How the Universe Works - S01E02 - Black Holes
Category
📺
TVTranscript
00:00The universe is home to real monsters.
00:04We can't see them, but we know they're out there.
00:07You really can't get anything bigger or stronger or scarier than a black hole.
00:13Black holes consume planets and stars.
00:17Anything that gets too close.
00:20Black holes give physicists no end of headaches, because they break all the rules.
00:25But they rule the universe.
00:30They are center stage.
00:34We now know they dominate the evolution of the universe itself.
00:59Black holes are the most mysterious objects in our universe.
01:04Their gravity is absolute.
01:10Nothing can escape.
01:13They can suck in whole galaxies.
01:18Black holes used to be science fiction.
01:21Now, we know they're real.
01:24When I was a PhD student, people used to giggle when you hear about black holes.
01:28They're like unicorns, mythical creatures.
01:31We called this the giggle factor.
01:33People would say, beam me up, Scotty.
01:35Well, no one is laughing anymore.
01:40So they're not science fiction.
01:42Even though we've never landed on one,
01:44we have enough evidence to know that they're really out there.
01:52This image might not look like much to you and me,
01:55but to a scientist, it's proof that black holes exist.
02:00It's an actual movie of a black hole devouring a star in the constellation of Aquila.
02:07Black holes are messy eaters.
02:09The red spots you see are gas that's being spit out of the hole into space.
02:16Eventually, over the next million years,
02:19this star will be eaten alive and disappear.
02:32A black hole is pretty much the end point of everything.
02:35It's the end point of a star. It's the end point of matter.
02:37It's the end point of energy. It's the end point of gravity.
02:41I mean, that's really it. That's the top of the scale.
02:49Although they have the power to destroy like nothing else in the universe,
02:54black holes also help build galaxies,
02:58a vital part of the great cosmic machine.
03:02Some astronomers think they could even be gateways to parallel universes.
03:13We are now entering the golden age of research in black hole physics.
03:19They could be the key to understanding the birth of the universe,
03:22its formation, and then its death.
03:31Black holes really represent, in one sense, the frontier of modern astronomy.
03:34They're changing our ideas about how galaxies form and, indeed, how the universe works.
03:41Their power comes from one of the primary forces in nature, gravity.
03:49I teach astronomy.
03:51We teach our students that the fundamental principle of gravity is gravity sucks.
03:58It keeps our feet on the ground and our planet orbiting around the sun.
04:06But in a black hole, the force of gravity is off the charts.
04:11So strong, it sucks in anything nearby.
04:15It can even bend the light from distant stars.
04:20And if that light gets too close, the black hole swallows it.
04:26Imagine a black hole as a waterfall.
04:30Gravity is the river flowing toward the falls and a beam of light, the kayak.
04:36Upriver from the waterfall, the current is weak.
04:39The kayaker can paddle against it and get away.
04:42But closer to the waterfall, the current is stronger and the kayaker struggles to escape.
04:51The edge of the waterfall is like the edge of a black hole.
04:57No matter how strong the kayaker is, he's going down.
05:02It's the same in space.
05:04The way black holes are really devastating is because when you get close to them, the gravity gets super strong.
05:16So strong that they eat light.
05:19That's why black holes are black.
05:27A black hole is like a roach motel.
05:30Everything checks in, nothing checks out.
05:37Anything that gets too close is doomed.
05:40Planets, stars, even whole solar systems.
05:50And don't think this is some faraway phenomenon.
05:54Black holes are on the loose right here in our own cosmic neighborhood.
05:59We now know there are wandering nomads throughout the Milky Way galaxy.
06:04Vagabonds throughout the galaxy where black holes can come up right behind you and perhaps gobble you up and they won't even burp.
06:14If one ever comes close, watch out.
06:17If a black hole found its way into our solar system, it would rip us apart.
06:23Any kind of black hole that could pass through the solar system would be pulling on all the planets harder than the sun does.
06:30And so it's just going to totally disrupt the gravitational balance of the solar system.
06:35The black hole would literally tear planets from their orbits and smash them into ashes.
06:41It would tear planets from their orbits and smash them into each other.
06:53It's just an epic disaster. It's a bull in a china shop.
07:01If it got close enough to, say, Jupiter, it could actually pull the moons of Jupiter away from the planet itself.
07:09It would just be flinging planets left and right everywhere as it whipped through the solar system, leaving disaster in its wake.
07:22If a black hole approached Earth, all that gravity would rip asteroids from their orbits and hurl them toward our planet.
07:39The Earth's surface would become an inferno. It would be the beginning of the end.
07:51First it would swallow up the atmosphere, then the planet itself.
08:02Destroying an entire solar system is nothing to a black hole.
08:06But it's more than just a big, empty, sucking piece of space. It's incredibly heavy.
08:15To get an idea of just how heavy and dense a black hole is, imagine the Earth.
08:21Now, start to crush it.
08:26And keep crushing until it's packed so tight even the atoms themselves collapse.
08:37When the Earth crushes down to just two inches across, that's the density of a black hole.
08:44It would be the size of a golf ball, yet weigh the same as the Earth, with the same amount of gravity.
08:53What can make something that small, that dense, and that powerful?
09:00We don't have external forces, large pistons in the universe, to create black holes.
09:06The only way the real black holes in the universe form is if gravity can do the job itself.
09:12There is only one place in the universe that generates that much gravity, and it's inside the largest stars.
09:21When massive stars, ten times heavier than our sun, die, gravity crushes them, creating a huge explosion, a supernova.
09:37But some stars are even bigger than that.
09:43These supermassive stars weigh 100 times more than our sun, and have 100 times more gravity.
09:51When one of these stars dies, it sets off the biggest explosion in the universe, a hypernova.
10:07This is the birth of a black hole.
10:16Our universe is full of stars.
10:21At the end of their lives, some die quietly.
10:26Others go out in spectacular numbers.
10:30At the end of their lives, some die quietly.
10:34Others go out in spectacular explosions.
10:38And some give birth to black holes.
10:44If you have a star, a supermassive star, that's 100 times the mass of the sun, at the end of its life, the core runs out of fuel.
10:52There's nothing left to hold it up, and the core collapses down into a black hole.
10:57When that happens, the enormous gravity generated at the heart of supermassive stars runs wild.
11:08This is the dying star VY Canis Majoris.
11:13It's more than a billion miles across.
11:16Like all stars, it's a giant nuclear fusion reactor, pumping energy outward.
11:23At the same time, the star's extreme gravity crushes inward.
11:29For a few million years, fusion and gravity are locked in standoff.
11:35But when the star runs out of fuel, fusion stops, and the stalemate begins.
11:42Gravity wins.
11:47In a millisecond, the core shrinks to a fraction of its original size, and a baby black hole is born.
11:56Immediately, it starts to cannibalize what's left of the star.
12:01As matter swirls into the black hole, it gets incredibly hot.
12:05And there are magnetic forces and frictional forces, and it's just a whirlwind.
12:09And there are magnetic forces and frictional forces, and it's just a witch's brew.
12:13A nightmare, what's going on right above the surface of the black hole.
12:17The new black hole in the middle keeps feeding on the body of the star around it.
12:22It eats the gas so fast, it chokes and coughs, blasting out huge beams of energy.
12:34They basically eat their way out from the star.
12:36This happens in milliseconds.
12:39It happens before the rest of the star even knows the core is gone.
12:43And so basically, the star is dead before it hits the ground.
12:51Finally, the star explodes.
12:54In one second, it blasts out a hundred times more energy than our sun will produce over its entire life.
13:06What's left is a new black hole and two jets of energy hurtling through the universe at the speed of light.
13:16These jets are called gamma ray bursts.
13:20They're incredibly energetic events.
13:23In terms of raw energy and power, gamma ray bursts are second only to the Big Bang itself.
13:31Most of them last only a few seconds, and they fry anything in their way.
13:36They're so intense that if there was a gamma ray burster in the region of our galaxy near our solar system,
13:42it could literally vaporize the entire planet.
13:45Fortunately, most gamma ray bursts occur outside our galaxy.
13:52And if you think about it, if you think about it,
13:56if you think about it, if you think about it,
14:00if you think about it,
14:02they occur outside our galaxy.
14:12But they tell us something important about black holes and how our universe works.
14:19What we were seeing every time a gamma ray burst went off was basically the birth cry of a black hole.
14:26By counting gamma ray bursts, astronomers can figure out how many black holes are being created.
14:33In 2004, NASA launched the SWIFT probe to scan the universe for gamma ray bursts.
14:40Five, four, three, two, one.
14:45We have ignition and we have liftoff of NASA SWIFT spacecraft on a mission to study and understand gamma ray bursts throughout the universe.
14:55This is the most powerful gamma ray burst SWIFT has detected so far.
15:08The flash of light announces the birth of a new black hole on the other side of the universe.
15:18SWIFT can only look at a fraction of what's out there.
15:26Still, it detects at least one gamma ray burst every day.
15:34That discovery rocked astronomy to its foundations.
15:41We once thought that black holes like unicorns could never be found.
15:46We now believe that there are perhaps billions of black holes in the night sky.
15:51When we look around our galaxy and other galaxies, it's clear that the universe is full of powerful black holes.
15:59Finding black holes is one thing.
16:02Figuring out how they work, that's a whole different ballgame.
16:05The only way to find out is to visit one.
16:08You'd have to take a spacecraft across the vastness of space just to get close to it.
16:14Then you'd have to go inside the black hole.
16:17There, you'd find a place where reality breaks down and time stands still.
16:26There are billions of black holes in the universe.
16:30We can detect them with telescopes and satellites.
16:34But we don't actually know what they're like up close.
16:38It's a long way off, but scientists are already speculating about a mission to a black hole.
16:44A one-way trip to the most dangerous place in the universe.
16:53Originally, physicists were horrified at the idea of black holes.
16:58They wanted to banish them because the laws of physics as we know them
17:03seem to break down at the instant of a black hole.
17:07Time stops.
17:09Gravity becomes infinite.
17:11This is a nightmare.
17:15Obviously, we can't send humans anywhere near a black hole.
17:19But a robot? Well, sure.
17:22A robotic probe could transmit data back just before it goes over the edge.
17:28That edge of a black hole is called the event horizon.
17:32It's the edge of time and space.
17:35At least, in the universe we know.
17:37We call the event horizon an event horizon
17:40quite simply because it separates space into two regions.
17:45It's not a physical surface.
17:47You might not even notice it if you were falling through it.
17:51But ultimately, once you're inside of it, you're doomed.
17:54As you approach the event horizon, gravity gets stronger
17:58and very strange things start to happen.
18:02As you fall into a black hole,
18:04your feet are closer to the black hole,
18:07and so the gravity they feel is stronger.
18:10Your head is not quite as close,
18:13and so the gravity it feels is less.
18:16And basically what happens is you get stretched out.
18:19Your feet are being pulled much harder than your head,
18:22and you're like a piece of taffy being pulled between two strong people.
18:27As you get thinner and thinner and thinner,
18:30as you get closer and closer and closer,
18:32you're undergoing a process we call spaghettification,
18:35because you're basically turned into a long, thin tube of pasta.
18:44Gravity would stretch our robotic probe to the limit,
18:47then rip it apart.
18:57But imagine if the probe was strong enough to survive.
19:00And keep going.
19:05As it gets close to the event horizon, everything goes crazy.
19:11Gravity is so extreme, it stops time.
19:16We think of time as being endless.
19:19However, in a black hole, in some sense, time stops.
19:25This sounds like it's nuts,
19:27but that's the way it works.
19:30It's in the math.
19:33It's actually woven into the fabric of the universe itself.
19:36If you were to watch from a distance,
19:39the robot probe would seem to slow down
19:42as it gets closer to the black hole.
19:45Then it would appear to stop completely.
19:48The whole process might just take a brief moment,
19:51but from the outside, you appear to freeze and fall ever more slowly.
19:55You actually can never observe an object
19:58fall all the way through the event horizon.
20:01It literally freezes at the surface,
20:04because its clock is going infinitely slowly compared to yours.
20:09In reality, the probe hasn't stopped at all.
20:12It keeps going and crosses the event horizon.
20:19If the probe points its cameras backwards
20:21towards the entrance of the black hole,
20:24it'll see light being sucked in.
20:29If it points the camera forward,
20:32at first it sees only black.
20:35But as it moves toward the heart of the black hole,
20:38it encounters the most bizarre place in the universe.
20:44The black hole's immense gravity
20:47pulls everything down to an unimaginably small mass.
20:49Scientists call it the singularity.
20:54We really just don't know
20:57what happens at the center of the black hole.
21:00The densities are so great
21:03that the laws of physics break down as we know them.
21:06A singularity is a point of infinite gravity
21:09where space and time become meaningless.
21:12Now, that is ridiculous.
21:15A singularity is basically a word
21:17for saying, I don't know.
21:20It's a word for saying, I'm clueless.
21:26Even now, scientists can't really answer the question,
21:29what is a black hole?
21:32It's upsetting a little bit to think that
21:35there are objects out there that are breaking the laws of physics.
21:38There must be bigger laws that are being used by these black holes,
21:41that are being obeyed by these black holes
21:44that we just don't understand yet.
21:48Okay, so the one thing we do understand
21:51is that black holes are born from dying stars.
21:57And most are small, around 20 miles across.
22:04But now, scientists have discovered
22:07that some black holes are much bigger.
22:10They're called supermassive black holes.
22:13They're the same size as our entire universe.
22:15They're the same size as our entire solar system.
22:18And one of these monsters
22:21lies at the heart of our own galaxy.
22:29Our solar system lies in the Milky Way galaxy.
22:33It's made up of billions of stars,
22:36including our sun.
22:40All revolving around a mysterious region
22:42right at the center.
22:46Children ask the question,
22:49if the moon goes around the earth,
22:52the earth goes around the sun,
22:55then what does the sun go around?
22:58It's a good question, and astronomers ask the same thing.
23:01Maybe there was something going on at the heart of the Milky Way.
23:04Perhaps a black hole at the very center.
23:08But because we can't actually see a black hole,
23:10the best they could do
23:13was look for telltale signs.
23:16Using infrared telescopes,
23:19they looked at the middle of the galaxy
23:22and discovered a densely packed swarm
23:25of millions of stars.
23:28But they couldn't see what was at the center.
23:35One team has spent 15 years
23:37looking for clues.
23:44High above the clouds on Mauna Kea in Hawaii,
23:47the giant Keck telescope
23:50has the power to see right through
23:53to the center of the Milky Way.
24:02The region which we have to study
24:04to prove that there's a black hole
24:07is incredibly small.
24:10It is absolutely the case of looking for a needle
24:13in a haystack,
24:16except we know exactly where the needle is.
24:19Andrea Ghez has spent countless nights
24:22scanning the center of the galaxy
24:25for signs of a black hole.
24:28To be able to do this experiment,
24:31one has to be able to see the stars
24:34very accurately.
24:37And this would be equivalent to me in Los Angeles
24:40looking at you in New York and seeing you
24:43be able to move your finger like this.
24:58As the Keck kicks into action,
25:01a laser beam detects tiny disturbances
25:04that would distort the image.
25:09Motors then adjust the huge 30-foot mirror
25:12to compensate.
25:15The image is clear enough
25:18to track the stars at the heart of our galaxy.
25:23Ghez has taken thousands of images
25:26over the last 15 years.
25:29And what they reveal is amazing.
25:31The stars at the center of the galaxy
25:34are moving at millions of miles an hour.
25:44The center of the galaxy is a very extreme environment.
25:47The speeds with which stars move
25:50is much higher than anywhere else in our galaxy.
25:53And that is absolutely the signpost of the black hole.
26:02They look like tiny planets
26:05racing around an invisible sun.
26:08But they're not planets.
26:11They're stars.
26:14It takes a lot of gravity to swing huge stars around
26:17in such fast, tight orbits.
26:20There's only one thing in the universe
26:23with that much pull.
26:26A supermassive black hole.
26:29Watching these things shows the presence
26:32of a 4 million times the mass of our sun black hole
26:35located right at the heart of our galaxy.
26:38It is a huge discovery.
26:41Everything in our galaxy, including our own solar system,
26:44orbits around a supermassive black hole.
26:49But the Milky Way isn't the only galaxy
26:52with a black hole in the middle.
26:55There are supermassive black holes
26:58in all the galaxies in the universe.
27:01The Andromeda Galaxy is our closest neighbor.
27:04It circles around a supermassive black hole
27:07weighing 140 million times more than our sun.
27:11Other galaxies, like this one, M87,
27:15have black holes weighing as much as 20 billion suns.
27:22How do black holes get so big?
27:25And what are they doing at the center of galaxies?
27:29For answers, we have to go back
27:32nearly 14 billion years
27:35to the beginning of the universe.
27:39Back then, the universe was filled
27:42with clouds of gas from the Big Bang.
27:45In some places, the gas was thick enough
27:48for millions of stars to form.
27:51Most of these new stars were supermassive.
27:55They burned hot and fast,
27:58and then exploded, creating lots of black holes.
28:12The early universe was a wild and crazy place
28:15where huge regions of mass were collapsing,
28:17catastrophically producing black holes.
28:20And in fact, the early universe
28:22might have been full of emerging black holes everywhere.
28:28Gravity pulled many of them together.
28:31All over the early universe,
28:33they merged, creating larger and larger black holes.
28:40Over hundreds of millions of years,
28:43each black hole grew,
28:44producing stronger gravity
28:46and pulling in more and more gas.
28:49New stars were born from the gas,
28:51forming primitive galaxies.
28:56But the black hole kept on sucking in gas
28:59until it could take no more,
29:01igniting the most powerful flamethrower in the universe.
29:15A young galaxy is a vast cluster of stars,
29:19stars that formed from clouds of gas.
29:28At the center of the new galaxy
29:30is a young, supermassive black hole,
29:33feeding on the gas,
29:35getting bigger and bigger.
29:37If you can imagine
29:39when a galaxy is very small,
29:40and still forming,
29:42there's a supermassive black hole
29:44forming at the core,
29:46and the gas is still falling into it
29:48and still forming the galaxy.
29:50Well, near that central black hole,
29:52things are getting very hot.
29:54That material's heating up.
29:56Gas is speeding into the black hole,
29:59but it overloads,
30:01and there's no room
30:03for all that excess hot gas.
30:07It has to be stopped.
30:09It has nowhere to go but out.
30:13It's blasted into space
30:15in huge jets of energy.
30:22Each jet is 20 times wider than our solar system
30:26and shoots clear through the galaxy.
30:31The supermassive black hole
30:33has ignited a quasar.
30:35Quasars are literally
30:37the brightest objects in the universe.
30:39They're so intense,
30:41they can outshine an entire galaxy.
30:43This is a real photograph
30:45of a real quasar
30:47in the galaxy N87,
30:4950 million light-years away.
30:56Quasars blast away
30:58huge quantities of gas
31:00from the surrounding galaxy.
31:05The equivalent of 10 Earths every minute.
31:13When you heat up a gas,
31:15it tends to expand,
31:17and it blows outward.
31:19And it's sort of like a wind,
31:21but on a huge scale.
31:23And you get a black hole wind,
31:25gas blowing out from the black hole.
31:27Black holes suck gas in.
31:29Quasars blow it out.
31:31But eventually,
31:32there's no gas left to make stars,
31:34and the galaxy stops growing.
31:36So we think that the eventual size
31:38that a galaxy can achieve
31:40depends on the black hole in its center.
31:43The two are tied together.
31:46With no gas left to feed on,
31:48the quasar jets shrink and die.
31:52What's left
31:54is a supermassive black hole
31:56at the center of the galaxy
31:58with a whole lot of young stars,
32:00just like our Milky Way
32:02back when it was young.
32:05Early on in the history of the Milky Way,
32:07when it was a young galaxy,
32:09we were probably a quasar.
32:11Probably every big galaxy was a quasar
32:13when it was young.
32:15But right now, we're old enough
32:17that the galaxy has quieted down.
32:20Now, astronomers are looking for quasars,
32:23the secret to finding more black holes
32:26and figuring out how they work.
32:30The Chandra Observatory
32:32has a space telescope
32:34that can detect the powerful X-rays
32:36quasars send out.
32:40It's found thousands.
32:43These remarkable images
32:45show quasars of all shapes and sizes
32:48firing out into space.
32:54Each one is a signpost
32:56for a young galaxy
32:58with a new black hole at its center.
33:03These quasars will eventually calm down
33:06as their galaxy matures
33:08and takes its final shape.
33:11I guess the universe is a lot like people,
33:13active when they're young,
33:15a little bit quieter and more relaxed
33:17when they get older.
33:20We now know that supermassive black holes
33:22and the quasars they create
33:24control galaxies.
33:27Black holes are central
33:29to understanding how galaxies form.
33:30They're a key to understanding
33:32how they evolve with time.
33:34So, in fact, rather than being obscura,
33:36they're fundamental to our understanding
33:38of our galaxies and our universe.
33:41The only way to find out more about black holes
33:44is to get a good look at one.
33:46And since an up-close visit is,
33:48well, not a good idea,
33:50astronomers are trying to devise a way
33:52to take a picture of the supermassive black hole
33:55at the heart of our own galaxy.
33:57To get it, they'll need a telescope.
33:59As large as Earth itself.
34:15There's a supermassive black hole
34:17at the center of the Milky Way.
34:23It's hidden by a dense cluster of stars
34:25circling the Milky Way.
34:28It's calling the heart of the galaxy.
34:33But soon, we hope we'll be able to see it.
34:39Seeing is believing.
34:41It would be spectacular
34:43if we can go right up there,
34:45nose to nose,
34:47with the event horizon of the black hole
34:49at the center of the Milky Way galaxy.
34:51And that's the Holy Grail.
34:55A supermassive black hole
34:56lies hidden at the center of most galaxies.
34:59We only know they're there
35:01because the stars around them
35:03are drawn in at millions of miles per hour.
35:06But there might still be a way
35:08to take a picture of the very edge
35:10of the black hole,
35:12the event horizon.
35:14Shep Dolman and his team
35:16are trying to capture an image
35:18that shows its outline.
35:20We're essentially looking for the shadow
35:22or the silhouette of the black hole
35:24within this cloud of gas
35:26swirling around it.
35:29This technique that we're exploiting
35:31is the best hope, I think,
35:33we have to actually image
35:35a region of the universe
35:37which has hitherto been
35:39completely invisible to us.
35:41Optical telescopes can't see
35:43the black hole directly.
35:46But the glowing, superheated gas
35:48surrounding the black hole
35:50sends out radio waves
35:52that can be used to make an image.
35:56Huge radio telescopes
35:58pick up these signals from space.
36:00The antenna will move in azimuth
36:02and elevation.
36:10This one at the MIT Observatory
36:12near Boston
36:14is more than 100 feet wide.
36:16It's big enough to detect
36:18very faint radio emissions
36:20from the black hole
36:22in our own galaxy,
36:2425,000 light years away.
36:26But it's not nearly big enough
36:28to capture an image.
36:31We need to take multiple copies
36:33of these telescopes,
36:35place them around the world
36:37to create a virtual telescope
36:39as large as the Earth itself.
36:41Dolman's team will link up
36:43radio telescopes around the globe
36:45from Hawaii to Chile
36:47to Africa.
36:54When the whole network
36:56is built,
36:58they'll have a virtual dish
37:00over 10,000 miles across
37:02with 500 times the power
37:04of a single telescope.
37:09They think it'll be powerful enough
37:11to take a picture
37:13of the event horizon
37:15of the supermassive black hole
37:17at the center of the Milky Way.
37:20They're already picking up signals
37:22from the dark heart of our galaxy.
37:24When we saw the first detection,
37:26it was a moment where I just
37:28looked at the computer screen
37:30and said to myself,
37:32my God, we've done it.
37:34We've actually seen something
37:36that's so small
37:38that it has to be coming
37:40from right around the event horizon.
37:42The signals are still too weak
37:44to give a complete picture,
37:46but Dolman expects the images
37:48to improve as more telescopes
37:50come online over the next few years.
37:52Eventually, the outline
37:54of the black hole itself
37:56should emerge.
38:00But even a picture can't compare
38:02to witnessing it for yourself.
38:07In the distant future,
38:09we may have the technology
38:11to actually enter
38:13and pass through a black hole
38:15and maybe even survive the journey.
38:22Then we might finally
38:24answer the question,
38:26what lies at the heart
38:28of a black hole?
38:32Some scientists believe
38:34we could use black holes
38:36as a kind of portal
38:38with the potential for travel
38:40across the universe.
38:42This is still very speculative,
38:44but the mathematics seem to indicate
38:46that as you fall through a black hole
38:48that you don't simply die,
38:49you fall right through
38:51a wormhole,
38:53which is a gateway,
38:55a shortcut through space and time.
38:57Perhaps we could simply
38:59rocket across the universe
39:01through a subway system
39:03that we call a black hole.
39:06If black holes are shortcuts
39:08through space and time,
39:10it could turn one of
39:12the coolest ideas
39:14from science fiction
39:16into reality.
39:17Time travel is possible,
39:19but not very practical.
39:21You see, the energy source,
39:23the material that you need
39:25to keep the throat
39:27of a wormhole open,
39:29is something so exotic
39:31that we cannot produce it
39:33in the laboratory.
39:35But if you could,
39:37it might be possible
39:39to exploit the power
39:41of black holes
39:43to visit yesterday.
39:45Perhaps our descendants
39:47or somebody knocks on your door
39:49and claims to be
39:51your great-great-great-great-great-granddaughter.
39:53Don't slam the door.
39:58Black holes might even be
40:00gateways to other universes.
40:02On the other side of a black hole,
40:04there could even be
40:06a Big Bang.
40:11As a black hole collapses
40:13and matter falls into it,
40:15perhaps the matter is blown out
40:17of sight in a white hole.
40:19Doesn't that sound like the Big Bang?
40:25If a Big Bang
40:27is just the flip side
40:29of a black hole,
40:31this could be how
40:33our own universe was born.
40:35If you look at the equations
40:37for a black hole
40:39and put in the parameters
40:41of the universe,
40:43the mass of the universe,
40:45the size of the universe,
40:47in other words,
40:49we could be inside
40:51an event horizon.
40:53Perhaps we are actually
40:55living inside a black hole.
40:57Every black hole
40:59might be the origin
41:01of an entirely separate universe.
41:03If that's true,
41:05there could be
41:07billions of universes out there,
41:12each one full of stars,
41:14planets,
41:15life.
41:17Whatever we figure out later,
41:19we know now
41:21that black holes are everywhere.
41:23They're bigger in size
41:25and more critical
41:27to the evolution of the universe
41:29than we ever imagined.
41:41Literally,
41:43our understanding of the universe
41:45that's visible to telescopes
41:47has been profoundly affected
41:49by our realization
41:51that black holes are everywhere.
41:55Once upon a time,
41:57people thought that black hole physics
41:59was too fantastic to be true.
42:02And now they are center stage.
42:04We now know they dominate
42:06the evolution of the universe itself.
42:10When I was a kid,
42:12black holes basically played a part
42:13in science fiction.
42:15It was always something to avoid,
42:17your spaceship,
42:19you try to get around them
42:21before you get drawn in.
42:23But what we've learned since then
42:25is that black holes play a huge role
42:27and a huge number of roles
42:29in the universe.
42:31It's not an exaggeration to say
42:33that if black holes did not exist,
42:35we wouldn't be here.
42:37We literally owe our existence
42:39to black holes.
42:44There's still much more
42:46to be discovered
42:48about the mysterious objects
42:50called black holes,
42:52the masters of the universe.