Latest / Boring Science / Science to Fall Asleep To _ The Universe Is Stranger Than You Think

Transcript

Science to Fall Asleep To _ The Universe Is Stranger Than You Think · Boring Science

• 0:00
  Speaker 1: Hello, and welcome to Boring Science to Sleep, a quiet
• 0:04
  Speaker 1: place where science becomes slow, soft, and easy to drift through. Tonight,
• 0:09
  Speaker 1: you are going to gently explore the most relaxing facts
• 0:13
  Speaker 1: about the universe. Not to learn everything, and not to
• 0:16
  Speaker 1: solve any of its great mysteries, but simply to notice
• 0:20
  Speaker 1: them slowly, calmly, one quiet idea at a time. You
• 0:25
  Speaker 1: will drift away from the familiar warmth of Earth, past
• 0:29
  Speaker 1: the quiet orbit of the moon, beyond the distant planets
• 0:32
  Speaker 1: of our solar system, and gradually toward the stars that
• 0:36
  Speaker 1: surround our small corner of space. Along the way, you
• 0:40
  Speaker 1: may encounter worlds that are frozen, worlds covered in deep oceans,
• 0:45
  Speaker 1: stars that glow faintly in the darkness, and places so
• 0:49
  Speaker 1: distant that their light has been travelling toward you for
• 0:52
  Speaker 1: years before finally arriving. But there is nothing you need
• 0:57
  Speaker 1: to remember. There is nothing you need to understand perfectly.
• 1:01
  Speaker 1: You are safe, there is nothing to do, and there
• 1:04
  Speaker 1: is nowhere you need to be. Just listen and drift.
• 1:08
  Speaker 1: If you truly enjoy these calm journeys through interesting facts
• 1:11
  Speaker 1: about science, you are welcome to like this video and subscribe,
• 1:16
  Speaker 1: only if it feels right for you. And when you
• 1:19
  Speaker 1: are ready, let me know in the comments where you
• 1:21
  Speaker 1: are listening from, and what time it is right now.
• 1:25
  Speaker 1: It is always a quiet joy to see how many
• 1:27
  Speaker 1: places and moments gather here together. Now, dim the lights,
• 1:32
  Speaker 1: maybe let a fan hum softly in the background, settle
• 1:36
  Speaker 1: into whatever position feels comfortable, and allow your breathing to
• 1:40
  Speaker 1: become easy. You do not need to travel anywhere tonight.
• 1:44
  Speaker 1: You can simply imagine that you are moving, slowly, quietly,
• 1:48
  Speaker 1: far beyond the familiar world beneath you, and as the
• 1:52
  Speaker 1: lights of earth begin to fade into the distance, we
• 1:55
  Speaker 1: can gently step into the darkness between the stars. Now,
• 2:00
  Speaker 1: very slowly, imagine that the room around you is becoming quieter.
• 2:04
  Speaker 1: The sounds near you begin to feel farther away, while
• 2:08
  Speaker 1: the darkness behind your closed eyes becomes a little deeper.
• 2:11
  Speaker 1: You are still here, resting comfortably, perhaps beneath a blanket,
• 2:16
  Speaker 1: perhaps with the quiet hum of a fan somewhere nearby,
• 2:20
  Speaker 1: and there is nothing you need to change. You can
• 2:23
  Speaker 1: simply imagine that you are looking upward. Above the roof,
• 2:27
  Speaker 1: above the clouds, above the familiar blue atmosphere, the darkness
• 2:31
  Speaker 1: of space begins. At first, the Earth still feels enormous.
• 2:36
  Speaker 1: It contains oceans, mountains, forests, cities, roads, lights, and all
• 2:41
  Speaker 1: the small sounds of ordinary life. But as you slowly
• 2:45
  Speaker 1: move away, the planet begins to become smaller. The oceans
• 2:49
  Speaker 1: merge into a single blue surface. The continents become softer
• 2:54
  Speaker 1: around their edges. The clouds become pale ribbons, and eventually,
• 2:59
  Speaker 1: Earth becomes a small blue world suspended in darkness. There
• 3:04
  Speaker 1: is no sound here, no wind, no rain, no distant traffic,
• 3:09
  Speaker 1: only the quiet motion of a planet continuing to turn.
• 3:13
  Speaker 1: You can let that image remain for a moment, Earth
• 3:16
  Speaker 1: turning beneath you, the moon following its long path around it,
• 3:21
  Speaker 1: and the sun shining quietly in the distance. Now you
• 3:24
  Speaker 1: drift farther, The Earth becomes smaller still, and the other
• 3:28
  Speaker 1: planets begin to spread around the Sun in their enormous,
• 3:31
  Speaker 1: quiet orbits. From this distance, the solar system does not
• 3:35
  Speaker 1: look crowded. It looks almost empty. There are worlds, certainly,
• 3:40
  Speaker 1: but there are also enormous stretches of darkness between them.
• 3:44
  Speaker 1: And when you leave the outer regions of the solar
• 3:46
  Speaker 1: system behind, something becomes even more noticeable. The space between
• 3:52
  Speaker 1: stars is vast. much vaster than the distances between the planets.
• 3:57
  Speaker 1: The nearest stars are not waiting just beyond the edge
• 4:00
  Speaker 1: of the solar system like lights along a nearby road.
• 4:04
  Speaker 1: They are separated from us by distances so large that
• 4:07
  Speaker 1: ordinary measurements begin to feel almost meaningless. So astronomers use
• 4:12
  Speaker 1: a gentler kind of distance. A light year is simply
• 4:15
  Speaker 1: the distance that light travels in one year. You do
• 4:19
  Speaker 1: not need to calculate it. You do not need to
• 4:21
  Speaker 1: remember the number. Just imagine a tiny beam of light
• 4:25
  Speaker 1: leaving the sun, moving through darkness, continuing for one year,
• 4:30
  Speaker 1: and still having only crossed a small part of the
• 4:32
  Speaker 1: enormous neighbourhood of the stars. The closest stellar system to
• 4:36
  Speaker 1: the sun is Alpha Centauri. It is a family of
• 4:40
  Speaker 1: stars rather than a single star, with two larger stars
• 4:44
  Speaker 1: accompanied by a much smaller red dwarf called Proxima Centauri.
• 4:49
  Speaker 1: And as you drift toward them, the sun slowly disappears
• 4:53
  Speaker 1: behind you. Not because it has become dimmer, not because
• 4:57
  Speaker 1: it has changed, only because you have moved so far away. Ahead,
• 5:03
  Speaker 1: another star begins to take its place. Proxima Centauri is
• 5:07
  Speaker 1: a small red dwarf, much smaller and fainter than our sun.
• 5:12
  Speaker 1: It does not blaze across the darkness like a bright
• 5:15
  Speaker 1: blue-white star. Instead, it glows softly, with a reddish light,
• 5:21
  Speaker 1: a small ember in an enormous night. And even though
• 5:25
  Speaker 1: it is our nearest stellar neighbour, it is still more
• 5:28
  Speaker 1: than four light-years away. For light, that journey is relatively short.
• 5:33
  Speaker 1: For anything carrying you, it would be unimaginably long. The
• 5:38
  Speaker 1: distance is so great that even our fastest spacecraft would
• 5:42
  Speaker 1: need an extraordinary amount of time to cross it. So
• 5:45
  Speaker 1: for tonight, you do not need a spacecraft. You can
• 5:48
  Speaker 1: simply drift. And as you approach Proxima Centauri, you may
• 5:52
  Speaker 1: notice something interesting. This tiny star has worlds of its own.
• 5:58
  Speaker 1: One of them is called Proxima Centauri b. It is
• 6:01
  Speaker 1: a planet not much larger than Earth, travelling around its
• 6:05
  Speaker 1: small red star much more closely than Earth travels around
• 6:08
  Speaker 1: the Sun. Its year is therefore very short. Only a
• 6:13
  Speaker 1: little more than 11 Earth days pass before it completes
• 6:16
  Speaker 1: one journey around its star. Imagine that! Eleven days passing
• 6:22
  Speaker 1: while the planet quietly completes an entire year. But being
• 6:26
  Speaker 1: close to a star does not necessarily mean being warm.
• 6:29
  Speaker 1: Proxima Centauri is much smaller and dimmer than the Sun,
• 6:33
  Speaker 1: and the planet may be cold overall. There is also
• 6:37
  Speaker 1: another possibility. Because Proxima Centauri b travels so close to
• 6:42
  Speaker 1: its star, it may have become tidally locked. That means
• 6:46
  Speaker 1: the planet may have gradually turned until the same side
• 6:50
  Speaker 1: always faces its star. One hemisphere would remain turned toward
• 6:55
  Speaker 1: the faint red sunlight, the other would remain turned away.
• 6:59
  Speaker 1: You might imagine a world divided between permanent day and
• 7:03
  Speaker 1: permanent night, although its real climate would depend greatly on
• 7:07
  Speaker 1: whether it has an atmosphere and how that atmosphere moves
• 7:10
  Speaker 1: heat around the planet. And this is where the universe
• 7:14
  Speaker 1: becomes wonderfully uncertain. We do not yet know exactly what
• 7:18
  Speaker 1: the surface of Proxima Centauri B looks like. We do
• 7:22
  Speaker 1: not know whether it has oceans. We do not know
• 7:25
  Speaker 1: whether it has a substantial atmosphere. We do not know
• 7:28
  Speaker 1: whether anything lives there. We only know that it is there,
• 7:32
  Speaker 1: orbiting a small star more than four light-years from you,
• 7:35
  Speaker 1: in the darkness beyond your own solar system. Its star
• 7:39
  Speaker 1: is also an active red dwarf, capable of producing flares
• 7:43
  Speaker 1: and releasing energetic material. Those outbursts may make the environment
• 7:48
  Speaker 1: difficult for a nearby planet, especially if its atmosphere is thin.
• 7:53
  Speaker 1: But there are still many things we do not know.
• 7:56
  Speaker 1: And tonight, you do not need those unknowns to become
• 7:59
  Speaker 1: questions that demand answers. They can simply remain unknown. A
• 8:04
  Speaker 1: distant planet can remain distant. A small red star can
• 8:08
  Speaker 1: continue glowing, and you can continue drifting. Behind you, the
• 8:13
  Speaker 1: sun is now only another star. Ahead of you, Proxima
• 8:17
  Speaker 1: Centauri is only another faint point of light. Between them
• 8:22
  Speaker 1: is an enormous darkness, filled with almost nothing that your
• 8:25
  Speaker 1: eyes could see. And yet, that darkness is not completely empty.
• 8:31
  Speaker 1: There are thin traces of gas and dust. There are
• 8:34
  Speaker 1: particles passing quietly through space. There are other stars, other
• 8:39
  Speaker 1: planetary systems, other worlds that may have their own long
• 8:43
  Speaker 1: nights and long mornings. their own silent skies, their own
• 8:48
  Speaker 1: slow journeys around distant suns. From our small place on Earth,
• 8:53
  Speaker 1: the stars can seem close together. But now, from between them,
• 8:57
  Speaker 1: you can begin to feel the true scale. Each star
• 9:01
  Speaker 1: is an island of light, and the darkness between those
• 9:04
  Speaker 1: islands is extraordinarily wide. You are simply floating there now,
• 9:09
  Speaker 1: with no need to cross it, no need to reach
• 9:12
  Speaker 1: the next star, no need to go anywhere at all,
• 9:16
  Speaker 1: You can let Proxima Centauri remain as a small reddish
• 9:19
  Speaker 1: glow in the distance. You can let the sun remain
• 9:22
  Speaker 1: somewhere far behind you. And you can rest for a
• 9:25
  Speaker 1: moment in the quiet space between them. Because even here,
• 9:30
  Speaker 1: in what seems like emptiness, the universe is still changing.
• 9:35
  Speaker 1: Stars are moving. Planets are turning. Dust is drifting. Light
• 9:40
  Speaker 1: is travelling. And somewhere beyond this first nearby star... There
• 9:44
  Speaker 1: are other worlds waiting quietly in the dark, each one
• 9:48
  Speaker 1: shaped by a different star, a different distance, and a
• 9:52
  Speaker 1: different history. For now, you can simply remain here, weightless
• 9:57
  Speaker 1: and still, listening to the faint ideas. that the universe
• 10:00
  Speaker 1: is much larger than the small piece of it you
• 10:03
  Speaker 1: can see from home. And perhaps, as you drift a
• 10:06
  Speaker 1: little farther from this familiar neighbourhood, some of those distant
• 10:11
  Speaker 1: worlds will begin to feel strangely close. You can let
• 10:17
  Speaker 1: the last light of Proxima Centauri remain somewhere behind you.
• 10:21
  Speaker 1: The small red star is still there, quietly glowing in
• 10:25
  Speaker 1: the darkness, while you continue to drift outward, slowly passing
• 10:29
  Speaker 1: through the nearby stellar neighbourhood. There is no road here,
• 10:33
  Speaker 1: no signposts, no sound to tell you where you are,
• 10:38
  Speaker 1: only distance and the occasional faint light of another star.
• 10:42
  Speaker 1: As you move farther away from the sun, the stars
• 10:45
  Speaker 1: begin to change. Some are small and cool. Some are
• 10:49
  Speaker 1: bright and hot. Some live alone. Others travel through space,
• 10:54
  Speaker 1: as members of quiet stellar families. And one of the
• 10:57
  Speaker 1: most interesting stars nearby is Barnard's Star, a small red dwarf,
• 11:03
  Speaker 1: moving through the darkness relatively close to us. Barnard's Star
• 11:07
  Speaker 1: is old, very old by the standards of the stars
• 11:10
  Speaker 1: around us. It is also much smaller and dimmer than
• 11:14
  Speaker 1: the Sun. From Earth, It is not a bright point
• 11:17
  Speaker 1: that catches your eye on a clear night. It is
• 11:20
  Speaker 1: much quieter than that. Its light is faint, its surface
• 11:24
  Speaker 1: is cooler than the sun's, and yet this little star
• 11:28
  Speaker 1: has been shining for an extraordinary length of time. Around it,
• 11:33
  Speaker 1: there appears to be a cold world known as Barnard's
• 11:36
  Speaker 1: Star B. It receives far less energy from its star
• 11:40
  Speaker 1: than Earth receives from the sun. So, if you could
• 11:44
  Speaker 1: somehow stand upon its surface... you would not find an
• 11:47
  Speaker 1: Earth-like warmth waiting for you. You would find a world
• 11:51
  Speaker 1: of deep cold. And yet, beneath the cold surface, something
• 11:55
  Speaker 1: interesting may still be possible. The interior of a planet
• 12:00
  Speaker 1: does not always have to match the temperature of its surface.
• 12:03
  Speaker 1: Internal heat can sometimes remain for a very long time,
• 12:07
  Speaker 1: warmed by the slow decay of radioactive materials or by
• 12:11
  Speaker 1: the gravitational effects of other bodies. So scientists have considered
• 12:16
  Speaker 1: the possibility that beneath a frozen exterior, liquid water could
• 12:21
  Speaker 1: exist below the surface. A hidden ocean. A dark ocean.
• 12:26
  Speaker 1: An ocean with no sunlight reaching its surface, perhaps resting
• 12:30
  Speaker 1: beneath layers of ice. You can imagine it very slowly,
• 12:34
  Speaker 1: without needing to decide whether such an ocean truly exists.
• 12:39
  Speaker 1: Above it, a silent frozen landscape. Below it, water moving
• 12:44
  Speaker 1: gently in darkness. And far above that hidden water, a
• 12:48
  Speaker 1: small red star shining across the cold. It is a
• 12:52
  Speaker 1: reminder that when astronomers speak about habitable worlds, they do
• 12:56
  Speaker 1: not always mean places that look like Earth. Sometimes the
• 13:00
  Speaker 1: possibility of water may be hidden. Sometimes warmth may exist
• 13:05
  Speaker 1: beneath ice. Sometimes a world that appears completely frozen from
• 13:10
  Speaker 1: far away may still contain a little movement deep inside.
• 13:15
  Speaker 1: And then, as you continue drifting, the darkness begins to brighten.
• 13:20
  Speaker 1: Ahead of you is Sirius. It is one of the
• 13:23
  Speaker 1: brightest stars visible from Earth, so different from Barnard's star
• 13:28
  Speaker 1: that the contrast almost feels like moving from a candle
• 13:31
  Speaker 1: into daylight. Sirius appears as a brilliant blue-white point, but
• 13:36
  Speaker 1: it is not alone. Sirius is actually a pair, The
• 13:40
  Speaker 1: brighter star Sirius A is accompanied by Sirius B, a
• 13:45
  Speaker 1: much smaller and extraordinarily dense white dwarf. From a distance
• 13:50
  Speaker 1: you might notice only the brilliant light of Sirius A.
• 13:53
  Speaker 1: The smaller companion is much harder to see, yet Sirius
• 13:57
  Speaker 1: B contains a remarkable story. It was once a more
• 14:01
  Speaker 1: ordinary star. Over immense stretches of time it used up
• 14:05
  Speaker 1: the fuel that had allowed it to shine, expanded during
• 14:08
  Speaker 1: its later life. and eventually shed its outer layers. What
• 14:12
  Speaker 1: remained became a white dwarf. A white dwarf is not
• 14:16
  Speaker 1: a normal star in the way you might imagine. It
• 14:19
  Speaker 1: no longer shines because ordinary stellar fuel is burning inside it. Instead,
• 14:25
  Speaker 1: it is the extremely dense remnant left behind after a
• 14:29
  Speaker 1: star has passed through much of its active life. You
• 14:32
  Speaker 1: can imagine the history of the star as a long exhale. First,
• 14:38
  Speaker 1: a glowing sphere of gas. then an ageing star, then
• 14:43
  Speaker 1: outer layers drifting away into space, and finally a small,
• 14:48
  Speaker 1: hot remnant remaining in the darkness. Sirius A and Sirius
• 14:53
  Speaker 1: B continue their slow orbital dance around their shared centre
• 14:57
  Speaker 1: of mass. Two stars with very different appearances, one brilliant
• 15:02
  Speaker 1: and blue-white, the other small, dense and faint beside its companion.
• 15:07
  Speaker 1: And this contrast continues, as you drift onward toward another
• 15:11
  Speaker 1: nearby system. Wolf 1061 is a small red dwarf, faint
• 15:16
  Speaker 1: and cool compared with the Sun. But around this modest star,
• 15:21
  Speaker 1: several planets have been found. They are not identical worlds.
• 15:25
  Speaker 1: They occupy different orbits, receive different amounts of energy, and
• 15:29
  Speaker 1: may experience very different conditions. One of them, Wolf 1061b,
• 15:34
  Speaker 1: is close to its star. It completes its journey around
• 15:39
  Speaker 1: the star in only a few Earth days. So close
• 15:43
  Speaker 1: to its parent star, it may be tidally locked, meaning
• 15:47
  Speaker 1: that one side could remain facing the star while the
• 15:50
  Speaker 1: other side turns away into a much darker sky. Another planet,
• 15:56
  Speaker 1: Wolf 1061c, travels farther out. It lies within what astronomers
• 16:02
  Speaker 1: call the habitable zone, the region where temperatures could under
• 16:06
  Speaker 1: the right atmospheric conditions, allow liquid water to exist on
• 16:10
  Speaker 1: a planet's surface. That phrase can sound almost magical, but
• 16:15
  Speaker 1: the habitable zone is not a promise. It does not
• 16:19
  Speaker 1: mean a planet has oceans. It does not mean it
• 16:22
  Speaker 1: has life. It simply means that, at the right distance
• 16:26
  Speaker 1: from its star, temperatures could potentially allow water to remain liquid.
• 16:31
  Speaker 1: Everything else depends on the atmosphere, the surface. the planet's history,
• 16:36
  Speaker 1: and many things we may not yet know. And perhaps
• 16:39
  Speaker 1: that is one of the gentlest mysteries of distant worlds.
• 16:43
  Speaker 1: We can measure their shadows, we can study the light
• 16:46
  Speaker 1: from their stars, we can estimate their sizes and orbits,
• 16:51
  Speaker 1: but the actual landscapes remain far beyond our reach. Some
• 16:55
  Speaker 1: worlds may be dry, some may be frozen, some may
• 16:59
  Speaker 1: have clouds, some may have oceans, and some may hide
• 17:03
  Speaker 1: their water beneath thick layers of ice. You can imagine
• 17:07
  Speaker 1: one of these distant planets from far away. There is
• 17:10
  Speaker 1: no need to imagine mountains or forests, perhaps only a
• 17:14
  Speaker 1: quiet sphere, slowly turning in darkness. Beneath its surface, somewhere unseen,
• 17:21
  Speaker 1: water may move. Above it, starlight falls across ice, and
• 17:26
  Speaker 1: around it, the universe remains almost completely silent. This is
• 17:31
  Speaker 1: how strange worlds can become strangely peaceful. They do not
• 17:35
  Speaker 1: need to be visited. They do not need to be
• 17:37
  Speaker 1: understood completely. They can simply exist, turning slowly around their
• 17:43
  Speaker 1: distant stars. And as you drift onward, the small red
• 17:47
  Speaker 1: dwarfs begin to disappear behind you. The faint worlds become smaller.
• 17:52
  Speaker 1: The brilliant light of Sirius fades into the distance. Farther ahead,
• 17:57
  Speaker 1: there are still more planets, more stars. more unusual places
• 18:02
  Speaker 1: where familiar things behave in unfamiliar ways. There may be
• 18:06
  Speaker 1: worlds where water becomes ice unlike anything found naturally on earth,
• 18:11
  Speaker 1: worlds where immense pressure changes the structure of ordinary materials,
• 18:16
  Speaker 1: and worlds so close to their stars that their surfaces
• 18:19
  Speaker 1: may be reshaped by heat. For now, though, you can
• 18:23
  Speaker 1: remain with the quiet thought of water beneath ice, a
• 18:26
  Speaker 1: hidden ocean. a small possibility beneath a frozen sky. And perhaps,
• 18:32
  Speaker 1: somewhere in the darkness ahead, another world is waiting with
• 18:36
  Speaker 1: an even stranger kind of landscape. You do not need
• 18:39
  Speaker 1: to reach it tonight. You can simply keep drifting. You
• 18:46
  Speaker 1: can remain with that quiet image of the frozen worlds
• 18:49
  Speaker 1: behind you. The small red stars are becoming more distant now,
• 18:53
  Speaker 1: their faint light slowly blending into the darkness. And as
• 18:57
  Speaker 1: you continue drifting, the temperature of the worlds around you
• 19:01
  Speaker 1: begins to change. Some planets live far from their stars,
• 19:06
  Speaker 1: where sunlight is weak and cold. Others travel much closer,
• 19:10
  Speaker 1: so close that their days are shaped by an almost
• 19:13
  Speaker 1: constant glow. These are worlds where familiar things begin to
• 19:18
  Speaker 1: behave in unfamiliar ways. Water may not remain water. Rock
• 19:23
  Speaker 1: may not remain solid. And a planet can slowly turn
• 19:27
  Speaker 1: beneath its star until one side sees almost endless daylight,
• 19:32
  Speaker 1: while the other side remains wrapped in darkness. One of
• 19:35
  Speaker 1: the clearest examples is a world called K2141b. You do
• 19:41
  Speaker 1: not need to remember its name. You can simply imagine
• 19:44
  Speaker 1: a dark planet passing very close to a small, distant star.
• 19:49
  Speaker 1: It travels around its star in less than one Earth day.
• 19:53
  Speaker 1: The journey is so quick that while you are settling
• 19:56
  Speaker 1: into one night of sleep, the planet can already have
• 19:59
  Speaker 1: completed another year. And because it is so close to
• 20:02
  Speaker 1: its star, the same side may remain turned toward that
• 20:06
  Speaker 1: brilliant source of heat. Imagine standing on the darker side
• 20:10
  Speaker 1: of such a world. Above you, the sky would be
• 20:13
  Speaker 1: unlike the familiar night sky of Earth. Somewhere beyond the horizon,
• 20:18
  Speaker 1: the star would remain fixed in one direction. The surface
• 20:22
  Speaker 1: beneath you would be incredibly hot on the side facing
• 20:25
  Speaker 1: the star, while farther around the planet, conditions would become
• 20:30
  Speaker 1: very different. Scientists think the day side of K2141b may
• 20:33
  Speaker 1: contain an ocean of molten rock not an ocean of water,
• 20:40
  Speaker 1: an ocean of lava, rock itself, heated until it flows.
• 20:45
  Speaker 1: And even here, the idea is not as simple as
• 20:48
  Speaker 1: imagining a completely motionless sea of fire. Material can move,
• 20:53
  Speaker 1: heat can travel. The atmosphere, if present, can carry energy
• 20:58
  Speaker 1: from one region toward another. The planet becomes a slow
• 21:02
  Speaker 1: circulation of heat, light, and material. It is strange, but
• 21:07
  Speaker 1: also strangely calm when viewed from far away. You are
• 21:11
  Speaker 1: not standing there, you are simply watching. A small dark
• 21:15
  Speaker 1: world turns around its star. One side receives relentless light,
• 21:20
  Speaker 1: the other side rests beneath a much darker sky, and
• 21:24
  Speaker 1: between them, the planet carries heat around its surface in
• 21:28
  Speaker 1: ways we can only partly understand. Farther away, another world
• 21:34
  Speaker 1: takes the idea of extreme heat even further. KELT-9b is
• 21:38
  Speaker 1: a giant planet orbiting extremely close to its star. It
• 21:42
  Speaker 1: is so hot that temperatures in its atmosphere can reach
• 21:45
  Speaker 1: levels where materials that would normally be solid on Earth
• 21:48
  Speaker 1: can exist as vapour. Imagine iron, not as a cool
• 21:52
  Speaker 1: metal beneath your feet, but as part of an atmosphere.
• 21:56
  Speaker 1: Imagine a planet where the distinction between a rock and
• 21:58
  Speaker 1: a cloud becomes strangely blurred. The atmosphere of such a
• 22:03
  Speaker 1: world is not permanent. Its intense star can slowly strip
• 22:07
  Speaker 1: material away. Layer by layer, tiny amounts of the atmosphere
• 22:11
  Speaker 1: may escape into space. The planet is therefore not completely unchanged.
• 22:16
  Speaker 1: It is slowly being altered by the light of its star.
• 22:20
  Speaker 1: And there is something deeply quiet about that process. Nothing
• 22:24
  Speaker 1: happens all at once. The planet does not suddenly disappear. Instead,
• 22:29
  Speaker 1: over immense stretches of time, a little material leaves. Then
• 22:34
  Speaker 1: a little more, and the star continues shining. The planet
• 22:39
  Speaker 1: continues orbiting. Space continues stretching between distant worlds. The changes
• 22:45
  Speaker 1: are almost impossibly slow when compared with a human lifetime.
• 22:49
  Speaker 1: You could watch for your entire life and never notice
• 22:52
  Speaker 1: the difference. And yet, over millions or billions of years,
• 22:57
  Speaker 1: those tiny changes can reshape an entire world. This brings
• 23:01
  Speaker 1: you to another kind of planetary story. a planet that
• 23:05
  Speaker 1: appears to have survived the dramatic transformation of its star.
• 23:09
  Speaker 1: Far away is a system known as V391 Pegasi. Its
• 23:14
  Speaker 1: central star is now a white dwarf, the compact remnant
• 23:18
  Speaker 1: left after a star has passed through a much later
• 23:21
  Speaker 1: stage of its life, but a planet appears to remain nearby.
• 23:25
  Speaker 1: V391 Pegasi b is a large gas giant. and models
• 23:31
  Speaker 1: suggest that it may have survived a remarkable period in
• 23:34
  Speaker 1: the history of its star. Long ago, the star expanded.
• 23:38
  Speaker 1: Its outer layers became enormous. The planet's orbit was close
• 23:42
  Speaker 1: enough that it may have spent part of that transformation
• 23:45
  Speaker 1: almost within the outer atmosphere of the swollen star. Imagine
• 23:50
  Speaker 1: that slowly. A planet continuing along its orbit. Its star
• 23:54
  Speaker 1: growing larger. The familiar light changing. The outer layers of
• 23:59
  Speaker 1: the star are expanding farther and farther outward, and somehow
• 24:03
  Speaker 1: the planet remaining. Eventually, the star shed much of that
• 24:08
  Speaker 1: outer material. The surrounding space changed again. The star became smaller,
• 24:14
  Speaker 1: and what remained was the compact white dwarf we see today.
• 24:18
  Speaker 1: The planet, altered by its journey through this extraordinary environment,
• 24:23
  Speaker 1: continued to exist. It is difficult to know exactly what
• 24:26
  Speaker 1: it experienced. Much of the ancient history has been erased
• 24:30
  Speaker 1: by time, but the possibility itself is enough to remind
• 24:35
  Speaker 1: you that planetary systems are not frozen scenes. They are
• 24:39
  Speaker 1: changing places, stars age, planets move, atmospheres escape, orbits can change,
• 24:47
  Speaker 1: worlds can survive, other worlds can disappear, and sometimes the
• 24:52
  Speaker 1: same star that gives a planet its light can also
• 24:56
  Speaker 1: slowly transform it. There is something almost peaceful in that
• 25:00
  Speaker 1: enormous timescale. A planet can lose part of its atmosphere,
• 25:04
  Speaker 1: and the process may take millions of years. A star
• 25:07
  Speaker 1: can expand and shed its outer layers, and the universe
• 25:11
  Speaker 1: simply continues around it. Nothing waits for us to notice.
• 25:15
  Speaker 1: Nothing needs our attention. The cosmos changes quietly whether we
• 25:20
  Speaker 1: are watching or sleeping. And perhaps this is one of
• 25:23
  Speaker 1: the gentlest things about looking into deep space. The universe
• 25:27
  Speaker 1: does not hurry. A planet can spend millions of years
• 25:30
  Speaker 1: circling the same star. A star can spend billions of
• 25:34
  Speaker 1: years changing almost imperceptibly. A cloud of gas can drift
• 25:38
  Speaker 1: through darkness for longer than human civilization has existed. And
• 25:43
  Speaker 1: you can let yourself become part of that slower rhythm
• 25:46
  Speaker 1: for a little while. Behind you are the cold worlds,
• 25:49
  Speaker 1: the hidden oceans, the quiet red stars. Ahead are stars
• 25:54
  Speaker 1: growing older, changing shape, and eventually leaving behind strange remnants.
• 26:00
  Speaker 1: Some will become white dwarfs, some will collapse into neutron stars,
• 26:06
  Speaker 1: and some will become even darker. For now, you can
• 26:09
  Speaker 1: simply rest with the warmth fading into the distance, while
• 26:13
  Speaker 1: somewhere far away, a planet continues its slow journey around
• 26:17
  Speaker 1: a star that will one day change too. And as
• 26:21
  Speaker 1: that distant light becomes softer, the story of the stars
• 26:25
  Speaker 1: themselves begins to come quietly into view. You can let
• 26:31
  Speaker 1: the strange worlds behind you slowly disappear into the darkness.
• 26:35
  Speaker 1: The planets that once seemed so unusual, the frozen worlds,
• 26:40
  Speaker 1: the hidden oceans, the molten surfaces, the enormous gas giants,
• 26:46
  Speaker 1: all of them continue quietly along their distant paths. And now,
• 26:50
  Speaker 1: as you drift farther away, your attention begins to move
• 26:54
  Speaker 1: from the planets themselves toward the stars. Because every planet
• 26:58
  Speaker 1: is shaped, in some way, by the star it follows.
• 27:02
  Speaker 1: A star provides light. It provides warmth. It can influence
• 27:07
  Speaker 1: the atmosphere of a nearby world. And over a much
• 27:10
  Speaker 1: longer stretch of time, a star can change the world
• 27:14
  Speaker 1: around it, simply by changing itself. From a distance, a
• 27:18
  Speaker 1: star can look almost perfectly still, a tiny point of light, unmoving, unchanging,
• 27:26
  Speaker 1: but inside every star there is a slow balance taking place.
• 27:31
  Speaker 1: Gravity gently pulls inward, the energy produced deep inside pushes outward,
• 27:37
  Speaker 1: and for millions or billions of years these two tendencies
• 27:42
  Speaker 1: remain in a delicate balance. You can imagine it as
• 27:45
  Speaker 1: a very slow breathing, not a breath you could see,
• 27:49
  Speaker 1: not a movement you could follow with your eyes. Just
• 27:53
  Speaker 1: a quiet rhythm continuing inside a sphere of glowing gas.
• 27:57
  Speaker 1: Our own Sun is doing this now. It has been
• 28:00
  Speaker 1: doing it for billions of years. And it will continue
• 28:03
  Speaker 1: for billions of years more. But eventually, every star changes.
• 28:08
  Speaker 1: The fuel at its centre gradually becomes different. The star
• 28:12
  Speaker 1: slowly moves into another stage of its life. For a
• 28:15
  Speaker 1: star somewhat like the Sun, One of the most remarkable
• 28:19
  Speaker 1: changes begins when the hydrogen in its central region becomes depleted.
• 28:24
  Speaker 1: The star's interior responds. Its centre becomes more compressed. The
• 28:29
  Speaker 1: surrounding layers change. And the outer part of the star
• 28:33
  Speaker 1: begins to expand. Very slowly the star grows larger. Its
• 28:38
  Speaker 1: surface becomes cooler. Its colour shifts toward red. And what
• 28:43
  Speaker 1: was once an ordinary star becomes a red giant. You
• 28:47
  Speaker 1: can imagine this happening over an amount of time far
• 28:50
  Speaker 1: beyond any human lifetime. There is no sudden transformation to watch,
• 28:56
  Speaker 1: no single morning when the star wakes up looking different. Instead,
• 29:00
  Speaker 1: the change is almost impossibly gradual. The star expands, the
• 29:05
  Speaker 1: outer layers become thinner, the surface cools, and the red
• 29:09
  Speaker 1: glow becomes softer. A familiar star becomes something enormous. One
• 29:14
  Speaker 1: of the most beautiful examples is CW Leonis. It is
• 29:19
  Speaker 1: a distant red giant surrounded by a large cloud of
• 29:22
  Speaker 1: material that has slowly escaped from the star. If you
• 29:27
  Speaker 1: could somehow place it where our sun is, its enormous
• 29:30
  Speaker 1: outer atmosphere would extend across a vast region of the
• 29:34
  Speaker 1: solar system. But you are not there. You are far away,
• 29:38
  Speaker 1: simply watching the light of this aging star. And the
• 29:42
  Speaker 1: longer you watch, the more you can imagine the material
• 29:45
  Speaker 1: around it slowly moving outward. The star is losing part
• 29:49
  Speaker 1: of itself. Its outer layers drift away. Gas and dust
• 29:53
  Speaker 1: spread into the surrounding space. And eventually, That material becomes
• 29:58
  Speaker 1: part of the environment from which other things may form.
• 30:02
  Speaker 1: Inside the star, another process is taking place. As the
• 30:06
  Speaker 1: centre becomes hotter and denser, helium begins to participate in
• 30:11
  Speaker 1: a new stage of stellar activity. The nuclei of helium
• 30:15
  Speaker 1: can combine to form carbon. This is one of those
• 30:18
  Speaker 1: places where the real language of astronomy can become rather technical,
• 30:22
  Speaker 1: but you do not need to carry the technical details
• 30:25
  Speaker 1: with you. You can simply imagine the centre of the
• 30:28
  Speaker 1: star becoming a little hotter, a little denser, and beginning
• 30:32
  Speaker 1: to work with a different kind of fuel. Astronomers sometimes
• 30:35
  Speaker 1: call one dramatic transition the helium flash. The name sounds violent,
• 30:40
  Speaker 1: but from the distance of the universe, it is better
• 30:43
  Speaker 1: imagined as a sudden change deep inside a star whose
• 30:47
  Speaker 1: outer surface remains unimaginably far away. The star's interior reorganises itself.
• 30:54
  Speaker 1: Its temperature changes. Its outer layers respond, and eventually the
• 30:59
  Speaker 1: star settles into another stage of its long life. C.W.
• 31:03
  Speaker 1: Leonis does something especially interesting. Its brightness changes over time.
• 31:10
  Speaker 1: The star slowly expands and contracts. Its outer layers rise
• 31:14
  Speaker 1: and fall. It is almost as though the enormous star
• 31:18
  Speaker 1: is breathing. This pulsation is extremely slow compared with anything
• 31:23
  Speaker 1: you experience in everyday life. A star can change its
• 31:26
  Speaker 1: brightness over hundreds of days, while you may notice only
• 31:30
  Speaker 1: the faintest difference from one season to another. And yet
• 31:34
  Speaker 1: those small changes tell astronomers something about what is happening inside.
• 31:39
  Speaker 1: Stars can have internal vibrations. Deep waves of pressure can
• 31:43
  Speaker 1: travel through their hot gas. They can make the star
• 31:47
  Speaker 1: gently expand and contract. Scientists can study these tiny changes
• 31:52
  Speaker 1: in brightness and surface movement to learn about the hidden interior.
• 31:56
  Speaker 1: This field is called asteroseismology. You can think of it
• 32:00
  Speaker 1: as listening to a star without actually hearing a sound.
• 32:04
  Speaker 1: The star is vibrating, the vibrations are carrying information, and
• 32:09
  Speaker 1: the light arriving across enormous distances allows astronomers to notice
• 32:14
  Speaker 1: those subtle changes. A star can therefore become something like
• 32:18
  Speaker 1: a distant instrument. Its light contains traces of its internal structure.
• 32:24
  Speaker 1: its slow rhythm reveals something about its age, its size,
• 32:28
  Speaker 1: and the conditions hidden beneath its surface. And while you
• 32:32
  Speaker 1: remain drifting here, you can imagine thousands of stars doing
• 32:36
  Speaker 1: something similar. Some are young, some are middle-aged. Some are ancient,
• 32:42
  Speaker 1: some are growing, some are contracting, some are shedding their
• 32:46
  Speaker 1: outer layers, each one following its own long rhythm. C. W.
• 32:51
  Speaker 1: Leonis is particularly interesting because the material leaving the star
• 32:56
  Speaker 1: has formed a surrounding envelope of gas and dust. The
• 33:00
  Speaker 1: star is not simply fading away. It is returning material
• 33:04
  Speaker 1: to space. That material can contain carbon, oxygen, water, and
• 33:09
  Speaker 1: other molecules. The exact chemistry is complex, but the quiet
• 33:14
  Speaker 1: idea is simple. A star does not keep everything it
• 33:18
  Speaker 1: was born with forever. Some of its material eventually leaves.
• 33:23
  Speaker 1: It drifts outward. It mixes with the surrounding space. And
• 33:27
  Speaker 1: over enormous periods of time, material released by older stars
• 33:32
  Speaker 1: can become part of new clouds, new stars, and new
• 33:35
  Speaker 1: planetary systems. The universe is constantly recycling matter. A star shines.
• 33:42
  Speaker 1: A star ages. A star releases part of itself. And
• 33:46
  Speaker 1: that material becomes part of the wider galaxy. There is
• 33:50
  Speaker 1: something almost comforting in that cycle. nothing needs to disappear completely.
• 33:56
  Speaker 1: A cloud of gas may once have been part of
• 33:58
  Speaker 1: a star, a future planet may contain atoms that were
• 34:02
  Speaker 1: once deep inside another sun, and even the material in
• 34:06
  Speaker 1: your own body has a history that reaches much farther
• 34:10
  Speaker 1: back than your individual life. But for now, you do
• 34:14
  Speaker 1: not need to follow that history all the way. You
• 34:17
  Speaker 1: can simply remain with the image of the red giant,
• 34:20
  Speaker 1: a huge, softly glowing star, its outer layers moving gently,
• 34:26
  Speaker 1: its brightness rising and falling, its surrounding cloud drifting outward,
• 34:31
  Speaker 1: and deep inside, a quiet transformation continuing. Eventually, C.W. Leonis
• 34:38
  Speaker 1: will lose more of its outer material. The star will
• 34:41
  Speaker 1: become smaller. The glowing giant will leave behind a compact remnant.
• 34:46
  Speaker 1: But that transformation is still far away on the scale
• 34:49
  Speaker 1: of human time. For now, The red giant continues its
• 34:53
  Speaker 1: slow breathing. Light leaves its surface. Gas drifts into space.
• 34:59
  Speaker 1: The surrounding darkness remains still. And somewhere beyond this ageing star,
• 35:04
  Speaker 1: there are even denser remnants waiting in the deeper story
• 35:07
  Speaker 1: of stellar life. Stars that have become smaller than you
• 35:11
  Speaker 1: might expect. Stars compressed into astonishingly compact objects. Stars whose
• 35:17
  Speaker 1: gravity becomes so strong that even light can be deeply affected.
• 35:21
  Speaker 1: For a little while longer though, you can simply rest
• 35:24
  Speaker 1: beneath the imagined red glow of an ageing star, listening
• 35:28
  Speaker 1: to the quiet rhythm of a universe in which even
• 35:32
  Speaker 1: enormous things are allowed to change very slowly. The red
• 35:38
  Speaker 1: glow of the ageing star is becoming softer now. You
• 35:41
  Speaker 1: can imagine the enormous outer layers drifting away, slowly spreading
• 35:46
  Speaker 1: into the darkness, becoming part of the space around the star.
• 35:50
  Speaker 1: For a while, The star seems to be giving something back.
• 35:54
  Speaker 1: Its outer material moves outward. Its centre becomes more compact.
• 35:59
  Speaker 1: And eventually what remains can become something very different from
• 36:03
  Speaker 1: the star you first imagined. Some stars leave behind white dwarfs. Others,
• 36:09
  Speaker 1: especially stars that began their lives with much greater mass,
• 36:12
  Speaker 1: can collapse much farther. Gravity begins to win. The outer
• 36:17
  Speaker 1: layers of the star may be thrown outward in a supernova.
• 36:21
  Speaker 1: while the central region falls inward with astonishing speed. And
• 36:25
  Speaker 1: from that collapse, one of the strangest objects in the
• 36:29
  Speaker 1: universe can remain, a neutron star. Imagine taking the mass
• 36:34
  Speaker 1: of a star and compressing it into a sphere only
• 36:37
  Speaker 1: about the size of a city. It is difficult to
• 36:40
  Speaker 1: picture because everything about it is concentrated. The star has
• 36:44
  Speaker 1: become incredibly small compared with its former size, but its
• 36:48
  Speaker 1: gravity remains enormous. you do not need to imagine standing
• 36:52
  Speaker 1: on its surface. It is enough to imagine looking at
• 36:55
  Speaker 1: it from far away, a tiny sphere, a faint point
• 36:59
  Speaker 1: of light, and around it almost nothing. Yet beneath that
• 37:04
  Speaker 1: small surface, matter exists in a state unlike anything you
• 37:09
  Speaker 1: normally encounter. The star has been compressed so intensely that
• 37:13
  Speaker 1: much of its material has been transformed into an extraordinarily
• 37:18
  Speaker 1: dense form dominated by neutrons. This is where the word
• 37:22
  Speaker 1: neutron star comes from. It is not a star that
• 37:26
  Speaker 1: shines like the sun. It is the compact remnant of
• 37:29
  Speaker 1: a star that has passed through a violent transformation, still
• 37:34
  Speaker 1: carrying the memory of the much larger object it once was.
• 37:38
  Speaker 1: And some neutron stars rotate incredibly quickly. Imagine a city-sized
• 37:43
  Speaker 1: sphere turning again and again, hundreds of times within a
• 37:47
  Speaker 1: single second. These rapidly rotating neutron stars are called millisecond pulsars.
• 37:54
  Speaker 1: They can behave like extraordinarily precise cosmic clocks. As they rotate,
• 37:59
  Speaker 1: beams of radiation can sweep through space. If one of
• 38:03
  Speaker 1: those beams happens to pass toward Earth again and again,
• 38:07
  Speaker 1: telescopes can detect a repeating signal, pulse, pause, pulse, pause,
• 38:15
  Speaker 1: a rhythm travelling across enormous distances. You cannot hear the
• 38:19
  Speaker 1: pulse with your ears. It is not a sound, but
• 38:22
  Speaker 1: in the data collected by astronomers, the rhythm is remarkably clear.
• 38:27
  Speaker 1: A distant star is turning, its light is sweeping across space,
• 38:32
  Speaker 1: and from Earth we can notice the repetition. There is
• 38:35
  Speaker 1: something almost soothing about that regularity. A star spinning in darkness,
• 38:41
  Speaker 1: a beam crossing the universe, another pulse arriving, then another,
• 38:46
  Speaker 1: and another. Some neutron stars carry an even more extreme property.
• 38:51
  Speaker 1: They are called magnetars. Their magnetic fields are vastly stronger
• 38:56
  Speaker 1: than Earth's magnetic field. You can think of Earth's magnetic
• 39:00
  Speaker 1: field as a gentle, invisible presence, quietly guiding a compass needle.
• 39:06
  Speaker 1: A magnetar is something entirely different. Its magnetic field is
• 39:10
  Speaker 1: so powerful that it can influence the matter around the
• 39:13
  Speaker 1: star in extraordinary ways. These objects can release bursts of
• 39:18
  Speaker 1: high-energy radiation, but even these events belong to an enormous
• 39:22
  Speaker 1: cosmic timescale. The star remains tiny, the surrounding galaxy remains enormous,
• 39:29
  Speaker 1: and the light from the magnetar travels quietly through the
• 39:32
  Speaker 1: darkness until, perhaps, a small fraction of it reaches a
• 39:36
  Speaker 1: detector on Earth. A tiny object. A distant signal. A
• 39:41
  Speaker 1: universe large enough to contain both at the same time.
• 39:45
  Speaker 1: And then there is another possible ending for a massive star.
• 39:49
  Speaker 1: The collapse can continue. Instead of leaving behind a neutron star,
• 39:54
  Speaker 1: gravity can compress the remaining material into a black hole.
• 39:59
  Speaker 1: At first, this can seem like an object that has
• 40:02
  Speaker 1: simply disappeared. There is no bright surface, no ordinary light
• 40:07
  Speaker 1: coming directly from the centre. Only the gravitational influence remains.
• 40:12
  Speaker 1: But black holes are not holes in space in the
• 40:15
  Speaker 1: ordinary sense. They are regions where matter has been compressed
• 40:19
  Speaker 1: so strongly that the geometry of space and time becomes
• 40:23
  Speaker 1: profoundly altered. Around a black hole, material can sometimes form
• 40:28
  Speaker 1: a glowing disk. Gas and dust spiral inward. As the
• 40:33
  Speaker 1: material moves faster and becomes extremely hot, it can shine brightly.
• 40:38
  Speaker 1: This creates one of the strangest contrasts in astronomy. The
• 40:42
  Speaker 1: black hole itself is dark. The material around it can
• 40:46
  Speaker 1: be brilliant. You can imagine a quiet black centre surrounded
• 40:50
  Speaker 1: by a slow whirl of glowing matter. The centre does
• 40:54
  Speaker 1: not need to shine, its presence is revealed by what
• 40:57
  Speaker 1: happens around it. And there is a boundary called the
• 41:00
  Speaker 1: event horizon. You can think of it as a point
• 41:04
  Speaker 1: of no return. Once something passes beyond that boundary, it
• 41:08
  Speaker 1: can no longer send light back outward to the distant universe.
• 41:13
  Speaker 1: The important thing is that a black hole does not
• 41:16
  Speaker 1: simply reach outward and swallow everything around it. From far
• 41:20
  Speaker 1: enough away, its gravity behaves according to the same basic
• 41:23
  Speaker 1: rules as the gravity of any other object with the
• 41:26
  Speaker 1: same amount of mass. A planet could, in principle, orbit
• 41:31
  Speaker 1: a black hole if it were far enough away and
• 41:33
  Speaker 1: moving in a stable orbit. The darkness itself is not
• 41:37
  Speaker 1: a cosmic vacuum cleaner. It is simply gravity, in one
• 41:41
  Speaker 1: of its most concentrated forms, and if you drift farther back,
• 41:45
  Speaker 1: you can watch material orbiting such an object. Gas circles.
• 41:51
  Speaker 1: Light bends. Stars move around invisible centres. Everything is responding
• 41:56
  Speaker 1: to gravity. Even the black hole itself can move. When
• 42:01
  Speaker 1: two black holes eventually merge, they can send ripples through
• 42:04
  Speaker 1: space and time. These gravitational waves travel outward like extremely
• 42:09
  Speaker 1: faint disturbances in the structure of the universe. And sometimes,
• 42:14
  Speaker 1: if the merger is uneven, the newly formed black hole
• 42:18
  Speaker 1: can receive a recoil, a kind of gravitational kick. It
• 42:22
  Speaker 1: may be pushed away from the place where the two
• 42:25
  Speaker 1: black holes met. A black hole can become a wandering object,
• 42:29
  Speaker 1: moving through the darkness, carrying no visible surface, no familiar glow.
• 42:36
  Speaker 1: Just mass, motion and gravity. You can let that image
• 42:40
  Speaker 1: become very small in your mind. A tiny remnant. A
• 42:44
  Speaker 1: distant pulse. A dark centre. A faint wave moving through space.
• 42:49
  Speaker 1: And all around them, the galaxy continues turning. The stars
• 42:53
  Speaker 1: continue shining. The clouds of gas continue drifting. Nothing stops.
• 42:59
  Speaker 1: Even the strangest objects remain part of the same quiet universe.
• 43:04
  Speaker 1: And as you slowly move farther away from these compact remnants,
• 43:08
  Speaker 1: their individual shapes begin to disappear. The pulsar becomes a point.
• 43:13
  Speaker 1: The magnetar becomes a point. The black hole becomes an
• 43:17
  Speaker 1: invisible centre. And beyond them, the Milky Way begins to
• 43:21
  Speaker 1: reveal itself as something much larger. What seemed like a
• 43:24
  Speaker 1: sky filled with separate stars is actually one enormous galaxy,
• 43:29
  Speaker 1: with countless stars moving together through space. You have been
• 43:33
  Speaker 1: looking at individual lights. Now, slowly, you are beginning to
• 43:38
  Speaker 1: see the shape that holds them all. The tiny remnants
• 43:43
  Speaker 1: of stars are beginning to disappear behind you. The neutron stars,
• 43:48
  Speaker 1: the pulsars, the magnetars, the black holes. From a distance,
• 43:53
  Speaker 1: each becomes only a faint point, and then even that
• 43:57
  Speaker 1: point begins to blend into the darkness. And as you
• 44:00
  Speaker 1: continue drifting backward... something unexpected begins to happen. The stars
• 44:06
  Speaker 1: are no longer appearing as separate lights. They begin to gather,
• 44:10
  Speaker 1: at first only a few, then hundreds, then thousands, and gradually,
• 44:16
  Speaker 1: the darkness itself seems to fill with a soft, milky glow.
• 44:20
  Speaker 1: You are beginning to see the galaxy, the Milky Way.
• 44:24
  Speaker 1: From Earth, it appears as a pale band stretching across
• 44:28
  Speaker 1: the night sky. Ancient people saw it long before anyone
• 44:31
  Speaker 1: understood what it was. They could see the light, but
• 44:35
  Speaker 1: not the individual stars responsible for it. Only much later
• 44:40
  Speaker 1: did astronomers understand that this faint band is the combined
• 44:44
  Speaker 1: light of enormous numbers of distant stars, stars so far
• 44:48
  Speaker 1: away that their individual points of light blend together. Now
• 44:53
  Speaker 1: you can imagine rising above that band. The shape becomes clearer.
• 44:58
  Speaker 1: The Milky Way is a barred spiral galaxy. At its
• 45:01
  Speaker 1: centre is a dense region of stars surrounded by a
• 45:05
  Speaker 1: broad disk containing gas, dust, star clusters and immense numbers
• 45:10
  Speaker 1: of stars. And somewhere within one quieter part of that
• 45:14
  Speaker 1: disk is the solar system. The place you started from.
• 45:18
  Speaker 1: From this distance the sun is no longer special. It
• 45:22
  Speaker 1: is simply one star among an enormous population of stars.
• 45:26
  Speaker 1: You can let that thought remain for a moment. One star.
• 45:30
  Speaker 1: One small planetary system. One quiet corner of a much
• 45:34
  Speaker 1: larger structure. And at the centre of this enormous galaxy
• 45:38
  Speaker 1: is something much darker. Sagittarius A star. A supermassive black hole.
• 45:44
  Speaker 1: It contains the mass of several million suns, compressed into
• 45:48
  Speaker 1: an extraordinarily small region of space. But you do not
• 45:52
  Speaker 1: need to imagine the black hole itself as a giant
• 45:55
  Speaker 1: object hanging in the middle of the galaxy. From far away,
• 45:59
  Speaker 1: it is better to think of it as an invisible
• 46:01
  Speaker 1: centre around which many stars move. The stars near the
• 46:06
  Speaker 1: galactic centre follow complicated orbits. They travel around the unseen mass,
• 46:12
  Speaker 1: some pass surprisingly close. Their movements allow astronomers to measure
• 46:17
  Speaker 1: the presence of something that cannot be seen directly. and
• 46:21
  Speaker 1: in recent years, radio telescopes have even produced an image
• 46:25
  Speaker 1: showing the dark central region surrounded by glowing material. The
• 46:30
  Speaker 1: image is not a photograph of the black hole as
• 46:32
  Speaker 1: though you were looking at a dark sphere against a
• 46:34
  Speaker 1: bright sky. It is more like a silhouette created by
• 46:38
  Speaker 1: the way light behaves around an extremely strong gravitational field,
• 46:43
  Speaker 1: a dark centre, a faint ring of light. and around it,
• 46:47
  Speaker 1: thousands of stars moving through one of the busiest regions
• 46:50
  Speaker 1: of the galaxy. Yet the centre is not simply a
• 46:54
  Speaker 1: black hole surrounded by empty space. There are enormous clouds
• 46:59
  Speaker 1: of gas and dust nearby. Some are dense, some are cold.
• 47:04
  Speaker 1: Some contain the raw material from which future stars may form.
• 47:08
  Speaker 1: The material is mostly made of simple elements and molecules,
• 47:12
  Speaker 1: quietly drifting through the darkness. You can imagine these clouds
• 47:16
  Speaker 1: as enormous regions of faint material, almost invisible to your eyes,
• 47:21
  Speaker 1: but glowing in other kinds of light. Some wavelengths can
• 47:25
  Speaker 1: pass through dust more easily than ordinary visible light. This
• 47:29
  Speaker 1: allows astronomers to look toward the galactic centre, even though
• 47:33
  Speaker 1: thick clouds would otherwise hide much of it. The farther
• 47:37
  Speaker 1: you move from the centre, the more the structure of
• 47:40
  Speaker 1: the Milky Way begins to reveal itself. The central region
• 47:44
  Speaker 1: widens into a large bulge, and through that bulge runs
• 47:49
  Speaker 1: a long bar of stars. From far above the galaxy
• 47:53
  Speaker 1: begins to resemble a vast luminous whirl, not a perfect circle,
• 47:58
  Speaker 1: not a rigid disk, but a living structure, filled with
• 48:02
  Speaker 1: different regions moving at different speeds and containing stars of
• 48:06
  Speaker 1: many different ages. Farther outward are the spiral arms. These
• 48:12
  Speaker 1: are among the most recognisable features of the Milky Way.
• 48:15
  Speaker 1: They contain many stars, but they are especially rich in
• 48:19
  Speaker 1: gas and dust. That makes them important places for new
• 48:23
  Speaker 1: stars to form. Deep inside these regions, clouds can become
• 48:28
  Speaker 1: dense enough for gravity to pull material together. Slowly, pieces
• 48:33
  Speaker 1: of gas gather. They become warmer. They become denser. Eventually,
• 48:39
  Speaker 1: new stars can begin to shine. So the Milky Way
• 48:43
  Speaker 1: is not only a collection of ancient stars, it is
• 48:46
  Speaker 1: also a place where new stars are still being born.
• 48:50
  Speaker 1: Some stars are almost as old as the galaxy itself.
• 48:54
  Speaker 1: Others may have appeared only a few million years ago.
• 48:58
  Speaker 1: When you look across the Milky Way, you are therefore
• 49:01
  Speaker 1: looking at many different moments in the galaxy's history at once.
• 49:05
  Speaker 1: Old stars. Young stars. Stars that are still forming. stars
• 49:11
  Speaker 1: that are dying, clouds that have not yet become stars,
• 49:15
  Speaker 1: and remnants of stars that disappeared long ago. Everything is
• 49:19
  Speaker 1: happening within the same enormous structure You can drift outward
• 49:24
  Speaker 1: again The central bulge becomes smaller behind you The spiral
• 49:28
  Speaker 1: arms stretch across the darkness And eventually, you reach the
• 49:32
  Speaker 1: region where our solar system lives The Orion Arm It
• 49:37
  Speaker 1: is not one of the largest structures in the Milky
• 49:39
  Speaker 1: Way It is more like a quieter branch within the
• 49:42
  Speaker 1: galaxy's larger spiral pattern. And somewhere inside this region, roughly 27,000
• 49:49
  Speaker 1: light-years from the galactic centre, is the Sun. You can
• 49:54
  Speaker 1: imagine finding it again. Not because it is bright from
• 49:57
  Speaker 1: this distance. It would be almost impossible to pick out.
• 50:01
  Speaker 1: But because you already know where home is. A tiny star.
• 50:05
  Speaker 1: A tiny planetary system. A small world orbiting within it.
• 50:10
  Speaker 1: And all around that world, the Milky Way continues its
• 50:13
  Speaker 1: slow rotation. The stars do not sit motionless. The galaxy turns.
• 50:19
  Speaker 1: Gas moves. Star-forming regions change. Old stellar streams slowly wrap
• 50:25
  Speaker 1: around the galaxy. And some stars that once belonged to
• 50:29
  Speaker 1: smaller galaxies have gradually become part of the Milky Way itself.
• 50:34
  Speaker 1: The galaxy has grown through time. It has gathered material.
• 50:38
  Speaker 1: It has interacted with other galaxies. It has changed shape.
• 50:43
  Speaker 1: And yet, from far away, all of this movement becomes
• 50:47
  Speaker 1: almost impossible to notice. The entire galaxy seems peaceful, quiet, slow,
• 50:54
  Speaker 1: like a luminous cloud turning in darkness. Now you can
• 50:58
  Speaker 1: begin to move above the bright disk. The stars become
• 51:01
  Speaker 1: more widely separated. The glow becomes thinner. The spiral arms
• 51:06
  Speaker 1: begin to flatten beneath you. And beyond them, another part
• 51:10
  Speaker 1: of the Milky Way comes into view, the halo. It
• 51:14
  Speaker 1: is much fainter than the bright disk. It contains old stars,
• 51:18
  Speaker 1: globular clusters, and long streams of stars that stretch through space.
• 51:22
  Speaker 1: Some of these streams may be the remains of smaller
• 51:25
  Speaker 1: galaxies that were gradually pulled apart by the Milky Way's gravity.
• 51:29
  Speaker 1: Stars that once travelled together now form long, delicate trails.
• 51:34
  Speaker 1: They wrap around the galaxy. And above all of this
• 51:37
  Speaker 1: is something even larger and much harder to see, an
• 51:41
  Speaker 1: enormous invisible halo of dark matter. You cannot see it directly.
• 51:46
  Speaker 1: There is no glow, no obvious surface, no edge you
• 51:50
  Speaker 1: could point toward. Yet its gravity influences the motion of
• 51:54
  Speaker 1: the visible galaxy. The stars move as though they are
• 51:58
  Speaker 1: embedded within something much larger than the light we can see.
• 52:02
  Speaker 1: And so, as you rise farther above the Milky Way,
• 52:06
  Speaker 1: The bright galaxy beneath you begins to look like only
• 52:09
  Speaker 1: the visible portion of something much larger. A luminous disk.
• 52:14
  Speaker 1: An ancient halo. An invisible gravitational presence. And beyond all
• 52:19
  Speaker 1: of it, an enormous darkness waiting quietly around the galaxy.
• 52:23
  Speaker 1: You have moved from a single planet to a single star.
• 52:27
  Speaker 1: From a single star to a stellar neighbourhood. And now
• 52:31
  Speaker 1: from that neighbourhood to an entire galaxy. but the Milky
• 52:35
  Speaker 1: Way itself is only one island of light. Far beyond
• 52:39
  Speaker 1: its outer halo, there are other galaxies, some close enough
• 52:43
  Speaker 1: to belong to the same gravitational family, others separated by
• 52:48
  Speaker 1: millions of light-years of nearly empty space. And as you
• 52:52
  Speaker 1: continue drifting outward, the darkness between galaxies will begin to
• 52:57
  Speaker 1: become just as important as the galaxies themselves. You are
• 53:03
  Speaker 1: now above the bright disk of the Milky Way. Far
• 53:06
  Speaker 1: beneath you, the spiral arms have become softer. The crowded
• 53:11
  Speaker 1: regions of stars have begun to thin. The warm glow
• 53:15
  Speaker 1: of the galaxy is fading into a wider darkness. And
• 53:19
  Speaker 1: as you continue to rise, you begin to notice that
• 53:22
  Speaker 1: the Milky Way does not simply end where its bright
• 53:25
  Speaker 1: stars become less visible. There is another region surrounding it,
• 53:30
  Speaker 1: a much fainter region, a vast halo. The galactic halo
• 53:35
  Speaker 1: extends far beyond the bright disk, containing old stars, globular clusters,
• 53:41
  Speaker 1: and long streams of stars that stretch quietly through space.
• 53:45
  Speaker 1: Some of these stars are ancient. They have been travelling
• 53:49
  Speaker 1: through the galaxy for billions of years, following paths that
• 53:52
  Speaker 1: can be difficult to see from within the bright disk,
• 53:56
  Speaker 1: and some of the streams have an even older story.
• 53:59
  Speaker 1: They may be the remains of smaller galaxies that once
• 54:02
  Speaker 1: travelled separately through space. Over enormous periods of time, gravity
• 54:07
  Speaker 1: slowly drew them toward the Milky Way. The smaller galaxies
• 54:11
  Speaker 1: were stretched, their stars were scattered, and eventually, what had
• 54:16
  Speaker 1: once been a separate galaxy became a thin stream of
• 54:19
  Speaker 1: stars moving through the larger one. You can imagine the
• 54:23
  Speaker 1: process without any sudden event. Nothing needs to explode. Nothing
• 54:28
  Speaker 1: needs to happen quickly. a small galaxy approaches. Gravity begins
• 54:32
  Speaker 1: to pull. Its shape slowly changes. Stars that once travelled
• 54:37
  Speaker 1: together begin to spread apart, and after millions or billions
• 54:41
  Speaker 1: of years, only a faint trail remains. The Milky Way
• 54:46
  Speaker 1: is therefore not a perfectly isolated island. It has grown
• 54:49
  Speaker 1: through interactions with other galaxies. It carries pieces of those
• 54:54
  Speaker 1: encounters within its own structure. Some of the stars around
• 54:57
  Speaker 1: you may have formed somewhere else. They may have begun
• 55:01
  Speaker 1: their journeys in another galaxy, long before the sun existed,
• 55:05
  Speaker 1: and now they quietly belong to this one. As you
• 55:09
  Speaker 1: drift farther outward, another part of the galaxy becomes harder
• 55:13
  Speaker 1: to ignore. Something enormous surrounds the visible stars, something that
• 55:18
  Speaker 1: does not shine. Dark matter. You cannot see it directly.
• 55:23
  Speaker 1: It does not glow like a star. It does not
• 55:26
  Speaker 1: form bright clouds like ordinary gas. There is no surface
• 55:30
  Speaker 1: to look at. And yet, its gravity affects the motion
• 55:34
  Speaker 1: of the visible galaxy. The stars near the outer regions
• 55:37
  Speaker 1: of the Milky Way move in ways that tell astronomers
• 55:41
  Speaker 1: there must be much more mass present than the visible
• 55:45
  Speaker 1: stars alone can provide. So you can imagine the galaxy
• 55:49
  Speaker 1: as having two layers. The first is the layer you
• 55:52
  Speaker 1: can see. Stars. gas, dust, nebulae, a faint spiral of light,
• 56:00
  Speaker 1: and around all of this is something much larger and
• 56:03
  Speaker 1: almost completely invisible, a gravitational structure that helps hold the
• 56:08
  Speaker 1: galaxy together. You do not need to imagine its exact shape.
• 56:13
  Speaker 1: You can simply imagine that the visible Milky Way is
• 56:16
  Speaker 1: surrounded by a quiet darkness that has weight, a presence
• 56:20
  Speaker 1: known not by its light, but by its influence. And then, slowly,
• 56:26
  Speaker 1: you begin to move closer to home again. Not all
• 56:30
  Speaker 1: the way back to Earth, just toward the quieter neighbourhood
• 56:33
  Speaker 1: around the Sun. The galaxy is enormous, but our own
• 56:37
  Speaker 1: stellar neighbourhood occupies a much smaller region within it. And
• 56:41
  Speaker 1: within this region is something particularly interesting, the local bubble.
• 56:46
  Speaker 1: Imagine a huge, faint cavity surrounding the solar system and
• 56:50
  Speaker 1: many nearby stars. The bubble is filled with extremely hot,
• 56:55
  Speaker 1: thin gas. Its story appears to reach back millions of years,
• 57:00
  Speaker 1: to a period when several massive stars in our neighbourhood
• 57:03
  Speaker 1: ended their lives as supernovae. Their explosions sent energy and
• 57:08
  Speaker 1: material outward. Over time, those events helped create a large
• 57:13
  Speaker 1: region of hot, rarefied gas. You are not floating inside
• 57:17
  Speaker 1: a completely empty space. You are inside a kind of
• 57:21
  Speaker 1: cosmic bubble. The gas is incredibly thin compared with the
• 57:25
  Speaker 1: air around you on Earth, yet it is extremely hot.
• 57:29
  Speaker 1: It is almost the opposite of what you might expect.
• 57:32
  Speaker 1: Very hot. And almost empty. That combination is difficult to imagine.
• 57:37
  Speaker 1: There is no warm wind against your skin. No sensation
• 57:41
  Speaker 1: of heat. The particles are simply too sparse. The temperature
• 57:45
  Speaker 1: describes the energy of the particles, not something you could
• 57:49
  Speaker 1: feel like the warmth of sunlight. and so the local
• 57:52
  Speaker 1: bubble can remain almost completely invisible to your senses. You
• 57:57
  Speaker 1: are simply surrounded by a faint, ancient environment, created by
• 58:01
  Speaker 1: stars that disappeared long ago. Somewhere within this bubble, the
• 58:06
  Speaker 1: sun continues its journey through the galaxy, the planets continue
• 58:10
  Speaker 1: their quiet orbits, Earth continues turning, and above the atmosphere,
• 58:15
  Speaker 1: the ancient history of nearby stars remains written into the
• 58:19
  Speaker 1: surrounding space. The local bubble is also not completely alone.
• 58:24
  Speaker 1: Other large regions of hot gas exist nearby. Some overlap.
• 58:29
  Speaker 1: Some interact. Some are separated by denser clouds of material.
• 58:34
  Speaker 1: The edges of these regions can become places where gas
• 58:37
  Speaker 1: gathers and new stars may eventually form. So even the
• 58:42
  Speaker 1: emptiness around the stars is changing. It expands. It mixes.
• 58:47
  Speaker 1: becomes denser in some places and thinner in others. The
• 58:51
  Speaker 1: galaxy is not a collection of isolated objects surrounded by
• 58:55
  Speaker 1: perfect nothingness. It is more like a vast environment with stars, gas, dust,
• 59:02
  Speaker 1: invisible matter and enormous regions of emptiness all connected by gravity.
• 59:08
  Speaker 1: Now let yourself drift out once more. The Milky Way
• 59:12
  Speaker 1: becomes smaller behind you. Its spiral shape begins to disappear.
• 59:17
  Speaker 1: Its halo becomes difficult to distinguish. And beyond it, another
• 59:21
  Speaker 1: galaxy comes into view. And then another. And another. The
• 59:26
  Speaker 1: space between them is enormous. The Milky Way and Andromeda
• 59:31
  Speaker 1: are separated by millions of light-years of extraordinarily thin space.
• 59:36
  Speaker 1: Yet they are not completely unrelated. Along with many smaller galaxies,
• 59:41
  Speaker 1: they belong to a gravitational family called the Local Group.
• 59:46
  Speaker 1: The name sounds simple, but the structure itself is enormous.
• 59:50
  Speaker 1: It contains galaxies, satellite galaxies, stars, gas, and vast amounts
• 59:56
  Speaker 1: of dark matter all moving through the same broad region
• 1:00:00
  Speaker 1: of space. And beyond the local group, the pattern continues.
• 1:00:04
  Speaker 1: Groups of galaxies gather into larger structures. Those structures connect
• 1:00:09
  Speaker 1: through long filaments. And between the filaments are enormous regions
• 1:00:14
  Speaker 1: where very few galaxies can be found. The universe begins
• 1:00:18
  Speaker 1: to look less like a collection of bright islands and
• 1:00:21
  Speaker 1: more like a delicate network separated by vast darkness. The
• 1:00:25
  Speaker 1: brighter regions become threads. The darker regions become spaces between them.
• 1:00:31
  Speaker 1: And from this distance, the emptiness no longer feels like nothing.
• 1:00:36
  Speaker 1: It becomes part of the structure itself. The quiet spaces matter.
• 1:00:41
  Speaker 1: The gaps matter. The enormous regions where almost nothing is
• 1:00:45
  Speaker 1: visible are part of the story of how the universe
• 1:00:49
  Speaker 1: is arranged. You can let the Milky Way continue shrinking
• 1:00:53
  Speaker 1: behind you, The local bubble disappears into the larger galaxy.
• 1:00:58
  Speaker 1: The galaxy becomes one member of a small family, and
• 1:01:01
  Speaker 1: that family becomes one small region within a much larger
• 1:01:05
  Speaker 1: cosmic landscape. You are now drifting somewhere between galaxies. There
• 1:01:10
  Speaker 1: is no need to hurry. There is almost nothing around you.
• 1:01:14
  Speaker 1: Only faint light, enormous distances, and the slow movement of
• 1:01:18
  Speaker 1: matter through a universe that is much emptier than it
• 1:01:21
  Speaker 1: first appeared. And somewhere ahead, beyond the familiar shape of
• 1:01:26
  Speaker 1: the Milky Way, those faint threads begin to gather into
• 1:01:30
  Speaker 1: a structure so immense that even entire galaxies become tiny
• 1:01:34
  Speaker 1: points within it. You are now drifting between galaxies. The
• 1:01:40
  Speaker 1: Milky Way has become very small behind you. Its spiral
• 1:01:44
  Speaker 1: arms have disappeared into the darkness, and the nearby galaxies
• 1:01:48
  Speaker 1: that once seemed enormous are beginning to look like scattered
• 1:01:52
  Speaker 1: points of light. But as you continue outward, something unexpected
• 1:01:57
  Speaker 1: becomes visible. The galaxies are not scattered completely at random.
• 1:02:02
  Speaker 1: Across the largest scales they gather into long, faint structures. Threads, filaments,
• 1:02:08
  Speaker 1: immense bridges of matter stretching through space. This is the
• 1:02:12
  Speaker 1: cosmic web. You can imagine it without making it too
• 1:02:16
  Speaker 1: solid in your mind. It is not a physical net
• 1:02:19
  Speaker 1: hanging in space. It is a pattern formed by galaxies, gas,
• 1:02:24
  Speaker 1: and the invisible influence of dark matter. Where these long
• 1:02:28
  Speaker 1: structures meet, galaxies gather into dense regions and clusters. Between
• 1:02:34
  Speaker 1: them are enormous spaces where very few galaxies can be found,
• 1:02:39
  Speaker 1: cosmic voids. The emptiness is so extensive that even the
• 1:02:43
  Speaker 1: word empty begins to feel different. There may be a
• 1:02:46
  Speaker 1: few scattered particles here, perhaps a little gas. perhaps a
• 1:02:50
  Speaker 1: faint trace of matter. But compared with the crowded regions
• 1:02:54
  Speaker 1: of the cosmic web, these enormous spaces are almost completely quiet.
• 1:02:59
  Speaker 1: And there is something strangely peaceful about that. The universe
• 1:03:02
  Speaker 1: is not filled evenly. It has bright places and dark places,
• 1:03:07
  Speaker 1: dense places and nearly empty places, threads and gaps. A
• 1:03:12
  Speaker 1: vast structure formed slowly under gravity over billions of years.
• 1:03:17
  Speaker 1: You can drift through one of those quiet regions now.
• 1:03:20
  Speaker 1: There are no nearby stars. No planets. No familiar horizon.
• 1:03:26
  Speaker 1: Only darkness. And yet, even here, something ancient is moving
• 1:03:31
  Speaker 1: toward you. Light. Very old light. When you look at
• 1:03:35
  Speaker 1: distant galaxies, you are not seeing them exactly as they
• 1:03:39
  Speaker 1: are now. You are seeing them as they were when
• 1:03:42
  Speaker 1: their light began its journey toward you. The farther away
• 1:03:45
  Speaker 1: the galaxy... the farther back in time you can see.
• 1:03:48
  Speaker 1: A telescope, therefore, does something rather beautiful. It looks through space,
• 1:03:54
  Speaker 1: but it also looks through time. The James Webb Space
• 1:03:58
  Speaker 1: Telescope can observe extremely distant galaxies whose light began travelling
• 1:04:04
  Speaker 1: long before Earth existed. Some of those galaxies may have
• 1:04:08
  Speaker 1: changed dramatically since the light left them. Some may have
• 1:04:11
  Speaker 1: merged with other galaxies. Some may have faded. Some may
• 1:04:15
  Speaker 1: no longer exist in anything like the form you see,
• 1:04:19
  Speaker 1: but their ancient light is still arriving, a faint image
• 1:04:22
  Speaker 1: crossing the universe. A message that does not know it
• 1:04:26
  Speaker 1: is a message. You can imagine that light travelling quietly
• 1:04:30
  Speaker 1: for billions of years. It leaves a young galaxy. It
• 1:04:35
  Speaker 1: crosses expanding space. Its wavelength gradually stretches during the journey,
• 1:04:40
  Speaker 1: shifting toward the redder part of the spectrum. Astronomers call
• 1:04:45
  Speaker 1: this cosmological redshift. You do not need to picture the mathematics.
• 1:04:50
  Speaker 1: Simply imagine a wave of light being gently stretched as
• 1:04:53
  Speaker 1: the space through which it travels expands. The light becomes longer, softer,
• 1:04:59
  Speaker 1: more distant in appearance. And eventually, after an almost unimaginable journey,
• 1:05:05
  Speaker 1: a small part of it reaches a telescope. The universe
• 1:05:08
  Speaker 1: is telling us about its past without speaking. And farther
• 1:05:12
  Speaker 1: back still … is the oldest light we can observe.
• 1:05:16
  Speaker 1: The cosmic microwave background. It is a faint glow coming
• 1:05:20
  Speaker 1: from almost every direction in the sky. It is not
• 1:05:24
  Speaker 1: the light of stars. It is not the light of galaxies.
• 1:05:28
  Speaker 1: It is the ancient afterglow of a much younger universe.
• 1:05:32
  Speaker 1: A time when everything was hotter, denser, and very different
• 1:05:36
  Speaker 1: from the quiet cosmos you see around you now. That
• 1:05:40
  Speaker 1: ancient glow has travelled for billions of years. It has
• 1:05:44
  Speaker 1: crossed enormous distances. It has passed through expanding space. And today,
• 1:05:50
  Speaker 1: it arrives as an extremely faint signal, a kind of
• 1:05:54
  Speaker 1: cosmic whisper. There are also subtle patterns within that ancient light,
• 1:05:59
  Speaker 1: tiny differences in temperature and density, ancient ripples that became
• 1:06:04
  Speaker 1: the seeds of later cosmic structure. Astronomers also find traces
• 1:06:09
  Speaker 1: of those early sound-like waves in the way galaxies are
• 1:06:12
  Speaker 1: arranged today. These are called baryon acoustic oscillations. The name
• 1:06:18
  Speaker 1: is complicated. The idea can be gentle. You can simply
• 1:06:21
  Speaker 1: think of them as ancient ripples from the young universe,
• 1:06:25
  Speaker 1: echoes of a time when matter and energy were moving
• 1:06:28
  Speaker 1: together in a much denser cosmic environment. Those ripples eventually
• 1:06:33
  Speaker 1: became part of the large-scale pattern of galaxies. So when
• 1:06:38
  Speaker 1: you look at the cosmic web, you are not only
• 1:06:40
  Speaker 1: looking at galaxies. you are seeing the very old consequences
• 1:06:45
  Speaker 1: of conditions that existed near the beginning of cosmic history.
• 1:06:49
  Speaker 1: And yet, the universe did not remain the same. It
• 1:06:53
  Speaker 1: continues to expand, space itself grows, distant galaxies become farther apart,
• 1:06:59
  Speaker 1: and the expansion appears to be accelerating. The mysterious influence
• 1:07:03
  Speaker 1: associated with this acceleration is called dark energy. We do
• 1:07:08
  Speaker 1: not yet know what dark energy truly is. It may
• 1:07:11
  Speaker 1: be related to the energy of empty space. It may
• 1:07:15
  Speaker 1: represent something deeper about the geometry of the universe. For now,
• 1:07:20
  Speaker 1: the most honest answer is simply that we know what
• 1:07:23
  Speaker 1: it does more clearly than we know what it is.
• 1:07:26
  Speaker 1: It changes the future of the cosmos. As space continues expanding,
• 1:07:32
  Speaker 1: galaxies outside gravitationally bound regions will gradually become more distant.
• 1:07:38
  Speaker 1: Star formation will eventually slow down, The supply of gas
• 1:07:42
  Speaker 1: available to create new stars will become less abundant. The
• 1:07:46
  Speaker 1: universe will slowly become darker. But this is not something
• 1:07:50
  Speaker 1: happening tonight. Not tomorrow. Not even on any human timescale.
• 1:07:55
  Speaker 1: In fact, almost all of cosmic history still lies ahead.
• 1:07:59
  Speaker 1: The universe is about 13.8 billion years old, which sounds
• 1:08:04
  Speaker 1: unimaginably ancient. But compared with the immense timescales of its
• 1:08:09
  Speaker 1: possible future, We may still be living relatively early in
• 1:08:12
  Speaker 1: its story. There are still stars being born. There are
• 1:08:16
  Speaker 1: still galaxies changing. There are still planets forming. There is
• 1:08:21
  Speaker 1: still light almost everywhere you look. We are living during
• 1:08:25
  Speaker 1: a remarkably active period of cosmic history, a period filled
• 1:08:29
  Speaker 1: with stars, filled with warm worlds, filled with galaxies, filled
• 1:08:35
  Speaker 1: with change. Much later, after enormous stretches of time, Stars
• 1:08:40
  Speaker 1: will become fewer. The remaining stars will gradually fade. White
• 1:08:45
  Speaker 1: dwarfs will cool. Black holes will slowly lose energy through
• 1:08:49
  Speaker 1: Hawking radiation. And over extraordinary timescales, even the darkest objects
• 1:08:55
  Speaker 1: may eventually disappear. The universe would then become colder, darker.
• 1:09:00
  Speaker 1: and more dilute. This possible distant state is often called
• 1:09:04
  Speaker 1: heat death. But there is nothing sudden about it. No
• 1:09:08
  Speaker 1: final explosion. No single moment when everything stops. Just a
• 1:09:12
  Speaker 1: gradual spreading of energy. A slow quieting. A universe with
• 1:09:17
  Speaker 1: fewer lights. more distance, more darkness. And perhaps, in that
• 1:09:22
  Speaker 1: far future, almost everything that once seemed permanent will have
• 1:09:27
  Speaker 1: become part of the past. Yet you are not there,
• 1:09:31
  Speaker 1: you are here, now. Lying quietly beneath the night, breathing, listening,
• 1:09:38
  Speaker 1: the universe is still young enough to shine, stars are
• 1:09:41
  Speaker 1: still burning, galaxies are still gathering, ancient light is still arriving,
• 1:09:47
  Speaker 1: and somewhere, Billions of light-years away, a galaxy is sending
• 1:09:52
  Speaker 1: out light that will continue travelling long after you have
• 1:09:55
  Speaker 1: fallen asleep. You can let that thought become smaller now.
• 1:10:00
  Speaker 1: The cosmic web becomes distant. The ancient galaxies fade. The
• 1:10:04
  Speaker 1: cosmic background becomes a faint whisper. The enormous future becomes quiet.
• 1:10:10
  Speaker 1: And slowly, you can return to the small space around you.
• 1:10:14
  Speaker 1: The room is still here, the bed beneath you. The
• 1:10:17
  Speaker 1: gentle weight of the blanket. The quiet rhythm of your breathing.
• 1:10:22
  Speaker 1: You do not need to carry the universe with you.
• 1:10:25
  Speaker 1: You can simply rest beneath it. The stars will continue
• 1:10:29
  Speaker 1: shining without your attention. The galaxies will continue moving. Space
• 1:10:34
  Speaker 1: will continue expanding. The ancient light will continue arriving. And
• 1:10:39
  Speaker 1: the questions that remain unanswered can remain unanswered. Perhaps there
• 1:10:43
  Speaker 1: are things about reality we will understand one day. Perhaps
• 1:10:47
  Speaker 1: there are things we never will. The universe does not
• 1:10:50
  Speaker 1: seem to mind. It continues, quietly, slowly, without needing to
• 1:10:55
  Speaker 1: explain itself. And perhaps that is enough for tonight. You
• 1:10:59
  Speaker 1: have drifted from one small world to distant stars, from
• 1:11:04
  Speaker 1: frozen planets to molten worlds, from ageing stars to neutron
• 1:11:08
  Speaker 1: stars and black holes, from the Milky Way to the
• 1:11:12
  Speaker 1: invisible architecture surrounding it, and finally outward into the immense
• 1:11:17
  Speaker 1: web of galaxies and ancient light. Now you can stop travelling.
• 1:11:22
  Speaker 1: There is nowhere else you need to go. You are safe,
• 1:11:25
  Speaker 1: there is nothing to do. Just listen, and drift. And so,
• 1:11:30
  Speaker 1: our journey drifts quietly to its end. Whether you are
• 1:11:34
  Speaker 1: still listening beneath the gentle glow of your screen, or
• 1:11:37
  Speaker 1: already floating somewhere between dreams and distant stars, you can
• 1:11:41
  Speaker 1: let the universe become softer now, The stars will keep burning.
• 1:11:45
  Speaker 1: The planets will keep turning. The galaxies will keep moving
• 1:11:49
  Speaker 1: through the dark. Ancient light will continue crossing the enormous
• 1:11:53
  Speaker 1: spaces between them. And the universe will carry on quietly
• 1:11:57
  Speaker 1: around you while you sleep. For now, you can simply breathe.
• 1:12:02
  Speaker 1: Let your body become heavy. Let your thoughts become distant.
• 1:12:06
  Speaker 1: There is nothing left to understand tonight. Only darkness. Only stillness.
• 1:12:12
  Speaker 1: Only the quiet feeling of being here, on one small world,
• 1:12:17
  Speaker 1: beneath an immense and beautiful universe. Rest well, the cosmos
• 1:12:22
  Speaker 1: can continue without you watching, and perhaps, somewhere in that
• 1:12:26
  Speaker 1: endless darkness, another faint light is already on its way.