We don't yet know where the edge of the universe is or what happens there; but thanks to cutting-edge technology and new discoveries, experts might finally reveal the secrets of the phenomena that can be found in deepest reaches of the cosmos.
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LearningTranscript
00:00Islands have edges.
00:08Planets have edges.
00:12Even galaxies have edges.
00:16But what about the universe?
00:20As explorers, as curious humans that we are,
00:25we're obsessed with boundaries and limits.
00:28And we want to know, does the whole thing, the universe, have a limit?
00:34Does the universe have an edge?
00:35Well, the answer is yes and no.
00:39It depends on what you mean by edge.
00:42The edge of what we can see?
00:45The edge of where we can go?
00:49Or the edge of reality itself?
00:52Looking out to the edge of the universe is tremendously important to understand our place in the universe itself.
01:00We're talking about our universe.
01:02We're talking about the thing that we exist within, the most fundamental thing there is.
01:06We're driven to understand it.
01:07There is always a desire to push the knowledge to the edge.
01:12So, can we ever find the edge of the universe?
01:17The Hubble Space Telescope turned toward a dark patch of sky in the constellation Ursa Major.
01:29It captured an image of an indistinct blob of light.
01:50The glow is from a distant galaxy called GN-Z11.
02:02The most distant galaxy we've ever observed.
02:08But, is this the edge of the universe?
02:11The universe all around us is filled with galaxies.
02:16So, it's kind of natural to say, would there be a final galaxy if you traveled far enough away?
02:21Would you finally be at the very last galaxy in the universe looking out into empty space?
02:28That's a difficult question to answer.
02:33Because there's a limit to how far we can see.
02:36It all comes down to the speed of light.
02:40And the age of the universe.
02:44The key to understanding the edge of the universe is that light travels very, very fast.
02:51But not infinitely fast.
02:53It takes time for it to get from one place in the universe to the other.
02:57You open the curtains, light fills the room.
02:59It doesn't seem to travel at all.
03:01But over the vast distances of the universe, you actually notice this travel time.
03:07Even the sun, 93 million miles away, the light takes eight minutes to get to us.
03:13When you look out at the stars, we start to think of distance in terms of light years.
03:17Because it takes years for the light to get from those stars to us.
03:21And then when you look at galaxies, then you're talking about millions or billions of light years.
03:25When we look at the light from galaxy GNZ 11, we're seeing light emitted 13.4 billion years ago.
03:37You can't really even find a galaxy too much farther away than that, because the universe is only 13.8 billion years old.
03:50And it takes a certain amount of time for galaxies to even form.
03:52So we're not going to find too many more galaxies farther away than this.
03:57If things are far enough away, there is no way that light can get to us in the age of the universe.
04:02What this means is there's a hard limit to the edge of the universe that we can see.
04:06And this is set by the age of the universe.
04:11GNZ 11 sparked into life early in the history of the universe, just 400 million years after the Big Bang.
04:21Before that, there were no stars to send out light.
04:25If you look in any direction at all, you get all the way back to when there were no stars, no galaxies, nothing but very, very hot gas.
04:35And that sort of forms a shell around us.
04:38That outer shell is the cosmic microwave background.
04:44It is the oldest light in the universe.
04:48The echo of the birth of the universe, the Big Bang.
04:52The edge of our universe, the very furthest thing that we can see, is one of the earliest relics of the formation of the universe itself.
05:02That is the cosmic microwave background.
05:05We call this the edge of our observable universe.
05:11So we have an observable universe.
05:13But beyond that, even if there are things out there, there's no way we can see them.
05:17Because the light just could not have gotten to us by now.
05:20As the name states, the observable universe is simply the part of the universe we can see.
05:30We can think of the observable universe as sort of like a spotlight, centered on wherever you're standing right now.
05:38And you can see to the edge of your spotlight and not beyond.
05:42But if you move a little bit to the left, a little bit to the right, your observable universe actually moves with you.
05:50For someone living in galaxy GNZ 11, a totally different part of the universe would be observable.
06:01So that distant galaxy is at the edge of our observable universe.
06:06And we are at the edge of their observable universe.
06:13We have different spotlights.
06:15One of the wonderful things to think about is that there are other spheres around other galaxies.
06:19There are other aliens looking up into the sky tonight, wondering what the true extent of the universe is.
06:24The true extent of our universe doesn't end with galaxy GNZ 11.
06:36But when astronomers use the Hubble Space Telescope to accurately measure the distance to GNZ 11,
06:43they find something shocking.
06:49It's 32 billion light years away.
06:53Three times further than thought possible.
06:58So if nothing can travel faster than light, and we measure the distance to this galaxy,
07:03how can it be 32 billion light years away?
07:06There hasn't been enough time in the history of the universe for light from GNZ 11 to reach us.
07:16There must be some mistake here, right?
07:19At this point, your brain is probably thinking of leaping out of your skull and running around screaming.
07:25Trust me. I know. I'm an astronomer. I've been doing this my whole life.
07:29And this stuff twists my imagination up. It's really hard to grasp this.
07:34How do we see a galaxy that's 32 billion light years away and only 13.4 billion years old?
07:46GNZ 11 is further away than it should be.
07:51Because something strange is going on with our universe.
07:55It's expanding.
07:57And if the universe is expanding, then where does its edge lie?
08:02And can we ever reach it?
08:05Can we ever reach it?
08:06The future of that is Eine.
08:16How does the universe-world change in a 부perate重要 state we have a higher energy?
08:19The discovering of the universe is already viable.
08:2113.8 billion years ago, a speck of energy burst into life.
08:24We call it the Big bang.
08:27energy burst into life. We call it the Big Bang. Space and time pushed out in all directions.
08:39Ever since, our universe has expanded. But the way it's expanding makes finding an edge
08:48a major challenge.
08:52The universe is expanding and expands according to a very simple law that the farther away
08:57a galaxy is from us, the faster it appears to be receding away from us.
09:04The furthest galaxies are moving at very high speeds. The most distant galaxy we've ever
09:10spotted, GNZ 11, seems to have moved 32 billion light years away from us in just 13.4 billion
09:21years. That's faster than the speed of light.
09:26We can measure the speeds with which galaxies are moving away from us. And many, many galaxies
09:31are moving away from us at speeds faster than the speed of light. This sounds like it's breaking
09:36the law, right?
09:37There's this idea that you've all been told that relativity says nothing goes faster
09:41than the speed of light. Okay, you've been lied to.
09:46Space itself can do what it wants. It makes the rules. It can break the rules. That rule
09:53applies to matter, not to space itself. Space can expand at whatever rate it wants.
09:58A simple way to think of this expansion law is imagine standing on an infinite rubber sheet
10:05that stretches all the way out into the distance. And you're standing on the same place. You
10:08can mark it with a little X. Now, all the sheet expands in every direction. So if it expands
10:15by a factor of two, another galaxy that was, say, one foot away from you is now two feet
10:20away from you as we stretch the sheet. But another galaxy was ten feet away from you. Expand
10:26that by a factor of two, and now it's twenty feet away from you. So in the same amount
10:30of time, one galaxy moved one foot, where another galaxy moved ten feet. So the more stuff there
10:37is, the more elastic between you and another galaxy, the more it seems to expand away from
10:42you.
10:45Expansion means our observable universe stretches for a colossal 46 billion light years in all
10:53directions, 92 billion light years across, and getting bigger by the second.
11:06This number is so incomprehensibly large that it's difficult to wrap your brain around.
11:13There are trillions of galaxies within this volume. It's staggering. It's so much larger
11:19than anything we're familiar with.
11:21If we were to travel to the edge of the observable universe, we would enter even more unfamiliar
11:29territory. Imagine we're in an ultra-fast spaceship. We leave the solar system, then the Milky Way.
11:40As we travel deeper into intergalactic space, things start to get really weird.
11:45For every million light years we go from the Milky Way, the galaxies move away from us at around
11:5713 miles per second faster.
12:02We have to accelerate just to keep up. But the galaxies keep on moving, always beyond our reach.
12:10Imagine you're a sprinter on a racetrack. If you're running towards the finish line, it may
12:29take you a few seconds to cross it. But now imagine that that finish line is moving away from you. If
12:34it's moving away from you at the same speed you're running, you'll never reach it. And if it's moving
12:39faster than the runner, then even faster runners won't reach it. And that's sort of what we're seeing
12:45here with the universe.
12:48Beyond a certain distance, galaxies are racing away from us faster than the speed of light.
12:54It's a line called the Cosmic Event Horizon.
13:00And 97% of galaxies we see in the observable universe are beyond this line and unreachable,
13:08people, including GN-Z11.
13:12They're sort of teasing us to say, look at me, what a nice piece of real estate. But we know even if we
13:18started going there now, we could never reach them.
13:22Anything that has crossed the Cosmic Event Horizon is out of our reach forever.
13:28But that's not the full picture, because the expansion rate of the universe is changing.
13:36A little over 20 years ago, astronomers discovered that the current rate of the universe's expansion is
13:42accelerating. It's speeding up. Astronomers suspect a mysterious force is at work.
13:49Dark energy.
13:53Dark energy is what we think is pushing the universe apart, causing this accelerating
14:00expansion. And the origin and true physical nature of dark energy is a big mystery.
14:06Thanks to dark energy, more and more galaxies are crossing the Cosmic Event Horizon and leaving the
14:16observable universe.
14:20These galaxies are lost to us forever.
14:24There are galaxies that we can see today that in a few million years, say, we won't be able to see,
14:33because the edge of the observable universe has basically moved in closer than that galaxy.
14:39That's going to happen all the time. And in a trillion years or something like that,
14:43all these galaxies that we see in our sky will be completely invisible, because they'll be beyond
14:48the edge of the universe.
14:53So eventually, every last galaxy will be so far away from us that light cannot reach us through that
14:59expanding space. It's almost as if you're driving through a dark desert in your car, and the very,
15:05very last town that ever exists has gone over the horizon, and there'll never be any light again.
15:14We can see less and less of the universe as we go into the future. What a strange thought.
15:21So that means we should build all the telescopes we can now.
15:27There's a limit to the universe we can see, even with the most advanced telescopes.
15:33But what lies beyond is one of the biggest mysteries in astronomy.
15:39The greater universe could be stranger than our wildest imagination.
15:49When you stand on the beach and you look at the horizon, and you kind of think,
15:52oh, what beautiful lands are there beyond the horizon? Things I've never imagined before.
15:58It's so natural, it's so human to ask, what lies beyond that? What is the true extent of the universe?
16:05The observable universe contains trillions of galaxies.
16:25It's about 92 billion light years across.
16:33But astronomers believe this isn't the full extent of the universe.
16:37What we don't know is how much of the universe is our observable universe.
16:46It could be a tiny microscopic speck of this much more vast universe. We just don't know.
16:53We have no idea how much stuff there is outside the observable universe, but because by definition
16:59it's outside the observable universe, we really don't know right now.
17:04So what is out there? One theory says that space outside the observable universe
17:10is pretty much the same as our own cosmic neighborhood.
17:16It's just more universe. It's just like here. It's just far enough away that we can't see it.
17:21So it's not like there's bizarre places where time runs backwards or aliens have two heads. Well, yeah, maybe.
17:29But further out in the deepest parts of the greater universe, all bets are off.
17:37We expect that as you go sort of twice or three times beyond the observable universe,
17:42it's probably very similar to the universe we inhabit. But if you go a thousand times or a million times
17:47farther, who knows what you might see?
17:49It might be very, very different if we go far enough away.
17:58Strangely, it all comes back to the expansion of the universe and one crucial detail in that process.
18:05There was a brief moment in the very early history of the universe where its expansion
18:12accelerated hugely. This acceleration is called inflation. And in a brief moment,
18:19the universe itself expanded at multiple times the speed of light.
18:23Inflation was a formative moment for our universe.
18:31By the time it stopped, the universe's basic characteristics were set.
18:35There are these fundamental constants that describe the phenomena in our universe,
18:42the fundamentals of matter and light and space time.
18:46But some scientists think there could be regions of the greater universe where inflation has never stopped.
18:57The idea is the greater universe is expanding at an insane speed. But here and there, occasionally,
19:04a little region will stop inflating and just expand at the normal rate.
19:09Inflation can end somewhere, and that gives rise to the universe we live in, while inflation continues somewhere else.
19:19Parts of the greater universe that continued to inflate would be left with different laws of physics.
19:27These incredibly violent inflation processes actually monkeyed with the very fabric of space itself,
19:33so that a lot of the things that we were taught are laws of physics are different there.
19:39So in essence, inflation gives us a very natural way to make this patchwork quilt of different parts of the universe where things seem different.
19:49So what we can imagine is a super large-scale structure where there's different regions of the universe, domains,
19:55then each domain has different local laws of physics.
20:02These different parts of the universe are separated by frontiers called domain walls.
20:09We have similar boundaries on Earth.
20:14Whenever you have something that can be in many different states, you can end up with a domain wall.
20:20If I were a fish swimming around in the Arctic near an iceberg, there would be a domain boundary between the water being in the liquid state where I am and the solid state inside the ice.
20:32A domain wall is the wall between two domains.
20:37If it's water, this could be ice, this could be liquid.
20:40If we're talking about space, this could be a kind of space maybe you can live in.
20:44This could be the kind of space where you don't want to be.
20:47Crossing a domain wall would be very bad news for anyone who dared to try.
20:53Cross that domain wall and the laws of physics could change dramatically.
20:59The number of dimensions could change.
21:01If we were somehow able to travel to places in the universe where the laws of physics are different, we would die.
21:07Because all of the chemistry going on in our bodies depends very, very sensitively on the laws of physics.
21:13So you could just dissipate like Thanos snapped and you're gone.
21:21Domain walls might be the closest we get to locating an edge in the universe.
21:27Depends on how you define the edge.
21:29If it is the realm where the laws of our universe operate, then these domain walls are in essence the edge of the universe.
21:40But this is all just theory.
21:43If we ever really are to work out what the true size and shape of the universe is,
21:51we're going to have to look for clues that are close to us.
21:54Clues that could answer the ultimate question.
21:58How big is the rest of the greater universe?
22:02And could it go on forever?
22:13For tens of thousands of years, mankind has gazed in wonder at the vastness of the cosmos.
22:28But just how extensive is it?
22:30If we could answer that question, it might help us to understand our place in the universe.
22:37One of the fundamental questions in science is, how big is the universe?
22:45To answer the question, how big is the universe, we have to answer the question, what shape is the universe?
22:50And by shape, I mean geometry. I mean, how is the universe curved on its larger scales?
22:58If we are to discover that the universe does have some sort of geometric curvature,
23:04then this might imply that it wraps around in on itself over incredibly large distances.
23:12And that if you could travel in one direction long enough, you would end up at your starting point.
23:18Another version is that the universe is more like an infinite flat plane, okay? No curvature at all.
23:25The further you travel, well, the further you get. And you never get back to where you started.
23:32To work out the shape of something, we would normally just step back and take a look.
23:37But clearly, moving outside the universe is a non-starter.
23:42We can't jump on a rocket and fly a thousand times larger than our cosmic horizon and see what the
23:48shape of the universe is. We just can't do that.
23:51Our human perspective on the larger universe is so limited.
23:55So if we want to figure out what the larger shape and scale of the universe is,
23:59we're going to have to be very clever indeed.
24:04One way to be clever is to think of the geometry of the universe in its simplest terms.
24:12When we talk about the geometry of the universe, we really are talking about geometry.
24:16In order to do geometry, you have to take measures. You need a cosmic ruler to do this. And it turns out
24:22there's a great cosmic ruler known as baryonic acoustic oscillations.
24:29Baryonic acoustic oscillations are ripples in the cosmic microwave background.
24:34The oldest light in the universe.
24:41As the universe expanded, these ripples were imprinted in space in a uniform way.
24:46They provide a cosmic ruler to measure vast distances over time so we can gauge if the
24:55universe expands in curved space or over a flat plane.
24:59When we use these cosmic rulers to try to back out the shape of the universe,
25:07we're sure to a few percent accuracy that the universe is flat.
25:13If the universe is flat, we could set off traveling into the cosmos and continue traveling forever.
25:20There may be no edge to our universe. Because a flat universe can be an infinite universe.
25:31Now we're thinking of the universe as something that really does go on forever.
25:35That the stars and galaxies never have an end. And how can something truly infinite really exist?
25:42Infinity is weird because it's a concept of, because it's endless. What does that mean? Who knows? I don't know.
25:55Infinity is a concept more than anything else. Our brains aren't evolved for that. We evolved
26:02living in the plains. We were apes looking for food. You know, we weren't evolved to think about the
26:09universe and all of this stuff. I just can't stop contemplating this stuff. The idea of infinity and
26:16these large numbers and even the tininess of everything. It's nuts. Yeah, thinking about
26:21infinity makes my head hurt a little bit. An infinite universe has profound implications for understanding
26:32our place in the cosmos. It guarantees we're not alone. If the universe is infinite, then there could be an
26:43infinite number of galaxies that have planets with life. An infinite number without life, then because
26:50life did appear here on earth, it's physically possible. Therefore, it will definitely happen elsewhere in
26:55the universe. In a flat universe, alien life could come in an infinite number of forms.
27:03But there is an altogether stranger guarantee. If the universe has no edge,
27:10this means that things that seem like they are impossible become possible.
27:17Every possible arrangement of matter, every possible history of a galaxy, of a solar system,
27:25of a planet like Earth is possible and is happening right now in parallel to us somewhere over there.
27:34So that means that there has to be another place that has a galaxy just like ours,
27:43and it would have an Earth just like ours, it would have people, it would have another version of you,
27:49another version of me. It's 100% guaranteed that there is another Max Tegmark out there,
27:54having exactly this conversation, and in fact many of them.
28:01An infinite universe full of Max Tegmarks may be a strange concept,
28:05but what's truly mind-bending is understanding the physics of a flat universe.
28:10If the universe is infinite, and it's expanding, what's it expanding into?
28:17And what did it expand from? Was there ever an edge to the universe?
28:22Fortunately, the answer is that it doesn't make sense to ask that question.
28:31Everything is expanding, including the universe that we exist within.
28:36So, in fact, it's not expanding into anything, because it is everything.
28:45To help understand what's going on in an infinite universe, we need to go back to the Big Bang.
28:52We want to think of the Big Bang as an explosion in space, like it happened someplace.
28:59But there wasn't any place before the Big Bang. Space existed inside of the Big Bang itself.
29:05So it's not an explosion in space, it's an explosion of space.
29:10We're sometimes told that at the Big Bang, the universe started out very, very small and then got big.
29:15But how can a finite point become infinite? Well, if the universe is infinite,
29:21then it was also infinite at the Big Bang. This is a tough thing to think about.
29:27Think about it this way. In an infinite universe, the galaxies go on forever.
29:32And now there's a great distance between every galaxy.
29:35But once upon a time, the galaxies were closer together, say, half their current distance apart.
29:40But they still went on forever. The universe was still infinite.
29:43In a flat universe, space was infinite from the beginning.
29:52There was never a single point in space where the Big Bang happened.
29:56It happened everywhere. An infinite universe offers infinite possibilities, but no edge to space.
30:11But there may be another kind of edge, one that will only reveal itself if the universe dies.
30:26There may be another kind of edge, one that will only reveal itself to the universe.
30:37We live in an infinite and expanding universe.
30:42Space has no edge. It goes on forever.
30:51But there could be a different kind of edge to our universe.
30:56The universe seems to have begun 13.8 billion years ago in the past.
31:03So there's some inclination, some impression that it's finite in time.
31:07What we call the Big Bang is, as far as we understand it, a beginning, a start of the universe.
31:14The universe has a finite edge. Now, does it have an edge in the future?
31:19We used to think that time would someday come to a catastrophic end, along with the planets, galaxies, and all life in the universe.
31:30If we know there's a big bang, if we know the universe started, expanded, and cooled, it's very natural to wonder whether or not someday the expansion will stop, reverse, and come back.
31:42And that's a big crunch.
31:48In a big crunch, our expanding universe would begin to contract.
31:52Stars and planets would smash into each other.
31:55Galaxies would collide.
31:59And all of the life left in space would be compressed with all the other matter into a singularity.
32:05If this theory is true, then the universe would have both a beginning and an end of time.
32:25If we live in a universe that will expand, stop expanding, and then go back into a crunch, then it has, in effect, two edges.
32:34But there's a much stranger possibility.
32:38Perhaps the end is but a beginning.
32:41Well, the universe is an oscillating universe.
32:44It has a big bang-like beginning.
32:45It expands to a maximum size, and then goes back into a big crunch, and does that over and over.
32:53We could be residents of a universe created from the ashes of another.
32:58A single universe in a stream of bouncing universes.
33:04Each full of galaxies, planets, and life.
33:09But our most recent observations of the universe suggest a big crunch isn't in the cards.
33:20Once again, dark energy is key.
33:22For a while, we didn't know if the expansion of the universe was going to slow, stop, and reverse itself because of gravity.
33:35There are all these galaxies in the universe, and they're pulling on each other by their gravity.
33:38And if the expansion isn't fast enough, that gravity might be strong enough to stop the expansion and re-collapse the universe.
33:45Now, with dark energy, we know that there's no way that can happen.
33:48The universe is going to expand forever because dark energy is pumping it full of acceleration.
33:55In order for there to be a big crunch, our understanding of dark energy would have to change a lot.
34:01That is, dark energy would have to be extremely weird and turn off in some very funny way for the universe to suddenly stop expanding and re-collapse.
34:13Without a big crunch, there is no future edge to time.
34:17The universe is not only expanding, but it's being driven by dark energy to expand faster and faster.
34:25And the dark energy doesn't dilute away, as far as we can tell.
34:28So, the simplest idea is that the universe will simply continue to expand eternally toward the future.
34:37Just like space, time will go on forever.
34:40That might sound like a better fate for life in the universe.
34:46But it's not.
34:50One of the consequences of this dark energy that's causing the acceleration of the universe
34:56is that we eventually are headed towards the big chill.
35:01I should say, we're eventually headed towards the big chill.
35:04So, the universe is getting colder and colder, and things are getting more and more spread out.
35:10So, the accelerated and continual and forever expansion of our universe might make for a, frankly,
35:17depressing end to time itself. This is the ultimate entropy-based heat death of the universe,
35:23where you would walk out and see no stars in the sky.
35:27You see absolutely nothing.
35:29There will come one day when the very last star in the universe just fizzles out, and that is it.
35:38In the future, space will be a cold, dark, and infinite void,
35:44where time goes on forever.
35:48There will be nothing to do but suffer in the eternal expanse.
35:53It's our inevitable fate that there's no future edge of time in the universe.
35:59But even if there isn't an edge to the universe, could there be edges within the universe?
36:10If you wanted to visit the edge of the universe, then go find your nearest black hole and jump on in,
36:16because that's a one-way trip.
36:18If you cross this edge, you will never return.
36:21April 2019, an international team of astronomers makes a special announcement.
36:43And we are delighted to be able to report to you today that we have seen and taken a picture of a black hole.
36:51Here it is.
36:52It's a picture of a supermassive black hole at the center of the M87 galaxy, 54 million light years away.
37:09It may also be the first image of an edge in the universe.
37:13Black holes create a really interesting scenario when we think about space and the universe having edges.
37:23The edge between space outside and inside a black hole is called the event horizon.
37:29The event horizon of a black hole is a region within which, once you cross inside, the gravitational tug is so strong that even light cannot escape,
37:40which means nothing can escape once you cross inside the event horizon.
37:46So that really is sort of an edge, because it really does create a boundary.
37:51The event horizon is not a physical barrier in space.
38:01The event horizon is an edge of the part of the universe we can visit.
38:05But it's not an edge in the sense that there's anything there.
38:09You would just pass right through it if you actually got right up to that place.
38:12So it's sort of a conceptual boundary between two different parts of the universe.
38:17If we sent a manned probe into a black hole, it would be a one-way trip.
38:27The event horizons of black holes are a sort of edge.
38:31Because once you pass through an event horizon, you are cut off from the rest of the universe.
38:38You can never go back out.
38:40You are outside of our universe.
38:44Once you've crossed inside that region, you are never coming back out.
38:49You know, and that's an edge.
38:52Once inside the black hole, the probe would be in a separate part of space,
38:58cut off from the rest of the universe.
39:02Falling through the event horizon of a black hole is like jumping over the edge of a cliff.
39:07You can see the edge, and you can see the edge go by.
39:10And then when you're at the bottom, you can look up and see what's happening at the top of the cliff,
39:15but you can never go back.
39:19At the bottom of this black hole cliff sits a singularity.
39:24A region of space where the laws of physics go off the rails.
39:30Deep toward that singularity could be as surprising as you might imagine,
39:34and yet still a possibility.
39:36If you map the space-time around a black hole in a very particular way,
39:40there emerges a sort of mirror universe, a parallel universe on the other side of the black hole,
39:46identical to our own and traversable via the black hole.
39:50So black holes are not just edges to our universe.
40:01They may also be gateways to other universes.
40:06It's highly conjectured, but if there's ever going to be a space where, or a region,
40:12where you're making connections with, say, some other universe,
40:15a black hole in principle could be a portal to that.
40:22But it's highly unlikely that anyone will ever want to venture beyond an event horizon to find out.
40:29And our pursuits of the other edges in the cosmos offer little hope either.
40:34We can never travel beyond the cosmic event horizon.
40:41We will never be able to see beyond the edge of our observable universe.
40:48So can we ever hope to discover the true edge of the greater universe, or find out if it even has one?
40:55My feeling is that probably we should not think about edges for the universe.
41:03Everything you've ever seen in your life is finite. It has an inside and an outside. It has an edge.
41:10The universe might not be like that. It's probably not like that.
41:13There's probably no sense in which the universe has an edge.
41:19We used to think that the ultimate limits on the future of life were set by nature.
41:25We couldn't get off the planet, or there was nothing beyond the solar system.
41:29Now we realize we have this vast, vast cosmos out there, and that the ultimate limits are actually
41:36simply our own imagination and our ability to do great things with it rather than self-destruct.
41:43Our future destiny is in our own hands, and I find that very empowering.
41:50It is beautifully frustrating to realize how limited we are,
41:54to realize that we're probably never going to get a true view of the real extent of the universe.
41:58We should keep an open mind. We should be humble.
42:00But I think that we should give up on the idea that things should have edges,
42:04because that's what we're familiar with. The universe is something special.
42:08What matters to us, and will only ever matter to us, is the observable universe.
42:15Because that's the limit of what we can see, and that is the limit of what we can know.
42:20So there is an edge to the universe. There's an edge to what we can know.