that's the girl still make the presentation Albert Einstein the icon of genius his theory of general relativity is one of the greatest feats of thinking about nature to come from a single mind it is now 100 years old how do you even study the universe how can you study everything all this mass all the stuff all the energy in the universe at one time turns out that you actually can do that with Einstein's theory of general ativy one mathematical sentence and from it you can derive the understanding of the entire universe on the largest scales and that is beautiful how did a theory that explains so much come from one person Ann Stein had a magical talent he could take a hard physical problem and boil it down to a powerful visual image thought experiment this is the story of how a young Albert Einstein imagined a series of thought experiments of fundamentally altered our view of reality the problems are formulated simply but it turns out that the answers revolutionize the whole of science [Music] the seeds for einstein's key thoughts were planted when he was just a child he grew up in a small house in Munich in southern Germany his unique personality was evident early on like many great innovators Einstein was a rebel a loner but deeply curious he was slow in learning to speak as a child so slow that his parents consulted a doctor but he later said that that's maybe why he thought in visual thought experiments his sister remembers in-building little card towers using playing card he was a daydreamer but he was deeply persistent Einstein's father Harriman manufactured electrical equipment he nurtured his sons interest in science on one occasion he brought him a compass this needle kicks and points you where to go but you can't see how or why and that kind of puzzlement is very characteristic of young scientists now you and I maybe remember getting a compass when we were kids and for like oh look the needle twitches and points north but then we're on to something else I go look there's a dead squirrel but for Einstein after getting that compass he developed a lifelong devotion to understanding how things can be forced to move even though nothing's touching them the young Einstein became gripped by a desire to understand the underlying laws of nature he developed a unique way of thinking about the physical world inspired by his favorite book the book Einstein love told little stories like what do we like to travel through space go through an electrical wire they made Einstein think visually these imagined situations that we often call thought experiments became a defining feature of Einstein's thinking one of the critical thought experiments at Einstein began to play with very young and around the age of 16 was trying to imagine what would happen if he could catch up with a light wave it's one thing to imagine light waves zooming past him at some impending the impossible speed but what if he could somehow just propel himself really quickly what would it look like if he could catch up with that light wave what would he see he said it caused him to walk around in such anxiety his palms would sweat now you and I may remember what's causing our palms a sweat at age 16 and it was not a light being but that's why he's Einstein this dreamlike thought about the nature of light was Einstein's first step on the path to his great theory it stayed with him throughout his time at school and college he was extremely gifted in science and math as a young person and very bad at other classes mostly because he kept cutting class and being very rude to his teachers many teachers from when his high school days on work and as he'd never amount to anything he was a discipline problem I mean he was bad news he applies to the second best University in Zurich the Zurich Polytechnic and gets rejected I'd love to meet the admissions director who rejected Albert eyes but eventually he gets in and he does moderately well but not good enough to get a teaching fellowship and so he ends up if the Bern Swiss Patent Office as a third class examiner Einstein started work at the Patent Office in 1902 age 23 here his job was to assess the originality of new devices he was immersed in the kinds of sort of technical details that he had been fascinated by as as a very young kid and here he was sitting in you know the kind of wave of the modern age this was the era of electrification so all the latest clever ideas for switching technology for coordinating clocks in particularly those are all passing through his office time zones had recently been introduced in Central Europe and accurately synchronizing clocks within regions was a major challenge of the day Switzerland was a world leader in time technology dozens of patents to link clocks pass through Einsteins office he could whip through these patent applications and then out of his drawer he pulled his physics notes and his boss was very indulgent and would sort of turn a blind eye as Einstein was doing his theories in the spare time it's really important to remember that theoretical physics was new when Einstein was a young man you could do quite a lot of this work by reading a relatively small number of science journals and making the calculations yourself Einsteins world in 1905 was dominated by two kinds of physics one was about 200 years old founded by Isaac Newton British natural philosopher for Newton all there is in the world is matter moving Newton showed that the motion of falling apples and orbiting planets are governed by the same force gravity his equations are so effective we still use them today to send probes to the farthest reaches of the solar system the other important theory of Einstein's day covered electricity and magnetism that branch of physics had been revolutionized in 1865 by the Scottish physicist James Clerk Maxwell Maxwell's theory describes light as an electromagnetic wave the travels at a fixed speed this prediction that the speed of light will be an absolute fixed value never faster never slower never stopping that is so surprising as ordinary things don't have a prediction from fundamental law what their speed is a basketball can be fast or slow or it can stop there's no fundamental fact of the speed of a basketball this notion of a fixed speed of light captivates Einstein he visualizes it in a brilliant thought experiment [Music] he imagines a man standing on a railway platform a lamp turns on a beam of light rushes past him and he observes the speed then he imagines a train traveling at close to the speed of light a lady on board sees the same beam Einstein visualizes that in Mutants world because the lady is moving at close to the speed of light she would see the beam pass her train window relatively slowly but in Maxwell's world the speed of light must be the same for both a man and the lady Einstein could see immediately that there's a contradiction between Newton and thanks well they just don't fit together the reason they don't fit together is that if Newton is right then if you measure the speed and light it will be different depending on how you're moving and what the Maxwell Ian's were saying was the speed of light is always going to turn out the same those two things cannot simultaneously be true and one of the things I'm Stein hated hated was contradiction if there's one kind of physics that says this and another kind of physics that says that and they're different that's a sign that something's gone wrong and it needs fixing for months Einstein wrestles with the problem eventually he makes his breakthrough he focuses on a key element of speed time he realized that any statement about time is simply a question about what is simultaneous for example if you say the train arrives at 7:00 that simply means that it gets to the platform simultaneous with the clock going to seven he feels this crucial notion of things happening at the same moment should depend on how you're moving and that would mean the flow of time might not be the same for everyone he explores this radical idea in another thought experiment again he imagines the man standing on the platform this time two bolts of lightning strike on either side of it the man is standing exactly halfway between them and the light from each strike reaches his eyes at exactly the same moment for him the two strikes are simultaneous [Music] then Einstein imagines the lady on the fast-moving train at close to the speed of light what would she see [Music] as the light travels out from the strikes the train is moving towards one and away from the other light from the front strike reaches her eyes first for the lady time elapses between the two strikes for the man on a platform there is no time between the strikes this simple thought has mind-blowing significance if different observers can't agree on what simultaneous then they can't agree on the flow of time itself if there's no such thing as simultaneity then there's no such thing as absolute time everywhere throughout the universe and Isaac Newton was raw the lady on the fast-moving train does measure the speed of light to be the same as the man because relative to him her time runs slower this concept the time and space are flexible depending on how you're moving became known as special relativity it led to remarkable results such as the famous equation relating energy to Mars Einstein published this article in 1905 - exactly no acclaim most people ignored it this was not setting the world on fire two years go by before a very eminent physicist johanna stark invites einstein to write a review article on einstein's own work precisely because no one was paying attention and he begins thinking about ways to generalize him to push his own results from 1905 what if he considers not only a train moving at a fixed speed past the platform what if that train begins to speed up or slow down what if his acceleration adding acceleration to the equations was his first task then there was that mysterious Newtonian force of gravity to contend with in Newton's theory gravity is a force that acts instantaneously but special relativity says that's impossible nothing can travel faster than light what Newton's theory tells you is that suppose the Sun were to disappear the orbit of the earth should change at that very moment but the notion of at that very moment in two different places is exactly one of these notions that special relativity has told you isn't a good physics notion so you've now got this challenge of trying to work out how to take the success of Newton's theory of gravity but fit it into this new special relativistic picture Einstein begins to think about how objects fall [Music] and one of the major features that gravity has was pointed out by Galileo that everything falls at the same rate in a gravitational field if you can ignore the effects of air resistance even heavy objects and light objects they all fall the same way when gravity pulls on them this bowling ball and feather inside the airless environment of a vacuum chamber fall and perfect unison I think figured that if everything falls at the same rate in a gravitational field then imagining that all you're allowed to do is look at the things around you you're not allowed to look at the wider world then you wouldn't even be able to tell that you were falling in a gravitational field because everything would be doing the same thing whatever that thing was so Einstein said well that's a very strange feature for a force of nature to have the things that are next to each other can't even tell that that force is there and again being Einstein he started to think well what kind of force of nature would have that property what what would it mean for a force of nature to act on absolutely everything in the same way Einstein feels that there must be an important link between gravity and acceleration [Music] we all know that if when we are accelerators and of course now we have cars and airplanes to give us the physical feeling if you were in an airplane and it's taking off you are pushed back in your chair you feel actually kind of a force pushing you back which feels very similar to the force of gravity but you need kind of the brilliance of Einstein to explain why they are related we have another moment here where Einstein is looking something familiar but then seeing it in a different way and concluding some remarkable new principles about it suddenly he hits upon what he describes as the happiest thought of his life what if gravity and acceleration are really the same thing [Music] again he examines the idea in a beautiful thought experiment he imagines a man in a box floating weightlessly in a distant region of space in zero gravity suddenly the man stops floating and finds himself on the floor what has happened either the box is no close to a planet and the force of gravity has pulled the man downwards or someone has attached a rope and the box is now being pulled and accelerated upwards [Music] so which is it gravity or acceleration without being able to see outside the man can't tell why he's on the floor Einstein realized that there is no way to tell the difference between sitting in a gravitational field and being accelerated these are equivalent situations the fact that these two effects are the same give the same result means that gravity is acceleration it's not just like acceleration it's the same thing it's a big breakthrough by extending his theory of special relativity to include acceleration he could begin to formulate a new theory of gravity [Music] by 1912 Einstein is living in Zurich with his wife Mileva and two young sons Hans and Eduard the academic world had realized the importance of special relativity and his career had taken off he's now a professor at the esteemed Swiss Federal Institute of Technology but spends as much time as possible working on his theory he needs to describe how objects move in space and time and soon realizes that the best tool for the job is a strange but powerful concept called space time if I think of space I know that I can find anything if I know where it is north south east west and up down three points but that doesn't mean I can find it I also have to know where it is in time and so if we start to think to know everything about an event in the universe I have to know not just its spatial coordinates but also its time coordinate I can begin to think about where it is in a space-time imagine a camera filming an action capturing each moment in time as a single frame Einstein basically tells us think of the movie reel so you have all these little pictures now cut them apart one by one and stack them on top of each other to get his pile and if you go up in the pile you go up in time and now kind of glue them all together into one big block and that block has both space and time and that's the space-time continuum it's almost looking at a movie not frame by frame but seeing the whole movie at once it would now be kind of two strands going up in space and time and they would be kind of spaghetti strands the fact we all are spaghetti strands moving in this space-time Einstein feels that space-time is the natural arena in which his theory of relativity should play out but now he needs sophisticated mathematics by your standard or mine Einstein was good at math he was Einstein but he was not really a mathematician per se he didn't prove theorems he didn't pour over math books he was a physicist he did thought experiments he thought of very tangible concrete situations and what would happen so when it came time for him to really bear down to the absolute cutting edge mathematics of his day he required help he has to have a better grasp of how to describe parts of objects as they move through space-time he needs new mathematics and he doesn't have that at his fingertips so he has to go look for it at university einstein had skipped the geometry classes letting his friend Marcel Grossman take notes for him Grossman had excelled in geometry and was no chairman of the math department he suggests Einstein uses advanced mathematics in which the shape of space and time could be curved because space-time has a geometry he thinks to himself well maybe it's the actual shape of space-time itself that is giving rise to gravity after months of work Einstein has an extraordinary idea what if space-time is shaped by matter and that what we feel as gravity in struggling to figure out what causes gravity then Einstein has this great insight it is simply that a mass distorts the shape of space-time around it so you get rid of this force of gravity and instead we have curvature of space-time in Einstein's universe then if space were empty it would be flat there'd be nothing going on but as soon as you put objects down they warp the space and time around them and that causes a deviation of the geometry so that now things start moving everything wants to move as simple as possible through space and time but Einstein tells us that mass sculpts pays on time and it's the curved motion through this sculpture as the force of gravity we have this feeling that the reason I can feel pressure on the soles of my feet that the reason things are going to drop when I throw them because there's a force attracting us down to the center of the earth what general relativity tells you is that's not the right way to think about what's going on there what's really going on is that your natural path in space-time would take you to the center of the earth and what's actually happening is the floor is getting in the way it's pushing you upwards we look at it we go off the force of gravity but Einstein says no no the curvature of space-time [Music] it's a stunning insight just as an aunt might feel forces pulling it left and right as it walks over crumpled paper when it's simply the shape of a surface dictating its path Einstein saw that what we feel as the force of gravity is in fact the shape of the space-time we're moving through that move to stop treating gravity as something spooky and inexplicable and start thinking of it as something that's absolutely to do with the very geometry of the world that then allowed him to begin to complete a general a universal theory of relativity Einstein now has everything he needs to formulate his final theory of gravity but he makes a critical mistake he misinterprets one of his equations and unaware of his error continues working on incorrect ideas [Music] the point at which Einstein is going to give the most essential equations of the theory Einstein considers something like them and then says ah but these don't work and then writes down the wrong equations what follows from alternations of confidence and despair as he convinces himself that everything is fine with this theory and then he realizes that things aren't so good with the theory it is a long dark period for Einstein as he struggles to reconcile himself with a theory that is just not working two years later Einstein is in Berlin at just 36 years old he has one of the most prestigious positions in physics but he is still struggling with his theory by 1950 we've reached the pinnacle of the profession he's in the Prussian Academy and a professor at the University of Berlin but his marriage is falling apart his wife and his two kids have moved back to Switzerland so he's pacing around almost all alone in this apartment in Berlin he changes fundamentally the way that he does his physics he had relied on physical intuition all the way through here and he'd let the mathematics take a backseat he decided that that was a mistake that he should have listened to the natural mathematics first and Einstein adopted that new method and started to write down not the equations that he thought were physically the most plausible but the equations that were mathematically the most natural but now he has a competitor Einstein had enthusiastically shared his ideas with the brilliant mathematician David Hilbert Hilbert was so impressed he decided to work on the theory himself Einstein is now in a race to the finish with one of the world's best mathematicians this is unfolding in a remarkably dramatic period in history World War one has begun to ravage Central Europe Einstein is not just toiling he sort of in the abstract he's toiling as as the world seems to fall apart that affects whom he can send letters to it affects what journals from other countries he can even receive in the midst of the blockade the world is certainly from the point of view of the middle of Germany is not looking like a bright happy place Einstein's feeling dejected because his work is not going well he's concerned that he's now in a race with a remarkably gifted colleague his family life is not particularly happy and the headlines every day scream war devastation and carnage by November 1915 Einstein is scheduled to present his work in a series of four weekly lectures at the esteemed Prussian Academy but he's struggling to formulate his ideas in the midst of this ordeal letters arrived from his wife in Zurich pressing the issue of his financial obligations to his family and discussing contact with his sons as his lectures begin his theory is still far from complete the pressure on Einstein is huge he would give a lecture revise it give it again spot mistakes correct them get up on the podium explain what was wrong in the previous week's lecture correct it and then move on and then do that again and again for four weeks running his work to convince them of the truth of this absolutely radical new theory of relativity that he was proposing is one of the most intense periods of work in the history of science somehow he's able to focus on his theory with an incredible intensity and he makes his breakthrough he tests his equations on a problem that Newton's theory of gravity couldn't solve the orbit of mercury Mercury's path around the Sun has an anomaly that Newton's theory can't explain it deviates slightly each time it goes round in Stine calculates the orbit with his new equations the answer is correct exactly what astronomers had observed he'd found the final equations for his general theory of relativity [Music] you have to think about the hubris of being Albert Einstein he had already thrown out Newtonian mechanics with special relativity and then he had gone off on his little personal quest to incorporate gravity and at the end of the day he boils it down to a prediction for a number that had been observed the precession of the orbit of mercury and miraculously when the pages of algebra work out to their end you get the right answer and suddenly it's not just playing with equations anymore he realizes this is how the world works all this abstract nonsense is the correct theory of reality [Music] Einstein is at last able to present a successful theory that's a triumphant moment one of the great moments in the history of physics and for Einstein a victory very much against the odds and he'd won on the 25th of November 1915 Einstein lays out his findings in his climactic fourth lecture at the Prussian Academy he presents general relativity the theory can be written as a single equation it condenses sprawling complexities into a beautifully compact set of symbols so the formula is really simple G mu nu equals true Jean for the shape of space-time and T for the distribution of mass and energy so this very simple formula captures all of nine science general relativity it's a beautiful simple equation but it's a lot of work to impac the symbols the mathematical symbols and see how in this very simple formula the whole geometry of the universe is hidden it's kind of an acquired taste to see the beauty it's also a signature formula for Einstein the true mark of his genius is that he combines two elements that actually live in different universes the left-hand side lives in the world of geometry of mathematics the right-hand side lives in a world of physics of matter and movement and so perhaps the most powerful ingredient of the equation is this very symbol equal sign here these two lines that actually are connecting the two worlds and it's quite appropriate they're two lines because it's two-way traffic matter tells space and time to curve space and time tells matter to move [Music] the idea that gravity is the curving of space and time is completely alien to most of us it's hard to imagine that time itself can be warped but it's real we can measure it the Earth's gravity the distortion of space and time reduces the further you are from the mass of the planet time flows quicker at altitude to put this to the test a team of specialists has placed a highly accurate atomic clock at the top of New Hampshire's Mount Sunapee 2,700 feet above sea level after four days they collect their clock [Music] and take it down the mountain to their lab [Music] they are they compare it to a second atomic clock that has remained just a few feet above sea level master clock in channel B you guys ready this is it right here the time interval counter is going to show us the time difference between these two clock ticks 20 nanoseconds you can see the time difference between them represented here graphically of the clock that was up at the mountain for 4 days in our master clock since gravity is weaker at altitude while the test clock was up the mountain time ticked faster it's now 20 nanoseconds 20 billionths of a second ahead of the sea level clock just as general relativity predicts this is really awesome but back in 1915 atomic clocks weren't available Einstein needed a way to show the world the bizarre features of his theory the general theory of relativity made predictions of things which looked really strange for example the idea that light bends when it passes near a very heavy body no one had ever looked for that no one had ever observed it Einstein was desperate desperate to get astronomers to make that test Einstein's theory predicts that when light from a distant star travels close to the Sun the Warped space around the Sun bends the lights path in me 1919 the English astronomer Arthur Eddington traveled to the African island of principie to record images that would show this phenomenon right at the end of the war Arthur Eddington very much keen to work with Einstein first because he took the general theory of relativity very seriously he was a huge admirer of Einstein but also because he was a Quaker a pacifist he wanted as quickly as possible to as he put it solve the wounds of war to bring the British and the Germans back together what Eddington had been able to do is take photographs of stars during a total eclipse of the Sun so the moon blocked most of the brightness of the Sun and little pinpricks of light could be seen around the Sun otherwise would be lost in the glare and Eddington and his colleagues were able to measure that the appearance of those stars had been shifted compared to where they would have been had that big mass of the Sun up and deflecting that light from far away edingtons able to show in November of 1919 just one year to the day after the end of World War one that Einstein's general relativity theory is right and a revolution in science has been accomplished [Music] when the Eclipse experiments prove Einstein's theory right he rockets to fame not just because he's explained a new way of looking at the universe but at the end of World War one you had the predictions of a German scientist be proven right by some British astronomers and it becomes headlines across the world New York Times says lights all askew at the heavens meant of science more or less a God this is back when newspapers knew how to write great headlines but Einstein kind of loves this fact that he is now an icon assignment Einstein becomes a worldwide celebrity the icon of genius we still recognize today the only person who was more widely known was Charlie Chaplin and they got on like a house on fire Chaplin said the reason they all loved me is cuz they understand everything I do and the reason they love you is that they don't understand anything you do can you explain that and I'm son said but in 1930s Berlin the Nazi Party is gaining power as a Jewish scientist Einstein becomes increasingly caught up in the political unrest Einstein's theories became a target they were deemed sort of aesthetically repugnant to a kind of Aryan Sensibility so people attacked not just Einstein the Jewish scientist but they would actually have people denouncing general relativity [Music] he begins to make trips to America where he is welcomed with open arms and in 1933 he settles in Princeton taking up a position at the Institute for Advanced Study today the Institute is headed by Professor Robert digraph he basically was still very much by himself just actually as he was in Berlin just concentrating on this almost deep ideas and struggling with the understanding the universe of course its office was here at the Institute Einstein worked to unify his theory of gravity with the other laws of physics with Einstein you see this phenomena to see with many great scientists that they climbed his very high mountain and instead of celebrating their success they privileged to see a much wider landscape and they see all these mountains behind it and I think he was very much aware how much till there was to be done till the very last days of his life he was trying to push these equations and and find a description of nature of nature in terms of the geometry of space and time but general relativity was fading from mainstream science physics was now focused on the quantum theory of atoms and tiny particles a theory incompatible with Einsteins ideas but one that could be tested in a lab most of general relativity was then beyond the reach of experiment when Einstein died in 1955 aged 76 the wider scientific community presumed his theory had reached a dead end but they couldn't have been more mistaken the best theories in physics always take us to places where the people who invented them didn't imagine and a truly wonderful theory like general relativity predicts all sorts of things that Einstein didn't conceive of the theory has a life of its own we understand general relativity much better right now than Albert Einstein ever did today huge telescopes peer deep into the universe it is general relativity that allows us to make sense of what they see and there's one prediction of Einstein's theory this technology has allowed us to explore that is straight out of science fiction a black hole [Music] everything that we're familiar with an ordinary life is made from matter but not black holes black holes are made from Warped space and time and nothing else a black hole is an object that is spherical like a star or like the earth with a sharp boundary called the horizon through which nothing can come out so it casts a shadow on whatever is behind it it's just a black black shadow unbelievably black this simulation shows the distortion of starlight around a black hole even though Einstein knew his theory predicted black holes he found it hard to believe they would really exist in nature in the 1960s professor Kip Thorne worked on the mathematical concept of black holes the idea made sense on paper and he began to feel that these science fiction like objects might actually be real must be kept made a bet with fellow physicist Stephen Hawking about whether or not a strong source of x-rays known as Cygnus x1 was in fact a black hole here we go some black holes yeah there it is so that is a copy of the famous bet the bet says whereas Stephen Hawking has such a large investment in general relativity in black holes and desires an insurance policy and whereas Kip Thorne likes to live dangerously without an insurance policy that's a that's a good characterization of myself as much to my wife's chagrin therefore be it resolved that Stephen Hawking bets one-year subscription to Penthouse magazine is against Kip Thorne's wager of a four year subscription to a political magazine called Private Eye that cygnus x-1 does not contain a black hole of mass above the Chandrasekhar limit it's witnessed this tenth day of December 1974 while Stephen is at Caltech with me we made that bet under circumstances where there was mounting evidence that Cygnus x1 really is a black hole Stephen Hawking had a terribly deep investment in it actually being a black hole and so he made the bet against himself as a insurance policy that at least he would get something out of it that's Cygnus x1 turned out not to be a black hole the amount evidence mounded thereafter over the period of the 70s and 80s and in June 1990 Stephen snuck into my office and signed off on the bet that finally the evidence was absolutely overwhelming that Cygnus x1 really is a black hole and Penthouse magazine arrived he sent me the British version of penthouse which was ever so much more raunchy than the American penthouse actually enough to terminate my face turned red when who and I received it at first today thanks to concepts built on Einstein's theory we have evidence suggesting there are millions of black holes in our galaxy alone and his general relativity tells us more just as a collision of two objects produces sound waves the collision of two black holes generates waves in space-time there are huge things in the universe happening like black holes colliding or stars exploding then they have created these gravitational waves waves in the shape of space and time they'll travel through the universe at the speed of light and so right now the space around me is being squeezed and stretched by gravitational waves just getting here from let's say to black holes colliding a billion light years away but the squeeze in stretching is so minut I absolutely could not personally detect it and so what we're trying to do is build an instrument that can in Louisiana and Washington state a vast experiment called LIGO is in the final phases of calibration it's hoped that laser beams traveling four kilometers between precisely aligned mirrors will measure the squeezing of space caused by gravitational waves the experiment is able to measure the difference between two mirrors at four kilometers and two mirrors at four kilometers plus or minus ten thousandth of the nucleus of an atom sometime between today and a few years from now we really expect to have made the first direct detection of gravitational waves to actually record the ringing of the shape of space and time a direct measurement of pure gravitation we're not collecting light we're not talking about matter we're not talking about anything just measuring pure modulations in space and time so it's pure general relativity of all of Einstein's theories remarkable breakthroughs the most profound is that our universe has a beginning the discovery that distant galaxies are moving outwards and the detection of background radiation from the very start of the universe provided evidence for the big bang and a universe that's growing with this picture of the expanding universe there is some natural questions is the universe slowing down as it expands is it so dense but someday it will come to a halt and collapse will the universe come to an end they seem by good questions to find answers in the 1990s saul and his team studied exploding stars called supernovae to track the growth of the universe when we made the measurement we discovered that the universe isn't slowing down enough to come to a halt in fact it's not slowing at all it's speeding up the universe is expanding faster and faster in order to explain the acceleration of the universe within Einstein's theory of general relativity we're considering a energy spread throughout all of space that we've never seen before we don't know what it is we call it dark energy and if so it would require something like 70% of all the stuff of the universe to be in this form of previously unknown dark energy so this is a lot to swallow and you might imagine that at that point you should go back and revisit your theory the problem is that Einstein's theory is so elegant and it predicts many many many digits of precision that it's very very difficult to come up with any other theory [Music] for a hundred years general relativity has proven correct time and time again but Einstein himself knew that his Greek Theory had limits the huge problem in theoretical physics now is to combine general relativity our best theory of space time and gravity with quantum mechanics our best theory of very small things two phenomenally successful theories that don't automatically gel with one another [Music] here at the Institute for Advanced Study where Einstein worked the world's leading theoretical physicists are trying to solve the problem Einstein never could finding a single set of rules that applies to both the cosmic and atomic scales a unified theory the holy grail of physics we are now in what at this time is the school of physics so here our people are still struggling with many of the same issues that Einstein was struggled and are still trying to capture the the laws of the universe from this very small to the very large in a single equation and it's still blackboards that had already the weapon of choice the brightest minds of the world are coming here to work 24 hours seven days a week struggling to to grasp the great mysteries of the universe and I think we're still driven by the same dream that at some point we can capture everything in elegant mathematics 100 years after Einstein transformed our understanding of nature the stage is set for the next revolution quantum mechanics was very different than general relativity came about by many people stumbling into it maybe that would be the way that we do it next time Einstein was this singular genius who managed to get gravity right he didn't manage to get quantum mechanics right when we finally moved beyond Einstein it might be another singular genius that comes along someone struggling in a poor school in Kenya right now that we don't know about or it might be 20 different people with 20 different points of view gradually building brick by brick to finally figure out a more comprehensive view that includes general relativity in it [Music] I think the most important thing that you learn from Einstein are just the power of an idea if it's correct you know it's just you it's unstoppable it's extremely encouraging that though he was able with pure thought to solve the riddle of the universe [Music] there are only a few moments in science history where we had to completely rethink our picture of the world that we live in and this was one of those moments the moment you enter the world of general relativity you encounter claims propositions that are doing nothing less than calculating how much matter there is in the universe whether the whole of space is curved so that what we thought was in a way beyond experience becomes a system that can be described can be tested that still seems to me to be an absolutely amazing fact well you know you have the huge universe and it's a base or two laws of nature but where in the universe are these laws actually discovered where they studied and then you go to this tiny planet and there's just this one individual Einstein who captures is the notice a small group of people walking in his footsteps and trying to push it further and often feel well you know it is a small part of the universe that actually is reflecting upon itself that try to understand itself you