How the Universe Works - S10E01 - Secrets of the Cosmic Web
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00:00The night sky. Countless stars and the majestic sweep of the Milky Way. But beyond our local
00:10neighborhood, across the cosmos, there are over two trillion more galaxies.
00:17When we first began to observe galaxies, we collected them like butterflies. Little by
00:22little, we realized that they formed a web.
00:25The cosmic web is the infrastructure that connects every corner of the universe.
00:32You don't know anything about our universe if you don't understand the cosmic web.
00:35It feeds galaxies. It forms galaxies. It is made of galaxies.
00:42It's the architect of everything. And our cosmic future depends on it.
00:48The cosmic web is one of the most important parts of our universe. It plays a key role
00:53in the evolution of the cosmos.
00:56Without the cosmic web, there would be no stars, no planets. Nowhere in the universe
01:02where the conditions of life could exist.
01:04How did the universe go from a hot soup of gas to a cosmic web sprinkled with galaxies,
01:11planets, and us?
01:23The universe may appear random. Two trillion galaxies spread across the cosmos. But in
01:40this cosmic chaos, scientists detect order.
01:45When we first saw that the universe was full of galaxies, it seemed like overwhelming chaos.
01:51But it's not. They are all connected.
01:55Galaxies link up in a gigantic cosmic network spanning the entire universe. How this pattern
02:03emerged may be cosmology's biggest puzzle.
02:08In some senses, you don't understand something unless you understand how it comes into existence
02:13and how it's formed. And galaxies are the basic building block of our universe.
02:20To solve this mystery, scientists need to go deep, to the very edge of the observable
02:26universe and study light from the first galaxies.
02:33Chile, 2021. Scientists point the VLT, or Very Large Telescope, towards the Hubble Ultra
02:42Deep Field.
02:45It's a patch of sky famously photographed by the Hubble Space Telescope in 1995. The
02:52VLT's power allows astronomers to see much deeper into space.
02:58Imagine you take a grain of sand and you put it on your fingertip and you hold your arm
03:03out like this and you block a part of the sky looking at that grain of sand. That's
03:09the size of the Hubble Ultra Deep Field. And yet it contains thousands of galaxies
03:15in it.
03:17The telescope stares at those galaxies for 155 hours and picks up the faintest of glows.
03:27Ancient hydrogen gas concentrated along a strand of space 15 million light years long.
03:36The filaments are just one tiny section of the cosmic web, the largest known structure
03:44in the universe.
03:48The scale of the cosmic web is enormous. It is, by definition, the largest thing that
03:53we can see in our universe.
03:55Today, the cosmic web is a lattice of filaments, linked streams of hydrogen gas that form an
04:04intergalactic network spanning the entire universe.
04:09Inside the nodes of the cosmic web you'll find galaxies, stars, black holes. Along the
04:15filaments you'll find gas that connects these nodes and the gas will connect to the other
04:20galaxies and clusters of galaxies. It's this beautiful super highway of large cities that
04:28are connected through these filaments.
04:32We can see the cosmic web about as far back as we can look, and really galaxies are forming
04:37along that web all the way back.
04:40This cosmic infrastructure dates back to the earliest days of the universe, 13.8 billion
04:50years ago. The universe ignites in a tiny ball of super hot energy. It expands and begins
05:00to cool. Energy transforms into primitive subatomic particles of matter. The heat from
05:10the Big Bang is so intense, gravity is effectively powerless.
05:16The very early universe was super hot, super energetic, and regular particles of matter
05:22were zipping around so fast that not even gravity could hold them together. But regular
05:27matter wasn't the only thing in the early universe.
05:30In the background, gravity is working on something else. Regular matter's ghostly cousin, the
05:38invisible substance known today as dark matter. It makes up about 85% of all the matter created
05:46in the early universe.
05:50Normal matter and dark matter both existed around the time of the Big Bang, but the way
05:54they played out was very different.
05:57Just 10 seconds after the Big Bang, the infant universe is billions of degrees Fahrenheit.
06:03Still far too hot for regular matter particles to clump together. But dark matter plays by
06:10different rules.
06:12Dark matter isn't affected by the Big Bang's intense radiation in the same way that regular
06:17matter is. And so because it's able to cool, it clumps together in a way that regular matter
06:23doesn't.
06:25As dark matter clumps grow, they exert a gravitational pull and begin to form shadowy structures.
06:33As soon as the dark matter gets a foothold, we have a place where there's a bit more stuff.
06:38Then that attracts more and more dark matter.
06:41380,000 years after the Big Bang, the intense heat drops to a few thousand degrees. Normal
06:49particles of matter move around more slowly. Protons and electrons bind together and form
06:57atoms of hydrogen and helium gas. Then gravity from dark matter starts to work on regular
07:05matter.
07:06Before you know it, you have this very clumpy universe with these huge dark matter halos
07:12that can now start to draw in also ordinary matter in the form of gas.
07:18A billion year building project begins. The dark matter clumps pull in clouds of gas.
07:27The foundations of the cosmic web and the galaxies.
07:32Just as when you build a building, you know, there's a lot of work that happens before
07:36the building goes up. Our universe spent a lot of time laying the groundwork for this
07:40cosmic web before it switched on the lights.
07:45The foundations are complete, but the job isn't finished. How did those clouds of gas
07:52transform into the greatest structure in the universe?
07:58The secretive dark matter that brought the gas together is also on site managing the
08:04build.
08:05It was really the dark matter that called the shots in cosmic clustering because it
08:10outweighed the ordinary stuff by a big factor.
08:15In essence, the cosmic web is made of dark matter. Tendrils of material are stretched
08:20out across the cosmos.
08:22As the sprawling structure builds, its gravitational pull strengthens, pulling in more dark matter.
08:30The clumps begin to collapse and shrink down into filaments. These meet at even more tightly
08:37packed clusters, creating a huge dark scaffold that drags in more hydrogen gas.
08:45Imagine drops of dew on a spider web. That's like hydrogen blobs being pulled into dark
08:51matter's cosmic web.
08:54After tens of millions of years of construction, strands of gas stretch across the cosmos.
09:02Fast forward to now. The web appears in all its star-spangled glory, lit up with galaxies.
09:11We know at some point stars and galaxies formed. The big question is when. What were the first
09:16galaxies like? That's a big mystery.
09:19So how then did the lights of the cosmos switch on? Evidence suggests that as the universe
09:26assembled its web of dark matter and hydrogen gas, the biggest stars that have ever lived
09:33set the cosmos ablaze.
09:382018, scientists study an ancient galaxy, the catchily named MACS 1149-JD1.
09:57There they find some of the oldest stars ever detected.
10:02This particular galaxy is exciting because it's forming stars just a very short time
10:07after the Big Bang.
10:10Those stars could hold clues as to how the cosmic web that supports the universe first
10:16lit up. But as astronomers study starlight from when the universe was just 250 million
10:22years old, they get a shock.
10:27The stars are not just made up of hydrogen and helium produced in the Big Bang. They
10:32also contain what astronomers call metals.
10:38Metals in astronomy is everything heavier than hydrogen and helium.
10:43No matter where it is on the periodic table, if you're not hydrogen or helium, you are
10:47a metal, even though that makes no sense. If I were king of astronomy, metals is right
10:53out.
10:55The Big Bang only made hydrogen and helium. Anything heavier than that was churned up
11:01in the cores of dying stars.
11:05The bright stars of this ancient galaxy, dating back to just 250 million years after the Big
11:11Bang, contain chemicals that were created in even earlier stars.
11:19Some of them seem to be nearly the age of the universe, extremely old, and yet they
11:23contain elements that guarantee they can't have been the first generation. As old as
11:29these stars are, there must have been something that came before.
11:34The earlier first generation of stars remains cloaked in mystery.
11:39How did the first stars ignite? And did they kickstart the formation of the first galaxies?
11:49It sounds like a classic creation myth. It's out of the darkness, out of nothing. Structure
11:56arrived and from that structure, the galaxies, the lights in the universe turned on.
12:04We've never seen a first generation star, but physicists have a theory of how they formed
12:10and what they were like.
12:14Let's step even further back in time, to around 100 million years after the Big Bang. The
12:20early cosmic web is dark. There are no stars to illuminate it.
12:28The universe is ready for stellar ignition.
12:34Cooled down after millions of years of expansion, the gas clouds clinging to the dark matter
12:40scaffold begin to contract. As the hydrogen gas clumps together, larger clouds form super
12:49dense ultra hot cores.
12:53If you can bring hydrogen together and actually get it hot and dense enough, hydrogen will
12:58begin to fuse into helium. There'll be a nuclear fusion reaction going on.
13:05Simulations suggest that some gas clouds are hundreds of times the mass of the sun. The
13:13stars they produce are unlike anything that exists today.
13:20So the stars around us today really top out at masses between, let's say, 70 to 100 times
13:26the mass of our sun. There's nothing larger than that.
13:30These first stars were up to a thousand times more massive than the sun. So if you plopped
13:36it in our solar system, it would extend all the way past Jupiter. So think about that.
13:42That is incredibly big. That scale is mind blowing.
13:48So what happened to these stellar behemoths?
13:52The lifetime of a star has a lot to do with its mass. The more massive a star is, the
13:57more gravity crushes the interior up to high temperatures and it burns through its nuclear
14:01fuel even faster. So incredibly, the more mass there is, the shorter a lifetime you
14:07get for a star.
14:09The first generation of stars are sort of like the rappers and rock stars of the universe.
14:16They live fast, they die young.
14:21First generation stars didn't live long enough to form complex galaxies, but they did set
14:27the process in motion. The lives of the first stars may have been rock and roll, but their
14:34explosive deaths in supernovas pumped the universe full of heavy metal.
14:42In the galaxy today, we see a supernova maybe every couple of years, close to us every couple
14:47of decades. This must have been a firework show. Giant supernovas going off all the time
14:53all around you.
14:56That act of destruction is actually an act of creation. What a star does in its core
15:02is it creates heavier elements from lighter elements.
15:08The first generation of stars must have been absolutely incredible. Simply exploding so
15:13quickly and unloading all of this wonderful new chemistry into the galaxy.
15:19Two hundred million years after the Big Bang, the remains of the first stars flood the interstellar
15:25medium with heavier elements like carbon, oxygen, silicon and iron.
15:33Crucial ingredients for the next wave of stars.
15:38It's such a beautiful story because suddenly the whole process of star formation changed
15:42and it literally became easier to make a star.
15:48Heavy elements suck heat out of the surrounding gas. Cooler clouds crunch down much faster.
15:55The smaller, second generation stars form rapidly and in much greater numbers.
16:02Somehow this mess of stars transformed into a network of young galaxies. But it wasn't
16:08easy because as these baby galaxies formed, a breed of matter-hungry monsters appeared
16:16in the young cosmic web.
16:2513.6 billion years ago, the dark scaffold that supports all the regular matter in the
16:32universe emerges, ablaze with stars.
16:39But how did this stellar array evolve into a structure littered with organized galaxies?
16:45It seems they formed under constant threat of destruction.
16:53October, 2020. Astronomers discover a monster lurking among the cosmic web's earliest
17:01structures, dating to 900 million years after the Big Bang, a supermassive black hole.
17:09Six galaxies surround this cosmic giant, caught in its grip, seemingly linked to the supermassive
17:17black hole by filaments of the developing cosmic web.
17:23It's like the universe has given supermassive black holes an umbilical cord.
17:29It's like an all-you-can-eat buffet right there.
17:34Supermassive black holes are hungry beasts. They feast on any matter that gets too close
17:40to them.
17:42Supermassive black holes are likely some of the most powerful objects in the universe.
17:47They can be anywhere between 100,000 to 10 billion times the mass of the sun.
17:54Supermassive black holes have been a nemesis for generations of scientists, not because
17:59of their fearsome nature, but because nobody knows how they grew so large, so early.
18:07I wish I knew where supermassive black holes came from. If I knew, I would have a Nobel
18:11Prize hanging around my neck, and I would wear it every single day.
18:16As someone who deeply loves supermassive black holes, whose career is based on studying supermassive
18:24black holes, it is very frustrating to not know where they come from.
18:29Regular stellar black holes are the collapsed cores of dead stars, ranging from three to
18:36thousands of solar masses. But supermassive black holes? Those are a different beast.
18:43Thirteen billion years ago, not enough stars had lived and died to build something as huge
18:50as a supermassive black hole.
18:53Now, the cosmic web offers scientists clues about the black hole conundrum.
19:01We now know supermassive black holes grow among the lattice of the young cosmic web,
19:08gorging on the hydrogen gas that travels along the filaments.
19:14At the same time, when the cosmic web is lighting up, supermassive black holes appear to be
19:20stealing star fuel from the young universe. You might think that would kill a growing
19:27galaxy. And yet, most mature galaxies have a supermassive black hole.
19:33They really dominate the physics of what happens in the centers of galaxies, and even how galaxies
19:38can evolve.
19:41We think these galactic monsters have been around from the start. How then did the web's
19:46young galaxies develop around supermassive black holes?
19:53Milky Way's supermassive black hole is called Sagittarius A-star. It's around 27 million
19:59miles wide and weighs in at just over 4 million solar masses.
20:07The environment around Sagittarius A-star is very dynamic. It can actually be a really
20:14hellish place. There's this accretion disk that's full of plasma seated to thousands
20:19of degrees. So you wouldn't necessarily think that that's a great place for star formation
20:25to happen.
20:28But that's exactly where astronomers decided to look. Using the Atacama Large Millimeter
20:35Array, or ALMA for short, scientists scanned the heart of the Milky Way for dense cores
20:41of gas and dust, stellar embryos.
20:46They found more than 800 within just a thousand light years of Sagittarius A-star, including
20:53more than 40 embryos with energetic jets blasting from their cores, the telltale sign of the
21:00birth of stars.
21:06It's really surprising to find those stars there. It's like hearing babies' cries from
21:11a wolf's den.
21:14It's not the place you would expect this to happen. But in fact, stars are forming
21:19there. Now, it's not as efficient as it is out here in the suburbs where things are quieter,
21:24but it works.
21:26Baby stars igniting and thriving around a supermassive black hole, the kind of hostile
21:33environment we know existed in the young cosmic web.
21:37Star birth is a key part of kick-starting young galaxies. This evidence suggests that
21:43star formation is more resilient than researchers thought.
21:49And they've developed a theory to explain it. Gas and dust race around the black hole
21:55in the accretion disk. Heated to incredible temperatures, plumes of gas break off and
22:01blast into space. The gas rapidly cools, collapses, and forms baby stars. These accretion disks
22:10are the most chaotic of stellar nurseries.
22:13You see this mechanism that you think is violently inhibiting star formation, and at the same
22:19time it's triggering the birth of new stars.
22:23Matter clumps at the cosmic web's intersections, feeding the supermassive black holes. Around
22:30them, stars burst into life, slowly building galaxies. This could be how our own Milky
22:38Way formed among the filaments of the young cosmic web.
22:44But new research suggests that growth in these baby galaxies requires murder and mayhem,
22:51and without them, we wouldn't exist.
22:58The infant universe is a dramatic place. Stars ignite, and stars die, even in the violent
23:12surroundings of supermassive black holes. Baby galaxies form with the cosmic web.
23:22But how do they grow? Scientists believe the critical factor is galactic turmoil.
23:29The universe does need to churn things up. You need to break some eggs to make an omelet.
23:34You need to introduce some chaos into your galaxy to rapidly form stars or grow black
23:38holes.
23:41Smashing things together is how the universe came to be.
23:46The Hubble Space Telescope discovers many distorted galaxies, twisted, battered, and
23:53torn, victims of violent collisions on a cosmic scale.
24:01Galaxies are never sitting quietly doing nothing. They're always undergoing change. They're
24:06constantly encountering and slamming into and colliding with and mixing with other galaxies.
24:14You can see images in Hubble of total car wrecks of galaxies that are trying to merge
24:18with each other.
24:22We know that galaxies collide now, but what about in the early universe, when the cosmic
24:28web was beginning to take shape?
24:32Astronomers study a strange galaxy named Himiko, born just 800 million years after the Big
24:39Bang. Three bright light sources suggest intense star formation. Detailed analysis
24:47reveals not one galaxy, but three baby galaxies, not yet fully formed.
24:56Scientists call these youthful star systems proto-galaxies. The trio that make up Himiko
25:04are in mid-collision.
25:07Future simulations of the early universe suggest proto-galaxies smash together with frightening
25:13regularity. These violent shake-ups trigger star birth.
25:21Proto-galaxies are rich in gas, and when they collide and merge, those gas clouds collide
25:25and collapse and form stars, sometimes at prodigious rates. And after a billion years
25:31or so, all of that structure forms and you get a formal galaxy.
25:36Picture the early universe, 500 million years after the Big Bang. It's smaller and more
25:42compact than today. Cosmic collisions are common.
25:48Imagine taking a bunch of cars and just letting them drive around in Nevada, where there's
25:51nothing but space, right? You're not going to get too many collisions. Now, squeeze them
25:56into a tiny little city block someplace and you're just going to have accidents everywhere.
26:00Well, it's the same thing with the universe. When the universe was younger, it was smaller
26:04and these proto-galaxies were everywhere. It was crowded. You were bound to get collisions
26:09between them back then.
26:12More and more baby galaxies form at the growing web's gas-rich intersections. A collision
26:18between small proto-galaxies might trigger modest amounts of star formation when regions
26:25of dense matter come together.
26:30But a merger involving proto-galaxies with rich reserves of gas can rev up the rate of
26:36stellar ignition, supercharging a growing galaxy.
26:41Gas-rich mergers can generate starburst galaxies where we see incredibly vigorous events of
26:47star formation.
26:50Astronomers think one such smash-up, around 10 billion years ago, kick-started the growth
26:55of the Milky Way. A group of stars called the Gaia Enceladus Cluster in the outer reaches
27:02of the galaxy behaves strangely compared to other stars around it.
27:07The stars in the Gaia Enceladus Cluster, they're different. They move differently. They act
27:14different. They're like kids from the next town over showing up at your school. You just
27:18know that they don't belong.
27:21The Milky Way had already largely formed, and then this massive cluster comes screaming
27:28in. It was a violent event that eventually ended up absorbing the stars from this cluster
27:36into the body of the Milky Way itself.
27:39Galaxies are built from these kinds of collisions.
27:44Less than a billion years after the Big Bang, the dark scaffold of the cosmic web begins
27:50to glow. Matter, channeled down the web's tendrils, creates dense clumps of gas. Even
27:58in the turbulent neighborhoods of supermassive black holes, stars burst into life. Baby galaxies
28:06collide and the young universe sparkles with light.
28:13But an important question remains. In the mayhem of the early universe, how did galaxies
28:20like our Milky Way survive and thrive?
28:26Galaxy evolution is very dynamic. Our understanding of galaxy evolution is very dynamic, and there's
28:32so much that we still don't know. There's a lot of different competing theories right
28:37now as to how galaxies grew into the galaxies that we see today. It's a huge open question
28:44and it's something that's a big deal in science right now.
28:48New research suggests that life and death in the cradle of the universe lay within the
28:55cosmic web.
29:0113.6 billion years ago, a proto-galaxy, the infant Milky Way, forms in the tendrils of
29:13the young cosmic web. Today, it bears the scars of many collisions. Each one could have
29:21torn it apart. So what controls if a young galaxy lives or dies?
29:28May, 2020. Scientists image a graceful galaxy that existed just 1.4 billion years after
29:37the Big Bang. Analysis of its light shows this is a starburst galaxy, pumping out newborn
29:46stars.
29:48Galaxies like our Milky Way are old and rather stately, and they don't form stars very rapidly.
29:53About the equivalent of the mass of the sun every year. Well, starburst galaxies, yeah,
29:59they form them a lot more quickly. Hundreds of solar masses per year. But BRI 1335-0417?
30:074,650 times the mass of the sun every year. It is blasting out stars.
30:16Some young galaxies in the early universe appear to be supercharged with star fuel.
30:22How can they grow at such an incredible pace? Scientists think the answer lies in the mysterious
30:31substance that's controlled the flow of gas since the beginning. The dark structure whose
30:37tendrils stitch the universe together. But exploring this cosmic network is no easy
30:45task. When it comes to dark matter, we're flying blind.
30:53May, 2021. An international team of researchers investigates dark matter in the local universe
31:01by observing its effect on the path of light. Gravity affects light. A massive object causes
31:11light to curve through space, even if that object is invisible, like dark matter.
31:19We can't see the dark matter directly, but we can see what it's doing to the light. It's
31:23stretching it. It's bending it. It's creating arcs in ways that would never happen unless
31:28the dark matter were there.
31:31Using an AI program, the team analyzes 100 million visible galaxies, looking for warped
31:38galactic light. Because the model is artificially intelligent, it gets better and better at
31:45finding dark matter.
31:49What's very clever about this kind of algorithm is that it's learning as it goes. It uses
31:55the information that it has to predict the existence of new structures.
32:02As the model teaches itself to see the dark matter behind the stars, it maps out new dark
32:08structures, never before seen highways between galaxies.
32:14There's a lot more filaments. There's a lot more intricacies. There's a lot more cosmic
32:18web there than what meets the eye. It's like, if you look how Manhattan is connected to
32:27the land around it, you can see all the bridges, but now we're also seeing the underwater tunnels.
32:34The new layout of dark matter reveals the local universe is a bird's nest of hidden
32:39channels feeding galaxies with gas.
32:45Cosmic structures seem to thrive at the cosmic web's most densely knotted intersections.
32:54Because multiple filaments are intersecting in those locations, and that is a location
32:59of very enhanced gravity relative to other locations, then material will be drawn in.
33:05So these galaxy clusters are likely feeding off the cosmic web.
33:11This connectivity could be the key to the rapidly forming galaxies in the early universe.
33:18But there's a catch.
33:21Sitting right at the densest regions of the cosmic web can be really good for galaxy growth.
33:26You have all of this gas being funneled in for new star formation, but being that plugged
33:32into the network isn't all good news.
33:35There is evidence that though the cosmic web gives life, it can also take life away.
33:43Scientists studying some of the universe's most heavily connected galaxies found something
33:47unexpected, plummeting rates of star birth.
33:52In some ways it's a little bit counterintuitive, right? If these nodes are meeting grounds
33:57for all of this gas, right, why aren't you forming more stars there?
34:03One explanation? In the all-you-can-eat buffet of the cosmic web's matter-rich junctions,
34:09a young galaxy might overindulge.
34:14As the cosmic web funnels more matter towards a junction and its growing galaxies, the gas
34:20influx doesn't just boost star formation, it fattens up the supermassive black hole
34:27at the galaxy's core.
34:29For a young galaxy, that's dangerous. Because when this monster overeats, it produces high
34:36energy jets and belches out super hot wind.
34:42These black holes radiate tremendous amounts of energy when they grow, and that radiation
34:48can slam into the material around them in the galaxy and blow it all out of the galaxy,
34:52launch it away, or heat it up to super high temperatures.
34:56Star formation requires stuff. So if you blow that stuff away, how are you going to
35:01form a star?
35:05And what's left behind would be what we call a quenched galaxy that basically can't form
35:10any new stars.
35:11The researchers found that although connectivity within the cosmic web can boost galactic growth,
35:18it was the super-connected galaxies that died the quickest, choked and stunted like over-watered
35:24plants.
35:27Perhaps our Milky Way got lucky.
35:32You could say that the Milky Way galaxy is sort of in this Goldilocks zone of galaxy
35:36formation. It's been receiving enough gas over time that it's been able to keep up with
35:41its star formation, but not so much gas that its central black hole has been fed enough
35:47that it would clear the galaxy out of gas.
35:51The cosmic web determined if galaxies lived or died. Its construction project brought
35:57order to chaos.
36:01The cosmic web is the architect, the engineer, the builder, the construction worker, even
36:07the interior designer of the cosmos.
36:12But now work is shut down. An invisible force threatens to tear apart the very fabric of
36:19the cosmic web. What does this mean for galaxies and for us?
36:36The cosmic web brought order to the early universe. The gravitational attraction of
36:42its dark scaffolding helped build galaxies and fueled their development. But growth tops
36:48out at the level of galaxy clusters. Nothing bigger will ever form.
36:56Something has stopped the formation of structure in our universe.
37:02To understand what's going on, we need to return to the Big Bang and the formation of
37:07the cosmic web.
37:1113.8 billion years ago, the universe sparks into life. A tiny ball of pure energy cools
37:21and expands. The energy transforms into regular matter and dark matter. But another force
37:31appears at the same time. Dark energy.
37:39Dark energy, as far as we understand it, which is not much, has always been here. It's always
37:45been a part of the universe, but it's been silent in the background.
37:51Dark energy is everywhere. It's over here. It's over there. It's between you and me.
37:56It's absolutely everywhere.
37:59One theory is that dark energy never formed, that it's just a constant in the laws of physics.
38:04It has always been there and always will be.
38:08Some physicists believe that dark energy is simply the force of emptiness.
38:15People used to take for granted that space was empty, vacuum. But the discovery of dark
38:22energy has made some people wonder if space is actually more of a substance and that space
38:28also might have pressure that causes things to push apart. So, yeah, whatever space is,
38:35it might be more interesting than we thought.
38:38Dark matter dominates the young universe. But as the dark scaffold of the cosmic web
38:45grows, it sows the seeds of self-destruction. As the network of matter takes shape, pockets
38:54of emptiness form between the filaments, cosmic voids. In these expanding, hollow spaces,
39:04dark energy grows.
39:07The weirdest thing about dark energy is that it has constant density. Constant density
39:12means the more volume you have, the more dark energy you have. So the larger the voids get,
39:21the more dark energy they contain.
39:24Dark energy pushes against the cosmic web, opening up huge chasms in the architecture
39:31of the universe. Five billion years ago, dark matter s strength of attraction is finally
39:37overwhelmed. Like bridge cables in a hurricane, the cosmic web s filaments stretch and snap
39:45and the universe s substructure fails. Galactic construction freezes as the universe expands.
39:54But darker times are ahead for the cosmic web.
40:00As time goes on, not only is it expanding, but this expansion gets faster and faster
40:05and faster.
40:08As the dark energy in the voids increases, the entire structure of the cosmic web begins
40:13to break up.
40:17The effects of dark energy will get stronger and stronger with time, until the very fabric
40:23of space-time gets torn apart.
40:26This isn t a superhero movie. The bad guy wins.
40:30The future of the cosmic web is looking bleak. Ultimately, it s going to be a cold, lonely
40:38universe.
40:40Our closest galaxies will accelerate away until they re just tiny pinpricks of light.
40:46Then the universe will go dark again.
40:51Everything will fade out. So the universe started with a bang, but it will die with
40:56a whisper.
40:59The cosmic web transformed the universe from a hot mess to a sparkling structure. It gave
41:06birth to billions of galaxies and us. Without it, space would be a much less interesting
41:14place.
41:15This giant structure, the largest thing that we know of in the universe, is responsible
41:20for nourishing the galaxies, creating the stars, making the conditions right to form
41:25life. We would not be here talking right now if it were not for this cosmic web.
41:32Understanding the cosmic web is understanding dark matter, is understanding dark energy,
41:38is understanding our past, is understanding our future.
41:43Really everything that we know about how the universe works is directly tied to the cosmic
41:47web.
41:49It's amazing to think that the overall structure of the universe that we witness today began
41:55in the earliest times of the universe and has yielded beings like ourselves who can
42:01now discover it and ponder about its existence. That's pretty dope.