The Big Bang is believed to be the single most important event to ever occur, and now, scientists have embarked on an elusive endeavor to determine the age of the universe as it could hold the key to understanding the origins of the cosmos.
Thanks for watching. Follow for more videos.
#cosmosspacescience
#howtheuniverseworks
#season10
#episode5
#cosmology
#astronomy
#spacescience
#spacetime
#space
#nasa
#universeorigin
#huntfortheuniversesorigin
Thanks for watching. Follow for more videos.
#cosmosspacescience
#howtheuniverseworks
#season10
#episode5
#cosmology
#astronomy
#spacescience
#spacetime
#space
#nasa
#universeorigin
#huntfortheuniversesorigin
Category
📚
LearningTranscript
00:01There's a mystery at the very heart of the universe.
00:05We don't know how old the cosmos is.
00:09Understanding the age of the universe is fundamental to understanding the universe at all.
00:14It's at the heart of everything.
00:17It's more than just celebrating a birthday.
00:20We want to know how much mass is in it, how much energy is in it, how it behaves.
00:23We have to have this number nailed down.
00:26The age of the universe enables us to not only understand where we came from, but potentially the fate of the universe.
00:34What will happen millions and billions of years from now.
00:37But our quest to discover the age of the universe is starting a war.
00:42Usually nature just whispers to us, now nature is screaming in our ear that we're doing something wrong.
00:49And that's exciting.
00:56We think the universe started with a bang.
01:06Everything that has ever existed is squashed up in the space smaller than a pinhead.
01:12And all of a sudden, space just starts expanding everywhere at once.
01:18The idea that the universe grew from a ball smaller than a pinhead is hard to understand.
01:25But figuring out when it happened sounds like it should be more straightforward.
01:30It seems like a simple question, right?
01:32But it turns out getting the age of the universe is pretty tricky.
01:36Scientists have just a single fact as their starting point.
01:40The universe is expanding.
01:43When people realized the universe was expanding, they thought they finally had a way to estimate the age of the universe.
01:49Take the universe now and run it backwards in time.
01:52Things get closer and closer until they come to a single point.
01:55That time, to that point, is the age of the universe.
01:59The expansion rate is so important, it's been given its own name.
02:05The Hubble constant.
02:07The Hubble constant is the present-day expansion rate of the universe.
02:13It is a key ingredient to understanding the entire expansion history of our universe and its age.
02:20Scientists discovered a strange radio signal permeating the cosmos.
02:26It's the remnants of ancient light from the early universe.
02:31We call it the Cosmic Microwave Background, or CMB for short.
02:37The Cosmic Microwave Background radiation is simply the afterglow of our Big Bang.
02:43The way the universe looked when it was 400,000 years old.
02:48The European Space Agency launched the Planck satellite.
02:52Using sensitive radio receivers, the orbiter studied the sky in every direction,
02:57measuring tiny changes in the temperature and polarization of the radiation signal.
03:03The CMB has all these variations in temperature, and they're not randomly generated.
03:09They are there because of physical processes that occurred when the universe was in its primordial fireball phase.
03:16The red blobs are where matter was hottest, and the blue areas are where matter was cooler.
03:23The smallest red blobs are where hot material was packed tightly together.
03:28That's where material in the universe would have been denser,
03:31and that's where galaxies would preferentially form.
03:34It's so cool to get to look at those blueprints and study them
03:39and see how that baby universe later grew up into the universe we see around us today.
03:45Although it doesn't look like much, hidden within this picture is almost everything we can know about the universe.
03:53In a complex process, using different mathematical models,
03:57cosmologists figured out how the ancient cosmos captured in the CMB became the universe we see today.
04:05They worked out how the universe got from small to big, and how fast that expansion happened.
04:13The data from the cosmic microwave background is absolutely the gold standard for cosmology.
04:19It's beautifully clean, we can understand it really well, and we have a lot of confidence that what we learn from it is pretty robust.
04:29By running the expansion backwards, we get an age, 13.82 billion years.
04:39Job finished.
04:41But it's not quite a slam dunk.
04:44The figure must be verified.
04:47We don't make a single measurement using a single technique.
04:50We make multiple measurements via multiple techniques.
04:53Another group of scientists use a totally different method to calculate the age of the cosmos,
04:59measuring objects that we can see in our universe to determine how far away they are,
05:05and how fast they're moving away from us as the universe expands.
05:10The most direct and most accurate measurements are using what is known as parallax.
05:16Parallax is the apparent shift in an object relative to the background when it's viewed from two different locations.
05:24So if I look at my thumb with one eye, and then I close it and look at the other eye, it looks like my thumb moves.
05:31If I move my thumb closer to my face, then the distance it moves back and forth changes.
05:38It appears to move back and forth more.
05:41That parallax difference as we move the thumb closer and farther from the face is the way we measure distances to distant objects.
05:48Using parallax, we can measure the distance to bright stars called Cepheids in the Milky Way.
05:56Cepheids are stars that burn 100,000 times brighter than our sun.
06:01So they're extremely bright and they pulsate, meaning they get brighter and dimmer over a regular time period.
06:07Cepheids that pulsate at the same rate have the same brightness.
06:13They're known as a standard candle.
06:16A standard candle is something that is a standard, meaning we know how intrinsically bright it is.
06:22So all we have to do is measure the brightness that we appear to perceive on Earth, and then you solve for the distance.
06:29So imagine that you're on this street.
06:32By looking down the street, you'll see that the street lights get dimmer and dimmer the farther away they are.
06:38But that's not their intrinsic brightness. Their intrinsic brightness is the same.
06:42So by seeing how faint the farthest away ones are, you can understand how far away they are from you.
06:49We can use standard candles to measure the distance to stars farther away.
06:56But there's a big problem.
06:58Throughout the universe, there's a competition between the expansion pushing things apart and gravity pulling things together.
07:08In the Milky Way, there's so much matter that gravity wins.
07:12Even looking at galaxies in our neighborhood, the expansion is tiny.
07:17But at cosmic scales of very different galaxies, matter is more spread out and expansion wins.
07:25So we can only measure expansion over massive distances.
07:30The way we start to measure distances to things that are farther and farther away is to use something we call the distance ladder.
07:37Each category of object that we observe is on a separate rung of this ladder.
07:44Measuring the distance to one will then inform us how far away the second rung is, and then the third rung.
07:52So each rung depends on the previous rung.
07:55And from stacking these together, we can start to measure things very, very far away from us.
08:04Using parallax to measure Cepheid stars in the Milky Way gives us a benchmark.
08:09We can then use their standard brightness to measure Cepheids in other galaxies.
08:15The next rung is a brighter standard candle called type 1A supernovas.
08:21They can be seen in galaxies farther away.
08:24Finally, we can measure light from distant elliptical galaxies.
08:29And by looking at how red the light is, we can work out how fast they're moving away from us.
08:36So those three things give us the nearby universe, the somewhat far away universe, and the very distant universe rung by rung.
08:44March 2021.
08:49Scientists measure the light from 63 giant elliptical galaxies, the farthest rung of the distance ladder.
08:58They hope to get the most accurate measurement of the Hubble constant to date, and a precise age for the universe.
09:07Their calculations make the universe 13.3 billion years old, not too far away from the figure of 13.82 billion years given by the cosmic microwave background.
09:20A difference of around 6%.
09:23That sounds trivial, but that equates to hundreds of millions of years of cosmic history that either happened or didn't happen.
09:31Fifty years ago, when we weren't quite as good at measuring everything about the universe, we would have been thrilled to have our numbers agreeing to this level.
09:39But nowadays, having a difference like this, it's unacceptable.
09:43Clearly, the two techniques do not agree.
09:46Cosmologists split into two camps.
09:49We had hoped that these two methods were like building a bridge from either side and then meeting in the middle, but they're not.
09:57Now we know that something is going on we don't understand.
10:00Even though these measurements are roughly the same, it's really dangerous to just accept them and assume that everything's fine.
10:08Because in science, usually the initial really big discoveries start off as small differences that then you pull on that thread and something wonderful emerges.
10:19So does a simple question, how old is the universe, unravel everything?
10:25The universe is expanding outwards.
10:37The rate it's growing is called the Hubble constant, and it's the key to working out the age of the universe.
10:44So the Hubble constant might just seem like some, you know, academic number that doesn't mean anything, but that number contains information about the composition, the evolution, and the fate of the universe.
11:00It's an important number, but there's a problem. Our best measurement methods don't match.
11:08It's incredibly frustrating to not know how old the universe is.
11:12It's even more frustrating to know that there's two experiments, which are excellent experiments that we firmly believe in, that completely disagree with each other.
11:21My hair fell out a long time ago over this kind of stuff.
11:24This has been the number one question for over half a decade.
11:30There must be something wrong with one of the methods.
11:33There's a definite sense in the community that whichever camp you happen to fall into, the problems lie on the other side of the fence.
11:42So if you're mainly working with the cosmic microwave background, you probably think something is up with the distance ladder.
11:49If there's a problem with the distance ladder, there's a prime suspect.
11:54The ladder relies on stars that have a predictable brightness called standard candles.
12:00But there's evidence that these stars are not always the same brightness.
12:06So if you expect an object to have a particular brightness and it has a different brightness, then whatever conclusion you draw that relies on the brightness of that object is going to be off somewhat.
12:18Think of the stars like streetlights.
12:21If one light is broken and dimmer than the others, you might think it's farther away.
12:27The concern with a distance ladder is that if any of the single rungs is not perfect, then the entire ladder might be out of whack by the time you get to the top.
12:38What we need is a fresh approach to measuring the age of the universe.
12:43We're hoping we could bring in a tiebreaker, a referee, a brand new method that didn't care about any of this or any of that, and tell us what is the Hubble constant.
12:54We may have just found one.
12:57This observatory doesn't have a telescope.
13:00It's hunting for an invisible wave, a disturbance in space-time itself caused by massive objects accelerating or colliding.
13:12It's known as LIGO.
13:15LIGO stands for the Laser Interferometer Gravitational Wave Observatory, and it is a ground-based gravitational wave detector.
13:23A perfectly stabilized beam of laser light bounces in a five-mile-long, L-shaped tunnel.
13:30As a gravitational wave passes through the detector, space stretches, forcing the light to travel a tiny bit farther.
13:40You're bouncing a laser over an incredible distance and trying to measure as space-time itself gets stretched and deformed whether that laser had to travel a tiny bit further or a tiny bit shorter.
13:54And a tiny bit here is the width of a single atom over miles and miles of distance.
14:01LIGO has already detected colliding black holes, but it's also received a signal from something less massive.
14:11Neutron stars are the densest thing in the universe other than black holes.
14:17They're the last stopping point before you would collapse all the way to form a black hole.
14:22They're the size of Washington DC, but they can have the mass of two suns.
14:29A collision between neutron stars is incredibly powerful.
14:33It's one of the most energetic events in the universe, and it distorts the fabric of space-time very strongly because their gravity is so strong.
14:41But unlike black hole mergers, neutron star collisions can also send out light.
14:48In 2017, LIGO sent out an alert.
14:52More than 70 telescopes on Earth and in space swung into action.
14:57This binary neutron star merger was the first time we'd witnessed gravitational waves and light waves coming from the same event.
15:07It was groundbreaking.
15:09This event is ideal for Hubble constant hunters.
15:14The light tells us how fast the colliding stars are moving away from us.
15:19Gravitational waves give us the distance.
15:23If we know how far away it is and how fast it's moving, that's the Hubble constant.
15:29Having neutron star mergers added to your arsenal of ways of measuring the universe's expansion is great because it's completely independent.
15:38It uses physics that's not related to either of the two competing methods we have so far.
15:44Sounds perfect.
15:46The result?
15:47So this brand new measurement that we're hoping would be a tiebreaker ended up coming right in between these two extremes.
15:58Thanks for the help.
16:00But it might not be as bad as it sounds.
16:04The number of neutron star collisions where we've detected gravitational waves and light?
16:11One.
16:12We shouldn't be at all disheartened by the fact that this hasn't actually decided the problem because there's a huge margin for error when you have just one object.
16:23We would like something like a hundred events like this neutron star merger.
16:26That might seem like a huge improvement we need, but actually it's very feasible that in the next decade we'll get there.
16:34Gravitational waves may give us a precise age of the universe, but there is a chance they'll tell us the problem isn't with our measurements, but with our understanding of the cosmos.
16:45If we keep getting different answers for the Hubble constant, especially depending on the method we use, that's a big clue that we don't understand something fundamental about the universe's evolution, its makeup, something important.
16:59Our search for the age of the universe just might destroy our model of how we think the cosmos works, plunging physics into chaos.
17:15We don't know the age of the universe.
17:23We had hoped that the results from our experiments would be like building a bridge, starting at opposite ends and meeting in the middle.
17:33As time goes on, as the evidence accumulates, these two sides of the bridge are not going to meet.
17:41Something has to give.
17:43Some believe the problem lies in the way we've interpreted the picture of the early universe.
17:50The pattern hidden in the cosmic microwave background.
17:54We're really confident in the data that we have from the CMB, but it's actually an indirect measurement of the universe's age.
18:02It depends on our model of the universe being right.
18:04It could be. It could very well be that our fundamental cosmological model that we've used to successfully describe the universe is coming up short, that there's something wrong in there, that that engine is broken.
18:20That engine is the standard cosmological model. Based on our knowledge of particle physics and general relativity, it's like an instruction manual for how the universe works.
18:32Rewriting it is a radical suggestion. For the most part, it matches what we see. But it does struggle with one thing.
18:42With one thing.
18:43As the universe expands away from the Big Bang, the intuitive thing you would expect is for gravity to start pulling it back together again.
18:52So over time, gravity would just reverse that and pull everything back in, back to a single point.
19:00But what we see in the data is completely opposite. What we see is that the universe is not only continuing to expand, but it's speeding up faster and faster all the time.
19:11To explain this weird phenomenon, the cosmological model relies on the existence of a strange, unknown force, dark energy.
19:19Dark energy is the most perplexing and mysterious thing I've encountered in my research.
19:26Dark energy is a term that we slap on this idea that the universal expansion is accelerating.
19:33That's about all we know about it. We don't know what's causing it. We don't know how it behaves.
19:38We don't know what it was like in the past or what it's like in the future. So we just call it dark energy.
19:43It's invisible. It fills the whole universe and pushes galaxies apart.
19:50In some sense, it's like a spring, a contracted spring, and you let it go and it wants to push everything away.
19:58And things get stranger. Dark energy doesn't dilute as the universe expands.
20:04As empty space gets created or expands, the dark energy associated with that stays the same. It basically populates all this empty space.
20:15Imagine I'm draining a bucket of water and water just magically appears out of nowhere.
20:20That's like how dark energy behaves as the universe is expanding.
20:24Dark energy plays an important role in the standard cosmological model.
20:28If our understanding of it is wrong, then so too is the model, which means the age of the universe we get from the CMB is wrong too.
20:40Since nobody has a clue what dark energy is, there are a lot of different theories.
20:44But the biggest question of all is simply, is it constant?
20:48Our standard assumption about dark energy is that it's pushing apart the universe with the same strength throughout the history of the universe.
20:56Now, physicists are wondering if that idea is wrong.
21:02Maybe in the early universe, dark energy acted differently.
21:07Hey, you know the whole dark energy thing that's messing with the universe today?
21:12Maybe it messed with the universe back then.
21:16It could be that dark energy really has affected the rate of expansion a lot more than we thought.
21:21This is going to throw a big monkey wrench into our idea of how old the universe is and what it was like at different eras.
21:30The theory is called New Early Dark Energy.
21:33So the idea behind New Early Dark Energy is that dark energy was present during the very early periods of the universe, but in a very different state.
21:45Just like you can think of water being present in two states, it can be liquid water if the environment is quite hot, or it can be frozen water if the environment is colder.
21:59We call that a phase change.
22:02Maybe in the early universe, dark energy underwent a phase change as well.
22:06It was different before then and acts differently now.
22:09According to the theory, this more energetic state of early dark energy pushed apart the early universe much faster than we thought.
22:18So that speeds things up in the opening moments of our universe, which starts to actually bring things back into agreement when you look at interpreting both the cosmic microwave background and the distance ladder measurements.
22:33One of the things that we see in the universe is that things change with time.
22:38Density changes, matter changes, energy changes. Why not dark energy?
22:43Adding New Early Dark Energy to the early universe changes the standard model.
22:49The CMB gives a higher figure for the expansion of the universe.
22:53And finally, an age that matches the one given by the distance ladder method.
23:00If you think about that bridge analogy, where the two parts just don't meet, the early dark energy adjusts the angle of the early universe part of the bridge and it just gets them to actually meet in the middle.
23:14It's still controversial, but new dark energy may be detected in detailed measurements of the cosmic microwave background.
23:24I mean, in one sense, like, do we really need to overcomplicate the universe here? But you know what? The universe is under no obligation to be simple.
23:34But there's one thing physicists can agree on.
23:37Dark energy truly is a can of worms we've just opened and there may be some big changes coming up.
23:44There is a more radical possibility.
23:47Maybe we need to ditch dark energy altogether and question one of the most famous theories of all, general relativity.
23:56Is it possible? Did Einstein make a colossal mistake?
24:00In trying to work out the age of the universe, physicists have started a revolution. A revolution that could overturn everything we thought we knew about how the universe works, including the bedrock of modern physics, Einstein's theory of gravity, general relativity.
24:28Underlying everything, all of cosmology is general relativity, but maybe we need a completely new understanding of gravity.
24:41Gravity is a strange force. It's always attractive. The earth pulling on us gives us our weight. The force of gravity acts over huge distances.
24:53The sun tugs on objects throughout the solar system. The Milky Way pulls on other galaxies.
25:02On the one hand, gravity is incredibly familiar to us. You know, the apple falling from the tree and all of that stuff.
25:08And we also know that gravity behaves in a very predictable way throughout our solar system, from all the spacecraft and things we've sent out.
25:17But when it comes to how it behaves on incredibly tiny scales, and also on incredibly large scales covering the whole universe, it's possible that we just don't yet have the right picture of what's going on.
25:30Einstein's model of gravity has remained largely the same for 100 years.
25:37So much of modern physics is really standing on Einstein's shoulders. But at the same time, we can't ever take anything for granted.
25:46Claudia de Romm works on a theory called massive gravity. It's based on a key part of Einstein's theory that says gravity doesn't have mass.
25:57Once you understand that general relativity is the theory of a massless particle, the immediate response should be, well, what if it was massive?
26:05The theoretical particle that carries gravity is called the graviton. If gravitons don't have any weight, then there's nothing to slow them down as they speed through the universe.
26:18They can act over infinite distances, just like photons of light.
26:24So one galaxy on this side of the universe can actually pull on a galaxy that's right on the other side of the universe.
26:31But if gravity has weight, things change.
26:36In some sense, we attach a little backpack to our graviton particle. Its effect is to slowly slow it down just enough so as to make its effect on very large distances being a tiny little bit weaker.
26:52And that's our way to switch off the effect of gravity on huge cosmological distances.
26:58If gravity is a little bit weaker, a galaxy on this side of the universe can't pull on one on the other side of the cosmos.
27:09It has a huge effect on the expansion of the universe.
27:12If the force of gravity actually just switches off at large distances, then you no longer have to counter the fact that everything's pulling everything else together, because it isn't anymore.
27:27So that would quite naturally explain why the expansion of our universe would be speeding up.
27:31This acceleration is what we see in the universe today.
27:38Currently, we use dark energy to explain it.
27:41So if the graviton has mass, that means that we can get out of the universe what we see without the need for dark energy.
27:52What if actually what we are observing is simply the first sign of gravity switching off at very large distances?
28:00Maybe we're just observing the first effect of the graviton having a mass.
28:07Without dark energy to deal with, the universe is a lot easier to explain.
28:13Maybe we don't need these complicated physics.
28:16Maybe it's just all the normal ingredients of the universe, but operating under a different set of rules.
28:22Claudia hopes her theory will soon be put to the test.
28:29Around 2037, we'll have a new gravitational wave detector, the Laser Interferometer Space Antenna, or LISA.
28:40It'll be bigger than LIGO and will orbit the Earth.
28:44When LISA gets out there in space, we'll even have a bigger handle on gravitational waves evolving throughout the whole universe.
28:51And so it will allow us to go very deep in our understanding of gravity.
28:56LISA is a system of three satellites, arranged in a giant triangular formation, 1.5 million miles apart.
29:07It should pick up very low frequency gravitational waves from more ancient events,
29:14perhaps even shock waves from the birth of the universe.
29:18If the graviton has mass, then the waves will arrive more slowly than predicted.
29:25But until we receive those signals, all bets are off.
29:29It's a big deal to propose a difference in gravity, but then again, we don't know.
29:34I'm making no bets. The universe has proven itself to be so deceptive.
29:41So I'm going to wait until it tells me what it is.
29:44The question of the age of the universe opens Pandora's box.
29:49And the expansion rate of the universe holds another secret.
29:55Our ultimate fate.
29:58How the universe will end.
30:00We know exactly how the Earth will end.
30:15In around 5.4 billion years, the sun will turn into a red giant, expanding to a thousand times its current size.
30:24The Earth will be destroyed.
30:28Humans, if we still exist, will have long deserted our home planet.
30:35But how will the universe end?
30:39The age of the universe enables us to not only understand where we came from, but potentially the fate of the universe.
30:49What will happen millions and billions of years from now.
30:53If scientists confirm the value of the Hubble constant, the elusive figure that tells us just how fast the universe is expanding,
31:02it will tell us the age of the universe and it will help us predict its end.
31:06Measuring the Hubble constant is measuring the expansion rate today, right now.
31:12It's like checking your speedometer at one moment.
31:15But just because it's your speed now, it doesn't mean it was the same speed when you left your home or the same speed when you'll be on the freeway.
31:23How the expansion changes over time will control the fate of the cosmos.
31:27So depending on the Hubble constant, the universe could continue to expand, it could accelerate its expansion rate, or it could be decelerating.
31:38At the moment, galaxies are racing apart.
31:43A continually expanding universe will cool down as it spreads out.
31:48Another name for this eternal expansion is the big freeze.
31:54Because as everything gets spread out, the density is lower and there's no more opportunities for temperature differences.
32:02Everything just gets colder and colder and colder and colder.
32:06Slowly, eternally approaching absolute zero.
32:09The more matter is spread out, the less chance there is for star formation.
32:15And so the universe's continued expansion means our night sky and every night sky in the universe will inevitably continue to get darker and darker and darker as things move further away and as stars die off.
32:29Eventually, all the stars will go out and there will just be the leftovers, which we call the degenerates. Black holes, white dwarves, rogue planets. It's going to be a very, very sad place.
32:46The last refuge of any matter at all will be black holes.
32:49You've got a big black hole in the middle of each galaxy over trillions of years, everything in galaxies fall in.
32:57So finally you're left with big black holes over vast distances, separated almost universes away.
33:04So getting towards the big freeze, black holes themselves start to evaporate.
33:12There won't even be black holes at the end of this accelerating universe.
33:16All that's left is very, very low energy photons and a little bit of matter dispersed throughout the universe and there's nothing left. That's it.
33:27We call that the heat death of the universe. There's no longer any place that has more energy or more heat. It's all just thin, barely there photons.
33:37It's fascinating scientifically, but from a human standpoint, not a lot of fun to think about.
33:42But if the Hubble constant, the expansion rate of the universe keeps increasing, then the end of the universe could be a lot scarier and come a lot sooner.
33:54A lot sooner.
33:57One possibility is that the expansion of the universe will accelerate and continue to accelerate forever, faster and faster and faster.
34:06And if that happens, we face a scenario that we call the big rip, where actually the whole of space essentially just gets ripped to shreds.
34:14So the solar system is going to get ripped apart. Then the sun and the planets themselves will start to get ripped apart.
34:23And finally, it works its way down to atoms and atoms gets ripped apart.
34:27And we're starting to see effects on space and time. Space is ripped apart. Time comes to a stop.
34:34So in this scenario, time and space have no meaning. If everything is infinitely far apart, then space doesn't really exist. It's sort of beyond our comprehension.
34:52Working out the expansion rate will tell us which scenario we face. But for now, the lifespan of the universe is unknown.
35:04Maybe we need to investigate the other end of the timeline. But how can we get a fix on the age of the universe without understanding its origin?
35:14As you go back in time towards the Big Bang, our knowledge of physics really goes out the window.
35:22Temperatures off the scale. Pressure off the scale. The way everything behaved is just so different that the rules we have now do not apply.
35:31The biggest problem of all? What came just before the Big Bang?
35:36The Big Bang. Einstein's general relativity predicts that all the matter and energy in the universe was concentrated down to a single point. A singularity.
35:48The singularity is like the part of those old maps that says, here be dragons.
35:55Singularities are a problem. We don't like them. This is where basically you have a finite amount of matter in the universe, but it's squeezed down into zero volume.
36:04So it would be infinitely dense. Infinite densities don't actually happen in nature. This is a sign that our math is breaking down.
36:13This is a sign that we need to replace that with a new understanding.
36:19Many now believe Einstein was wrong. There was no singularity. Begging the question, could the age of the universe be infinite?
36:34Scientists investigating the age of the universe are struggling to understand its origins. Could that be because there was no beginning? Could the universe be infinite?
36:49Because we think we live and we die, we project that onto the universe. But that may not be the case.
36:56The idea of an infinite universe is no more strange than the idea of a singularity. And in fact, throughout most of history, astronomers thought that the universe was probably infinite.
37:07The foundation of our mathematical understanding of the universe, Einstein's general relativity, has a problem. It doesn't translate to the world of the very tiny, which is why its laws break down close to the Big Bang.
37:23General relativity does a great job at describing things on scales that you and I are familiar with, and things like how planets move and how galaxies evolve, all the big stuff.
37:35Quantum mechanics, on the other hand, describes the world of the very small, the world of the atoms. The problem is that these two theories don't fit well together at all.
37:45A new theory, known as loop quantum gravity, brings quantum theory and relativity together. And it makes a stunning prediction.
37:57So, one possibility is that the end of the universe could kind of match onto the beginning of a new universe and create a cycle of universes, one after the other.
38:08Nicknamed the big bounce, it predicts a universe that stops expanding and switches into reverse.
38:17And the idea here is that the universe can expand for a time, stop expanding and then begin to contract again. And some have suggested that perhaps there's a cycle of expanding and compressing, it bounces back over again.
38:32One of the appeals of the bouncing model is that it allows us to get beyond the singularity.
38:36A bit like recycling on Earth. All the components get crushed down and then reused, giving the cosmos no beginning and no end.
38:48If the universe is cyclic, does the age even have a meaning?
38:53Age is a construct of humanity because we need to count time. But if the universe is infinite, maybe it doesn't matter in the big scheme of things.
39:00A contracting and expanding universe messes with the concept of age. But the very idea of an expanding universe provides another cosmic curveball.
39:13It might not be alone. It might be just one ageless universe among many.
39:18It's an idea embedded in the math of the big bang.
39:24The most popular theory we have in astrophysics for what put the bang into our big bang is inflation.
39:29This idea that there was a kind of dark energy on steroids that made our universe double over and over, not every seven billion years, but every split second, creating out of almost nothing, a big bang.
39:43When the universe was just a hundredth of a billionth of a trillionth of a trillionth of a trillionth of a second old, it underwent a period of rapid expansion called inflation.
39:55It doubled in size at least 90 times, going from the size of a subatomic particle to that of a golf ball.
40:04The problem with this inflation is, but it doesn't really stop. It just makes this ever bigger space and says that, yeah, well, OK, there was one region of space where this crazy doubling stopped and galaxies formed and that's us.
40:18But there's this vast realm out there where inflation is still happening.
40:22In the spots where inflation stops, parallel universes form.
40:28This eternal inflation means that new universes are popping to existence all the time, but they're completely separated one from the other.
40:37Many of my colleagues hate parallel universes.
40:41They just don't like the idea that our universe is so big and most of it is off limits for us.
40:45If you are willing to be a bit more humble and accept that the reality might be much, much bigger than we will ever see, then parallel universes feel pretty natural.
40:57It's really interesting how everything in the universe is tied together.
41:02We can start with a simple question like, how old is the universe?
41:05How old is the universe?
41:06And here we are questioning virtually everything about the universe.
41:11Cosmology's century long search for the age of the universe forces us to question our cosmological model, the nature of gravity and even time itself.
41:23The age of the universe does bring up sort of profound philosophical questions about how a universe can even start.
41:33How can you create something from nothing?
41:36The vast majority of whatever the universe is, is eternally hidden to us.
41:44So we answer the questions, how big, how old?
41:48And those very answers show us that we don't even know if we've asked the right questions to begin with.
41:53We'll see you next time.
41:54We'll see you next time.
41:55Bye.
41:56Bye.
41:57Bye.
41:58Bye.
41:59Bye.
42:00Bye.
42:01Bye.
42:02Bye.