretching. still rearranging its
57:15
vast network of matter. If you could observe the universe
57:18
over billions of years, the changes would become visible. Filaments
57:23
would drift slowly apart, clusters would grow slightly more isolated,
57:29
and the cosmic voids between them would expand like enormous
57:32
bubbles in the fabric of space. Eventually, the universe may
57:37
become dominated by these immense empty regions. Galaxies will remain
57:42
clustered together in their gravitational communities, but the spaces between
57:46
them will grow ever larger. The universe will become quieter,
57:51
more spacious, more silent. From a human perspective, these changes
57:57
are unimaginably slow. They unfold across billions of years, yet
58:03
they are happening right now. The universe around us is
58:06
slowly expanding. The cosmic voids are gradually widening, and the
58:12
great web of galaxies continues to evolve. So when we
58:16
imagine cosmic voids tonight, those enormous silent regions between the galaxies,
58:20
it is important to remember that they are not static emptiness.
58:24
They are living parts of the universe's structure. They expand.
58:29
They merge. They reshape the cosmic web itself. In the
58:33
next part of our journey, we will explore another fascinating
58:37
feature of these vast regions. Because cosmic voids are not
58:41
only empty, they are also some of the coldest and
58:45
quietest places in existence. Places where the energy of the
58:49
universe becomes faint, and the silence of space grows deeper still.
58:56
As we continue our slow journey through the vast emptiness
58:59
of cosmic voids tonight, we arrive at another remarkable characteristic
59:04
of these enormous regions. Cosmic voids are not only empty,
59:08
they are also among the coldest and quietest places in
59:12
the entire universe. Far from the crowded clusters of galaxies,
59:17
far from the energetic centers of stars and black holes,
59:20
the interiors of voids exist in a kind of cosmic stillness.
59:25
A silence that stretches across millions of light years, To
59:29
understand why voids are so quiet, we first need to
59:33
consider the sources of energy in the universe. Galaxies are
59:37
filled with activity. Stars burn brightly, releasing enormous amounts of
59:43
light and heat. Supernova explosions send shock waves through interstellar space.
59:49
Black holes swallow matter and emit powerful jets of radiation.
59:53
Even ordinary star formation creates energetic environments where gas clouds
59:58
collapse and ignite. In galaxy clusters, these processes occur across
1:00:03
thousands of galaxies at once. The result is a rich
1:00:07
and active cosmic environment filled with light, radiation and motion.
1:00:12
But cosmic voids are very different. Inside these immense regions,
1:00:18
galaxies are incredibly rare. Without galaxies, most of those energetic
1:00:23
processes simply do not occur, and so the environment becomes
1:00:27
far quieter. One of the most fundamental measures of cosmic
1:00:31
temperature comes from something called the cosmic microwave background. This
1:00:36
faint radiation fills all of space. It is the leftover
1:00:40
glow from the early universe, created shortly after the Big
1:00:43
Bang nearly 13.8 billion years ago. Today, this radiation has
1:00:49
cooled dramatically as the universe expanded. Its temperature is now
1:00:53
about 2.7 degrees above absolute zero. That means the entire
1:00:58
universe is bathed in a faint background warmth that is
1:01:02
only slightly above the coldest temperature possible. Even the emptiest
1:01:06
regions of space still contain this gentle cosmic glow. But
1:01:11
inside cosmic voids, other sources of heat and radiation become
1:01:15
extremely scarce. Galaxies are distant. Stars are rare. Energetic events
1:01:22
are uncommon. As a result, Voids represent some of the
1:01:26
least energetic environments in the cosmos. In many ways, they
1:01:31
are the closest natural examples of true cosmic emptiness. Places
1:01:36
where matter, radiation, and energy all exist at very low levels.
1:01:41
Another important factor influencing the quietness of voids is the
1:01:46
absence of large gravitational disturbances. In galaxy clusters, gravity pulls
1:01:52
galaxies together. Galaxies collide. Gas clouds interact. Dark matter halos overlap.
1:02:00
These interactions generate motion and turbulence throughout the cluster environment.
1:02:06
But inside voids, gravitational forces are weaker because there is
1:02:10
less matter present. Galaxies are widely separated. Their gravitational influence
1:02:16
rarely reaches one another. Without frequent interactions, the environment remains calm.
1:02:23
It is a place where cosmic events unfold slowly and gently.
1:02:27
This peaceful environment makes cosmic voids fascinating for astronomers, because
1:02:33
they allow scientists to observe the universe under extremely quiet conditions.
1:02:38
Without the energetic noise of crowded galaxy clusters, certain subtle
1:02:43
cosmic signals can become easier to detect. For example, astronomers
1:02:48
sometimes study the way light from distant galaxies passes through voids.
1:02:53
Because voids contain less matter, light can travel through them
1:02:56
with fewer distortions. These observations help scientists learn more about
1:03:01
the structure of the universe and the distribution of dark
1:03:05
matter across cosmic space. Voids are also interesting when studying
1:03:09
how temperature varies across the universe. Because matter is so
1:03:13
sparse inside voids, the gas that does exist there tends
1:03:17
to be extremely thin and cold. Some regions may contain
1:03:21
only a few atoms per cubic meter. To put that
1:03:25
into perspective, the air you breathe contains billions of billions
1:03:29
of atoms in a single cubic meter. Inside cosmic voids,
1:03:33
the density of matter can be so low that space
1:03:36
becomes almost unimaginably empty. And with so little matter present,
1:03:42
very little heat can accumulate. If you could somehow travel
1:03:46
through one of these regions, you would experience one of
1:03:49
the most tranquil environments imaginable. There would be no nearby
1:03:54
stars blazing in the sky, no bright clusters of galaxies,
1:04:00
no dramatic explosions of stellar energy, only faint distant galaxies
1:04:05
scattered along the far edges of the void. The darkness
1:04:09
between them would stretch across enormous distances, a quiet cosmic
1:04:14
ocean where light itself becomes rare. Yet even in this
1:04:18
profound emptiness, the universe remains subtly alive. Invisible dark matter
1:04:24
still threads through space. The faint glow of the cosmic
1:04:28
microwave background continues to bathe the void. And the expansion
1:04:32
of the universe gently stretches the fabric of space itself.
1:04:37
The void is not truly nothing. It is simply very
1:04:41
close to nothing. A place where the activity of the
1:04:44
cosmos becomes soft and distant. For scientists, cosmic voids offer
1:04:50
a unique window into the fundamental properties of the universe.
1:04:54
By studying how matter behaves in these quiet regions, astronomers
1:04:58
can test theories about gravity, dark matter, and the expansion
1:05:02
of space. Sometimes, the best way to understand the universe
1:05:06
is not by studying its brightest objects, but by exploring
1:05:10
its quietest places. And so, as we continue drifting through
1:05:14
the silent interiors of cosmic voids tonight, we find ourselves
1:05:18
surrounded by one of the most peaceful environments imaginable. Regions
1:05:23
where the temperature is near absolute zero. Where radiation is faint.
1:05:29
Where galaxies are distant. Where the universe itself feels calm
1:05:33
and still. In the next part of our journey, we
1:05:37
will imagine something even more intriguing. What would it be
1:05:41
like if we could actually travel into one of these
1:05:43
enormous cosmic voids? What would the sky look like? How
1:05:48
empty would the universe feel? And how different would that
1:05:52
experience be from the star-filled sky we see from Earth?
1:05:57
As our quiet exploration continues tonight, we now arrive at
1:06:01
a question that invites the imagination to wander far beyond
1:06:05
the limits of our present technology. What would it be
1:06:08
like to enter a cosmic void. Could we ever travel
1:06:12
into one of these vast empty regions between the galaxies?
1:06:16
And if we could, what would we see? At the moment,
1:06:21
the idea of traveling to a cosmic void belongs firmly
1:06:24
in the realm of imagination. The distances involved are enormous.
1:06:29
Even reaching our nearest neighboring galaxy, Andromeda, would require traveling
1:06:34
about 2.5 million light years. With the fastest spacecraft humanity
1:06:40
has ever built, such a journey would take tens of
1:06:43
billions of years. That is longer than the current age
1:06:47
of the universe itself. Intergalactic travel remains far beyond our
1:06:52
present capabilities, yet thinking about it can reveal something profound
1:06:57
about the scale of the cosmos. Imagine that sometime in
1:07:01
the distant future, a civilization develops the ability to travel
1:07:05
between galaxies. a spacecraft leaves the familiar spiral arms of
1:07:10
the Milky Way and begins a journey into intergalactic space.
1:07:15
At first, the sky might still appear rich with galaxies.
1:07:20
The Milky Way would glow behind the travelers like a
1:07:23
vast river of stars stretching across the darkness. Ahead of them,
1:07:28
the Andromeda Galaxy might slowly grow brighter as they approach.
1:07:33
But as the journey continues farther from these galactic islands,
1:07:36
something remarkable would begin to happen. The sky would slowly
1:07:41
grow emptier. Galaxies would begin to disappear from view, not
1:07:46
because they ceased to exist, but because the distances between
1:07:50
them are so enormous. The light from distant galaxies would
1:07:54
grow fainter. Some would shrink to tiny smudges of light
1:07:58
barely visible against the darkness. Others would fade completely beyond
1:08:02
the reach of the human eye. The travellers would gradually
1:08:06
enter one of the most isolated environments in existence, the
1:08:10
interior of a cosmic void. Inside such a region, the
1:08:15
nearest galaxy might lie tens of millions of light-years away.
1:08:19
For comparison, our nearest large galaxy is only a few
1:08:22
million light-years distant. But inside a void, the cosmic neighbourhood
1:08:27
becomes dramatically emptier. The sky might contain only a handful
1:08:32
of faint galaxies scattered across the darkness. Between them would
1:08:37
stretch enormous regions where no bright objects appear at all.
1:08:41
It would feel as though the travellers had entered a
1:08:44
vast cosmic ocean where the islands of light lie far
1:08:47
beyond the horizon. From such a vantage point, the universe
1:08:51
would appear profoundly quiet. On Earth, the night sky feels
1:08:56
rich with stars. Thousands sparkle above us. But inside a
1:09:01
cosmic void, the sky could appear almost empty. The distant
1:09:06
galaxies would glow faintly along the edges of the void,
1:09:10
like tiny lanterns placed far across an enormous plane. Between
1:09:15
them would be deep, uninterrupted darkness. perhaps darker than any
1:09:19
sky humans have ever seen. Even the Milky Way, if
1:09:24
it were visible from that distance, might appear as only
1:09:27
a faint distant glow, a soft spiral of light drifting
1:09:31
at the edge of perception. The familiar constellations we see
1:09:35
from Earth would vanish entirely. Instead of patterns of nearby stars,
1:09:41
the travellers would see only the faint outlines of distant galaxies.
1:09:45
each one representing billions of stars gathered together in a
1:09:49
faraway island of light. The sense of scale inside a
1:09:53
void would be overwhelming. In most regions of the universe,
1:09:58
galaxies are connected through filaments of the cosmic web. But
1:10:02
inside a void, those filaments lie far away. The travellers
1:10:07
would find themselves surrounded by a region where the density
1:10:10
of matter is extremely low. The nearest gravitational influences might
1:10:15
lie millions of light years away. For long stretches of
1:10:19
their journey, the spacecraft might pass through space where almost
1:10:23
nothing exists nearby at all. No stars. No nebulae. No
1:10:29
galaxy clusters. Just the thin background glow of the universe itself.
1:10:35
And yet, even within this deep cosmic silence, the universe
1:10:39
would still whisper its presence. the faint radiation of the
1:10:43
cosmic microwave background would still fill space. This ancient light
1:10:48
from the early universe would glow softly across every direction
1:10:52
of the sky. Invisible to human eyes, but detectable by
1:10:56
sensitive instruments. It would serve as a reminder that even
1:11:00
in the quietest corners of the cosmos, the history of
1:11:04
the universe still surrounds us. There would also be subtle
1:11:07
gravitational influences, Invisible dark matter might still drift through the void. Occasionally,
1:11:15
the travelers might encounter a lonely galaxy moving slowly through
1:11:20
the emptiness. These rare void galaxies would appear as isolated
1:11:24
islands of stars drifting quietly through enormous cosmic distances. Seeing
1:11:30
such a galaxy after traveling through millions of light years
1:11:33
of darkness would feel like discovering a distant lighthouse in
1:11:37
a vast ocean. But perhaps the most striking experience would
1:11:41
be the silence of structure. In most parts of the universe,
1:11:45
galaxies gather into clusters and filaments. Gravity pulls matter into
1:11:50
vast networks. Inside a void, that structure fades away. The
1:11:56
cosmic web lies far beyond the horizon. The universe becomes smooth, open,
1:12:03
and still. A place where distances stretch almost beyond comprehension.
1:12:08
Such a journey would remind us how unusual our own
1:12:11
cosmic environment truly is. We live inside a galaxy filled
1:12:16
with stars. Our galaxy sits within a filament surrounded by
1:12:21
other galaxies. And those galaxies form part of the enormous
1:12:25
cosmic web. But most of the universe's volume is not
1:12:29
like this. Most of it lies inside the quiet regions
1:12:33
we have been exploring tonight. The cosmic voids. And so,
1:12:38
even though humanity may never travel into the centre of
1:12:41
one of these vast empty spaces, imagining the journey helps
1:12:45
us understand the scale of the universe. It reveals just
1:12:50
how large the cosmos truly is, how far apart its
1:12:54
islands of light can drift, and how profound the silence
1:12:58
of space can become. In the final part of our
1:13:02
journey tonight, we will look far into the future of
1:13:05
the universe itself, Because as cosmic voids continue to expand
1:13:10
over billions of years, they may eventually dominate the structure
1:13:14
of the cosmos. Galaxies will drift farther apart, the cosmic
1:13:19
web will stretch thinner, and the universe may gradually become
1:13:23
an even quieter place. As our journey through the quiet
1:13:28
regions of the cosmos gently approaches its final stretch tonight,
1:13:32
we turn our attention far into the future. Not thousands
1:13:37
of years from now. Not even millions. But billions, trillions,
1:13:43
and perhaps far longer into the distant future of the universe.
1:13:47
Because cosmic voids are not just features of the universe today.
1:13:51
They may play an even greater role in the universe
1:13:54
of tomorrow. Over the vast timescales of cosmic evolution, the
1:13:59
universe continues to change. Galaxies slowly move through the cosmic web.
1:14:05
Gravity pulls matter toward dense clusters. And at the same time,
1:14:10
the expansion of space gradually pushes galaxies farther apart. These
1:14:15
two forces, gravity and cosmic expansion, shape the long-term future
1:14:20
of the universe. Inside galaxy clusters, gravity keeps galaxies bound together.
1:14:27
But beyond those clusters, expansion slowly stretches the distances between galaxies.
1:14:34
and inside cosmic voids, where gravity is weakest, that expansion
1:14:38
becomes especially noticeable. As billions of years pass, the voids
1:14:44
will grow larger. Matter will continue flowing toward the filaments
1:14:48
and clusters of the cosmic web. Meanwhile, the interior of
1:14:52
voids will become even emptier. Galaxies near the edges may
1:14:56
slowly drift toward the surrounding filaments. Some voids will merge
1:15:01
together with neighboring voids, forming even larger cosmic cavities. The
1:15:06
cosmic web itself will stretch and thin as the universe expands.
1:15:11
What we see today as enormous voids may eventually grow
1:15:14
into regions far larger still. Imagine the universe as a
1:15:19
vast network of bubbles. Over time, those bubbles slowly expand.
1:15:25
The walls between them stretch. The empty interiors grow larger.
1:15:31
Something similar happens on the scale of the cosmos. The
1:15:34
filaments of galaxies remain like thin strands stretched across the
1:15:38
expanding universe. But the spaces between them grow wider. Gradually,
1:15:45
the galaxies become more isolated from one another. This process
1:15:49
is driven largely by dark energy. Dark energy appears to
1:15:53
act like a kind of repulsive pressure built into the
1:15:56
fabric of space itself. Instead of pulling objects together, it
1:16:01
pushes space to expand faster and faster. Astronomers discovered this
1:16:06
surprising acceleration in the late 1990s while observing distant supernova explosions.
1:16:12
Since then, dark energy has become one of the most
1:16:16
important mysteries in cosmology, and it may shape the ultimate
1:16:20
fate of the universe. As dark energy continues driving the
1:16:24
expansion of space, galaxies outside our local gravitational neighborhood will
1:16:29
gradually drift beyond our cosmic horizon. Their light will stretch
1:16:33
and fade as the distances between galaxies grow larger. Eventually,
1:16:38
galaxies that are currently visible through telescopes may disappear from
1:16:42
view entirely. They will move so far away that their
1:16:46
light will no longer reach us. In the distant future,
1:16:50
observers in the Milky Way, or whatever remains of it,
1:16:53
may see a far emptier universe. Within our own local
1:16:57
region of space, gravity will continue to hold certain galaxies together.
1:17:02
The Milky Way and the Andromeda Galaxy, for example, are
1:17:06
already moving toward one another. In about 4 billion years,
1:17:11
they will likely merge into a single large galaxy. Other
1:17:15
nearby galaxies in the local group may also join this
1:17:18
cosmic union. Together they will form a new, larger galaxy
1:17:22
drifting through the expanding universe. But beyond that local group,
1:17:27
most other galaxies will slowly disappear into the expanding darkness.
1:17:32
As the universe ages further over trillions of years, the
1:17:35
cosmic web will become increasingly stretched. Clusters will remain gravitationally
1:17:41
bound islands of galaxies. But between them, the cosmic voids
1:17:45
will dominate. The distances between galaxy clusters will grow larger
1:17:50
and larger. The universe will become quieter. Darker. more spacious.
1:17:57
Cosmic voids will occupy an even greater fraction of the
1:18:01
universe's volume. If intelligent observers exist in such a distant future,
1:18:06
their view of the cosmos may be dramatically different from ours.
1:18:10
From their vantage point, the universe might appear almost empty.
1:18:15
Only their local cluster of galaxies would remain visible. The
1:18:20
rest of the cosmic web would lie far beyond their
1:18:23
observable horizon. They might not even know that billions of
1:18:26
other galaxies once existed. The universe would appear small, quiet,
1:18:32
and isolated. The memory of the vast cosmic network we
1:18:36
see today would be hidden by the expansion of space.
1:18:41
Yet even then, the universe would continue evolving. Stars would
1:18:46
slowly burn through their fuel. Galaxies would change shape as
1:18:50
stellar populations age. Black holes would continue consuming matter. And
1:18:56
the enormous voids between clusters would keep expanding silently. The
1:19:01
cosmos would become a quieter place with each passing epoch.
1:19:05
But tonight, as we reflect on these distant futures, We
1:19:09
can also appreciate the extraordinary moment in cosmic history that
1:19:13
we inhabit. We live at a time when the universe
1:19:17
is still rich with visible galaxies. The cosmic web remains
1:19:21
clearly observable. Clusters, filaments, and voids are all part of
1:19:27
the grand structure we can explore with telescopes and imagination.
1:19:31
The universe has not yet faded into the long, quiet
1:19:34
era that may one day arrive. And so as our
1:19:37
journey through cosmic voids comes to an end, we are
1:19:40
left with a sense of wonder. The universe is both
1:19:43
crowded and empty, filled with galaxies, yet dominated by vast
1:19:49
regions of space where almost nothing exists. The cosmic voids
1:19:54
remind us that emptiness itself plays a crucial role in
1:19:57
shaping the universe. The silent spaces between the islands of light,
1:20:03
the vast oceans between the galaxies, places where the universe
1:20:07
grows quiet and the scale of the cosmos becomes almost
1:20:11
impossible to imagine. Soon, we will drift gently into the
1:20:16
final reflection of tonight's journey, one last peaceful moment among
1:20:21
the quietest regions of the universe before we rest beneath
1:20:24
the stars. As our quiet journey through the vast structure
1:20:29
of the universe slowly comes to an end tonight, it
1:20:33
is comforting to pause and reflect on what we have
1:20:35
discovered together. When we look up at the night sky
1:20:38
from Earth, the universe appears full. Stars sparkle above us.
1:20:44
The Milky Way stretches across the heavens like a glowing
1:20:47
river of light. Through telescopes we see distant galaxies, nebulae,
1:20:52
and clusters of stars filling the cosmos with brilliance. But
1:20:56
when we step back and look at the universe on
1:20:59
its largest scales, something surprising becomes clear. Most of the
1:21:04
universe is empty. The galaxies that shine so brightly are
1:21:10
only small islands scattered across an enormous cosmic ocean. Between
1:21:15
those islands lie the vast regions we explore tonight. The
1:21:19
cosmic voids. Enormous stretches of space where galaxies are rare
1:21:24
and the universe grows quiet. In these immense regions, Distances
1:21:30
become almost unimaginable. Galaxies may lie tens of millions of
1:21:35
light years apart. The sky grows darker. The familiar patterns
1:21:40
of stars fade away. And the universe reveals just how
1:21:44
vast it truly is. Yet even in that great emptiness,
1:21:49
the universe remains alive. Gravity continues its slow work. Dark
1:21:55
energy stretches the fabric of space. and faint ancient radiation
1:22:00
from the early universe still glows softly across the cosmos.
1:22:04
The void is not truly nothing. It is simply the
1:22:07
quiet background against which the great structures of the universe
1:22:11
are written. In a way, the cosmic voids remind us
1:22:15
of something simple and beautiful, that the universe is not
1:22:19
only defined by what exists within it, but also by
1:22:23
the spaces between. Just as music needs silence between its notes,
1:22:28
The cosmos needs emptiness between its galaxies. Those quiet spaces
1:22:33
allow the cosmic web to take shape. They give the
1:22:36
universe its grand structure. They provide the calm background against
1:22:41
which the islands of light can shine. So tonight, as
1:22:45
you allow your mind to drift towards sleep, imagine yourself
1:22:49
floating gently through one of those vast cosmic oceans, far
1:22:54
from crowded clusters of galaxies. far from the bright glow
1:22:58
of stars, just drifting peacefully through the quiet depths of space.
1:23:03
Around you, the universe stretches endlessly in every direction. A
1:23:09
few distant galaxies glow softly along the far horizon, but
1:23:13
most of the sky is calm and dark, a peaceful
1:23:17
cosmic silence. Let that quietness settle around your thoughts. Let
1:23:22
the vastness of the universe feel gentle rather than overwhelming,
1:23:27
Because within that immense emptiness lies a kind of calm
1:23:31
that few places in existence can offer. The calm of
1:23:34
deep space. The calm of the cosmic voids. Now it's
1:23:40
time to rest. Allow your breathing to slow. Let your
1:23:44
thoughts drift softly like galaxies moving through the quiet universe.
1:23:49
And as the ambient music begins to play, imagine yourself
1:23:52
continuing this peaceful journey through the great emptiness of space.
1:23:57
Good night, sleep well, and may your dreams drift gently
1:24:02
among the silent cosmic voids.
1:24:21
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