0:00:09 > 0:00:11There's an idea, once thought
0:00:11 > 0:00:16so radical that just mentioning it was considered pure insanity.
0:00:20 > 0:00:24But now, these scientists are daring to believe it's actually true.
0:00:26 > 0:00:30They think that our universe is not alone.
0:00:30 > 0:00:35It's just one of an infinite number of weird and wonderful worlds.
0:00:37 > 0:00:40Some, where life is familiar.
0:00:40 > 0:00:43Others, where things turned out a little differently.
0:00:44 > 0:00:48The dinosaur-killing asteroid, that was our lucky break,
0:00:48 > 0:00:53missed Earth, so there are no humans, just dinosaurs in Winchester today.
0:00:53 > 0:00:56Some of these worlds are so strange that the laws of nature no
0:00:56 > 0:00:58longer apply.
0:01:00 > 0:01:03So these students might, for example, be going to
0:01:03 > 0:01:06class in five dimensions, rather than four dimensions.
0:01:06 > 0:01:09Or they might be talking about a whole different force,
0:01:09 > 0:01:11the blue force, that we don't have in our universe.
0:01:13 > 0:01:17In others, infinite copies of you are playing out every
0:01:17 > 0:01:20possible storyline of your life.
0:01:20 > 0:01:24So, I every time I flip a coin, say heads or tails, that is
0:01:24 > 0:01:26just some little quantum accident.
0:01:26 > 0:01:30The universe is splitting into two worlds.
0:01:30 > 0:01:33It sounds like a plot stolen straight from Hollywood,
0:01:33 > 0:01:37but some scientists think they've actually found the evidence
0:01:37 > 0:01:40to prove the theory is true.
0:01:40 > 0:01:45I was so elated and happy and couldn't believe my eyes that
0:01:45 > 0:01:49I allowed myself for a few minutes to jump up and down.
0:01:58 > 0:02:01And if these scientists are right, the question isn't
0:02:01 > 0:02:06whether multiple universes exist, it's which one are we in?
0:02:21 > 0:02:25Ever since we've been studying the night sky, we've been able to
0:02:25 > 0:02:30rely on one simple idea to describe everything around us,
0:02:30 > 0:02:35everything on Earth and beyond, all the planets, all the stars
0:02:35 > 0:02:37and all the galaxies.
0:02:41 > 0:02:44This idea is what we call "our universe".
0:02:49 > 0:02:53The universe as one beautiful unique thing, the sum total of all
0:02:53 > 0:02:56the stuff we can see and everything we know about.
0:02:57 > 0:03:03And for a long, long time, we've been pretty happy with this idea.
0:03:03 > 0:03:05It makes total sense.
0:03:11 > 0:03:14But recently, a few inconvenient
0:03:14 > 0:03:16scientists are finding flaws
0:03:16 > 0:03:19with this long-cherished idea.
0:03:21 > 0:03:24In fact, they think it's time to throw the whole notion out
0:03:24 > 0:03:26the window.
0:03:36 > 0:03:39For cosmologists, the universe extends to the furthest point from
0:03:39 > 0:03:44which light has had time to reach us, since the beginning of time.
0:03:44 > 0:03:48It's what we call the Observable Universe,
0:03:48 > 0:03:50beautifully captured in this one image.
0:04:00 > 0:04:04This is what we affectionately call "our universe",
0:04:04 > 0:04:07this spherical region of space from which light has the time to
0:04:07 > 0:04:12reach us so far, during the 13.8 billion years since our Big Bang.
0:04:15 > 0:04:19You can ask - is that really everything that is or is this
0:04:19 > 0:04:21just everything we can see?
0:04:21 > 0:04:24And we've come a long way in cosmology to a point where we
0:04:24 > 0:04:27have pretty strong evidence that the actual universe,
0:04:27 > 0:04:30the whole universe, is much, much bigger than this.
0:04:30 > 0:04:34It's hard to imagine how we cannot ask the question - what is
0:04:34 > 0:04:38beyond the walls of this object and what was there before the Big Bang?
0:04:42 > 0:04:45So, although I think this is everything that we can observe,
0:04:45 > 0:04:49I don't think this is everything that exists.
0:04:49 > 0:04:52So, this may really only be just
0:04:52 > 0:04:55a small part of something that,
0:04:55 > 0:04:58you know, is really much, much bigger.
0:05:01 > 0:05:05So this universe, stretching out 13.8 billion light
0:05:05 > 0:05:10years into space, is a beautiful thing, but it's not the only thing.
0:05:10 > 0:05:12So I'm afraid, universe,
0:05:12 > 0:05:15it's time for you to retire as the only thing out there.
0:05:15 > 0:05:18You've had a good run, given us a lot of good times,
0:05:18 > 0:05:20but it's time to go.
0:05:20 > 0:05:24Why don't you just go down to Florida and buy a condo?
0:05:24 > 0:05:25A very large condo.
0:05:37 > 0:05:41Sending the universe into retirement might seem like a bad joke,
0:05:43 > 0:05:45but for these scientists,
0:05:45 > 0:05:51the idea of just one universe simply doesn't make sense.
0:05:59 > 0:06:03They are convinced that for different reasons,
0:06:03 > 0:06:06our universe is just one of an infinite number of others.
0:06:12 > 0:06:16One universe in a vast, vast multiverse.
0:06:22 > 0:06:25# If I was a flower growing wild and free
0:06:25 > 0:06:27# All I'd want is you to be my sweet honey bee
0:06:27 > 0:06:30# And if I was a tree growing tall and green
0:06:30 > 0:06:31# All I'd want is... #
0:06:31 > 0:06:35The maths is devilishly complicated, but they stem from questions
0:06:35 > 0:06:38so simple, a child could ask them.
0:06:38 > 0:06:41So, where does the universe really end?
0:06:49 > 0:06:52Max Tegmark is a professor of cosmology.
0:06:52 > 0:06:55When he isn't playing Lego, he spends his time contemplating
0:06:55 > 0:06:59some of the big questions about life, the universe and everything.
0:07:01 > 0:07:04# All I'd want is you to shade me and be my leaves... #
0:07:06 > 0:07:10And there's one particular question that's been bothering him.
0:07:10 > 0:07:16Is there an end to space? Or does it go on for ever?
0:07:16 > 0:07:18When I was a little kid,
0:07:18 > 0:07:22I used to wonder whether space went on for ever and I used to think
0:07:22 > 0:07:27- it has to be infinite, because it would be silly for it to have an end.
0:07:27 > 0:07:31Would there be a sign there, saying 'Warning, space ends here.
0:07:31 > 0:07:35'Mind the gap'? And if so, what's on the other side?
0:07:38 > 0:07:41So we don't have a shred of evidence suggesting that space actually
0:07:41 > 0:07:44ends here, exactly at the edge of what we can see
0:07:44 > 0:07:48and I don't have a single colleague in physics either who believes that.
0:07:48 > 0:07:51It would be a little bit like believing if you're
0:07:51 > 0:07:54in the boat in the ocean, that the ocean ends exactly at your horizon.
0:07:54 > 0:07:56Why should it?
0:07:58 > 0:08:01The idea that space goes on for ever seems simple enough.
0:08:01 > 0:08:06But this relatively straightforward concept has profound implications.
0:08:08 > 0:08:11Just as this house is made out of fundamental building
0:08:11 > 0:08:15blocks that we call Legos, everything in our world is
0:08:15 > 0:08:18made of fundamental building blocks we call elementary particles.
0:08:18 > 0:08:21And if you have some random process,
0:08:21 > 0:08:25arranging elementary building blocks in a finite volume, there
0:08:25 > 0:08:29are of course very many different ways in which it could do this.
0:08:29 > 0:08:32And that means that if this process repeats,
0:08:32 > 0:08:35and an infinite number of other volumes of the same size,
0:08:35 > 0:08:37then we're guaranteed that eventually,
0:08:37 > 0:08:40it's going to create every possible arrangement.
0:08:44 > 0:08:49According to Max, and the hard and fast laws of probability,
0:08:49 > 0:08:53our universe is one of an infinite number of others,
0:08:53 > 0:08:56each one about 90 billion light years across
0:08:56 > 0:09:00and each containing a finite number of particles.
0:09:00 > 0:09:05And just like Max, if you assembly these Lego bricks enough times,
0:09:05 > 0:09:08you'll create every possible variation of them,
0:09:08 > 0:09:13eventually ending up with two model houses exactly the same.
0:09:13 > 0:09:17Likewise, rearrange the particles in the universe often enough
0:09:17 > 0:09:22and you end up with an identical universe and an identical Earth.
0:09:22 > 0:09:29And even a Max over there who is identical to me, not just
0:09:29 > 0:09:34in his physical appearance, but in that he actually feels that he is me.
0:09:34 > 0:09:40So, the answer to Max's question of what's at the edge of space
0:09:40 > 0:09:43leads unavoidably to a world where other universes are not only
0:09:43 > 0:09:47likely, but are a mathematical certainty.
0:09:49 > 0:09:52But there's another idea that questions our unique
0:09:52 > 0:09:54place in the cosmos.
0:09:56 > 0:10:00This time, it's based not on a question of where space ends,
0:10:00 > 0:10:03but rather, how did it all begin?
0:10:18 > 0:10:21Professor Anthony Aguirre has been grappling with the sticky
0:10:21 > 0:10:24matter of the origins of our universe.
0:10:28 > 0:10:31And his attempts to find answers lead to a completely
0:10:31 > 0:10:33different sort of multiverse.
0:10:40 > 0:10:43This picture is actually something pretty amazing.
0:10:43 > 0:10:46It's a picture of our observable universe,
0:10:46 > 0:10:49just a couple of hundred thousand years after what
0:10:49 > 0:10:52we call the Big Bang and it's a picture that's been
0:10:52 > 0:10:56taken in what's called the cosmic microwave background radiation.
0:10:56 > 0:11:00This is radiation that's come to us to telescopes like this one
0:11:00 > 0:11:05and many others since and it gives us an actual image
0:11:05 > 0:11:09of what the state of the universe was like at incredibly early times.
0:11:12 > 0:11:16The image, which depicts both the edge of the universe as well as the
0:11:16 > 0:11:21earliest light we can see, revealed that all the matter in the universe,
0:11:21 > 0:11:25all the stars and all the galaxies, were very evenly distributed.
0:11:26 > 0:11:30It suggested something happened to make it that way.
0:11:32 > 0:11:36And that something is a process called inflation.
0:11:36 > 0:11:38The theory of inflation is that early on,
0:11:38 > 0:11:42the universe didn't just expand, but it expanded exponentially,
0:11:42 > 0:11:46meaning it doubled in size over and over again in a very small
0:11:46 > 0:11:47fraction of a second.
0:11:47 > 0:11:53Now, what this did was it took a pattern of variations
0:11:53 > 0:11:57in the density of the universe, the same pattern we see now, and it took
0:11:57 > 0:12:01it from a tiny size and stretched it over the entire observable universe.
0:12:05 > 0:12:09According to inflation, while our universe was just a hot
0:12:09 > 0:12:13pool of fire, the very fabric of space inflated.
0:12:13 > 0:12:16It was so rapid that that the uniformity of the baby
0:12:16 > 0:12:17universe was preserved.
0:12:19 > 0:12:24But for Anthony, inflation was more than just a method of expansion.
0:12:24 > 0:12:29It was a driving force that created our universe in the first place and
0:12:29 > 0:12:33if it could happen once, there was nothing to stop it happening again.
0:12:33 > 0:12:34And again.
0:12:34 > 0:12:36And again.
0:12:38 > 0:12:41This is eternal inflation.
0:12:41 > 0:12:46So inflation was a little bit like a genie that you let out of a bottle.
0:12:46 > 0:12:50You open the bottle and you ask the genie, "Make me a universe,"
0:12:50 > 0:12:52and the genie does a spectacular job of it,
0:12:52 > 0:12:55but then the genie says, "Well, I'm going to make another universe."
0:12:55 > 0:12:57"Wait a minute, I just wanted one."
0:12:57 > 0:13:00"Nah, I'm going to make ten more universes." "No, I just wanted one."
0:13:00 > 0:13:02"I'm going to make an infinite number of universes."
0:13:02 > 0:13:05That's what we're talking about with eternal inflation.
0:13:05 > 0:13:08Once the genie gets out of the bottle, it just never stops.
0:13:11 > 0:13:16So, asking two simple questions have, for different reasons,
0:13:16 > 0:13:18led to the same conclusion.
0:13:18 > 0:13:23What we see when we look up at the night sky is just a tiny
0:13:23 > 0:13:26fraction of the story of our existence.
0:13:30 > 0:13:33However, things get even stranger
0:13:33 > 0:13:35when you consider the hardest question of all.
0:13:41 > 0:13:43How does the universe actually work?
0:13:52 > 0:13:56Professor Seth Lloyd resides in the totally weird world of quantum
0:13:56 > 0:14:00physics, where nothing is quite as it seems.
0:14:03 > 0:14:07And where things can be in two places at the same time.
0:14:07 > 0:14:11HE CHUCKLES
0:14:11 > 0:14:15The important thing to remember about quantum mechanics is it's weird.
0:14:15 > 0:14:16So, stop, stop, stop, stop!
0:14:16 > 0:14:18I don't understand that,
0:14:18 > 0:14:22but I console myself with the fact that nobody understands that.
0:14:24 > 0:14:27It was from an attempt to make sense of this strange quantum
0:14:27 > 0:14:30world that the idea of many universes was born.
0:14:33 > 0:14:35It all began in the 1950s,
0:14:35 > 0:14:39when maverick genius Hugh Everett tried to explain weird
0:14:39 > 0:14:44phenomena at the heart of the now infamous Double Slit experiment,
0:14:46 > 0:14:50where electrons can be waves and particles at the same time.
0:14:52 > 0:14:55The famous Double Slit experiment in quantum mechanics where
0:14:55 > 0:14:59a beam of electrons go through space and then they go through two slits.
0:14:59 > 0:15:03Now, the wave goes through both slits at once and on the far side,
0:15:03 > 0:15:06the wave interferes with itself and then hits a screen
0:15:06 > 0:15:10and makes an interference pattern. You might say - come on!
0:15:10 > 0:15:11There's lots of electrons.
0:15:11 > 0:15:14Like some of the electrons have waves, big deal.
0:15:14 > 0:15:17But in fact, if you attenuate this beam of electrons,
0:15:17 > 0:15:19so there's only one electron going through at a time,
0:15:19 > 0:15:22you still see this interference pattern, even though
0:15:22 > 0:15:24there's only one electron,
0:15:24 > 0:15:27so the wave for one electron goes through both slits at once.
0:15:27 > 0:15:30Ends up on the screen, interferes and makes this pattern.
0:15:30 > 0:15:31In the experiment,
0:15:31 > 0:15:35when single electrons are fired through two slits,
0:15:35 > 0:15:38you'd expect them to create two vertical stripes on the screen
0:15:38 > 0:15:43behind, but in fact, they mysteriously create three.
0:15:43 > 0:15:46The pattern is only possible
0:15:46 > 0:15:49if the individual electrons behave as waves,
0:15:49 > 0:15:54passing through both slits at the same time.
0:15:54 > 0:15:56It's completely counterintuitive
0:15:56 > 0:15:59and simply doesn't make sense.
0:15:59 > 0:16:03The trouble is it seems to be true.
0:16:03 > 0:16:08It's a problem that even the finest minds in physics have battled with.
0:16:08 > 0:16:12Actually, there's a lot of resistance to quantum mechanics.
0:16:12 > 0:16:16The most famous resistor of quantum mechanics was Einstein,
0:16:16 > 0:16:21who famously got his Nobel prize for work he did on quantum mechanics,
0:16:21 > 0:16:26but he nonetheless didn't like it, "God doesn't play dice," he said.
0:16:26 > 0:16:29But he was wrong. Suck it up, Albert!
0:16:33 > 0:16:37And like Einstein, Hugh Everett was also unhappy with the existing
0:16:37 > 0:16:39interpretation of the experiment.
0:16:40 > 0:16:43And so, he came up with a radical new theory.
0:16:44 > 0:16:48In the mid 20th century, Hugh Everett came up with what
0:16:48 > 0:16:52he originally called the Many Worlds theory of quantum mechanics.
0:16:52 > 0:16:54So, the idea here is that
0:16:54 > 0:16:57when you make a measurement of a particle that's here
0:16:57 > 0:17:01and there at the same time, and you find the particle over here,
0:17:01 > 0:17:05then there's a you which finds the particle over here in this world,
0:17:05 > 0:17:09but at the same time, there's another world over there where another
0:17:09 > 0:17:12you has found the particle over there.
0:17:12 > 0:17:15And both of these worlds are equally real.
0:17:18 > 0:17:22Hugh Everett's big idea was that at the point when the particle can go
0:17:22 > 0:17:27through one slit or the other, the universe literally splits in two.
0:17:28 > 0:17:31The particle goes through both slits at once,
0:17:31 > 0:17:34but it does so in two separate universes.
0:17:36 > 0:17:39It was both ingenious and terrifying,
0:17:39 > 0:17:44and at the time, it seemed totally bonkers.
0:17:46 > 0:17:49Despite the fact that now it really is a widely accepted
0:17:49 > 0:17:52theory of quantum mechanics, at the time, it got a very frosty reception.
0:17:52 > 0:17:55And he couldn't get a position in physics.
0:17:57 > 0:17:59Everett's extreme idea set him at loggerheads
0:17:59 > 0:18:02with the establishment, and sadly, he died
0:18:02 > 0:18:05before ever receiving the recognition he deserved.
0:18:05 > 0:18:10But in recent years, there's been a remarkable turn-around.
0:18:10 > 0:18:13Everett's idea of many universes,
0:18:13 > 0:18:17bizarre and counter-intuitive as it seems,
0:18:17 > 0:18:21is now considered by many to be the only way to explain
0:18:21 > 0:18:23how the world really works.
0:18:25 > 0:18:27Everybody's intuition about quantum mechanics is wrong
0:18:27 > 0:18:30and so if you're going to demand that your intuition be right,
0:18:30 > 0:18:33you're just going to be unhappy. On the other hand,
0:18:33 > 0:18:36if you can just accept that your intuition is wrong, you know,
0:18:36 > 0:18:39grab your quantum surfboard and surf that quantum wave,
0:18:39 > 0:18:40then life can be good.
0:18:44 > 0:18:49In spite of the weight of evidence now pointing towards a multiverse,
0:18:49 > 0:18:54until very recently, anyone dabbling in this field risked career suicide.
0:18:55 > 0:18:57I couldn't get a job to save my life.
0:18:57 > 0:18:58When I was a grad student,
0:18:58 > 0:19:03I used to secretly print out my multiverse related papers
0:19:03 > 0:19:06when my adviser was far from the laser printer
0:19:06 > 0:19:08and I didn't even show these papers to him
0:19:08 > 0:19:10until after he'd signed my dissertation
0:19:10 > 0:19:13because it was considered mostly science fiction
0:19:13 > 0:19:14and speculation back then.
0:19:14 > 0:19:19This job at MIT was the only job I was ever interviewed for.
0:19:19 > 0:19:23I was on the verge of having to drive a taxi cab.
0:19:23 > 0:19:25HE CHUCKLES
0:19:26 > 0:19:31Three entirely different questions have all led to the same conclusion,
0:19:31 > 0:19:35the multiverse is now impossible to ignore.
0:19:40 > 0:19:43Beyond the realm of our most powerful telescopes,
0:19:43 > 0:19:48Max believes infinite universes to be a mathematical certainty.
0:19:49 > 0:19:52He thinks the universe simply cannot end...
0:19:54 > 0:19:57..while for Anthony, the quest to understand our origins
0:19:57 > 0:20:01provides a tantalising glimpse of a time before,
0:20:01 > 0:20:06when inflation brought countless other universes into existence.
0:20:08 > 0:20:14And, as if that wasn't enough, Seth's strange quantum world
0:20:14 > 0:20:18suggests the universe splitting into multiple others all around us.
0:20:20 > 0:20:23The notion of one universe is clearly resting
0:20:23 > 0:20:26on perilously shaky foundations.
0:20:26 > 0:20:30It's a dramatic turn of events that could fundamentally change
0:20:30 > 0:20:33the way we view ourselves for ever.
0:20:39 > 0:20:43But while these scientists might agree that the universe needs
0:20:43 > 0:20:49to be retired, deciding what the multiverse actually looks like
0:20:49 > 0:20:51is an entirely different matter.
0:21:08 > 0:21:12The first and perhaps most straightforward model is
0:21:12 > 0:21:14the infinite patchwork multiverse.
0:21:16 > 0:21:19Arguably, it's the least controversial idea,
0:21:19 > 0:21:23but nonetheless, it has some pretty astounding consequences.
0:21:29 > 0:21:33Even if the multiverse, all of space, is infinite,
0:21:33 > 0:21:35the part of space that we can observe,
0:21:35 > 0:21:38our universe, is finite, with a finite amount of stuff.
0:21:38 > 0:21:41Only about 10 to the power of 80 atoms,
0:21:41 > 0:21:44which can only be arranged in a finite number of ways.
0:21:44 > 0:21:48So if you start considering all the other regions of space,
0:21:48 > 0:21:50if you roll the dice infinitely many times,
0:21:50 > 0:21:54eventually, we are guaranteed to find an identical copy
0:21:54 > 0:21:58of our whole universe, as well as countless variations
0:21:58 > 0:22:01where things are similar to here but still different.
0:22:04 > 0:22:09The infinite multiverse is a bit like an endless patchwork quilt.
0:22:09 > 0:22:13Each patch is another universe, the same size as our own,
0:22:13 > 0:22:16each one containing a finite number of particles,
0:22:16 > 0:22:20each with its own configuration that forms a universe.
0:22:23 > 0:22:27So what might these other universes be like?
0:22:27 > 0:22:32We know exactly what our universe looks like, the familiar everyday.
0:22:32 > 0:22:34And yet another one,
0:22:34 > 0:22:38the dinosaur-killing asteroid that was our lucky break
0:22:38 > 0:22:41missed Earth, so there are no humans,
0:22:41 > 0:22:43just dinosaurs in Winchester today.
0:22:44 > 0:22:48There is another one where the powers that be decided
0:22:48 > 0:22:51to film this interview not here in Winchester
0:22:51 > 0:22:53but at Niagara Falls,
0:22:53 > 0:22:56and yet another one, I didn't make it as a physicist,
0:22:56 > 0:22:59but I'm actually enjoying life working as a bartender.
0:22:59 > 0:23:02Then there's a whole bunch which are very similar
0:23:02 > 0:23:05where I just chose to dress a little bit differently.
0:23:05 > 0:23:10In this multiverse, every single possibility is played out somewhere.
0:23:10 > 0:23:14There are infinite copies of Earth, some familiar,
0:23:14 > 0:23:18others where history took an entirely different course.
0:23:18 > 0:23:22One where, actually, Germans won World War II
0:23:22 > 0:23:24and wir reden alle Deutsch jetzt,
0:23:24 > 0:23:29and finally, if we go a bit over a googolplex meters away, where -
0:23:29 > 0:23:32a googolplex is 1 with a googol zeroes,
0:23:32 > 0:23:34and a googol is 1 with 100 zeroes -
0:23:34 > 0:23:40then we come to a universe that looks exactly like this one.
0:23:40 > 0:23:46It sounds like fantasy, but this is exactly what the maths predicts.
0:23:46 > 0:23:51Somewhere right now, you're being attacked by aliens.
0:23:51 > 0:23:54Another you has just won Olympic gold.
0:23:54 > 0:23:57In one world you're behind bars,
0:23:57 > 0:24:00in another you've just been elected president.
0:24:00 > 0:24:04The possibilities are only limited by your imagination.
0:24:10 > 0:24:15An infinite multiverse with infinite copies of you
0:24:15 > 0:24:18is probably more than enough to be getting on with.
0:24:21 > 0:24:25But this is just the first stop on the magical multiverse tour.
0:24:29 > 0:24:33Anthony has a very different vision of the multiverse.
0:24:33 > 0:24:37It's a place of even more mind-bending diversity,
0:24:37 > 0:24:41where not even the laws of nature are the same.
0:24:43 > 0:24:46Imagine this lake is that inflationary substance
0:24:46 > 0:24:48that existed before our Big Bang.
0:24:48 > 0:24:51But this medium has the property that it inflates the universe,
0:24:51 > 0:24:54it doubles its volume in size every tiny fraction of a second.
0:24:55 > 0:24:59That's the inflating background, but then within that background,
0:24:59 > 0:25:00bubbles can form.
0:25:05 > 0:25:08And although these bubbles start small, they grow.
0:25:08 > 0:25:12They grow, in fact, infinitely big, and so within one of these bubbles
0:25:12 > 0:25:16could reside our entire observable universe and even a whole lot more.
0:25:16 > 0:25:19As this process goes on, you end up with a huge
0:25:19 > 0:25:22and infinite, even, number of these bubbles.
0:25:22 > 0:25:25Some could be our observable universe,
0:25:25 > 0:25:29some could be other universes with potentially different properties.
0:25:32 > 0:25:34And it's these different properties
0:25:34 > 0:25:38that mark this multiverse out from the rest.
0:25:38 > 0:25:42Unlike the others, in the inflationary multiverse,
0:25:42 > 0:25:47the laws of physics vary from one universe to the next,
0:25:47 > 0:25:51making it a very strange place indeed.
0:25:51 > 0:25:54What's fascinating about this sort of multiverse is that
0:25:54 > 0:25:56these universes could have incredibly diverse properties.
0:25:56 > 0:25:58Some of these might be like our universe.
0:25:58 > 0:26:00They might have very low energy,
0:26:00 > 0:26:03they might have electromagnetic force,
0:26:03 > 0:26:06they might have about the same strength of force as we have.
0:26:06 > 0:26:08Atoms, planets, stars, galaxies,
0:26:08 > 0:26:11everything we see could be in some of these other bubbles as well.
0:26:11 > 0:26:14But they could be radically different.
0:26:14 > 0:26:15For example, some of the bubbles
0:26:15 > 0:26:17might not have an electromagnetic force.
0:26:17 > 0:26:19Some of them might have an electromagnetic force
0:26:19 > 0:26:22but it's much stronger than ours and atoms wouldn't exist
0:26:22 > 0:26:24because they would all collapse or explode.
0:26:24 > 0:26:25In these other universes,
0:26:25 > 0:26:27there might be physics students taking physics class
0:26:27 > 0:26:30but as well as learning different things in history class,
0:26:30 > 0:26:32they learn different things in physics class
0:26:32 > 0:26:33than physics students in our universe.
0:26:33 > 0:26:37So these, these students might for example be going to class
0:26:37 > 0:26:39in five dimensions rather than four dimensions,
0:26:39 > 0:26:43or they might be talking about a whole different force,
0:26:43 > 0:26:46the blue force, that we don't have in our universe.
0:26:46 > 0:26:47They might not have atoms.
0:26:47 > 0:26:50They might have other strange collections of quarks
0:26:50 > 0:26:53that combine in some strange way and create more complicated forms
0:26:53 > 0:26:56that can form life in physics students.
0:26:56 > 0:27:01There might be... boy, I haven't thought about this very much.
0:27:01 > 0:27:03I'm just making it up!
0:27:03 > 0:27:06HE LAUGHS
0:27:07 > 0:27:11Infinite bubble universes bobbing around
0:27:11 > 0:27:15on an inflationary sea where the laws of physics run riot.
0:27:16 > 0:27:18Maybe it's making you feel like
0:27:18 > 0:27:20you've consumed too much bubbly yourself.
0:27:23 > 0:27:27But this is nothing compared to life in the quantum multiverse.
0:27:29 > 0:27:33In a world where things can be in two places at once,
0:27:33 > 0:27:36there are multiverses lurking right under your nose.
0:27:41 > 0:27:42Great!
0:27:43 > 0:27:44Mmm.
0:27:44 > 0:27:47Pan-fried dumplings, my favourite.
0:27:48 > 0:27:51The quantum multiverse could be all around us,
0:27:51 > 0:27:53but we can't see it, because it operates
0:27:53 > 0:27:57according to the utterly bizarre laws of quantum mechanics.
0:28:00 > 0:28:04So the quantum multiverse is not separated from us by distance.
0:28:04 > 0:28:06It's not some place very, very far away.
0:28:06 > 0:28:09It's some place that's effectively here in space,
0:28:09 > 0:28:11but the complexity of the quantum dynamics
0:28:11 > 0:28:15prevents these different branches from talking to each other.
0:28:16 > 0:28:20The quantum multiverse comes from Hugh Everett's idea
0:28:20 > 0:28:24that every single event that can happen does happen.
0:28:24 > 0:28:28They just take place in parallel worlds.
0:28:29 > 0:28:33It's like an infinite garden of endlessly forking paths.
0:28:33 > 0:28:37How do we make sense of this wacky quantum multiverse
0:28:37 > 0:28:41in which all possibilities exist simultaneously?
0:28:41 > 0:28:45So every time I flip a coin, say heads or tails,
0:28:45 > 0:28:47that is just some little quantum accident.
0:28:47 > 0:28:51The universe is splitting into two worlds every time it comes up
0:28:51 > 0:28:54heads or tails, so our experience of this splitting
0:28:54 > 0:28:59is like the experience of walking through a garden of paths that fork.
0:28:59 > 0:29:03When we come to a fork in the path, we take one or the other,
0:29:03 > 0:29:05heads or tails.
0:29:05 > 0:29:08But both forks exist at the same time.
0:29:08 > 0:29:10We only experience one of them.
0:29:10 > 0:29:15Every time I flip a coin, the universe splits into two worlds.
0:29:15 > 0:29:18Heads I stick around, tails I'm out of here.
0:29:20 > 0:29:22OK, it's heads, I stick around.
0:29:22 > 0:29:29So in that other universe, where I got tails, the interview is over.
0:29:29 > 0:29:32Sorry, lady. HE CHUCKLES
0:29:33 > 0:29:35To understand what this might be like,
0:29:35 > 0:29:37imagine Seth's next few hours
0:29:37 > 0:29:40determined by the toss of a coin alone.
0:29:41 > 0:29:43I'd had enough of that interview. Let's see.
0:29:43 > 0:29:48I flip the coin again, heads I go left, tails I go right.
0:29:50 > 0:29:53Already, the universe has split into two,
0:29:53 > 0:29:57a Seth in a restaurant and another Seth wandering the streets.
0:29:57 > 0:29:59Maybe I should take a short cut over to the Bowery
0:29:59 > 0:30:03through this little alleyway here. Should I do it? Looks a little dark.
0:30:03 > 0:30:05Let's let the coin decide.
0:30:09 > 0:30:13Another flip and the universe splits again.
0:30:13 > 0:30:17In this one, Seth makes the fateful decision to walk down the alleyway.
0:30:32 > 0:30:33Hey!
0:30:33 > 0:30:35Hey, hey, hey, hey!
0:30:41 > 0:30:43But in another universe,
0:30:43 > 0:30:47the Seth who didn't take the short cut is safely taking a taxi home.
0:30:48 > 0:30:53So we can continue, so the me that went left went home,
0:30:53 > 0:30:55back to the hotel, good night's sleep.
0:30:55 > 0:30:59The me that went right said, "Let's see what Chinatown has to offer.
0:30:59 > 0:31:03"Here's an arcade. Shall I go in or not?"
0:31:03 > 0:31:07Another split, and one Seth decides to try his luck.
0:31:10 > 0:31:12MACHINE PINGS
0:31:15 > 0:31:17Yes, yes, yes!
0:31:18 > 0:31:21The other Seth chooses to walk home,
0:31:21 > 0:31:26which results in the great New York coffee disaster.
0:31:45 > 0:31:50After a few hours, multiple Seths occupy multiple universes.
0:31:55 > 0:32:01Each one irrevocably separated, existing in their own reality.
0:32:02 > 0:32:05Quantum accident, like setting down this alleyway...
0:32:05 > 0:32:08Each with its own independent future.
0:32:10 > 0:32:13This bewildering quantum multiverse
0:32:13 > 0:32:15is what's known as the Hilbert space.
0:32:16 > 0:32:20It's a place of endlessly forking paths and parallel realities.
0:32:22 > 0:32:25A place where every version of every event
0:32:25 > 0:32:30for every living organism on Earth is happening, somewhere.
0:32:33 > 0:32:37The number of possibilities is growing exponentially,
0:32:37 > 0:32:40doubling every time I flip a coin.
0:32:40 > 0:32:44There are literally gajillions of universes out there
0:32:44 > 0:32:46of which ours is only one.
0:32:46 > 0:32:50Actually, I calculated one day, that if you look at the total
0:32:50 > 0:32:52number of bits there could possibly be in the universe,
0:32:52 > 0:32:57so let's ask how many quantum coins could have been tossed since
0:32:57 > 0:33:01the universe began 13.8 billion years ago, a simple calculation
0:33:01 > 0:33:04tells you that the maximum number is ten to the 120.
0:33:04 > 0:33:08There have been ten to the 120 quantum coin tosses,
0:33:08 > 0:33:12which means that they're two to the ten to the 120
0:33:12 > 0:33:14different possible universes.
0:33:14 > 0:33:15It's a large number but it's finite.
0:33:15 > 0:33:17I just told you what it was.
0:33:17 > 0:33:18It's not infinite.
0:33:21 > 0:33:24The quantum multiverse feels like something
0:33:24 > 0:33:26straight out of a science fiction story.
0:33:28 > 0:33:32But, for some physicists, it's an inescapable reality.
0:33:34 > 0:33:38Whether you like it or not, the fact that we live in a multiverse
0:33:38 > 0:33:41is the dominant scientific paradigm.
0:33:42 > 0:33:45Suck it up, if I may say so again!
0:33:54 > 0:33:56This magical multiverse tour
0:33:56 > 0:34:00has taken us to some weird and wonderful places indeed.
0:34:00 > 0:34:03We've journeyed across an infinite multiverse quilt
0:34:03 > 0:34:07and dived into a giant inflating sea,
0:34:07 > 0:34:09and as if that wasn't enough,
0:34:09 > 0:34:12we've wandered through a thoroughly dizzying quantum maze.
0:34:13 > 0:34:16So, if you were starting to feel like you'd fallen down a rabbit hole
0:34:16 > 0:34:21into Wonderland, it's worth pausing for a moment to ask...
0:34:22 > 0:34:24Which theory is right?
0:34:25 > 0:34:27And can anyone actually prove it?
0:34:30 > 0:34:34For its most vociferous critics, the multiverse is unscientific
0:34:34 > 0:34:36because it can't be tested...
0:34:37 > 0:34:39..even in principle.
0:34:44 > 0:34:49So, without proof, doesn't this make the whole idea of the multiverse
0:34:49 > 0:34:50simply a waste of time?
0:34:54 > 0:34:56Well, not necessarily.
0:34:59 > 0:35:00Exciting new discoveries
0:35:00 > 0:35:03now mean that evidence for the multiverse
0:35:03 > 0:35:05might not be as far away as we think.
0:35:07 > 0:35:10In fact, one scientist thinks she may have already found it.
0:35:13 > 0:35:16# She's a true original... #
0:35:24 > 0:35:28Professor Laura Mersini-Houghton has a radically new vision
0:35:28 > 0:35:29of the multiverse.
0:35:29 > 0:35:34It's bold and daring and, even by the standards of the multiverse,
0:35:34 > 0:35:37it's considered highly controversial.
0:35:37 > 0:35:39Truth goes through three stages.
0:35:39 > 0:35:41First it's ridicule,
0:35:41 > 0:35:43then opposed strongly,
0:35:43 > 0:35:46and finally, it becomes self-evident.
0:35:48 > 0:35:51Perhaps now we are reaching the stage of self-evident.
0:35:54 > 0:35:57Laura's major breakthrough was to take two big ideas
0:35:57 > 0:35:58and put them together.
0:35:58 > 0:36:01She combined the physics of string theory
0:36:01 > 0:36:03with those of quantum mechanics.
0:36:05 > 0:36:08The mathematics involved is fiendishly complicated,
0:36:08 > 0:36:11and Laura is probably one of just a handful of people
0:36:11 > 0:36:13who can even begin to comprehend it.
0:36:15 > 0:36:17But, for us mere mortals,
0:36:17 > 0:36:23one way to picture it is as a landscape and a wave.
0:36:26 > 0:36:29Before our universe went through the Big Bang,
0:36:29 > 0:36:34we can think of the pre-Big Bang era as a space which is abstract,
0:36:34 > 0:36:38it's an energy space, and various places on this landscape,
0:36:38 > 0:36:42on this energy field can produce different universes.
0:36:46 > 0:36:51We can think of these waves leaping over the rocks as the wave function
0:36:51 > 0:36:55of the universe, trying to travel through this landscape structure.
0:36:55 > 0:36:58If I think of the rocks as the energy field,
0:36:58 > 0:37:01and each pocket on these rocks representing an energy valley
0:37:01 > 0:37:04on the landscape, as the waves come through,
0:37:04 > 0:37:07many of them will be trapped in different pockets,
0:37:07 > 0:37:09rather than travel any further.
0:37:10 > 0:37:13Each of these little pockets can be a potential birthplace
0:37:13 > 0:37:15for a universe similar to ours.
0:37:17 > 0:37:19Laura's idea was to represent space
0:37:19 > 0:37:23a bit like a mountain range of different energies.
0:37:23 > 0:37:26She thinks that our universe started out as a wave.
0:37:26 > 0:37:30As it crossed the landscape, some energy got trapped,
0:37:30 > 0:37:34creating different universes with different properties.
0:37:37 > 0:37:39It is without doubt a radical notion...
0:37:42 > 0:37:45..but Laura also predicted a series of anomalies,
0:37:45 > 0:37:47which she believed could actually be observed
0:37:47 > 0:37:49in our own night sky.
0:37:50 > 0:37:53One of these would even reveal how our universe
0:37:53 > 0:37:58was once entangled with another, through a process called cross-talk.
0:38:02 > 0:38:05These universes are not only producing space time,
0:38:05 > 0:38:07but they are also separating from one another.
0:38:07 > 0:38:10Each one of those is taking its own identity.
0:38:10 > 0:38:14However, traces of that infancy,
0:38:14 > 0:38:18of that cross-talk between all the surviving universes
0:38:18 > 0:38:20and the landscape structure,
0:38:20 > 0:38:23those are imprinted forever in our sky
0:38:23 > 0:38:27because, after all, what we look at today in the sky
0:38:27 > 0:38:30is just a blown-up version, a re-scaled version,
0:38:30 > 0:38:34of what once was in our universe when it was in its infancy.
0:38:34 > 0:38:38Laura predicted that this cross-talk would leave an imprint
0:38:38 > 0:38:42on our early universe, a bit like a birthmark,
0:38:42 > 0:38:47and we could see this as a cold spot in the cosmic microwave background.
0:38:48 > 0:38:52The detection of the cold spot was one of the signatures
0:38:52 > 0:38:56that we predicted by tracing forward the quantum entanglement
0:38:56 > 0:39:00of our universe with all the other surviving universes.
0:39:00 > 0:39:03We predicted that there should be a large area in the sky
0:39:03 > 0:39:07of about ten degrees, and indeed that's what was observed
0:39:07 > 0:39:10about seven months after we made the prediction.
0:39:11 > 0:39:15Remarkably, all Laura's predictions have since been observed,
0:39:15 > 0:39:17including this cold spot,
0:39:17 > 0:39:21which she claims is a trace of another universe
0:39:21 > 0:39:23once entangled with our own.
0:39:24 > 0:39:27It's a discovery beyond anything she dared hope for.
0:39:29 > 0:39:31That felt incredibly good.
0:39:31 > 0:39:33It was unbelievable.
0:39:33 > 0:39:37I really got excited, and allowed myself for a moment
0:39:37 > 0:39:40to think that there might be something more to this idea,
0:39:40 > 0:39:43and when I heard the list of anomalies,
0:39:43 > 0:39:47I was so elated and happy
0:39:47 > 0:39:49and couldn't believe my eyes,
0:39:49 > 0:39:53that I allowed myself for a few minutes to jump up and down.
0:39:53 > 0:39:54I was jumping on the balcony.
0:39:54 > 0:39:57I wonder what the neighbours thought?!
0:40:02 > 0:40:05# She's a true original... #
0:40:05 > 0:40:09It's a thrilling thought, that somewhere up there in our own sky
0:40:09 > 0:40:13could be a clue to the presence of another universe.
0:40:15 > 0:40:17Laura's ideas are considered radical
0:40:17 > 0:40:20and she's yet to convince many of her critics,
0:40:20 > 0:40:24but it's a major breakthrough for an idea most people dismissed.
0:40:24 > 0:40:26Then, in 2014,
0:40:26 > 0:40:30scientists claim to have made another important discovery.
0:40:30 > 0:40:33NEWS REPORT: Space scientists hail a great advance,
0:40:33 > 0:40:35claiming the first direct evidence
0:40:35 > 0:40:38of what happened in the first moments of the universe.
0:40:38 > 0:40:42An international team of leading space scientists say they've
0:40:42 > 0:40:46found the first direct evidence of how the universe was born.
0:40:46 > 0:40:49Scientists had been scanning the sky,
0:40:49 > 0:40:52looking for evidence of gravitational waves.
0:40:52 > 0:40:55The news that they thought they had found them caused a sensation,
0:40:55 > 0:40:59because, if confirmed, it offered yet more tantalising clues
0:40:59 > 0:41:02to the existence of the multiverse.
0:41:02 > 0:41:04So this has been a really exciting time
0:41:04 > 0:41:06to be studying the theory of inflation
0:41:06 > 0:41:09because inflation predicts that there would be
0:41:09 > 0:41:12gravitational waves formed during the inflationary process,
0:41:12 > 0:41:15these are ripples in space time.
0:41:15 > 0:41:18It turns out that those gravitational waves
0:41:18 > 0:41:19leave a telltale signature
0:41:19 > 0:41:22in a pattern on the microwave background radiation,
0:41:22 > 0:41:25and that signature has been searched for for a long time
0:41:25 > 0:41:27because it's a prediction of inflation.
0:41:32 > 0:41:35The data in 2014 turned out to be a false alarm.
0:41:37 > 0:41:39But the theory is solid.
0:41:41 > 0:41:44The idea is that the violent nature of inflation
0:41:44 > 0:41:45created gravitational waves.
0:41:47 > 0:41:49These waves would have warped the fabric of space
0:41:49 > 0:41:53and produced a particular pattern of ripples in the cosmic
0:41:53 > 0:41:57microwave background, enabling us to observe them, even today.
0:41:59 > 0:42:02The hunt is still on for evidence of gravitational waves.
0:42:02 > 0:42:05But, if they're discovered, it would be a huge leap forward
0:42:05 > 0:42:07for the idea of the multiverse.
0:42:08 > 0:42:10Gravitational waves, I think,
0:42:10 > 0:42:14makes the multiverse more likely in two ways.
0:42:14 > 0:42:19The first is that the multiverse is a prediction really of inflation,
0:42:19 > 0:42:21and so because this makes inflation more likely,
0:42:21 > 0:42:24it then makes the multiverse more likely.
0:42:24 > 0:42:28Second, I would say that the sorts of models,
0:42:28 > 0:42:31the simple models that people have been thinking about for 30 years
0:42:31 > 0:42:35that give rise to eternal inflation, are precisely the sort of models
0:42:35 > 0:42:37that are compatible with these theories.
0:42:37 > 0:42:41Scientists are still looking for proof of gravitational waves,
0:42:41 > 0:42:45but if found, it will be a major step forward in cosmology.
0:42:46 > 0:42:50So, this really makes me feel excited to be a cosmologist
0:42:50 > 0:42:52and be alive and working now.
0:42:52 > 0:42:53This is a spectacular time
0:42:53 > 0:42:56that we're never going to have in human history again.
0:42:56 > 0:42:59We've learned what the history of the universe is,
0:42:59 > 0:43:02and now we're learning where the universe came from,
0:43:02 > 0:43:05how was it born, were there other universes born?
0:43:05 > 0:43:06And we're actually making progress.
0:43:06 > 0:43:09We're not just talking, we're learning real things,
0:43:09 > 0:43:13and we've come incredibly far in that quest.
0:43:16 > 0:43:18These new ideas have given great support
0:43:18 > 0:43:21to theories of the multiverse,
0:43:21 > 0:43:24and to those critics that suggest the idea of the multiverse
0:43:24 > 0:43:29is a waste of time, it's given them something to think about too.
0:43:48 > 0:43:51While some scientists are looking for evidence
0:43:51 > 0:43:54for the multiverse in the distant regions of space,
0:43:54 > 0:43:57others believe our best hope of detecting the multiverse
0:43:57 > 0:44:02might lie much closer to home in the dizzying world of quantum computing,
0:44:02 > 0:44:08where today this team at MIT have switched on their latest machine.
0:44:09 > 0:44:13The type of evidence we can get for the quantum multiverse
0:44:13 > 0:44:15is much more immediate than that that we get
0:44:15 > 0:44:19for the inflationary multiverse, for instance.
0:44:19 > 0:44:21So, for the inflationary multiverse
0:44:21 > 0:44:24we're never going to actually have access to these other worlds,
0:44:24 > 0:44:27so we're just going to have to believe in inflation
0:44:27 > 0:44:29and thereby believe that these exist.
0:44:29 > 0:44:33But, we could indeed do some quantum virtual reality experiment
0:44:33 > 0:44:37which demonstrated the existence of the quantum multiverse,
0:44:37 > 0:44:40at least in the context of virtual reality.
0:44:40 > 0:44:42In the quantum multiverse,
0:44:42 > 0:44:46each universe that splits apart is permanently severed,
0:44:46 > 0:44:50but quantum computers might have an extraordinary ability
0:44:50 > 0:44:51to access them.
0:44:52 > 0:44:55So, a quantum computer is like a regular computer,
0:44:55 > 0:44:56but really, really small.
0:44:58 > 0:45:01That is to say, the bits of the computer,
0:45:01 > 0:45:04so the places where you store information,
0:45:04 > 0:45:06are individual atoms,
0:45:06 > 0:45:11or individual elementary particles, like photons or electrons.
0:45:11 > 0:45:15An ordinary digital computer processes information
0:45:15 > 0:45:19by busting up the information to its smallest pieces
0:45:19 > 0:45:23which are called bits, so a bit is a small chunk of information.
0:45:23 > 0:45:26It only has two possibilities which are usually called zero or one,
0:45:26 > 0:45:29but they could also be yes or no, heads or tails, true or false.
0:45:29 > 0:45:33So, a quantum computer also divides up information into bits,
0:45:33 > 0:45:35but now they're quantum bits,
0:45:35 > 0:45:37so if I'm an electron that can be over here,
0:45:37 > 0:45:41we call that zero, or over here we call that one,
0:45:41 > 0:45:43so this quantum bit or Q-bit,
0:45:43 > 0:45:46in some weird funky quantum way that nobody really understands
0:45:46 > 0:45:49registers zero and one simultaneously.
0:45:49 > 0:45:52And this gives quantum computers a power
0:45:52 > 0:45:55that ordinary classical computers don't have.
0:45:55 > 0:45:58Because quantum computers have the ability
0:45:58 > 0:46:00to operate in many states at once,
0:46:00 > 0:46:04performing a staggering number of calculations at the same time,
0:46:04 > 0:46:10some believe these calculations are taking place in parallel worlds.
0:46:10 > 0:46:13Some people believe that quantum computers already prove
0:46:13 > 0:46:15the existence of the multiverse.
0:46:15 > 0:46:16They say that the quantum computer
0:46:16 > 0:46:20is doing all these different computations in different worlds,
0:46:20 > 0:46:24and then to get the answer to the question, it recombines all this
0:46:24 > 0:46:27information from these different worlds to give you the answer.
0:46:29 > 0:46:31And there's one famous maths problem
0:46:31 > 0:46:34that if a quantum computer could solve,
0:46:34 > 0:46:38could one day prove the existence of the quantum multiverse.
0:46:38 > 0:46:42The killer app for quantum computers is factoring large numbers,
0:46:42 > 0:46:47so factoring is taking a number and dividing it up into its factors
0:46:47 > 0:46:49so four is two times two,
0:46:49 > 0:46:5115 is three times five,
0:46:51 > 0:46:5321 is three times seven.
0:46:53 > 0:46:56Now that's pretty easy to do,
0:46:56 > 0:46:59and you and I can factor small numbers pretty easily,
0:46:59 > 0:47:03but when the numbers get very, very large, so I have a 512 digit number
0:47:03 > 0:47:09that's a product of two 256 digit numbers, it starts to get very hard.
0:47:09 > 0:47:13And, in fact, there's no known method on a classical computer
0:47:13 > 0:47:17to factor such numbers without taking a very, very large amount of time,
0:47:17 > 0:47:19maybe the age of the universe.
0:47:19 > 0:47:23However, a very small quantum computer with only a few
0:47:23 > 0:47:27tens of thousands of quantum bits could, in fact,
0:47:27 > 0:47:31factor a 512 digit number very rapidly,
0:47:31 > 0:47:33and how does it do that?
0:47:33 > 0:47:35It basically breaks up all the possible ways
0:47:35 > 0:47:37of factoring the number,
0:47:37 > 0:47:42and then all of these different parts get tried out together,
0:47:42 > 0:47:45and then recombined to give you the answer to the problem,
0:47:45 > 0:47:48to give you the factors of the number.
0:47:49 > 0:47:53These colossal calculations would take a classical computer
0:47:53 > 0:47:57more than the age of the universe to arrive at the correct answer,
0:47:57 > 0:48:00but a quantum computer could, in theory,
0:48:00 > 0:48:02tap into the multiverse,
0:48:02 > 0:48:06doing all the calculations in different universes
0:48:06 > 0:48:07at the same time.
0:48:08 > 0:48:12We're on the verge of a quantum computing revolution.
0:48:12 > 0:48:15The fact that these engineers might be building the first
0:48:15 > 0:48:20machines to access these hidden worlds is a spine-tingling thought.
0:48:20 > 0:48:22I am excited.
0:48:22 > 0:48:26I am, now that the thing is up and running as of this morning,
0:48:26 > 0:48:29I am going to come up with all kinds of fiendish
0:48:29 > 0:48:33and nefarious uses for this beautiful quantum computer.
0:48:33 > 0:48:34Wa-ha-ha!
0:48:38 > 0:48:43The multiverse is, admittedly, more than a little bewildering.
0:48:45 > 0:48:48A dizzying array of inflating bubbles,
0:48:48 > 0:48:49split personalities,
0:48:49 > 0:48:51and undulating landscapes.
0:48:54 > 0:48:57But, if you're struggling to choose
0:48:57 > 0:49:00which multiverse model you are actually in,
0:49:00 > 0:49:02you might not have to
0:49:02 > 0:49:06because we could exist in all of them at once.
0:49:15 > 0:49:19Max believes all the multiverses could happily live together...
0:49:21 > 0:49:26..in one extraordinary, humungous mathematical multiverse.
0:49:30 > 0:49:34The idea that all of this is completely mathematical
0:49:34 > 0:49:38sounds pretty nutty at first since it doesn't seem mathematical at all,
0:49:38 > 0:49:43but actually, when we look closer, there is mathematics everywhere.
0:49:43 > 0:49:48Here we see some beautiful mathematical circles forming,
0:49:48 > 0:49:51and whose spreading over the water is perfectly described
0:49:51 > 0:49:54by a mathematical equation called the wave equation.
0:49:55 > 0:49:59This tree here doesn't look very mathematical at first sight,
0:49:59 > 0:50:01but if we look really closely at this bark,
0:50:01 > 0:50:04it's made of cells, that are made of molecules,
0:50:04 > 0:50:05that are made of atoms,
0:50:05 > 0:50:08that are made of quarks and electrons,
0:50:08 > 0:50:09and as far as we can tell,
0:50:09 > 0:50:12neither the electrons nor the quarks,
0:50:12 > 0:50:15nor any of the other particles that make up all of this
0:50:15 > 0:50:19have any properties at all, except for mathematical properties.
0:50:21 > 0:50:24Understanding how our physical world of stuff can come from
0:50:24 > 0:50:29something as intangible as maths, is hard to get your head round.
0:50:29 > 0:50:33But we experience worlds of numbers all the time.
0:50:53 > 0:50:55Hi, my name is Shawn Robertson.
0:50:55 > 0:50:57I'm the animation director at Irrational Games,
0:50:57 > 0:50:59and I'd like to introduce you to Elizabeth.
0:51:01 > 0:51:04She's curious about the world, I mean, you know,
0:51:04 > 0:51:07from a personality standpoint, so she wants to touch everything, she
0:51:07 > 0:51:10wants to take a look at everything, she wants to see everything.
0:51:10 > 0:51:14Elizabeth's world is a representation of our own,
0:51:14 > 0:51:18but look closer and it all boils down to sets of numbers.
0:51:19 > 0:51:24So, here we're looking deep under the hood at just one of the objects
0:51:24 > 0:51:26that's in the game. So the initial, look at it, it looks
0:51:26 > 0:51:30fairly realistic. It's got shape to it, it's got textures to it.
0:51:30 > 0:51:34But if you look at what this is really built out of at its barest
0:51:34 > 0:51:38level, it's just a bunch of vertices and polygons and, you know, we can
0:51:38 > 0:51:42go in and we can manipulate these as artists and really change everything
0:51:42 > 0:51:47that's, you know, that the end user is going to see in the game.
0:51:47 > 0:51:51The only properties left here that this object has is a bunch of
0:51:51 > 0:51:56numbers, an X, Y and a Z coordinate here for each of your points.
0:51:56 > 0:51:59It's like you can put in some more numbers here
0:51:59 > 0:52:01and they would specify colour and texture
0:52:01 > 0:52:05and so on, but ultimately both this world and our physical world
0:52:05 > 0:52:11seems really at the bedrock level of description to be just numbers.
0:52:11 > 0:52:16Max believes our world, like Elizabeth's, is also made of maths.
0:52:16 > 0:52:19Maths is as real as the ground under your feet.
0:52:21 > 0:52:24And he also believes that equations are the foundations
0:52:24 > 0:52:26on which the multiverse is built.
0:52:29 > 0:52:32If we accept that our physical reality is actually
0:52:32 > 0:52:37a mathematical structure and nothing more, then we have to accept
0:52:37 > 0:52:43that any mathematical structure is a physical reality and nothing less,
0:52:43 > 0:52:47which makes me wonder, what about all these other mathematical
0:52:47 > 0:52:51structures that mathematicians have discovered and classified, and can
0:52:51 > 0:52:55make a whole atlas containing one after the other, what about them?
0:52:59 > 0:53:03This is Max's mathematical multiverse,
0:53:03 > 0:53:04home to all the other theories.
0:53:06 > 0:53:09These weird and wacky worlds have all been given life
0:53:09 > 0:53:12by the equations that describe them.
0:53:12 > 0:53:16Every equation is a multiverse in its own right,
0:53:16 > 0:53:20and each is a part of one giant mathematical structure.
0:53:22 > 0:53:26By his own admission, it's a radical idea.
0:53:33 > 0:53:36Whenever in the history of physics someone puts forward an idea
0:53:36 > 0:53:39which sounds kind of radical,
0:53:39 > 0:53:41a lot of other people are going to jump up and say, "Oh, this is nuts,
0:53:41 > 0:53:44"this is crazy, I can't believe our world is so weird,"
0:53:44 > 0:53:49but our job as scientists is not to tell our world how to be to conform
0:53:49 > 0:53:53with our aesthetic preconceptions for how...
0:53:53 > 0:53:55For how it ought to behave.
0:53:55 > 0:53:58Our job is to simply follow the evidence wherever it leads us
0:53:58 > 0:54:04and try to, with an open mind, determine how our world actually is.
0:54:04 > 0:54:07And I think it's abundantly clear already from the history of physics
0:54:07 > 0:54:12that the world is vastly stranger than we ever thought it was.
0:54:16 > 0:54:21So, on another world in another universe, could there be
0:54:21 > 0:54:25another Hugh Everett who is finally getting the recognition he deserves?
0:54:27 > 0:54:31One who is witnessing how the ideas once dismissed as the ramblings
0:54:31 > 0:54:36of a crazy eccentric are now part of the scientific mainstream?
0:54:38 > 0:54:43There are still many more questions for future generations to answer...
0:54:43 > 0:54:46but these ideas, and the people advocating them,
0:54:46 > 0:54:49are bringing about a scientific revolution.
0:54:51 > 0:54:53It's a truly thrilling place to be.
0:54:55 > 0:54:59Now we've come to a remarkable time where observational
0:54:59 > 0:55:02evidence about the universe combined with our theories of what's going on
0:55:02 > 0:55:05at the most microscopic quantum mechanical level
0:55:05 > 0:55:10give very strong evidence for the existence of these other worlds
0:55:10 > 0:55:14and these other universes in the multiverse.
0:55:16 > 0:55:18We used to think we were unique.
0:55:20 > 0:55:23We believed that the Earth, our home,
0:55:23 > 0:55:26was at the centre of the universe.
0:55:27 > 0:55:30But little by little, we've been forced to change
0:55:30 > 0:55:35our perspective, learning that we are just one planet revolving
0:55:35 > 0:55:40around the sun, which is just one star amongst countless others.
0:55:43 > 0:55:48Now it seems we may have to give up the long-cherished notions
0:55:48 > 0:55:50of the universe altogether,
0:55:50 > 0:55:53accepting instead that it could be just one
0:55:53 > 0:55:56of an infinite number of others,
0:55:56 > 0:56:01just a humble part of a truly infinite multiverse.
0:56:05 > 0:56:10When I think of our universe as a humble member in the vastness,
0:56:10 > 0:56:13I can only marvel at the beauty of nature.
0:56:13 > 0:56:18I am not surprised because, of course, nature always has new
0:56:18 > 0:56:22and beautiful surprises in store for us that are out there to be
0:56:22 > 0:56:27discovered, but I also feel very fortunate that I am
0:56:27 > 0:56:32at the right time and place where I can take part in that discovery,
0:56:32 > 0:56:36even if it's just one small step beyond what's already known.
0:56:37 > 0:56:40And there is an awe inspired by that beauty,
0:56:40 > 0:56:43complexity, and yet simplicity of nature.
0:56:49 > 0:56:51Some people feel that when they think about
0:56:51 > 0:56:53how big even the observable universe is, it makes
0:56:53 > 0:56:57them feel tiny and insignificant and that's right, physically -
0:56:57 > 0:57:00we're just really specks -
0:57:00 > 0:57:03but mentally, when you think of our understanding of the universe, that
0:57:03 > 0:57:07we have been able to conceive of the laws that govern the evolution
0:57:07 > 0:57:12and creation and complexity of the universe, we're huge.
0:57:12 > 0:57:14We're giants in that sense,
0:57:14 > 0:57:17and I feel excited to be a part of that process and it makes the
0:57:17 > 0:57:21universe, the interior universe, the mental universe, feel vast to me.
0:57:26 > 0:57:30Some people don't like multiverses cos they say it makes them
0:57:30 > 0:57:34feel insignificant, but I think it's actually good news,
0:57:34 > 0:57:37because we humans have again and again and again underestimated
0:57:37 > 0:57:41not only the size of our cosmos, realising that everything
0:57:41 > 0:57:45we thought existed was just a small part of a much grander structure -
0:57:45 > 0:57:50a planet, a solar system, a galaxy, a universe and a whole hierarchy
0:57:50 > 0:57:54of parallel universes - but we also repeatedly underestimated the power
0:57:54 > 0:57:59of our human minds to understand our cosmos and that's a wonderfully
0:57:59 > 0:58:03empowering thing, which shouldn't make us feel insignificant at all.