- 4/12/2025
Space is not as empty as it seems. It conceals a secret structure called spacetime - an invisible field that governs our lives and controls the universe. This strange four-dimensional substances will also determine how our universe will end.
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LearningTranscript
00:00What is our universe made of?
00:05It's the biggest unanswered question in science.
00:09Despite the name, space is not an empty space at all.
00:13Space itself is something.
00:16There's a hidden structure and a force that exists within space itself.
00:21Spacetime is something absolutely real.
00:24It's absolutely fundamental.
00:25It's really part of the fundamental architecture.
00:28A force that connects everything in our universe.
00:32It's an active player in the game of life.
00:36It underpins our reality.
00:39Tying together all of space and time since the very beginning.
00:43We call it...
00:45Space-time.
00:48It's everything. Space-time is what the universe really is.
00:53Space-time is how our universe works.
00:57But what exactly is it?
00:59And how does it control our past, present and future?
01:05We can't see it. We can't touch it.
01:06But without space-time we wouldn't be here.
01:07We can't see it. We can't touch it.
01:24But without space-time we wouldn't be here.
01:34Space-time is the fabric of our reality. It shapes and governs our lives.
01:39If we want to understand the story of the universe, it's absolutely crucial we understand how space-time behaves.
01:45Space-time has been active since the beginning of everything and is the key to the evolution of everything.
01:55We have to understand space-time in order to understand the history of the universe.
02:00To understand how the universe began, how it evolved and what's going to happen in the future.
02:05The story of space-time is the story of our universe.
02:10To know how the story evolves and how it will end, we need to go back to the very beginning.
02:17To a time when there was nothing.
02:22No stars. No space. A time before there was time. Then, all of a sudden...
02:37Our entire universe was born in the Big Bang.
02:41It started in an instantaneous moment where, from nothing, our universe was created.
02:47The very definition of the moment of the Big Bang is that space and time were created at that instant.
02:54It is, as far as we currently know, the coming into existence of space and time itself.
03:02The infant universe.
03:05A tiny speck of energy and space-time materialized from nowhere.
03:11Then, the universe suddenly expanded.
03:15The idea of inflation is that a very tiny region in an incredibly short amount of time,
03:20far shorter than a second, grew by many, many, many orders of magnitude.
03:25So, imagine myself suddenly becoming the size of a galaxy.
03:31In a fraction of a second, the universe grew from smaller than the size of an atom to the size of a cricket ball.
03:38In cosmic terms, it's similar to a grain of sand growing almost to the size of the observable universe.
03:48The universe, at the instant of inflation, actually expanded faster than the speed of light.
03:53It seems to be a violation of everything you've heard in physics.
03:56You may be thinking, hey, hey, hey, Mr. Astronomy Guy, nothing can move faster than the speed of light.
04:00It turns out, that's kind of true.
04:03But the rule is, nothing can move through the universe faster than the speed of light.
04:08In inflation, it's space itself that is expanding.
04:11So, there is no violation, there is no paradox.
04:20Inflating fast, the universe went through a phenomenal growth spurt.
04:26At the moment of the Big Bang, space-time was this entity that was flying out in all directions.
04:31It was space itself that was expanding.
04:35However, the universe didn't expand evenly.
04:38One spot in the universe was ever so slightly more dense than a spot right next to it.
04:43And we're talking about a tiny, tiny fraction of a percent.
04:46One part in 100,000.
04:49But that was enough.
04:52Fluctuations in expanding space-time created areas with higher density.
04:59Inflation made these high-density regions larger,
05:02which enabled our universe to take shape.
05:08When parts of the universe didn't inflate quite the same way as others,
05:11all of a sudden, things could start to come together.
05:17As the universe cooled, energy turned into matter.
05:21In the denser regions, that matter started to clump together.
05:26And crucially, these regions had more mass than others.
05:35Mass bends space-time.
05:37So anything that is made of matter bends space-time.
05:40And the more matter you have in one place, the more you bend it.
05:43In fact, I'm bending space-time right now.
05:45When I flex, I bend it even more because of my incredibly high bustle density.
05:49I don't bend at the maximum.
05:51I don't want to destroy the Earth and the solar system.
05:54But, you know, it's an effect.
05:55It's a real thing.
05:56Space isn't constant.
05:57It's not something that is always the same everywhere.
06:00It actually bends, curves.
06:02It warps depending on the matter inside of it.
06:05We'd see the curving grid of space-time moving and reacting to objects within it.
06:17And we'd feel the curving of space-time as the force we call gravity.
06:24Gravity is different from all the other forces.
06:27It is intimately connected with the curvature of space-time.
06:31Something that can bend space and time has gravity.
06:34That's what gravity is.
06:36The bending of space and time itself.
06:41It's hard to visualize this.
06:43But a good analogy is a trapeze artist and their safety net.
06:50You can imagine a trapeze artist falling into a net on purpose.
06:54That net is flat and looks like a nice, orderly, evenly spaced grid.
06:58But when they fall into it, they distort that grid.
07:01Well, that's a lot like space.
07:03If you have matter in space, it warps the framework.
07:07When the trapeze artist is resting in the net, they're bending that space-time grid a little bit.
07:13If you had two trapeze artists in there, double the mass in roughly the same volume, you would get a bigger dip.
07:19You have a bigger distortion.
07:20And that's how space-time works.
07:22More mass equals a bigger curve in space-time, which equals more gravity.
07:32But understanding the nature of gravity and space-time is no easy thing.
07:37It's an idea developed by one of the greatest minds ever.
07:41Einstein had the idea that space itself is something, something that can be bent, something that can be stretched, that we are all bound together by space-time.
07:55Einstein says that space and time have a geometry.
07:59They have a life of their own.
08:01They have dynamics.
08:03These dynamics are what we call gravity.
08:07The more dense the region of matter, the greater the gravity, the deeper the curve.
08:15This connection is the foundation of our physical reality.
08:19It's the interaction between matter and energy and space-time that created the universe that we see around us today.
08:27However, that doesn't mean we fully understand it.
08:31There's much more that we don't know, and that's frustrating.
08:35With the laws of physics, I can talk about how space-time behaves, but it does appear to be something that stretches, that contracts, and that gravity is the embodiment of space-time.
08:45Born in the Big Bang, space, time, and energy combine to create our infant universe.
08:55These basic materials were the foundations.
08:58But how did we get to the incredible, complex structures we see today?
09:04How did space-time build our majestic universe?
09:09Our entire universe was created in the Big Bang 13.8 billion years ago.
09:31Everything came from nothing.
09:36Yet the modern universe is a complex mosaic of matter.
09:43When we marvel through our telescopes at the fantastic structure of our universe and its galaxies, you've got to ask, where did that come from?
09:52Matter in the universe arranges itself on a vast cosmic web.
09:56Galaxies and galaxies clusters are strung out on sheets and filaments.
10:00It seems this intricate web is organized by a cosmic architect.
10:07Space-time.
10:09It shaped everything from planets to galaxies, atoms to cities.
10:15The universe is made of space-time.
10:19Whatever the substance is, time and space bound together, that's expanding and creating the universe we see around us.
10:26It's everything. Space-time is what the universe really is.
10:33It's a hard concept to grasp, and even harder to visualize.
10:41Scientists observe the universe in different wavelengths of light.
10:44This is the sun. Invisible light, X-ray, and ultraviolet.
10:51Now, imagine if we could see it in the space-time spectrum.
10:55We would see space-time distorting as objects move through it.
11:00Space-time can warp and push things around. It can expand and pull things apart.
11:07But it's the shape of space-time that dictates how we experience it.
11:14Imagine you're in your car. You go up hills and you go down hills.
11:18So the shape of Earth's surface determines how you travel across Earth's surface.
11:23In the same way, the geometry of space-time determines how light and matter move through space-time.
11:30The rules are simple. Any object with mass tells space-time how to curve.
11:41The curvature of space-time tells matter how to move.
11:45Because the shape of space-time tells matter how to move, what we call gravity,
11:53this means that gravity and the shape of space-time tells matter how to clump together and form larger and larger structures.
12:02But at the beginning, the space-time landscape was very different to today's.
12:08So the very first matter started to change the shape of space-time.
12:17So this space right here has a tiny bit more matter in it than this over here.
12:22Wherever there was a little bit of extra mass, that would bend space a little bit more.
12:27Well, if you're bending space a little bit more, then more mass would collect there.
12:31In the early universe, these denser regions of matter created deeper curves in space-time.
12:40And as the mass gets bigger, as stuff falls into that well, it gets deeper and deeper and deeper and attracts more stuff.
12:46And it's just a runaway process.
12:48Gravity increased, pulling in more and more matter.
12:53Got more dense, got more dense, got more dense.
12:55And then before you know it, you've got a star.
12:58And you've got a bunch of stars, and you start to make a galaxy.
13:01And these stars evolved and began forming large structures.
13:04They sort of burned through all their nuclear fuel and exploded, and they made all the heavier elements.
13:09And with time, we got down to having things like planets, atmospheres, people, all the things that we care about today.
13:21All of this started out as energy fluctuations in expanding space-time.
13:25These, at first, very tiny fluctuations became these gigantic structures that we actually see today.
13:32And over billions of years, that material began to coalesce into individual galaxies, stars, planets, and you.
13:40Fluctuations in the expansion of space-time laid out the pattern of the universe.
13:45The curvature of space-time controlled the evolution of everything we see today.
13:52If space-time didn't have that property of bringing mass together, then all we would be is a thin haze of hydrogen gas.
14:02Not a very interesting universe at all.
14:04If space-time didn't curve because of matter inside of it, the universe would be a really weird place.
14:11I mean, there'd be no gravity. There'd be nothing to make things stick together.
14:15No force of gravity means no stars, no planets, and no people.
14:20We owe our existence to space-time.
14:27But even scientists struggle to understand it.
14:31I wish I knew what space-time is.
14:35We know things about space-time, but at the same time, we feel like we know almost nothing about space-time.
14:41But sometimes, scientists get a glimpse of this elusive puppet master in action.
14:57In 2016, astronomers witnessed a strange optical phenomenon.
15:03A weird circle of light, similar to a cosmic halo.
15:06This is actually what you would see in the sky if your eyes were as sensitive as a telescope.
15:12They're real. This is not some artifact of how we adjust the images.
15:17Something is actually bending space and time itself into a lens.
15:23That something is a red galaxy, which is over seven billion light-years away from Earth.
15:29It's bending the light from a blue galaxy, which should be hidden behind it.
15:36It's called gravitational lensing.
15:40Gravitational lenses are caused by objects with huge masses, say clusters of galaxies,
15:46that distort space and time so much that when light comes from farther objects
15:50and has to pass around the galaxy clusters, the light bends.
15:55It really is a true warp in space-time.
15:59Mass from the foreground galaxy creates curves in space-time, which we know as gravity.
16:06Light follows those curves and is warped, so it bends around the galaxy.
16:12Massive objects like clusters of galaxies can bend the path of light through space-time.
16:19A lot like a piece of glass can bend the path of light.
16:25So when we look at a distant galaxy, as the light passes through a galaxy cluster,
16:30we see multiple images of the same galaxy.
16:34We see arcs and circles as if that galaxy cluster were made of glass.
16:39We are seeing the warping of space-time literally played out in front of our very eyes.
16:46Gravitational lensing gives us a way of seeing the effects of space-time on light.
16:53However, it's only an indirect observation of space-time.
16:57Is there another way of experiencing space-time right here on Earth?
17:09Not everything that happens in space can be seen.
17:12Sometimes you have to listen for it as well.
17:14Believe it or not, space is a material much like this iron sheet.
17:24And like this iron, space can distort.
17:27If I put a very heavy weight on this sheet of metal, its shape is going to change and it's going to distort.
17:32Amazingly, space can carry waves, and so can this iron sheet.
17:35But to get this sheet wavy, you need something really powerful.
17:40Something like me and my hammer.
17:48Did you see those waves travel through that iron sheet?
17:52Well, waves pass through space in exactly the same way.
17:57We call these gravitational waves.
17:59Gravitational waves are vibrations from cosmic events transmitted through the material of space-time.
18:10To set off waves in space, you need the biggest, baddest, most powerful events in the universe.
18:16Something like the collision of two black holes.
18:19When two black holes collide,
18:21the energy released sends shock waves through space-time across the universe.
18:26By the time they reach Earth, they're so small they're almost immeasurable.
18:38But in 2015, scientists at the LIGO Observatory made a groundbreaking observation.
18:45They had detected ripples in space-time.
18:49Gravitational waves.
18:51Rumors began flying, but it became clear after a while that this was indeed the first direct detection of gravitational waves seen by man-made instruments on the Earth.
19:04When we discovered gravitational waves, it had been so long that we'd been waiting for signals.
19:11Not only did most of us not believe it, I went so far as to be so skeptical as to look into all kinds of conspiracy theories for ways it could be fake.
19:19When I saw this data, I still think back on it now and the emotional impact it has on me.
19:27The only thing comparable is when I saw my daughter's face for the first time after she had been born.
19:31It was that kind of emotional impact, just having all of these things that we had worked for coming to fruition in one moment.
19:42It's mind-blowing.
19:46And we can actually hear these gravitational waves.
19:49Part of what makes this so amazing, it's a bit of a coincidence, but it's a really cool coincidence, is that the signals that LIGO actually measures are in the same frequency band as the sounds that the human ear is sensitive to.
20:03We can hear the waves change frequency as the two black holes get closer and collide.
20:11It's a swoop up in frequency that sounds like whoop.
20:17What we were hearing in that whoop were two black holes that are orbiting around one another and then coming together. That was it.
20:28Listening to ripples in space-time has given us a powerful new tool to investigate the universe.
20:35We are now hearing things in gravity for the first time. It's a sense that we have never been able to apply to the universe and we're beginning to learn what is out there.
20:46The observation of gravitational waves from black holes is one of the most significant findings in astronomy by anyone in the recent hundred years.
20:56It's hard to overstate the importance of gravitational wave astronomy.
21:00Much like when Galileo first pointed his telescope at the stars to see something new, we now have an entirely new window into the universe.
21:11Gravitational lensing and gravitational waves offer us an insight into the complex relationship between gravity and space.
21:19However, what about the other half of the equation? Time.
21:30But it turns out, you know, it's space-time. Gravity not only distorts space, it actually distorts time, too.
21:39We think of time as something that can't be changed. It simply flows ahead at a constant rate. But that's not the universe we find ourselves in.
21:46In some crazy circumstances, my time might even, according to you, stop.
21:55It might even be possible to travel through time and go back to the future.
22:16For science fiction fans, space is the final frontier. For scientists, exploring time is a much bigger challenge.
22:31Originally, we thought of time as the same thing as the sun rising and setting.
22:36But now we've come to realize that time is a more fundamental concept than that.
22:43Time isn't just something that passes. Time is an essential part of our universe.
22:50It's part of the fabric of space-time.
22:52The Big Bang was the beginning of space and time. Since then, space has been expanding and time has been ticking forward.
23:06It's been doing this for 13.8 billion years, creating the universe we see today.
23:12They're sort of two sides of the same coin. You can't have time without space, or space without time.
23:20So, when matter influences space-time, it's not just creating deformations in space, it's also affecting the flow of time.
23:29This is where space-time becomes really cool.
23:31Just as gravity bends space, it also distorts the flow of time.
23:38This isn't how we perceive time. This is actually the rate at which time flows.
23:44Very massive objects can warp and twist space-time itself.
23:48So, not only is space distorted, but time itself can slow down or even stop.
23:53The stronger the gravity, the greater the distortion.
23:57What has the most gravity? A black hole.
24:02Out in space, near a strong gravitational tug from a black hole, clocks can do funny things.
24:10And this is where things start getting really interesting.
24:13Around a black hole, space-time warps and twists, slowing time down.
24:20Scientists dream of sending a probe there to test their hypothesis.
24:25There's a famous way of thinking about this called the twin paradox, where two twins are born at exactly the same time, right?
24:33So, they're the same age. But one of them zips very, very close to a black hole, hangs out a while and then comes back.
24:38If I had an identical twin who stayed back on Earth while I flew near a black hole, when we had our daily video phone calls, he would see me go, hi there.
24:51And I would see him say, oh my goodness, I'm a little bit concerned about you because you're talking so funny.
24:54We would literally notice that time is running at a different pace for the other one.
25:01The closer to the black hole, the slower time passes.
25:06If instead of coming back home, I accidentally fell backwards into the black hole, my twin back on Earth would see me slow down even more.
25:13I'd go, ohhhh!
25:16And completely grind the hole and seem frozen on the event horizon.
25:22Time appears to stand still.
25:26I would just have a sinking feeling that I would never be able to come home again.
25:30But if the twin could escape from the black hole, he would be returning to the future.
25:38Maybe it's only been a few days or weeks experienced by the one that traveled to the black hole.
25:44While the other is, you know, gray-haired and has grandkids by now as it lived decades here on Earth.
25:51The black hole warps space-time so much that the ultimate science fiction fantasy would become a reality.
26:04Time travel is a staple of science fiction.
26:08And we know that time travel into the past appears to be ruled out in our universe.
26:14But time travel into the future is totally acceptable.
26:18Time travel isn't possible just yet.
26:24But space-time has a very real effect on our daily lives.
26:29It controls how we age.
26:34The key to different rates of flows of time is gravity.
26:40If you experience a different gravitational environment, you will have a different flow of time.
26:45As I climb up these stairs and I put myself further away from the mass of the Earth, my own clock runs a little bit faster.
26:56If you go down closer to the surface, the more your clock slows down.
27:01We have sensitive enough clocks that we can measure this different flow of time.
27:07Exaggerate this effect and we would see the flow of time change in front of us.
27:15Those closer to the Earth would appear slowed down.
27:19Those higher up, the opposite.
27:23And this means the wealthy in their penthouses actually age faster than people on the ground.
27:28This is a mind-blowing concept, but it's reality.
27:36Earth's gravity even controls time high above the planet.
27:4120,200 kilometers up, there's an array of global positioning satellites crucial to the navigation systems in our cars and mobile phones.
27:50We here on Earth use the global positioning system as a way of getting around.
27:56Most people these days would be lost if they have to go more than about a kilometer from their house unless they have their GPS app on their phone to tell them where to go.
28:04The GPS receiver in your mobile phone bounces signals over four satellites to figure out exactly where you are.
28:11It's an exercise in precision timing.
28:16On board each satellite is an atomic clock.
28:22The weaker gravity in orbit means these satellite clocks tick fractionally faster than those on the ground.
28:30If we didn't know, to correct for the fact that the clocks in our satellites move at different rates, the GPS system here on Earth would not work.
28:38It would actually lose accuracy at such a rate that the entire global positioning system will become useless in less than an hour.
28:46We correct for that every moment of every day.
28:49Think about this as you go through your everyday life.
28:54Every time you go up a flight of stairs, you're actually experiencing a slightly different flow of time.
29:00But what exactly do we mean by flow of time?
29:04In space, I can go anywhere I want. I can go left or I can go right.
29:11But time, it appears I can only go from the past to the future.
29:17So if you were to play a movie backwards, it would be immediately obvious that it's flowing backwards.
29:23Our perception is that time only runs in one direction, from the past to the present to the future.
29:34But some of the most fundamental laws of nature work both forwards and backwards.
29:40They're time reversible.
29:41We don't fully understand why time has an arrow, why it has a flow from the past to the future, why the past is different from the future, and why we only experience it in the present.
29:55The fundamental aspects of time and why there's an arrow is one of the biggest unanswered questions in modern physics.
30:03What's even more confusing is that all points in time are equal.
30:09In space-time, there's no difference between past, present, and future.
30:14There is nothing magical about now. Past, present, and future is just illusory talk.
30:25The future is no more special as a part of space-time than what's in front of me.
30:31It's similar to watching this program or a film.
30:34You might not know how it will end, but you do know that the end already exists.
30:42If we think of life as a movie, then space-time is the entire DVD.
30:47And if this particular moment in my life is a scene in the movie, then, of course, the past that happened before that scene and the rest of the film, the ending, it's all in there.
31:00They all exist exactly to the same extent.
31:04Understanding the true nature of time is key to understanding how the universe works.
31:11There's got to be physics behind it, and we're trying to figure out what it is.
31:16Without understanding that, we can't understand the origins of the universe.
31:22Space-time has controlled every phase of the universe's evolution since its birth.
31:27Now, we're discovering space-time will also dictate how the universe will die.
31:34Our universe started with a bang 13.8 billion years ago.
31:35And, ever since, it's been expanding.
31:36Our universe started with a bang 13.8 billion years ago.
31:41And, ever since, it's been expanding.
31:42However, will this expansion last forever?
31:43Or, will our universe come to a violent end?
31:44It's been expanding.
31:45However, will this expansion last forever?
31:49Or, will our universe come to a violent end?
31:50For almost a hundred years, we've now known that the universe's evolution of the universe
31:51has been expanding.
31:52It's been expanding.
31:53It's been expanding.
31:54It's been expanding.
31:55Everything in the universe is expanding away from everything else.
31:56It's been expanding, a world's growth for the universe, things like me as a data type
31:57as aextony day.
31:58So, it is empty.
31:59In the universe, it's long.
32:00It's been being revived by Earth around the earth.
32:01It's been changing.
32:02In the universe.
32:03A nearing day, it's focused almost as late in the sky, old.
32:05He is still moving on by a gem, and who doesn't do it, and how do this change
32:19can be a future?
32:21universe is expanding away from everything else this can be tested by
32:26measuring light from exploding stars type 1a supernovas all explode with the
32:33same brightness so scientists can accurately work out their distance from
32:38Earth
32:41for decades astronomers have measured this light being stretched by expanding
32:45space-time the universe is expanding and there's matter in it that matter has
32:52gravity and that is distorting the curvature of space-time so it made sense
32:57to us that as the universe expanded all of the matter in the universe would hold
33:01on to each other gravitationally if there's enough matter in the universe it
33:06can actually pull on itself enough that the expansion gets slower but in 1998
33:14astronomers took new measurements and made a sensational discovery people had
33:20expected it to be slowing down to decelerate but instead they found the
33:24opposite the expansion is accelerating if expansion was slowing then these
33:31distant lights should seem brighter instead they were dimmer they were getting
33:38further away much faster than expected and this could only mean one thing
33:43that expansion is getting faster it's accelerating every day this discovery
33:52turned our understanding of the universe upside down for the first seven
33:58billion years of the universe the rate at which the universe was expanding was
34:02going slower and slower but then something crazy happened it was as if gravity had
34:10become the opposite instead of attracting the galaxies it was
34:14almost as if it was pushing them apart that's a very surprising result we're still struggling to
34:20understand it was gravity losing its power or was something else pushing space apart
34:28there's another ingredient in our universe an ingredient that behaves very oddly the
34:38mysterious quantity called dark energy similar to space-time dark energy is all
34:45around us it can't be seen but it makes up seventy percent of the stuff in our
34:51universe but what is it exactly dark simply means that we have no idea what it is we don't know what form it is in
35:00something is pouring energy into the universe causing it to accelerate we don't know
35:05what it is no clue whatsoever we don't understand it it's the greatest mystery out
35:10there today dark energy behaves in mysterious ways ordinary matter is attractive dark energy is
35:22repulsive that's why it's causing an acceleration ordinary matter feels gravity it comes together but
35:29this stuff doesn't is dark energy a new force in the universe or like gravity could it come from
35:38space-time itself dark energy may very well be a property of space-time it may be that space itself
35:46has an energy and it's this energy that's driving it to accelerate in its expansion dark energy is a
35:52thing we don't really know exactly what it is but it will have a huge effect on the future changes in
35:57the universe so what will happen if dark energy continues to keep accelerating the expansion of
36:04our space-time universe because of the presence of dark energy it'll expand faster and faster and
36:11faster which means the universe is going to become a lonelier and lonelier place to be all the galaxies are
36:18accelerating away from each other the universe gets dimmer and dimmer and colder and colder everything
36:25gets darker and more desolate and right now that is the leading candidate for what's going to happen in
36:30our future eventually our space-time universe will freeze the big freeze is the ultimate end game
36:39of the universe as we know it it is an ugly fate it's a depressing fate but luckily for us it's not
36:46until an unimaginably long time from now trillions of years from now the universe could end in a big freeze
36:56but a 2017 study hinted at an even more frightening possibility dark energy might be getting stronger
37:11one horrible scenario for the ultimate fate of the universe is if dark energy eventually grows so strong
37:22enough that it can overwhelm the gravitational attraction of a galaxy itself it's even able to rip black holes apart
37:29the very fabric that holds everything together could be ripped apart this idea is called the big rip
37:37first clusters then galaxies such as our own milky way will be torn apart
37:44then our solar system will break up and in the final half hour of the universe the earth
37:52will explode in the final second atoms will vaporize everything in the universe would individually be torn apart
38:04by the expansion of space we don't understand dark energy is it constant is it getting stronger is it
38:11getting weaker at this stage we simply don't know
38:18so it seems that space-time not only controlled the birth of our universe but will also dictate its death
38:26will also dictate its death
38:31and we're now discovering these two events may be linked
38:35a link that reveals a floor in our understanding of the big bang
38:41all the galaxies all the planets and stars all of this matter
38:45was compressed into a tiny volume shrunk down to infinitely small size
38:52we call this tiny infinitely dense point a singularity
38:59singularities are predicted by the general theory of relativity
39:03but the universe is also governed by another set of rules
39:09quantum mechanics
39:13quantum mechanics is our description of the subatomic realm of
39:19fundamental particles and fields and forces and how they interact
39:26quantum mechanics states that nothing can be infinitely small or dense
39:33so singularities can't exist
39:38singularity is a bit where everything kind of goes to hell because the densities become infinite
39:43gravitational forces become infinite
39:45things just sort of break down there in the equation sort of stop making sense
39:50and no singularity would mean no big bang as we understand it
39:56so then how did the universe spark into existence
40:02scientists now think they have an answer
40:04a solution that works with both general relativity and quantum mechanics
40:11quantum spacetime
40:15a successful theory of quantum spacetime should answer the question of what really happened in the earliest moments of our universe
40:22hopefully the correct quantum theory of gravity won't have any singularities
40:27it will replace the big bang with something else
40:30if we only knew what that something else was we might have a clue as to how and why the universe began
40:37in a quantum spacetime big bang there was no singularity bursting from nothing
40:44instead the universe formed from the remnants of another dying universe
40:50it's possible before the big bang there was still universe there was still space and time
40:57but rather than expanding the universe was contracting
41:03perhaps universes don't end in rips or freezes perhaps they collapse
41:13an ancient universe expands but then begins to collapse under its own gravity
41:18crunching spacetime down to a speck
41:25but instead of forming a singularity
41:29spacetime explodes once again
41:32as matter gets more dense then as the matter crunches down
41:36this force will push everything back out
41:39the universe would bounce and reignite in a new round of expansion a new big bang
41:46what we perceive as the big bang is the aftermath of that bounce
41:53this suggests that the spacetime that dictates our lives today
41:58comes from the collapse of an old universe
42:01and we live in an infinite spacetime cycle of birth death and rebirth
42:07a bouncing spacetime universe
42:14if we live in a bouncing universe it's very plausible the universe is infinitely old
42:17that it's gone through an infinite series of bounces and there is no absolute beginning
42:22it could be that we are just one iteration of an infinite number of cycles in the lifetime of some meta universe
42:29we barely understand spacetime
42:36perhaps we will never understand it completely
42:40but one thing is clear
42:42without spacetime
42:44we would not be here
42:47spacetime is something absolutely real
42:49it's really part of the fundamental architecture the furniture of reality
42:52to really understand the ultimate fate of our cosmos it's not enough just look more with our telescopes
43:02we also have to understand the basic nature of spacetime
43:05I think the biggest thing to take out of all of this is that the universe is weird
43:17when you hear about these very weird things that we talk about when we study the universe
43:24and cosmology and relativity it sounds like it could be all made up
43:28but trust it's not
43:30you really are right now living in a far more complex and beautiful universe
43:37than the human mind can comprehend
43:40and what you do
43:41in the universe
43:42that you really get the knowledge
43:43and that you really don't know
43:44about the universe
43:45that you're really ready to experience
43:46in a better youtube series
43:47the universe
43:48in a better world
43:49that you can do
43:50that you can see
43:51and that you can see
43:53the universe
43:55of pass from punkt
43:57that you can see
43:59it's not just a moment
44:00you can see
44:06the universe
44:07that you can see
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