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00:00According to a Japanese fairy tale written over a thousand years ago,
00:29our universe was created by the young and beautiful Izanami and her fierce husband, Izanagi,
00:37when they met on the bridge between emptiness and nothingness which straddled the sea of chaos.
00:43They were, of course, gods, but homeless gods with nowhere to live, no place to go.
00:51Neither space nor time had yet been created.
00:54As they surveyed the sea of chaos billowing beneath their feet, Izanagi looked to his young bride for inspiration.
01:09Taking matters quite literally in her own hands, Izanami called forth a jewel-encrusted golden spear from the heavens,
01:18a magic spear.
01:29Izanagi took the spear from Izanami and with all his power,
01:34he began to summon the elemental forces of nature.
01:37As the young goddess looked on, Izanagi plunged the spear into the sea of chaos and began to stir.
01:49Slowly, all of space and all of time and all of the matter in it began to form.
02:00Our universe, a place for the gods to live, a place that would be called Japan, or so this story goes.
02:07Since the beginning of culture, civilizations have tried to understand how the universe came into being and what it's made of.
02:17This is the basis of much of the myth and religion.
02:21Nowadays, science, in a sense, has replaced myth and religion,
02:27and it is the modern way of asking how the universe began.
02:31And some of the ideas in science sound almost as weird as ancient religions.
02:35And in particular, one of the most exciting current ideas suggests that the universe,
02:40the whole universe and the matter inside it, is made of string.
02:46Yes, string.
02:48But not common or garden supermarket string. Far from it.
02:52The strings which fascinate scientists today are called superstrings.
02:57And if they exist at all, they'll be so small that no microscope will ever be able to see them.
03:02And yet, if they do exist, they'll be so fundamental to the way the universe is constructed
03:08that everything, literally everything, will have to be made from superstrings,
03:14including empty space.
03:17Some physicists believe that superstring theory may shed light on a few of the most important questions in science,
03:24including a description of how the universe was created.
03:27Who knows if superstrings live up to their expectations?
03:33We might actually have in place a mathematical formula or scheme,
03:36something you can wear on your t-shirt, perhaps,
03:38that would capture the whole of reality at this reductionistic level.
03:43And in one sense, that would be the scientific creation myth.
03:47That would be creation.
03:48That would be all of the entities that exist.
03:50Space, time, the particles of matter,
03:52even an account of how the universe came into being.
03:55We'd have everything encapsulated in a single scheme, a single principle.
04:00I'm sure that we wouldn't know why that particular principle
04:02is the one that, as it were, takes on wings and flies,
04:05rather than some other.
04:07But we would surely have there the modern version of the creation.
04:12I think there's no doubt about that.
04:13The conventional version of creation suggests
04:21that our universe popped into existence
04:23around 15 billion years ago.
04:32But as it expanded, it cooled.
04:34And as it cooled, a host of exotic particles of matter were created,
04:38many of which only existed fleetingly before vanishing forever.
04:42Slowly, under the relentless tyranny of the force of gravity,
04:57those particles began to clump together
04:59into what would become galaxies.
05:02And within those galaxies, suns were born.
05:05About four and a half billion years ago,
05:13a rather amiable blob of iron, silicon, carbon, hydrogen and oxygen,
05:18that would one day be called Earth by its inhabitants,
05:21began to form from the interstellar dust in orbit around a small star.
05:25For countless millennia,
05:31that star bathed the little planet in just enough light
05:35and just enough warmth
05:36to trigger an extraordinary,
05:38possibly unique, chemical miracle.
05:41A chemical miracle called life.
05:44Over time, the planet bore witness
06:00to yet another possibly unique chemical miracle.
06:03Some of the creatures that were evolving here
06:06were beginning to think
06:07and then to question
06:09what was it all about?
06:13What was going on?
06:21Amongst the diversity and variety which surrounded them,
06:25nothing seemed permanent.
06:26Everything was constantly changing.
06:28And yet, if there were any Neanderthal scientists,
06:32they would also have noticed
06:34that there are patterns in the way nature operates,
06:36that there are cycles
06:37which could be exploited for their survival,
06:40cycles in which the sun, moon and stars
06:43seem to play a crucial role.
06:46And like the scientists who would one day follow,
06:49Neanderthal professors may well have wondered
06:51whether there are some underlying principles
06:53or fundamental laws
06:55governing the way the universe works.
06:58Not surprisingly,
07:02after so many dawns and sunsets,
07:04one of the conclusions mankind soon came to was
07:07that the Earth was obviously
07:09at the centre of the celestial web,
07:12at the centre of the universe,
07:14and that the sun, moon and stars
07:16were almost certainly orbiting gods.
07:23And why not?
07:24Given the unremitting evidence
07:26of the data available to them,
07:28this wasn't such a stupid interpretation
07:30of the way the heavens worked.
07:37Well, the idea that the sun
07:40might actually go around the Earth
07:42rather than the Earth going around the sun
07:43is not at all stupid.
07:45In fact, the theoretical predictions
07:47around the time when Copernicus was working
07:51on his new theory of that old model
07:54fit the observations actually pretty well.
07:58And Copernicus's model,
08:00where he put the sun at the centre of the solar system
08:03and all the planets moving in circular orbits around it,
08:06when he tried to calculate where the positions of the planets
08:09ought to be on the sky,
08:10he actually got a hopeless fit with the observations.
08:14It was only when Kepler came along in the next century
08:16and decided that the orbits of the planets
08:20had to be elliptical and not circular
08:22that we actually got a model
08:24or a theory that fit the observations.
08:26At the time, Copernicus and Kepler's idea
08:32that the sun might be at the centre of the solar system
08:35with the planets in orbit around it
08:36was a serious challenge
08:38to many deeply held religious assumptions
08:40about the universe and man's place in it.
08:43In 1604, an Italian mathematician called Galileo
08:51devised a proof for the idea
08:53and a few years later was able to check his calculations
08:56using a new invention called a telescope.
08:59He was arrested and found guilty of heresy.
09:03The debate raged throughout the early 17th century,
09:07but in 1642, the year that Galileo died,
09:10a young Englishman called Isaac Newton was born.
09:15Up to the time of Newton,
09:17the way in which science had been pursued
09:20was very different from the way in which we think of science today.
09:23In some sense, Newton can be thought of
09:25as the first experimental scientist.
09:28He realised that by observing the way things were
09:31in different places and even in different regions of the universe,
09:35you might understand some universal principles
09:37which all objects obeyed.
09:40The most notable of these, of course,
09:42is that he discovered the way in which the force of gravity acts
09:45and he realised that the same force
09:48that is responsible for the way objects fall to earth
09:51is also the force that holds the planets in motion around the sun.
09:56And this was a huge advance in the way we think about the world.
10:00Newton's mathematical model of the universe
10:02was not only astoundingly elegant,
10:04but it was powerfully predictive too.
10:07It was literally a clockwork universe
10:10and with it he had a means of calculating
10:12the positions of the planets far into the future.
10:17Newton had found what all theoreticians seek,
10:20an underlying principle which unifies a variety
10:23of different natural phenomena.
10:25It's a quest which has haunted all of the giants of science since Newton.
10:31One of the truly great examples of the way
10:33that two apparently different phenomena in the physical world
10:37are in fact different aspects of the same
10:39more fundamental way of thinking
10:41was the unification of electricity and magnetism
10:45that took place essentially in the time of Faraday and then Maxwell.
10:49And what Faraday did was truly astonishing.
10:54Faraday was the ultimate experimentalist.
10:57He did the most amazing experiments
11:00involving the motion of magnets near electric wires
11:03and he discovered the principle of the electric motor
11:06and the principle of the generator.
11:08And it was in the course of these discoveries
11:10that he realized that electricity and magnetism,
11:13which appear to be very different kinds of forces,
11:16are in fact different aspects of the same underlying principle.
11:20And this culminated eventually in the work of Maxwell,
11:23who understood that you could express the results of Faraday,
11:27the experimental results of Faraday,
11:29in a very concise mathematical form.
11:32This extended, if you like,
11:34the forces that were understood
11:36from the force of gravity,
11:38which had been understood by Newton,
11:39to include the electric and magnetic forces.
11:42As the 19th century drew to a close,
11:48the new insights into the laws of physics,
11:50which men like Faraday and Maxwell were achieving,
11:54seemed to be reflected in the ever more inventive technologies
11:57of the Industrial Revolution.
12:00Together, it seemed science and technology
12:02could answer any question, solve any problem.
12:05And in 1880, the chief of the Prussian patent office
12:09even declared that everything that ever would be invented
12:12had been invented.
12:17The thought found an echo in America
12:19when the noted physicist Albert Michelson wrote,
12:23The more important fundamental laws
12:25and facts of physical science
12:26have all been discovered.
12:28But even as Michelson was penning those immortal words
12:33amid the exuberant celebrations
12:35that attended the dawn of the 20th century,
12:38a fatal arrow was being aimed
12:40at the very heart of classical Newtonian physics.
12:44A number of theorists were beginning to notice
12:47that Maxwell's laws of electromagnetism
12:49and Newton's laws of motion
12:51just didn't seem to fit together.
12:54A German mathematician called Albert Einstein
12:58was about to enter the picture
13:00with a radical solution to the problem.
13:06Einstein had an idea
13:08which was to overturn two centuries
13:10of conventional thinking.
13:13Well, physics was in a real crisis
13:15around about the turn of the century.
13:17There had been these amazing developments
13:20in the form of Maxwell's equations
13:22which explained the electromagnetic force,
13:26but it then became apparent
13:27that this explanation
13:28seemed to be in conflict
13:30with Newton's laws of motion.
13:31These were the sacrosanct laws
13:33which had been around
13:34for a couple of hundred years,
13:35and it seemed that
13:37if you tried to describe the motion
13:39of charged particles,
13:41then there was a conflict
13:42between Maxwell's equations on the one hand
13:45and Newton's laws on the other.
13:47Now, many people felt
13:49that in that case
13:50there must be something wrong
13:51with Maxwell's equations
13:52since Newton was so sacred.
13:55And in a sense,
13:55it was part of Einstein's genius
13:57to realize that in fact
13:59it was Newton's equations
14:00which needed to be modified.
14:02Newton's view of space and time
14:04is what I think you would say
14:05was most normal people's view
14:07of space and time.
14:08We're all conscious of living in a space
14:10which is three dimensions.
14:11You have to go in three directions
14:12to specify where you are.
14:14and we're all conscious
14:15of the march of time.
14:18What Einstein did
14:20was to really overthrow
14:20that picture entirely.
14:23He said,
14:23no, you can't think of reality like that.
14:25It's not that really
14:25we live in a space
14:27and then things change
14:28in a universal time,
14:29which was Newton's idea,
14:30but rather space and time
14:32are locked together
14:32in some way.
14:34Excuse me, sir.
14:36Do you happen to know
14:37what time Oxford stops at this train?
14:48It's extremely doubtful
14:49whether Albert Einstein
14:51ever uttered those oft-quoted words,
14:53although if he had,
14:54it would certainly not have been
14:56a simple slip of the tongue.
14:58He believed that it was
14:59just as logical to ask
15:01what time Oxford would stop at the train
15:03as it was to ask
15:04what time the train would stop at Oxford.
15:07He suggested that you couldn't tell
15:09whether it was the train
15:10that was remaining stationary
15:12while the track moved underneath it
15:14or whether it was the track
15:16that was stationary
15:16while the train moved along it.
15:19It was all,
15:20as we might now say,
15:22relative.
15:23And indeed,
15:24the concepts that Einstein produced
15:26came to be known
15:27as relativity theory.
15:30Now, relativity theory
15:32has a number of very curious consequences.
15:35For example,
15:36the speed of light
15:37turns out to be constant
15:38whenever and wherever
15:40you measure it,
15:41and yet both space and time are not.
15:44Energy and matter
15:45turn out to be closely related
15:47to each other too.
15:52Einstein also completely vindicated
15:55Maxwell's earlier ideas,
15:57showing that Newton,
15:58while not exactly wrong,
16:00was only approximately right.
16:02There are,
16:03said Einstein,
16:04tiny but significant errors
16:07in the classical Newtonian way
16:09of thinking about space and time.
16:14Einstein's theory
16:15agrees with Newton's theory
16:17quantitatively
16:18under almost all circumstances.
16:21The deviations are really rather small
16:23and difficult to achieve.
16:24And so you might think,
16:26well, what's the big deal?
16:27You know,
16:27why is it such a revolutionary thing?
16:29The two theories agree
16:30for most of the time.
16:32And the answer is
16:33that Einstein
16:34had really swept away
16:35the entire conceptual scheme
16:37that Newton had.
16:39Prior to Einstein,
16:40space and time
16:41were really just
16:41parts of philosophy.
16:43They weren't part of physics.
16:44They were there as a backdrop.
16:46But after Einstein,
16:47space and time
16:47became part of physics
16:48and it then became important
16:50to understand
16:50how they change and move
16:52and how the affairs
16:53of space and time
16:53interweave
16:55with the affairs of matter.
16:58But as scientists
16:59and philosophers alike
17:00grappled with the apparently
17:02trivial
17:02but actually profound observation
17:05that time and space
17:06are somehow woven
17:07into the fabric
17:08of the universe,
17:09Einstein was wondering
17:10whether there wasn't
17:11some other deeper truth
17:13staring him in the face.
17:15How was it that space
17:17and time
17:18were members of the cast
17:19rather than simply
17:20the stage on which
17:21the drama was being played out?
17:23And how are the stars
17:25and galaxies
17:26that populate the heavens
17:27affected by such new ideas?
17:30The unexpected answer was
17:32that all matter
17:33causes dents
17:34in the fabric of space-time.
17:37The larger the object,
17:38the larger the dent.
17:40It was a geometrical theory
17:42of gravity which worked.
17:44time and again
17:45its predictions
17:46were borne out
17:47by observation
17:48and experiment.
17:50It was a theory
17:51which predicted
17:52black holes
17:53and galactic clusters,
17:55a theory of gravitation
17:56that was as elegant
17:57as it was powerful.
17:59It was a picture
18:01of the universe
18:01that wove matter
18:03and time
18:03and space
18:04and energy
18:05irreversibly together
18:07in a tapestry
18:08of theory
18:08that came to be known
18:09as general relativity.
18:13General relativity
18:14is a beautiful theory
18:15that has been well tested
18:16and explains
18:17many features
18:18of cosmology,
18:20the motions of galaxies,
18:21the expansion
18:22of the universe
18:22and other phenomena.
18:24However,
18:25it has nothing to say
18:25about microscopic physics
18:27at the atomic
18:28or subatomic level.
18:30Now,
18:30it's intriguing
18:32that Einstein
18:33developed general relativity
18:34at about the same time
18:35that other people
18:37were beginning
18:37to understand
18:38the laws
18:40that govern
18:40the behavior of matter
18:41at these most microscopic scales.
18:44And eventually,
18:44this gave birth
18:45to the idea
18:45of quantum theory.
18:46The word quantum
18:49means a parcel
18:50or packet
18:50and quantum theory
18:52is a description
18:53of nature
18:53based on tiny packets
18:55of matter and energy.
18:57Light can be described
18:58in these terms.
18:59The packets
19:00are called photons
19:01which stream out
19:02of any radiant objects
19:04like a light bulb.
19:07But there is a problem
19:08with light.
19:09It can also be described
19:11quite persuasively
19:12in terms of waves
19:13of energy
19:14radiating from the source
19:16like ripples
19:16on a pond.
19:18So what is light
19:19made of?
19:20Waves or particles?
19:23Time for an experiment.
19:35The experiment
19:36was devised
19:37by Albert Michelson,
19:38the one who
19:3920 years previously
19:40had said
19:41that there was nothing
19:42left to discover
19:43in science.
19:43quite simply
19:46it splits
19:47a beam of light
19:48in this case
19:49a laser
19:49into two
19:50and sends
19:51one beam
19:52to the left
19:52and the other
19:53beam to the right.
19:55A little further on
19:56the beams
19:56are brought together
19:57again
19:57and the result
19:58is photographed.
20:01According to
20:02the wave theory
20:03of light
20:03the two beams
20:04will create
20:05a pattern
20:05of bright
20:06and dark patches
20:07what are called
20:08interference patterns
20:09where the peaks
20:10and troughs
20:11of the light
20:12waves
20:12either add up
20:13or cancel
20:14each other out.
20:16In the Michelson
20:17experiment
20:18this is exactly
20:19what happens
20:20and a camera
20:21placed at the end
20:22of the laser path
20:23does indeed
20:23see interference
20:24bands of light
20:25and dark.
20:28But there's a
20:29profound philosophical
20:30sting in the tale
20:31of the Michelson
20:32interferometer experiment
20:34as Professor
20:35Chris Isham
20:35explains.
20:37The basic idea
20:38is very simple
20:39that you have
20:39a light source
20:40that you split off
20:41into two beams
20:42and then recombine
20:43so that they interfere
20:44and that's a perfectly
20:46normal demonstration
20:47actually of the
20:47wave nature
20:48of light.
20:49Indeed it was precisely
20:50through that sort
20:51of experiment
20:51that the notion
20:52that light was a wave
20:53first came into place.
20:55Now the interesting
20:55thing however
20:56occurs when you
20:57turn down the amplitude
20:58of the light
20:58make it weaker
20:59and weaker.
21:00Now according to
21:01classical physics
21:01all that should happen
21:02is that the image
21:03will get dimmer
21:04and dimmer
21:04and dimmer.
21:05But in fact
21:06what happens
21:06if you look at it
21:07carefully
21:08is you'll see
21:09it doesn't just
21:09get dimmer
21:10it breaks up
21:10into dots
21:11and those dots
21:12each one of those
21:13dots is in fact
21:13the effect of a
21:14single photon.
21:16So what you begin
21:16to see is how
21:17this apparent
21:18interference pattern
21:18is made up
21:19of individual photons.
21:22In terms of
21:23quantum mechanics
21:23one says
21:24well why that's
21:25happening
21:25is that what is
21:26really going through
21:27this equipment
21:29is not so much
21:29a light wave
21:30which would be
21:30the classical view
21:31but a probability
21:32wave.
21:33if you wish
21:34and what is
21:34happening
21:35the probability
21:35waves are interfering
21:36and this is also
21:37a very difficult
21:37thing to think
21:39about
21:39but it's what
21:39the mathematics
21:40suggests
21:40and then
21:42when the probability
21:42waves peak up
21:43together
21:44they save as a
21:45high probability
21:45you'll get a particle
21:46there
21:47and when they
21:48of course
21:48cancel out
21:49they save as a
21:50low probability
21:51and therefore
21:52what should happen
21:53according to the
21:54theory is you'll
21:54get speckles
21:55appearing
21:56on the pattern
21:57lots of speckles
21:57where the bright band
21:58was and not very
21:59many speckles
21:59where the dark was
22:00and in fact
22:01that's what you see
22:01if you look at the
22:02screen you'll see
22:02that's what happened
22:03now that in itself
22:05is not that remarkable
22:05until you start asking
22:06how does it come about
22:08that each individual
22:09photon as it were
22:10knows what to do
22:11and the only way
22:13you can explain this
22:14is by saying
22:15in some sense
22:15the photon itself
22:17splits
22:17whereas classically
22:19the light beam split
22:20you now have to
22:21somehow get hold
22:21of this idea
22:22that the photon
22:22is somehow aware
22:24of both paths
22:25this is a very
22:26very strange concept
22:28in quantum theory
22:29one abandons
22:30the possibility
22:31of predicting
22:31the exact result
22:33of any given experiment
22:34what one does
22:35is one predicts
22:36with extremely good
22:37accuracy
22:37the probability
22:38of a certain outcome
22:39every student
22:41who has ever studied
22:42quantum theory
22:43has really been shocked
22:45by some of the
22:45implications by it
22:46it's something
22:47that's very difficult
22:48to accept
22:49the idea that we
22:50there is a fundamental
22:51uncertainty
22:52that we cannot
22:53predict the outcome
22:54of an experiment
22:55to 100% accuracy
22:56we can only predict
22:58probabilities
22:58is very different
23:00than our experience
23:02in everyday life
23:03Nils Bohr
23:05is said to have
23:06once said
23:07that anybody
23:07who wasn't
23:08absolutely shocked
23:09by the statements
23:10of quantum physics
23:11simply hasn't understood
23:12the theory
23:13and I think that's
23:14completely correct
23:14it's a great pity
23:16in a way
23:17that ordinary basic
23:18quantum ideas
23:19aren't better known
23:20because they do
23:21produce these profound
23:23paradoxes about the
23:24nature of reality
23:24it comes back
23:26to the same point
23:27you cannot interpret
23:28quantum mechanical
23:29statements using
23:29ordinary common sense
23:30language and ideas
23:32and yet it lies at the
23:34heart of the structure
23:35of matter
23:35I mean the reason
23:36for example
23:37why the whole universe
23:37isn't just a great
23:38amorphous mass
23:39a solid single ball
23:41of gunge
23:42as it were
23:43is precisely because
23:44of quantum mechanics
23:45so the stability of matter
23:46the existence of ourselves
23:47depends totally
23:48on quantum mechanical effects
23:49and yet they have this
23:51paradoxical nature
23:52brought into their heart
23:53one of the most
23:56fundamental paradoxes
23:58in quantum theory
23:59springs from the way
24:00atoms
24:00the very building blocks
24:02of matter
24:02are constructed
24:03this is an atom of iron
24:05quantum theory suggests
24:07that the particles
24:09that make up this atom
24:10live in a curious
24:11maybe world
24:12they may be here
24:14they may be there
24:15there's a fundamental
24:16uncertainty about them
24:18which seems to defy
24:19normal notions of reality
24:20it's an idea
24:23that has come to be known
24:25as the uncertainty principle
24:27one of the authors
24:28of quantum theory
24:29Owen Schrodinger
24:31wondered what would happen
24:32if you used an uncertain
24:34subatomic quantum event
24:36like radioactive decay
24:38to determine the outcome
24:39of a large scale
24:41everyday experiment
24:42in his mind's eye
24:48the good doctor
24:48imagined how
24:49the experiment
24:50might work
24:51first he'd need a box
24:53into which he could
24:53place a suitable object
24:55next he'd need
25:03some quick acting poison
25:05but the key ingredient
25:14would be a radioactive substance
25:16which would give off
25:17particles as it decayed
25:18in an entirely random manner
25:20according to quantum theory
25:22if the radioactive source
25:24were then placed
25:25inside a screen detector
25:27linked to the poison flask
25:29which in turn
25:29would be linked
25:30to a cat-sized box
25:31then the experiment
25:33would be ready to proceed
25:34the question
25:46Dr Schrodinger pondered
25:48was
25:48what was happening
25:50to the cat
25:50during the experiment
25:52was it alive
25:53or was it dead
25:54what would he find
25:56when he opened the box
25:58the question facing
26:14Dr Schrodinger was
26:16what had happened
26:17inside the box
26:18while he'd been waiting
26:19for the experiment
26:20to run its course
26:21and once the experiment
26:23had been conducted
26:24would the random effects
26:26of quantum mechanics
26:27have caused the release
26:28of a fatal dose
26:29of poison gas
26:30into the box
26:31containing the cat
26:32was the cat alive
26:39or was it dead
26:40would Schrodinger's
26:42curiosity
26:43kill the cat
26:44well this is central
26:57to the whole
26:57standard interpretation
26:59of quantum mechanics
26:59now when you open the box
27:01according to conventional
27:02quantum theory
27:03what will happen
27:03is you will either see
27:04the cat dead
27:05or alive
27:06and at that precise instant
27:07in some way
27:08which has never really
27:09been explained
27:10the state of the cat
27:12changes
27:12and it really becomes
27:13dead
27:14or really becomes alive
27:16so before you open the box
27:18before you make the measurement
27:19all you can say
27:20is that the cat
27:21is potentially
27:22dead or alive
27:23but you can't say which
27:25and in fact it would be wrong
27:26to say it is either
27:27dead or alive
27:27that is actually incorrect
27:28it really is in some sort
27:30of strange
27:31twilight state
27:32between these two
27:33you open the box
27:34you make the measurement
27:35the cat as it were
27:36flops
27:37into a state of deadness
27:38or a state of aliveness
27:39now of course
27:40Schrodinger never actually
27:41carried out this experiment
27:42in real life
27:43but its value
27:44as an imaginary experiment
27:45is that it highlights
27:47what appears to be
27:48a key paradox
27:49in quantum mechanics
27:50it's complete nonsense
27:51for a cat
27:52to be described
27:53as being both dead
27:54and alive
27:55at the same time
27:55and there have been
27:57various attempts
27:58to find alternative
28:00interpretations
28:00of the quantum theory
28:01over the years
28:02and in one such
28:03interpretation
28:05the many worlds
28:06interpretation
28:07there are parallel
28:08universes
28:09in one of these
28:11universes
28:11the cat
28:12is alive
28:12and in another
28:13universe
28:14it's dead
28:14and it's only
28:16when we open
28:16the box
28:17that we discover
28:18which of these
28:18two universes
28:19we are living in
28:21the many worlds
28:23this idea of parallel
28:24universes
28:25has been very attractive
28:26to many people
28:27perplexed by quantum theory
28:29the notion is
28:31that there are
28:32an infinite number
28:33of universes
28:34which are unfolding
28:35in parallel with ours
28:36some are subtly different
28:38while others
28:39are radically different
28:41and every time
28:42and every time we make a decision
28:43or a choice
28:44in our universe
28:44we determine
28:45which of these
28:46parallel universes
28:47we are about to enter
28:48but can this
28:50sort of
28:51make it up as you go
28:52along theory
28:53really be true
28:54a theory
28:56a theory in which light
28:56can be waves
28:57or particles
28:58or both at the same time
29:00a theory of uncertainty
29:02and probability
29:03a theory in which
29:04the particles
29:05which make up atoms
29:06aren't really there
29:07a theory which seems
29:09to imply
29:09an infinity
29:10of parallel universes
29:12in conflict with ours
29:14can it really be
29:17a sensible description
29:18of nature
29:19the nature we see
29:20can quantum mechanics
29:22possibly be true
29:24quantum mechanics
29:27is by no means
29:28something that's
29:29very esoteric
29:30and has no effect
29:31on our everyday experience
29:32perhaps 25%
29:33of the gross national product
29:35of every country
29:36depends upon the laws
29:37of quantum mechanics
29:38transistors
29:39lasers
29:40all modern electronics
29:41works upon the laws
29:42of quantum mechanics
29:43well your television camera
29:45is a classic example
29:46of it working
29:47of course
29:47it's stacked full
29:48of solid state electronics
29:50and that works entirely
29:51on quantum mechanics
29:52every time anybody
29:53turns on a television
29:54these days
29:54or a radio set
29:55they're seeing
29:56quantum mechanics
29:57at work
29:57modern computers
29:58entirely
29:58based on
29:59quantum mechanical devices
30:09and in fact
30:10in that sense
30:10in a real
30:11sort of practical
30:12electronics
30:13quantum mechanics
30:14quantum mechanics
30:14has been verified
30:15millions of times
30:16thousands of millions
30:18of times
30:18so at that level
30:20quantum mechanics
30:21is fine
30:21it tells you
30:22what happens
30:22on the average
30:23what the probability
30:24is of certain things
30:25happening
30:25and if you just accept
30:27it at that level
30:27there's no difficulty
30:28the problems only arise
30:30when you start asking
30:30what does it mean
30:31about reality itself
30:32what picture does it
30:33give us
30:33of reality
30:34the pictures
30:38of quantum reality
30:40are taken here
30:41at the European
30:42particle physics
30:44laboratory
30:44in Geneva
30:45known in the trade
30:46as CERN
30:47this is where
30:49they probe
30:50into the heart
30:50of matter
30:51this is where
30:52they smash atoms
30:53in order to discover
30:54how they're made
30:55as the bits
30:58of these collisions
30:59fly apart
31:00they leave tracks
31:01which the particle
31:02physicists
31:03can analyse
31:03and interpret
31:04giving them clues
31:05about how the universe
31:07began
31:07I'm a cosmologist
31:09I want to study
31:10the universe
31:11on very large scales
31:12to understand
31:13how the universe
31:14got the way it is
31:15we're observing it today
31:17how the galaxies
31:19and clusters of galaxies
31:20that we see
31:21got that way
31:22where they came from
31:23and in order to understand
31:24where they came from
31:25you need to understand
31:26the physics
31:27of the very early universe
31:29and in the very early universe
31:30we're dealing with
31:31very high densities
31:33very high temperatures
31:34and at those energies
31:37and temperatures
31:38the theories that we need
31:40involve high energy
31:41particle physics
31:42the idea of the accelerator
31:47is essentially
31:49it's like a big
31:50incredibly powerful microscope
31:52and it's looking
31:53into the constituents
31:54of the particles
31:55inside the nucleus
31:56of the atom
31:56well high energy
31:58particle physics today
31:59is sort of the natural
32:00continuation
32:01of the historical idea
32:03that we should look
32:04inside of objects
32:05to see what they're made of
32:07so that we build microscopes
32:09to peer inside of objects
32:11and then we discover
32:13that they're made of atoms
32:14and then we discover
32:14the atom is made of
32:15a nucleus with electrons
32:17going around
32:17and then we can discover
32:19what the nucleus is made of
32:20by for example
32:22smashing things
32:23into the nucleus
32:24and breaking it up
32:25now the nucleus
32:26is made of particles
32:27like the protons
32:28and neutrons
32:29and these particles
32:30are the objects
32:31which are used
32:33if you like
32:33in accelerators
32:35like the ones at CERN
32:36and these particles
32:38are smashed into each other
32:39to see what they are made of
32:41it's a sort of terrestrial astrophysics
32:47the processes that occurred
32:49in suns billions of years ago
32:51are being recreated here on earth
32:53the energies involved
32:55are inconceivable
32:57the forces unimaginable
32:59it's a quest
33:01which reaches back in time
33:03to moments
33:04which were unbelievably ferocious
33:06a quest which worries
33:08at the very moment of creation
33:10a quest
33:11which unites cosmologists
33:13and physicists
33:13in their search
33:15for the ultimate answer
33:16a particle accelerator
33:19is in a very real sense
33:20a time machine
33:21it recreates the conditions
33:23that were present
33:24in the very early universe
33:25it never ceases to amaze me
33:28that you can apply
33:29these esoteric ideas
33:31these ideas that at first
33:33may not make sense
33:34they seem complicated
33:36but yet they work
33:37quantum mechanics works
33:38general relativity works
33:40it never ceases to amaze me
33:42that we can use the laws of physics
33:44to actually predict
33:46the origin of the universe
33:47and the evolution of the universe
33:49in much the same way
33:56that particle accelerators
33:57are time microscopes
33:59observatories are time telescopes
34:01gazing out at the heavens
34:04the views they capture
34:05are history
34:05ancient history
34:07some of the light
34:09that reaches us today
34:10was first released
34:11before our solar system
34:12was born
34:13some of the light
34:15we see
34:16began its journey
34:17back at the beginning
34:18of time
34:18but then
34:20so did we
34:21look deep
34:25into an astronomer's eye
34:26and you will find
34:27blood vessels
34:28and in those blood vessels
34:29and in those blood vessels
34:30you will find blood cells
34:32and in those blood cells
34:34you will find molecules
34:36of haemoglobin
34:37inside those molecules
34:41you'll find one of the most extraordinary atoms
34:44in the universe
34:46an atom of iron
34:47this atom has had a remarkable life
34:52and we're going to tell its story
34:54it's a story
34:56it's a story that will take us back to the beginning of the universe
34:58to the moment of creation
35:00before it became bound up in an astronomer's bloodstream
35:05this iron atom was quietly minding its own business as part of a continental shelf
35:10this was a geologic formation
35:13that erupted from the volcanic milestone
35:15that was the early earth
35:17prior to that
35:19it had been the gravitational field
35:21of the newborn earth
35:22which had drawn our atom towards the planet
35:24as it drifted through interstellar space
35:27but this was an atom
35:34which had been places
35:36seen things
35:37ours was not the first sun system it had visited
35:40before being drawn to the solar disk that had created the earth
35:45it had been drifting through space
35:47if we track our iron atom back through time
35:51we'll get a glimpse of how it
35:52and the universe were created
35:54unwanted, unhurried
36:00this was an atom which didn't care
36:02but as we go back in time
36:05we begin to see that here's an atom
36:07which has experienced stardom in a big way
36:10here's an atom which was created inside
36:14one of the biggest bangs there is
36:16a supernova
36:18when the universe was only 5 billion years old
36:34our atom burst from an exploding supernova
36:37and as we track it back in time
36:40we can see how it came into being
36:42deep within the star
36:54collision after collision
36:56welded the nucleus of the iron atom together
36:58and now
37:00as we roll back the clock
37:01we can see the components which created it
37:04further inside the star
37:10it's clear that our complex iron atom
37:12was actually built
37:13from a host of simpler atomic constituents
37:16and rolling the clock back even further
37:19we can see that everything is made
37:21from the simplest possible elements
37:23hydrogen and helium
37:40the universe is now just 4 billion years old
37:59and gravity is about to release its grip on this early star
38:03the iron atom has melted into the nucleus soup from which it came
38:08and now as we race further back in time
38:11the earliest stars go out
38:13and the universe becomes a seething mass of gas
38:17it's getting hot
38:18with no iron atoms left to befriend
38:21we'll now hitch a ride on a hydrogen atom
38:24the universe is now just 2 billion years old
38:42and all there is is hot hydrogen and helium gas
38:45the effect of that gentle giant gravity is being slowly undone
38:50and by the time the universe is a mere 300,000 years old
38:54all that seems to be left is a ball of hot goo
38:58and getting hotter
38:59before long hydrogen and helium atoms are beginning to fall past us
39:05and as the universe hots up even more
39:07the electrons, protons and neutrons begin to split apart
39:12the universe is now just one second old
39:27and it's become a sizzling soup of fundamental particles
39:31all manner of strange interactions are going on
39:35as we travel back in time
39:36to when the universe was only one tenth of a second old
39:40it's difficult to tell which particles are which
39:43the universe is now less than a hundredth of a second old
40:08it's getting very dense
40:10it's getting very dense and the electrons are behaving rather oddly
40:12they're beginning to smash into the neutrons and protons
40:16and when they do something rather curious seems to be happening
40:20the protons are becoming neutrons
40:22and neutrons seem to be able to become protons
40:26as we travel back past one thousandth of a second
40:39the temperature hits a trillion degrees
40:42yet further back in time
40:48when the universe was just a millionth of a second old
40:51we can begin to see that even our fundamental protons and neutrons
40:56are made from smaller bits
40:57bits called quarks
40:59and it's the nature of the quarks
41:02which accounts for the strange behaviour of the neutrons and protons
41:05as our journey back in time
41:10takes us past the moment when the universe
41:12was merely a billionth of a second old
41:14all we can see is a rapidly contracting cauldron of quarks
41:19finally we arrive at a universe so compressed
41:27that it would all fit within the orbit of the earth
41:30and would have been a sweat making thousand trillion degrees
41:33by a trillionth of a second after the big bang
41:43everything there is in the universe
41:45would have melted back into a soup of quarks and electrons
41:50and yet there's a problem with this picture of the origin of the universe
41:54it doesn't account for gravity
41:57every time the physicists try to build this most fundamental force into their equations
42:02what do they get?
42:04infinity
42:09we don't know whether these infinities that arise in physics
42:15are a fundamental flaw in physics
42:17or if that's just the way nature works
42:19some physicists feel that any theory that has infinity in it
42:23has to be sick and it's not a complete theory
42:26usually in physics when you're doing mathematical calculations
42:30the sorts of infinities that we're talking about occur as singularities
42:35and a singularity in mathematics is when you take an expression
42:39and you end up dividing that expression by zero
42:42and you know that if you divide a number like one or two by zero
42:46the answer is not well defined
42:48you try it on your calculator you'll get an error
42:51now to a physicist a singularity is about the worst thing that can happen
42:56when a physicist finds a singularity in a calculation
43:00they pull out the hair and scream and jump up and down and kick the dog
43:04some people are very upset that the laws of physics as we understand them
43:09predict a singularity at the instant of the big bang
43:12modern physics is based upon the twin pillars of the theory of relativity
43:17on the one hand that's a theory of space and time
43:20and quantum physics on the other hand that's a theory of matter
43:24and much of what we have around us in the sense of technology or advanced experiment
43:30stems from one or other of these theories or the two theories together
43:34now the difficulty is this that mathematically when you try to marry these two theories
43:39and have a unified theory of relativistic quantum mechanics
43:44then you run into difficulties
43:46and it's particularly acute if you go to the so-called general theory of relativity
43:50which is a theory of gravitation
43:52you try to put gravitation together with quantum physics
43:54and the two just don't want to go together
43:57what you get is essentially nonsense
43:59you get these infinities popping up all over the place
44:01destroying the predictive power of the theory
44:03so what do you conclude from that?
44:05well I guess you have to conclude that either one or the other or both are wrong
44:10which is where super strings come in
44:13if they exist at all
44:15every quark, every electron and even the forces between them
44:18will be made from tiny vibrating strings
44:21which can join up and reform into all the particles known to physics
44:25and the way they vibrate will determine what they are
44:29physicists are optimistic about super strings
44:32because they appear to obey the laws of quantum theory
44:35while at the same time conforming to the principles of general relativity too
44:40and at last here's a theory which not only explains gravity
44:44it actually predicts it
44:46but it's even more curious than that
44:48space and time will be made of string too
44:51and the only problem is
44:54it will never be possible to see them
44:56they're just too small
44:58well according to super string theory
45:02the fundamental particles are literally string like extended objects
45:07but of an incredibly small size
45:09just to get an idea of how small I mean
45:12they are as small compared to the size of the nucleus of an atom
45:16as the nucleus is compared to the size of the sun for example
45:20so that we're talking about physics at incredibly short distances
45:24and we're also talking about objects which appear to exist in no less than ten dimensions
45:31the four of space and time which we're familiar with
45:35and six more which only intrude into our world at subatomic levels
45:39now we can't show ten dimensions on television
45:43so instead imagine a two-dimensional world where only edges can be seen
45:48into that two-dimensional world comes an object that exists in three dimensions
45:53at first it's impossible to tell what these alien shapes represent
45:58are they connected? is there a pattern here?
46:01the inhabitants of the two-dimensional world might never know what it is that's invading their lives
46:07and yet to those of us familiar with a third dimension
46:11it's readily apparent what the object is
46:14once we're permitted to see that extra dimension
46:17and so it is with super strings
46:20what physics sees as separate particles are simply different manifestations of objects poking through
46:26into our universe from their own multidimensional space
46:30but can something as simple as vibrating string seriously provide us with a theory of everything?
46:36what I think is new about the present ideas is that they're more than just hand-waving
46:45they're more than just a good idea
46:48they are a detailed technical theory
46:51if we take something like super strings as the best example of something we have
46:55this is not just an attempt to write a catalogue or a shopping list of entities
47:01you've got atoms of this type, particles of that type, you've got space and you've got time
47:05you've got various fields and so on
47:07let's sort of collect them all together and say that's the theory of everything
47:10it is something which interweaves all of these entities
47:13it's something which combines space, time, the forces of nature, the particles of nature
47:17the whole caboodle together in a single, all-embracing, one hopes self-consistent mathematical scheme
47:25that's what's new
47:26it is a theory of totally everything
47:28not just a sort of ragbag of things put together and saying, you know, that's all that there is
47:33if strings are the correct description of nature
47:36then any attempt to understand the origin of the universe without taking into account the string
47:44stringiness of nature is doomed to failure
47:47if strings are the correct theory it would change how we view the origin of the universe
47:51and necessarily the subsequent evolution of the universe
47:55we as physicists have a rather limited viewpoint on the universe
47:59and we would like to explain certain specific facts in an elegant and economical way
48:05and our hope is that we can explain all of those facts
48:08the forces that we know of and the particles we know of
48:10in terms of a single underlying principle
48:13that principle is what we would then call a theory of everything
48:16but of course it almost certainly will not be everything
48:19the history of science is full of lessons
48:22which indicate that just when physicists think they have a theory that explains everything
48:26they discover there's an absolute crisis in their subject
48:29and there are many phenomena that they hadn't noticed before
48:32which need explanation
48:34but it may even be that there is an absolute limit to what science can know
48:39a moment so far back in time that even super string theory may not be able to describe what was going on
48:47at the time the entire universe would have been smaller even than a super string
48:52and at such dimensions physics encounters a barrier so impassable
48:57that we cannot know what happens beyond it
49:00the fact that we can see as far as we do is a tribute to these giants of physics
49:05whose insight has given us such hindsight
49:08but nevertheless our journey back in time stops here
49:13the traditional laws of physics break down at this point
49:18and we need some new idea
49:19now super string theory seems to provide us with the hope of getting a glimpse of what is happening beyond the barrier
49:25but it seems doubtful at least to me
49:27that it will actually provide an explanation for the creation of the universe itself
49:31for the moment we may as well believe any of the beautiful ancient creation myths
49:36who knows maybe the universe was created by a couple of Japanese gods stirring up the sea of chaos
49:42I suppose the origin of the universe is the place where you might most expect to encounter God so to speak
49:48because until recently it was not possible to account for how the universe came into being
49:53without having some sort of supernatural input
49:55so I think there's been a lot of attention given to this sort of creation event as it's sometimes called
50:01but one of the remarkable things that's come out of very recent work in quantum gravity and applying
50:13quantum theory to the universe as a whole
50:15is that you actually don't need to have a supernatural button pushing creator back at the beginning to set the whole show gang
50:21it's possible to have the universe so to speak pop into existence on its own
50:25entirely spontaneously entirely uncaused
50:28and entirely in accordance with the laws of physics
50:34but even if super string theory does turn out to be a description of all of space
50:39and all of time and all of the matter in it
50:41it's still hard to imagine that the majestic complexity of the universe we see around us
50:47may be no more than a quantum hiccup
50:51it all seems to have been so exquisitely well designed
50:55and yet the uncertainty principle clearly indicates that it could all be a huge unplanned accident
51:02a freak event that had no cause and fulfills no purpose
51:07just one of an infinity of universes popping into existence simply because it can
51:13it's an idea it strikes at the foundations of mankind's self-esteem
51:19and of course his religious beliefs
51:22this is a description of creation which doesn't need a creator
51:26there are those however who suggest that someone or something
51:31had to devise the rules of nature
51:34the laws of physics
51:36and that God
51:38whatever God is
51:40is a mathematician
51:42it's people who want to know
51:47everything
51:51is written
51:52this is definitely
51:53like that
52:08THE END
52:38THE END
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