"The universe is falling apart." "Something is forcing galaxies to rush away from each other at ever-increasing speeds." "Ever since this alarming discovery, physicists have struggled to understand what might be causing it." "So far, they've come up with a name." "They've called it dark energy." "Dark energy is basically our name for that thing that we don't understand." "It's not the color dark." "It's just an expression of our ignorance as to what is the stuff." "The discovery of dark energy really surprised theoretical physicists and remains a deep mystery of nature." "We are absolutely still lacking great ideas." "So, it is crying out for some new breakthrough, new thinking." "Scientists all over the world are on the hunt for answers to modern science's most enduring problem... to paint the biggest picture of all, to finally solve the mystery of dark energy. captions paid for by Discovery communications" "Energy is all around us." "It comes from the sun, from chemical reactions, from electricity." "Energy powers our vehicles, heats our homes, lights our nights." "Understanding energy has transformed our planet and our lives." "Dark energy is something altogether different." "It seems to serve no useful purpose at all except to show us that we understand less than we thought we did." "Dark energy arrived entirely unexpectedly at the very end of the 20th century." "In 1998, a young scientist named Saul Perlmutter was thinking some very big thoughts indeed." "As a graduate student," "I really wanted to find a project that would answer some... or at least be looking at some very philosophical questions, something that felt like it was meaningful about the world we live in in some, you know, deep way." "The question that's been really exciting me is whether the universe will last forever." "Do we live in a universe that is infinite or, some day, will it come to an end?" "The two big options at the time were that the universe could expand forever but just slow and slow and slow but forever be expanding." "Or if there was enough stuff in the universe to gravitationally attract it, it could slow to a halt and then collapse and come to an end." "Perlmutter was measuring the way the universe was expanding by observing exploding stars called supernovae." "One particular kind of supernova always explodes the same way because it waits until just a critical amount of mass has fallen on it, and then it explodes." "So, they all look very similar to each other." "They brighten as a firework, then fade away, and they reach the same brightness." "And you can then use that as an indicator of how far away it is by just looking to see how bright it appears to you." "Because they explode with exactly the same intensity, these supernovae are known as standard candles." "By comparing their relative brightnesses, relative distances can be calculated." "Perlmutter expected the stars to show what everyone thought at the time... that the universe was slowing down." "Fainter ones are further, just like when you watch, you know, a car recede into the distance, you can tell how far away it is by how faint the taillights look." "If you can use the brightness of a supernova to tell you how far away it is, that's really telling you how long ago the explosion occurred, because you know how long it takes for light to travel that great distance." "So, now we have an object where it explodes, and its brightness tells you when it exploded, how far back in time it exploded." "No matter how good the theory, the practical problem of catching an exploding star at just the right time is immense." "But Perlmutter and his team applied the very latest computer technology to the problem." "Finally, we have the analysis completed, at least the computer's part of the analysis, and it's beginning to show us on the screen what it thinks might be a supernova." "Eventually, after the team had identified 42 such dying stars, the calculations began." "What Perlmutter discovered shocked him." "The data was telling the wrong story." "The universe didn't appear to be slowing down." "We... we thought that that's what we would see, and it looked like the opposite was taking place, and, in fact, the universe was speeding up in its expansion." "These distant supernova were fainter than you would have thought, and very significantly fainter." "They were, you know, probably 20% or more." "And that's the hallmark of a universe that's actually speeding up in its expansion." "To say that this result was a surprise would be a major understatement." "It was so unexpected that the initial reaction was disbelief." "Everybody knew Saul, and everybody knew the experiment he was doing." "And I remember sitting in the audience and Saul getting up and expecting him to present an update on the results he'd given a year ago that actually the universe was slowing down." "And so, I was absolutely amazed that, based on only twice as many objects as he had the year before, that suddenly, he was saying that we lived in a universe that was accelerating." "I remember it just being just incredible." "I mean, all the astronomers walking around, scratching their heads, saying, "this can't be right."" "Surely it can't be right."" "It was not the result that people had been expecting." "And such an extraordinary claim demands extraordinary evidence... more than a few data from a handful of stars." "So, here we are on a beach where there's about a billion pebbles." "And if you think you're trying to understand this beach, you wouldn't think you could understand it from 42 pebbles." "But Saul was right." "He was able to work out that the universe was accelerating just from 42 supernovae, which is quite incredible when you think about it." "On the one hand, this was a good result." "It was new science and produced a nobel prize for Saul Perlmutter." "On the other, it raised an obvious question." "Once you know that the universe is actually speeding up, then you're faced with the question of," ""Well, what could make it speed up?"" "So far, the only real progress on that question has been to give the phenomenon a name." "It's become known as dark energy." "Dark energy is just the term we use to describe whatever it is that makes the universe accelerate in its expansion, what makes it expand faster and faster." "We don't know what that is." "It's a mystery." "And so, we call it dark to reflect our ignorance, not because the color is dark." "The mystery is so deep, so beguiling, that wherever there are physicists, there are people hoping that they will solve the mystery of dark energy." "People safe in the infuriating knowledge of what they're looking for, if it's there at all, is all around them." "But the fact that no one has yet been able to identify what the dark energy might actually be has opened a can of worms not seen in science since the last time a physicist got involved in cosmology." "In 1915, it seemed that the work of physics was nearly at an end." "Everything made sense." "Newton had explained the heavens by invoking gravity." "And atoms had been identified as the smallest invisible units of matter." "Job done." "But then a German man who liked to muse on trains turned up with a totally new set of ideas." "I very rarely think in words at all." "A thought comes." "And I might try to express it in words afterwards." "Einstein called these little flights of fancy his thought experiments." "And they would lead him to develop his theory of general relativity, which totally changed how the workings of the universe were understood." "According to Einstein, space isn't simply a void." "It's more like a four-dimensional fabric, woven from both space and time." "The mass of planets can warp and distort the fabric, gathering other celestial objects, like moons, around them." "And it's this bending of space-time that creates the effect we experience as gravity." "So, Einstein's theory of general relativity is a beautiful theory." "It's incredibly elegant, and it's been, now, around for 100 years." "It's very predictable." "You can write things, make predictions of what the universe should look like and what objects should look like in the universe, and we can test those." "And as far as we can tell, it's passed every test." "The power of general relativity is that, like Newton's version of gravity before it, it's predictive." "Bizarre as the curvature of space-time may sound, it's eminently testable." "In 1919, British astronomer Arthur Eddington pointed his telescope at a patch of sky near the sun during an eclipse and observed a star known to be actually out of view, behind the sun." "Its rays of light had been bent by the distorted space-time created by the sun's mass." "Einstein's theory had held up." "A paradigm had shifted, and the crowd went wild." "Einstein was suddenly famous, undoubtedly the cleverest yet most incomprehensible man on earth." "This is what all the fuss was about." "This is the equation that the porters and waiters were discussing." "On the one side, the geometry of space-time." "On the other, the mass and energy of the universe, which acts on it." "Not incomprehensible at all, at least not to its author." "But there was one aspect of general relativity that Einstein himself didn't understand." "The problem that Einstein had is when he solved his equations of general relativity, what he found was that he predicted that the universe should actually be expanding, and that was radically different from the perceived wisdom at the time," "which is that we lived in a static universe... both static in time and in space." "So, he put in an extra term into the equation." "He called it the cosmological constant." "He used the Greek variable lambda." "But effectively, it was really just what, you know, a physics undergraduate would call a fudge factor that was just designed to make the equations come out right." "And it would just make the universe sort of stand still." "When you add the lambda term, it means that the equation is not quite as simple as it was before." "So, in that sense, it's not as beautiful as an equation." "The static universe was restored, but Einstein always felt he'd added lambda against his better judgment." "Despite the fudge factor... lambda, the cosmological constant..." "Einstein continued to be celebrated as the world's cleverest man..." "Until, in 1929, he became even more clever." "In the U.S., an astronomer, Edwin Hubble, was about to get a reputation for scientific cleverness himself." "He'd been using the world's largest telescope at Mt." "Wilson in California to peer deeper into space than anyone had ever looked before." "What he discovered completely changed the meaning of the word "universe."" "Until Hubble, it had been thought that the universe was our galaxy." "What Hubble saw was that, in fact, our galaxy is just one of countless millions but, more importantly, that all these galaxies were moving apart from each other." "The universe wasn't static after all." "This had huge implications." "It introduced the notion of a beginning and an age for the universe." "But more importantly for Einstein, it meant that he could ditch his fudge factor, the cosmological constant, and return general relativity to its former glory." "Einstein was over the moon." "In 1931, he went to Mt." "Wilson to shake Hubble's hand and thank him for putting beauty back into his equation." "Lambda, he later confessed, was the biggest blunder in his career." "I think that the reason that he said that... that it was a blunder was because if he had just not introduced that term, then he would have said that, you know, the universe must be expanding" "and done that 14 years before the discovery of the expansion of the universe by Edwin Hubble, which would have been a great achievement." "But despite Einstein's blunder, general relativity has stood the test of time." "It is perhaps the single most successful scientific theory yet." "Every observation we make of gravity, from the smallest scales to solar-system scales to galactic scales all the way to the universe... all of that can be described using the single theory that Einstein created." "So, it's the most successful and beautiful theory we have of our universe." "Or at least it was." "For all its beauty and simplicity, general relativity doesn't account for the effects of dark energy." "Expansion as reported by Hubble works fine, but the accelerated expansion of the universe that Saul Perlmutter found isn't part of the deal." "That it's there at all is bad enough, but worse, the way that dark energy seems to work is unlike anything that's been observed before." "The density of anything is the amount of stuff you have within a given volume." "And dark energy is an usual phenomenon in that even though the volume of the universe is increasing as it expands, the density is staying the same." "So, it's almost as if there's new dark energy being created all the time as the universe expands, meaning that its density remains the same, constant." "So, you can think of it as you get more space, you actually get more dark energy, which is like getting something for nothing, which is clearly ridiculous." "I mean, it's clearly against all our training as physicists." "There is one way to adapt general relativity to cope with this magically constantly self-replenishing force, and that is to simply add it to the equation." "100 years after Einstein's biggest blunder, the cosmological constant is back." "Lambda is being written once more, this time not to keep the universe still, but to account for its unexplained accelerating expansion." "The values are different, but the concept is exactly the same." "All this leads to one of two equally alarming conclusions." "Either we need another Hubble or we need another Einstein." "But before we consign Albert to the scientific scrap heap, there is a branch of physics which might help, an area where things popping in and out of existence is quite normal." "Welcome to the strange and wonderful world of Clare Burrage and of quantum mechanics." "Quantum mechanics is the theory of what happens to really, really small things." "It's the theory of how the fundamental particles in the universe work... atoms, electrons, protons." "And quantum mechanics is intrinsically uncertain." "Einstein hated quantum mechanics." "But even though Einstein didn't like it, quantum mechanics could shed light on dark energy and come to the aid of his once-more-under-fire theory, in theory." "Quantum mechanics tells us that particles can come in and out of existence in the vacuum." "And the fact that those particles have mass and potentially are moving around... they have a little bit of energy." "And so, when they pop into existence, they give a little bit of energy to the vacuum." "And, yes, they disappear again, but the fact that that process is going on all of the time means that there's some energy stored in the vacuum." "And because Einstein told us that energy and mass are the same thing, having lots of energy stored in space affects space-time that caused the expansion of the universe to accelerate." "So, it seems that quantum mechanics should, in theory, be able to explain how the cosmological constant works and how dark energy appears in the vacuum of space and is driving the acceleration of the universe." "But there's a problem." "When they came to calculate this vacuum energy, they discovered how spectacularly wrong they were." "If you were to say there was one pebble on this beach, you'd be wrong by one part in a billion." "If you were to say there was one particle in the universe, you'd be off by 10 to the 80." "But the vacuum energy was calculated to be off by 10 to the 120." "That is a googol." "That is spectacularly wrong." "The fact that our predictions are so far off from what we see tells us that there's something fundamentally missing in the way that we understand physics, that we understand the world around us." "So, there's still a mystery, still a puzzle there." "It might be tempting to simply ignore dark energy." "You could argue that the apparent accelerated expansion is, in fact, a trick of the light, that it may be a function of other, inaccessible dimensions at play, that it just looks like dark energy but is actually something else." "But dark energy isn't just an irritating threat to Einstein's beautiful equations." "It's also a very practical solution to a fundamental question in cosmology, namely, what is the universe made of?" "When Einstein was busy thinking about gravity on trains, the answer was simple." "The universe was made of the same stuff that you and I are made of, the stuff of stars, planets, coke cans, tennis rackets... atoms, made from electrons, protons, and neutrons." "But physics was about to get a surprise." "It turned out there was something else out there that the universe was also made of... matter of a different kind." "In 1975, astronomer Vera Rubin made an unexpected discovery." "If we plot the velocity of the planets as a function of distance from the sun..." "Mercury, Venus, earth, Mars, Jupiter, Saturn," "Uranus, Neptune, Pluto... and you can see that Mercury orbits much more rapidly than pluto." "The graph is called a rotation curve." "It is the embodiment of the law of gravity." "The further away you travel from the sun, the weaker its gravitational force." "Galaxies work in the same way as our solar system except that, instead of planets orbiting a central sun, in a spiral galaxy, stars are held in orbit by a gravity-providing black hole." "Vera Rubin decided to plot the rotation curves in galaxies." "She focused her telescopes on Andromeda, the galaxy closest to our own." "I came out with sets of numbers, and I plotted them on pieces of paper, and I discovered that the stars, as you went further and further out, did not slow down." "They were moving just as fast as the stars near the center." "We find that their velocities remain flat all the way to the edge of our observations." "And that was a surprise, and a surprise that had to be explained." "By all accounts, the stars should have flown off into space." "But they didn't." "And wherever spiral galaxies were measured, the same flat curves appeared." "It was decided that the only explanation was that their must be more stuff out there that we couldn't see providing the extra gravity, holding the galaxies together, and flattening the curves." "They called this stuff dark matter." "The new dark matter was a surprise in more ways than one." "The very fact of its existence was almost overshadowed by the fact that when the calculations were made, this new form of matter outweighed the atomic form of stuff by about 90 to 1." "In the 1980s, when new ways of measuring dark matter were developed, it was discovered that there simply wasn't enough of it to make the universe work as it clearly does." "The universe was short on stuff to the tune of about 70%." "Cosmology scratched its head." "Then, in 1998, a young scientist," "Saul Perlmutter, was thinking some very big thoughts indeed." "Something that felt like it was meaningful about the world we live in in some deep way." "The universe was speeding up in its expansion." "The dark energy that earned Perlmutter his Nobel prize was an interesting and troubling concept, but it also had a number, and that number was very significant." "We know from Einstein that energy and mass are related... that energy, "e,"" "equals mass times the speed of light squared." ""E" equals m-c squared." "Plug dark energy into that equation and you get the missing mass that dark matter couldn't account for." "The universe was complete." "It was made up of about 4% baryonic matter, the stuff that we're made from," "26% dark matter, and the gaping 70%-sized hole was filled with dark energy." "Despite heroic efforts to find it and overwhelming evidence that it exists, no one has identified what dark matter is." "And, of course, dark energy, both useful and confounding, is barely in its infancy when it comes to a convincing explanation." "But there is an idea in cosmology that dark matter and dark energy may be linked by more than just a common adjective." "And if they are, a new European spacecraft called the Euclid may shed light on what that link might be." "The Euclid consortium is staffed by 1,200 scientists from 14 countries." "Here are some of them having their picture taken at their annual conference in lausanne." "They're hoping that by taking pictures of the universe, they will be able to figure out how it's expanded over its lifetime and, by determining that, the nature of dark energy will become clearer." "The way we think about it is that it's either some new stuff in the universe, some particle or even just a new field that you put into the universe to explain the properties of the universe." "Alternatively, you could say that the equation you wrote down is not correct." "It's not wrong, but it's sort of... we like to say it's incomplete." "So, you could sort of fiddle with the mathematics of the equation." "So, actually, what you could do is maybe come up with a natural explanation for it." "So, Euclid should be able to tell us which of those alternatives it is." "The satellite will launch and start sending data back to earth in 2020." "The all-important camera for the Euclid space telescope is being built and tested in the u.K." "In this country house in the surrey hills." "Not only will Euclid be able to measure the historic acceleration of stars and galaxies in all directions, it's hoped that it will also provide data about how dark matter around galaxies has expanded over time." "This is possible because of an effect called gravitational lensing." "So, in general relativity, mass bends space and time, and then light is bent around large, massive objects, just like Eddington measuring the star behind the sun." "And so, we use the same technique for Euclid." "I can illustrate it using this wine glass and this image of the universe." "So, as we draw the wine glass across the image, what you see is that the galaxies behind the wine glass get distorted, and that distortion is caused by the lens." "In general relativity, the lens is mass, because it bends the light." "And that can be shown in this picture." "You have a large clump of mass here, which is like the lens, like our bottom of the wine glass." "And what you can see are all the distorted galaxies behind that lens." "And what you can do with an image like this is you can calculate how much mass would I need within the lens to create the distortions that I see." "And what you find is quite remarkable." "What you find is there is about 100 times more mass here than you see from the light in the image." "And that missing mass, that mass you cannot see is what we call dark matter." "So, Euclid will make an image of the whole sky at this resolution, and it will find all these distorted background galaxies." "And from that, it can infer the distribution of dark matter in the universe." "Euclid will compare lensing all over the universe and, by doing so, will help paint an accurate picture of how the universe is tearing itself apart under the influence of dark energy." "So, Euclid may tell us that it's the cosmological constant, and then we have to explain that." "It might tell us that our theory of gravity is not complete, and we'd have to explain that." "It could tell us that actually the dark matter and dark energy are two sides of the same coin and that actually there might be a unified dark sector." "But we'd have to explain that." "Uh, it could be another theory that we haven't even come up with yet." "And so, Euclid will give us a coherent data set that we can test all these theories against." "Whatever the case, the devil's in the details, and these days, the details can be interrogated to degrees not thought possible when Einstein first reluctantly inserted his cosmological constant into general relativity." "Cosmology is one of the fields that is actually pushing the boundaries of cosmology itself but also statistics and computing." "It is the frontier, I think." "Euclid will be pushing the boundaries like never before." "It will stream more data from space than has ever been processed in the past." "At the end, it will have about 1.5 billion galaxies." "It will observe 1.5 billion galaxies, so it's huge." "And a lot of the times, your eyes cannot just pick up patterns, okay?" "So, this cannot be possible without computers and statistics." "The computer-aided searches should give unprecedented clarity on how science should be thinking about dark energy." "There will be winners and losers." "The amount of data that we have on dark energy hasn't been enough to be able to tell us which path we have to go down to." "So, we have, like, lots of theories and a lot of... hundreds of models that could still fit our data." "When Euclid comes, lots of these can be thrown away, and it could, like, you know, narrow down the possibilities of what this dark energy is." "The Euclid telescope is not the only show in town when it comes to mapping the expansion of the universe." "And kitt peak in Arizona, risa wechsler is hoping to use the proposed dark energy spectroscopic instrument, desi, to make a map of part of the universe, like this one but 100 times more accurate" "so that she can check the validity of computer simulations of the universe that she's created." "One of the things that I do is try to simulate the entire universe and tie what we think about the physics of the evolving universe to what we actually see with surveys like desi." "What we're trying to do in these simulations is take a whole bunch of hypothetical universes." "Some of them will have a cosmological constant." "Some of them will have a different, time-evolving dark energy." "Some of them will have more or less amount of dark matter." "And then, when we compare that to what we actually see, we can rule out a lot of these ideas." "So, some of them will not be consistent with what we measure, and then we can determine that that's not the universe we live in." "When desi starts producing data in 2020, it might be that one of risa wechsler's simulations strikes gold." "It'll be up against a lot of competition." "In the absence of hard data, this is boom time for theories." "Multi-galileons, ghost condensates, and the higher co-dimensional branes worlds theory jostle for attention in the race to explain dark energy." "Many of these theories usually try to provide a global solution to the dark energy problem, a fix to general relativity." "But Clare Burrage is working on an idea that suggests Einstein may have been both right and wrong at the same time, depending on where you are." "We know that Einstein's theory works very well on earth and in the solar system." "We've tested it, and it works phenomenally well." "But we don't have ways of testing that theory on the kinds of distance scales that are relevant to cosmology." "And so, it could be that whilst relativity's a good description of what's happening around us, it doesn't work as a description of the universe as a whole system, and maybe you need to change the theory." "Clare's solution involves something called a chameleon a particle that tries to blend in not by changing color, but by changing how it exerts its force." "There are two types of particles in the universe." "There are the ones that make up matter, like electrons and protons and neutrons and quarks." "And then there's another set of particles, and those are the ones that transmit forces." "So, for example, the photon, which makes up light, also carries the electromagnetic forces." "It's exactly like what we're doing with the ball and the magnet." "We don't see the photons transmitting the force directly, but we see the fact that the magnet makes the ball move." "In physics, the greater a particle's mass, the smaller the distance over which its able to exert any force or field it might have." "The mass of a particle tells you how far it can carry information." "If a particle that's transmitting a force is heavier, it only transmits the force over a shorter distance scale." "So, the range that you can transmit the force over changes depending on where you're looking." "The idea here is that when the chameleon comes into contact with other stuff, it interacts with it and becomes heavy, and its force-transmitting capability all but disappears." "But in regions of deep space, where there's very little in the way of anything, the chameleon has no stuff with which to interact and so is very light and can transmit its force over vast distances." "We're looking for this simple, elegant solution to this strange accelerated universe, and nothing yet has given us that." "Where that simple solution will eventually come from is anyone's guess." "That is one of the infuriating things about science." "It can't always produce the rabbit out of the hat on time and on budget." "Sometimes, it takes an unexpected turn of events or what the media like to call a genius, though the geniuses themselves have a rather different take on their exploits." "I'm not more gifted than anybody else." "I'm just more curious than your average person." "And I will not give up on a problem until I have found the proper solution." "I think that curiosity is what drives most cosmologists and physicists..." "a curiosity about the universe." "What is the universe made out of?" "Why are we here?" "How did the universe begin?" "What will happen to the universe in the future?" "All of these are questions which are driven by curiosity." "I have no special talent." "I am only passionately curious." "Curiosity, I think, is... well, it's the best motivating force, okay?" "Working hard doesn't necessarily get you to an answer." "Working too hard can actually stifle creativity." "With our work, you know, it's a mixture of inventiveness and persistence and the hard work." "It's a combination." "It's the end of the Euclid conference in lausanne." "The conference organizers have arranged a social evening, cruising around lake Geneva." "It's a chance for the delegates to unwind and maybe even think a little about the biggest picture of all." "Yeah, so, Einstein's theory was motivated for a reason, right?" "He had an equivalent..." "Yeah, and, I mean, we're gonna measure a lot of things about the nature by looking at how it evolves... how dark energy actually evolves with red shift." "The problem is the zero-point energy, the vacuum energy, the quantum mechanical part that you add there." "Try and study the nature of dark energy, and at the same time, try and test if general relativity works." "So, there's, like, a lot of work and a lot of discoveries that are gonna happen down the road." " Exactly." " And I'll drink to that." " Exactly." " Yeah." "The process of scientific discovery sometimes makes progress through sheer hard work, and sometimes it needs someone to take an inspired alternative view." "We learned an awful lot about animals and plants by simply observing them." "But it took Darwin with a radical idea to give us a context to understand life itself." "And in our efforts to understand the wider world and even the universe, observations are critical." "The ideas of dark matter and dark energy come courtesy of people watching stars." "But just as Einstein musing on his train managed to take all the known science and see it from a different, more useful angle, it might be that to solve the dark energy problem, someone needs to pull off a similar trick" "and come up with an even better idea." "There are an awful lot of very smart people in the world." "I wouldn't be surprised if we end up with another Einstein somewhere along the line here." "I don't know whether it will be in our lifetime, but we... i think we have a good shot at it." "We need teams like Euclid." "That's the only way you can get the data that you need." "But to understand that data, to give it some interpretation, to give it an idea could come from one person." "That could be the next Einstein." "A genius could come up and put all the observations that we have so far... put it together and come up with a new theory." "Yeah." "It is quite possible." "I'm kind of hoping it's me." "The tantalizing truth is that all it might take to solve the mystery of the dark energy is one big idea, for someone out there to see things differently, someone perhaps like you." "And if that new Einstein is you, if you manage to solve the mystery of dark energy, you're likely to become very famous indeed... as famous as the original Einstein."