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00:00Hello. My name is Stephen Hawking. Physicist, cosmologist, and something of a dreamer.
00:15Although I cannot move, and I have to speak through a computer, in my mind, I am free.
00:23Free to explore the most profound mysteries of the cosmos. Such as, why is the universe the way it is?
00:36Why does it follow rules and laws? Why is there order instead of chaos?
00:46Finding out leads us to the very deepest of secrets.
00:49To the one principle that's at the heart of everything in the cosmos.
00:59Check it out.
01:01The Aurora Australis, or Southern Lights, seen from the International Space Station.
01:19I've devoted my life to the search for an explanation to such beautiful mysteries.
01:29Because I believe it will lead us to the secrets of the universe itself.
01:34This is the search for what I call the grand design.
01:43The key to the cosmos.
01:47The good news is, I think we found it.
01:52Almost.
01:53Getting here has been quite a journey.
02:00It began one night, 350 years ago, in the small English town of Cambridge.
02:06The year was 1665.
02:19Death stalked the land as England fell under the plague's dark spell.
02:23A student, called Isaac Newton, fled town to escape the threat.
02:33We're fortunate he got away.
02:38Because Newton was a radical thinker who dared to see the universe in a completely new way.
02:44Right!
02:59Newton took the first steps in the search for the grand design.
03:04By looking for the mysterious laws that govern nature.
03:07He asked, why do things move?
03:13Why do they stop?
03:15And most famously, why do they fall to earth?
03:24You may not think answering such simple questions would change the world.
03:30But it did.
03:32Because Newton realized there was a force at work deep within the fabric of the universe.
03:39That makes all objects attract one another.
03:42The force of gravity.
03:46Gravity works not just on earth.
03:48But throughout the cosmos.
03:51And its strength depends on just a couple of fundamental things.
03:55The mass of the objects.
03:57And their distance apart.
04:01To find his answers, Newton invented a completely new mathematical language.
04:16Called the calculus.
04:17You don't need to know how it works.
04:18But it wasn't bad for a 23-year-old.
04:32Scientists all over the world still use it every day.
04:35Newton's work made it possible to predict everything from the orbits of planets around the stars.
04:52And the precise timing of eclipses.
04:56To the trajectories of raindrops.
04:59Today, we theoretical physicists are still doing the same sorts of things as Newton.
05:19Only thankfully we don't have to worry about the plague.
05:22Although our work may seem complex, it's really quite simple.
05:30We're trying to unravel the hidden mechanism that underlies everything.
05:36We can only do this because we stand on the shoulders of giants.
05:47Scientists who, piece by piece, discovered what makes the universe tick.
05:58Amongst those giants was another of my scientific heroes.
06:01James Clark Maxwell.
06:02Maxwell was fascinated by light, which in 1861 led to him inventing colour photography.
06:14But that was just the beginning of what this remarkable man achieved.
06:18It was when he began to investigate a completely different realm of physics that everything changed.
06:33This was the strange, almost magical connection between magnetism and electricity.
06:39There's nothing complicated about it.
06:47Move a magnet near a wire and you will cause electricity to flow through the wire.
06:53Put electricity through a wire and it will act like a magnet and deflect a compass.
07:14So what connected them?
07:17Maxwell's big idea was that magnetism and electricity
07:21are actually two facets of the same thing.
07:26A wave of energy that was part electrical, part magnetic.
07:32He called them electromagnetic waves.
07:40But then came a surprise.
07:41The mathematics told him these electromagnetic waves traveled at an extraordinary speed.
07:50186,000 miles per second.
07:54The exact same speed that had already been determined to be the speed of light.
08:00This led to a stunning conclusion.
08:06Light is an electromagnetic wave too.
08:10Maxwell connected electricity, magnetism and light in a series of four equations that I consider to be one of the greatest discoveries in the history of the world.
08:26The equations, called Maxwell's laws, govern everything from the auroras that dance over the north and south poles to the modern electrical and communications technology that powers the planet.
08:52Virtually every machine in the modern world, from a computer to a power station to a washing machine, works to the rules Maxwell revealed.
09:06Electromagnetism quite literally lights up our planet.
09:10A fitting testament to a great mind.
09:19But light is much more interesting than even Maxwell himself realized.
09:25Although he didn't know it, he had actually uncovered one of the fundamental clues to the grand design.
09:32That clue is the speed of light itself.
09:43By the late 19th century, it looked like some of the great mysteries of the universe would be all wrapped up, thanks to the groundbreaking discoveries of Newton and Maxwell.
09:54But then two American physicists stumbled into a completely unexpected discovery.
10:07Albert Michelson and Edward Morley were investigating the implications of Maxwell's revelation that light is a form of wave traveling at 186,000 miles per second.
10:19They figured that just as water waves are waves of energy traveling in water.
10:31And sound waves are waves of energy traveling through air.
10:38So light waves must also travel through something.
10:42They called this something the luminiferous ether.
10:53Michelson and Morley proposed that space, including the space between the Sun and the Earth, was filled with this mysterious ether.
11:03They believed that sunlight must travel through the ether to reach Earth.
11:09Since the Earth also moved around the Sun, then it must be traveling through this ether too.
11:16If so, this movement would cause what they called an ether wind to blow over the surface of our planet.
11:26Michelson and Morley believed this ether wind should be detectable here on Earth, and designed an experiment to measure its effects.
11:44They ran their experiment in a cramped basement.
11:49But to understand the principle behind it, I thought we'd get them out of the lab, and stage it out here on the beach.
11:55Since the Earth is constantly orbiting the Sun, then the ether wind would be ever present, and would affect the speed of light here on Earth.
12:01If a beam of light was traveling, with the ether wind behind it, the light should move faster.
12:22But if light was traveling in the exact opposite direction, and so was fighting the oncoming ether wind, the speed of light should slow down.
12:40And the difference between those two speeds should be measurable.
12:54But they couldn't detect any difference.
12:59Whichever way the light waves were pointing, they couldn't find any slowing down or speeding up.
13:05This result was deeply disturbing.
13:11The luminiferous ether could not exist.
13:15What's more, it meant the speed of light must be constant in all directions.
13:24Modern experiments have repeatedly confirmed this discovery.
13:29The speed of light remains fixed, regardless of the direction in which it is traveling.
13:36Michelson and Morley were deeply embarrassed about having to report they'd been wrong.
13:42The ether simply wasn't there.
13:46But the experiment wasn't a total disaster.
13:52It's one of the most important mistakes in the history of science.
13:57Light is a wave that travels through nothing.
14:06What a strange idea.
14:08And the discovery that its speed cannot be varied is also very odd.
14:13Luckily, we physicists like strange things, because they often lead us to breakthroughs.
14:23And this discovery led to the biggest breakthrough of all.
14:26The discovery that the speed of light is fixed would challenge everything we scientists believed about the universe.
14:38It would take another of my heroes, Albert Einstein, to discover the deep truth about the nature of light.
14:48To explain how he did it, let me take you back to my childhood.
14:53My old toy train is a perfect way of illustrating Einstein's profound questioning of what the fixed speed of light meant for the universe.
15:10Einstein started with a simple question.
15:16How fast is something like this little train moving?
15:22Well, this is the 1950s, and toy trains weren't all that good.
15:28So, let's say it's traveling at about one mile per hour.
15:41But change where you look at it from, and you get a different answer.
15:51The Earth spins on its axis at around a thousand miles per hour.
15:55So, seen from up here, my train is actually traveling much faster.
16:02But, of course, the Earth as a whole is orbiting the Sun at 67,000 miles per hour.
16:12And even the Sun isn't stationary.
16:15It is orbiting the center of the Milky Way.
16:20And the Milky Way is moving through space, too.
16:23So, how fast is the train really moving?
16:33Well, it all depends on where you see it from.
16:40It could be one mile per hour, a thousand miles per hour, 67,000 miles per hour, or many times faster.
16:50So, what's the problem?
16:53Anyone can understand that speed is relative to your perspective.
16:58But when you remember that, unlike the speed of the toy train, the speed of light is fixed, no matter what your perspective,
17:05then that common sense view of things starts to break down.
17:17To explain why, Einstein imagined a train, too.
17:20Only his was full-sized.
17:21He devised a thought experiment, asking how something as simple as the lighting of a cigarette lighter would look to people with different points of view.
17:37He imagined a man playing with his lighter in the center of a railway car, being watched by two people at either end.
17:51Both at exactly the same distance from the lighter.
18:01Einstein said the interesting question is not what do these two people see, but when do they see it?
18:07Because they are in the same car, all moving together at the same speed, the two observers see the light at exactly the same time.
18:16But what about someone outside?
18:34What does she see?
18:36From her perspective, with the train moving forward, the beam of light needs to travel a little bit further before it reaches the man at the front.
18:55On the other hand, the light moving towards the man at the back has a slightly shorter distance to go.
19:02Since he is moving towards it.
19:05So she sees the light reach the man at the back before it hits the chap at the front.
19:17What that means is that an event on a moving train takes place simultaneously if you're on the train.
19:25But at different times when you're standing on the platform.
19:29Stop a moment.
19:45And think about the implication of that.
19:50It means that we can't say if the events really happen at the same time or not.
19:59Reality itself depends on where you are.
20:08Scale this up to the universe as a whole and it gets even weirder.
20:13If reality depends on where you are, then how can you know what's really going on in the universe?
20:22What's more, what chance do we stand of finding the key to how the universe works if we can't even tell if two events are simultaneous or not?
20:39Don't worry, because Einstein thankfully came up with the answer in his famous theory of special relativity.
20:51Einstein proposed that reality is flexible because time itself is flexible.
21:07It might sound strange, but this flexibility is just the start of a whole new concept in physics.
21:16Einstein went on to suggest that just like magnetism, electricity and light, both time and space are inextricably linked in what he called space time.
21:32This space time is flexible as well.
21:36It can be bent and warped by the sheer mass of heavy things like stars and planets and galaxies.
21:44But what's really amazing is these distortions also explain that mysterious force discovered by Newton so many years ago.
22:01gravity is the warping of space time.
22:08Now, curving space and time may sound tricky to wrap your head around, but it's not.
22:19Imagine a boat locked on a straight course across the flat surface of a lake.
22:33A lake that stretches away forever.
22:36The flat lake is like undistorted space time.
22:53Now imagine a giant hole appears beneath the lake and water begins to drain away.
23:00The lake has become distorted, just as space time is by a planet.
23:08The effect would be to drag the boat towards the hull so that it begins to curve around it, even though the boat is still being driven in a straight line.
23:23And it's exactly that same effect a massive star or planet has on space time.
23:40It causes space time to distort around it, pulling things towards it.
23:50And that's why things fall to Earth.
23:55Einstein had looked deep into the fabric of the universe and seen its inner workings.
24:12Ten years after he explained the fixed speed of light, he discovered that the distortion of space and time produces gravity, a fundamental force of nature.
24:24His work brought us much closer to discovering the secret key to the cosmos.
24:31But not even Einstein was prepared for what happened next.
24:41Although Einstein had begun to reveal the universe's hidden clockwork, he still couldn't quite yet see how it operated.
24:51His theories drew on the nature of light as a super-vast electromagnetic wave racing through the emptiness of space.
25:01But they revealed nothing about what these waves really are.
25:06That challenge was taken up in 1919 by a German theorist named Theodor Kalutzer, a mathematician with a passion for purity and elegance, the next great scientist in my pantheon of heroes.
25:27Kalutzer was a man who took all forms of theory very seriously indeed.
25:36It's said that he taught himself to swim solely by reading a book on the subject.
25:42Kalutzer was fearless in putting theory into practice.
26:07Luckily for Kalutzer, the theory of swimming was well understood.
26:14But in 1919, that couldn't be said for a theory that explained the universe.
26:23A theory of everything.
26:27Inspired by Einstein's success in explaining gravity, Kalutzer wondered if the same idea might be applied to electromagnetism and light.
26:42Were light waves ever more complex distortions of space-time, like ripples in the very fabric of the universe?
27:03It was a bold notion, and the answer was yes.
27:13Despite that flash of genius, Kalutzer's timing was unfortunate.
27:20His ideas were swept aside by a new branch of physics that threw everything into question.
27:27Quantum mechanics.
27:28This had happened when physics had turned its attention to studying some of the very smallest things in the universe.
27:41Inside the atom, the universe was revealed to be a strange, chaotic place, where the familiar rules of physics just didn't seem to hold sway.
28:00Just how odd this quantum world was would be revealed in a deceptively simple experiment using tiny subatomic particles called electrons.
28:13A stream of electrons was fired through two tiny slits towards a detector.
28:28Common sense tells us the electrons should hit the detector in these two highlighted areas right behind the slits.
28:33But that's not what happened.
28:38Instead, the detector picked up a pattern of not just two lines, but many.
28:50This is simply not what anyone expected electrons or any small lumps of matter to do.
28:55The tiny electrons appeared to be defying the laws of physics.
29:09To get your head around just how weird this really is, let me scale up the electrons to something a bit more familiar.
29:17Like a soccer ball.
29:24This striker is about to take a free kick.
29:32Obviously, he'll do his best to hit the ball past the defensive wall and the goalie and into the net.
29:37And they will do their best to stop that from happening.
29:56So far, it all makes sense.
29:58But apply the rules of the subatomic or quantum world, and things work differently.
30:08And that's why physicists started to get very worried.
30:11Instead of taking a single, definable path, the ball, like the electrons, will take any and every route.
30:29Leaving the goalkeeper without a chance.
30:51Once in the goal, the ball reverts back to one reality.
30:54But in the moments before that, it is everywhere and anywhere.
31:06I told you it was weird.
31:16It's hard to overstate just how disturbing this view of reality is.
31:20If everything is actually chaotic at the subatomic level, then could the project started by Newton,
31:30continued by Maxwell, and refined by Einstein and Kaluza have boiled down to this?
31:36Something as random as a game of roulette?
31:42Perhaps the secrets of the universe are ungraspable.
31:46And beyond the power of the human mind.
31:49The seeming contradictions between the chaotic workings of the subatomic world, and the order of the rest of the world, was a real problem for us physicists.
32:08But not for long.
32:12In the fifties, along came a man with an instinctive grasp of randomness and probability.
32:19Meet Richard Feynman.
32:23Party animal, inveterate gambler, and something of a genius.
32:28Feynman brought the mathematics of his favourite vice to the uncertainty of the quantum world.
32:39He argued that just as a roulette ball obeys the laws of chance,
32:46so should an electron.
32:56As any roulette player knows,
32:59even though you can't predict for certain which number the ball will land on,
33:04you can work out the odds.
33:05One in 37, as it happens.
33:16Using probability, Feynman was able to deduce the peculiar rules that governed how a particular quantum event might unfold.
33:23With that, the quantum world was tamed, and science itself brought back from the brink.
33:43Richard Feynman did physicists a great favour.
33:46It's not just that some of his much-needed glamour rubbed off on us.
33:52His discovery that the quantum world could be predicted,
33:57meant science could resume the search for the grand design.
34:01Physics now turned to finding connections between what happens,
34:06at the very smallest scale,
34:08to the universe at the very largest.
34:10It did so by returning to the long-neglected work of that eccentric German physicist and self-taught swimmer,
34:20Theodor Kalutzer.
34:28Physicists began looking at how his theories might apply to some of the tiniest things in nature.
34:37The world inside the atom.
34:41Where electrons spin around a central nucleus composed of other particles,
34:47called neutrons and protons.
34:53Inside them are even smaller entities known as quarks.
34:59Quarks are themselves made from something we physicists call strings,
35:04which are ever more intricate distortions of space and time.
35:15You can think of them as being a bit like vibrating violin strings.
35:18Just as a violin string can vibrate to produce different musical notes,
35:32each subatomic string also vibrates, producing a different kind of fundamental particle.
35:37And it's these tiniest particles that give shape to the universe around us.
35:50Building on the ideas of Kalutzer and Einstein,
35:53string theory suggests that the vibrations of the strings produce tiny distortions in space-time,
35:59at a microscopic scale.
36:03And they do so in a mind-boggling ten dimensions.
36:08If the string vibrates in one way,
36:16it produces a certain kind of fundamental particle, say a quark.
36:22And if it vibrates in another way,
36:28it creates a neutrino,
36:33which is another kind of particle.
36:36But here's the clever bit.
36:40String theory has the potential to explain why these particles interact with each other
36:47in the precise way they do,
36:50just like the harmony in a piece of music.
36:58And this is where the laws of physics come from,
37:02the laws that control everything in the universe.
37:05from the behavior of black holes,
37:16to the life and death of stars.
37:27Take something as simple as a roll of paper falling to the floor,
37:31or the flickering of a magnetic compass needle.
37:36The simplest but most fundamental of actions,
37:40all governed by the rules of string theory.
37:48Currently, there are several different versions of this string theory,
37:52which are all put together and called M theory.
37:56Nobody seems to know what the M stands for.
37:58It could be Master, Miracle, or Mystery.
38:04Perhaps all three.
38:09Either way, there's still lots of work to do.
38:15But even before it's finished,
38:18this M theory is making one remarkable prediction.
38:22That ours is not the only universe.
38:25There are many, many more.
38:26Physics has come a long way since Newton and Maxwell.
38:28And I must say I'm very glad to have lived through what I think will prove to be an historic turning point.
38:29At the perimeter, there are many, many more.
38:30There are many, many more.
38:31There are many, many more.
38:40Physics has come a long way since Newton and Maxwell.
38:43Physics has come a long way since Newton and Maxwell.
38:44And I must say I'm very glad to have lived through what I think will prove to be an historic turning point.
38:58At the Perimeter Institute for Theoretical Physics near Toronto,
39:02my colleagues and I have been thinking about what string theory could mean about our place in the universe.
39:12One extraordinary prediction string theory is making
39:16is that there should be hundreds of billions of billions of other universes.
39:22Perhaps more universes than there are stars in the known cosmos.
39:36To get your head round this, let's return to that idea that the strings of string theory are like notes played by a string quartet.
39:43Each vibration of the strings gives rise to the fundamental particles and to the forces of nature,
39:54which between them make up everything in the universe.
40:01But of course the quartet could just as well be playing a different tune with different vibrating notes.
40:07And mathematically, that different tune would produce different particles and different forces of nature,
40:25meaning a different universe.
40:37Change again, and that's another universe.
40:50So just as there are an endless number of possible tunes,
40:55so our universe must be just one of billions of universes.
40:59We can't see them because they are beyond the limits of our own universe,
41:14each with their own history and properties.
41:23Some are unstable and collapse back to where they came from.
41:26Some will produce no stars or planets, and so be dark and cold.
41:37Others will expand and go on to produce stars and galaxies like ours.
41:56As we ponder this, we should not be surprised to find ourselves in a universe that is perfect for us.
42:07Our very presence means our universe must be just right.
42:12So the search for the key to the universe has had one unexpected result,
42:18we have found the key to every other universe too.
42:21It seems that M-theory is the system of laws that governs everything.
42:27The grand design.
42:29From the mystique around the world.
42:31To be found, we are awaiting the subject of humanity.
42:32In a digital empire.
42:34dimensionality, both
42:59Amen.