Inside Einstein's Mind FULL SPECIAL | NOVA | PBS America

NARRATOR: It is a mysterious force that shapes our universe. It sounds familiar, but it's much stranger than anyone would have imagined. And yet, one man's brilliant

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dominated him. Gravity. Using simple thought experiments, Albert Einstein made a surprising discovery: time and space are shaped by matter. CLIFFORD JOHNSON: If we get rid of this force of gravity, we will have a curvature of space-time. JANNA LEVIN: Right now, the space around me is tightening and stretching. NARRATOR: He called it the "General Theory of Relativity." How did one person, working almost entirely alone, change everything we thought we knew about the universe?

DAVID KAISER: Einstein works hard while the world seems to fall apart. ROBBERT DIJKGRAAF: With pure thought he was able to solve the riddle of the universe. NARRATOR: "Inside Einstein's Mind," right now on NOVA. NARRATOR: Gravity. The most familiar but most mysterious of the forces of nature. 100 years ago, Albert Einstein made a

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-blowing discovery: what we feel as gravity is actually the push and pull of space and time themselves. He called his idea "general relativity." Perhaps the most remarkable feat of thinking about nature is starting from a single mind. CLIFFORD JOHNSON: General relativity is undoubtedly one of the greatest scientific theories ever conceived.

It is a theory of space, time and gravity. JANNA LEVIN: A mathematical phrase, and from it you can derive the understanding of the entire universe on the largest scales, and that's beautiful. NARRATOR: Only now, a century after it was first proposed, do we have the technology to explore the extremes of Einstein's grand theory. Supermassive black holes in the centers of galaxies. Gravity waves that distort space and time. The evolution of our entire universe. How did a concept that explains so many things emerge from the mind of one man? JOHN NORTON: Einstein had a magical talent. He could take a difficult physical problem and reduce it to a powerful visual image, a thought experiment.

SEAN CARROLL: He suddenly realizes: "This is how the world works. All this abstract nonsense is the correct theory of reality." NARRATOR: To understand Einstein's mind and the true wonder of general relativity, we must trace the crucial thought experiments that led to his breakthrough. The seeds of his ideas were planted when he was just a child. Einstein grew up in a small house in Munich, southern Germany. His unique personality was evident from the beginning. WALTER ISAACSON: Like many great in

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tors, Einstein was a rebel, a loner, but deeply curious. As a child he was slow to learn to speak, so slow that his parents consulted a doctor, but he later said that perhaps that was why he thought in visual thought experiments.

His sister remembers him building little towers of cards using playing cards. He was a dreamer, but deeply persistent. NARRATOR: Einstein's father, Hermann, manufactured electrical equipment. He encouraged his son's interest in science. On one occasion he brought her a compass. ISAACSON: Now, you and I might remember that when we were kids we got a compass and we thought, "Oh, look, the needle moves and points north," but then we moved on to something else, like, "Oh, look, There's a dead squirrel." But Einstein, after getting that compass, developed a lifelong devotion to understanding how things can be forced to move even if nothing touches them.

NARRATOR: The young Einstein was caught by the desire to understand the underlying laws of nature. He developed a unique way of thinking about the physical world inspired by his favorite book. ISAACSON: The book Einstein loved told little stories, like what it would be like to travel through space or walk through an electrical wire. And that made Einstein think visually. NARRATOR: These imagined situations we often call "thought experiments" became a defining characteristic of Einstein's thinking. DAVID KAISER: One of the critical thinking experiments that Einstein started doing very young, around age 16, was trying to imagine what would happen if he could reach a light wave.

It's one thing to imagine a light wave passing by you at a seemingly impossible speed, but what if it could somehow propel itself very fast? What would it be like if he could reach that light wave? What would I see? ISAACSON: He said that he made him walk so anxiously that his palms were sweating. Now, maybe you and I remember what caused our palms to sweat at age 16, and it wasn't a silver lining. But that's why he is Einstein. NARRATOR: This dreamlike thought about the nature of light was Einstein's first step on the path to his grand theory.

It stayed with him throughout his time at school and university. KAISER: As a young man he was very talented in science and mathematics and very bad in other classes, e

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ly because he kept skipping classes and being very rude to his teachers. Many teachers from his high school days onward were convinced that he would never amount to anything. It was a discipline problem and it was bad news. ISAACSON: He applies to the second best university in Zurich, Zurich Polytechnic, and is rejected. I'd love to meet the admissions director who turned down Albert Einstein. But in the end he gets in and does moderately well, but not enough to get a teaching scholarship.

And so he ends up at the Swiss patent office in Bern as a third-class examiner. NARRATOR: Undeterred by his university results, Einstein began working in the patent office in 1902, at the age of 23. Here, his job was to evaluate the originality of new devices. KAISER: He was immersed in the kind of technical details that fascinated him when he was very little. And here he was, sitting on the sort of wave of the modern era. This was the era of electrification. So all the latest clever ideas for changing technology, particularly for coordinating clocks, came through his office. NARRATOR: Time zones had recently been introduced in central Europe, and accurately synchronizing the clocks was a major challenge at the time.

Switzerland was a world leader in weather technology. Dozens of patents for linking clocks passed through Einstein's office. ISAACSON: He could quickly review these patent applications and then pull out his physics notes from his drawer, and his boss would be very lenient and turn a blind eye while Einstein made his theories in his free time. SIMON SCHAFFER: It's really important to remember that theoretical physics was new when Einstein was young. You could do much of this work by reading a relatively small number of scientific journals and doing the calculations yourself. Einstein's world in 1905 was dominated by two types of physics.

One was about 200 years old and was founded by Isaac Newton, a British natural philosopher. For Newton, the only thing in the world is matter in motion. NARRATOR: Newton showed that the motion of falling apples and orbiting planets are governed by the same force: gravity. His equations are so effective that we still use them today to send probes to the farthest reaches of the solar system. The other important theory of Einstein's time involved 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 that travels at a fixed speed.

In Newton's world, the speed of light is not fixed. SCHAFFER: Einstein could see that there is a contradiction between Newton and Maxwell. They just don't fit. And one of the things Einstein hated (he hated) was contradiction. If there is one type of physics that says this and another type of physics that says that and they are different, that is a sign that something has gone wrong and needs to be fixed. NARRATOR: For months, Einstein wrestles with the problem. Finally, to resolve this contradiction, he focuses on a key element of speed: time. ISAACSON: He realized that any statement about time is simply a question about what is simultaneous.

For example, if you say that the train arrives at 7:00, that simply means that it arrives on the platform simultaneously with the clock showing 7:00. NARRATOR: In a brilliant thought experiment, he questions what "simultaneous" really means and sees that the flow of time is different for an observer who is moving versus one who is standing still. He imagines a man standing on a railway platform. Two lightning bolts strike on either side of him. (ray) The man is standing exactly halfway between them and the light from each ray reaches his eyes at exactly the same moment. For him, the two attacks are simultaneous. (rumbling thunder) So Einstein imagines a woman on a fast-moving train, traveling at close to the speed of light, what would she see?

As the light leaves the strikes, the train moves toward one and away from the other. The light from the frontal blow reaches his eyes first. For the woman on the train, time passes between the two blows. (rumbling thunder) For the man on the platform, there is no time between the blows. (rumbling thunder) This simple thought has mind-blowing meaning. The simultaneity and flow of time itself depends on how you move. If there is no simultaneity, then there is no absolute time in the entire universe, and Isaac Newton was wrong. NARRATOR: This concept that time, and also space, are relative became known as

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relativity.

It led to notable results, such as the famous equation relating energy to mass. Einstein published this article in 1905 to no acclaim. Most people ignored it. This wasn't setting the world on fire. Two years pass before a very eminent physicist, Johannes Stark, invites Einstein to write a review article on Einstein's own work, precisely because no one was paying attention. And he begins to think of ways to generalize and boost his own results from 1905. What if he considers not just a train moving at a fixed speed past the platform? What happens if that train starts to speed up or slow down?

What happens if there is acceleration? NARRATOR: Adding acceleration to the equations was his first task. Then there was the mysterious Newtonian force of gravity to contend with. In Newton's theory, gravity is a force that acts instantaneously. But special relativity says that is impossible: nothing can travel faster than light. ELEANOR KNOX: What Newton's theory says is that suppose the Sun were to disappear, the Earth's orbit would have to change at that very moment. But the notion of "at that same moment" in two different places is exactly one of those notions that special relativity has said is not a good physical notion.

So now we have the challenge of trying to figure out how to take advantage of the success of Newton's theory of gravity but fit it into this new special relativistic picture. NARRATOR: It was only when Einstein began to understand the link between gravity and acceleration that things began to fall into place. We all know that when we accelerate, and of course now we have cars and airplanes to give us the physical sensation, if you are on a plane and it is taking off, you are pushed back in your chair, you actually feel like a force pushing you back, which feels very similar to the force of gravity.

But it takes the brilliance of Einstein to explain why they are related. NARRATOR: Suddenly, he has what he describes as the happiest thought of his life. If gravity and acceleration feel the same, maybe they are the same. Once 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 accelerates downward until he stops on the box. What has happened? Either the box is now near a planet and the force of gravity has dragged the man to the ground, or someone has tied a rope and the box is now continually dragged and accelerated upward.

Then what is? Gravity? Or acceleration? Without being able to see outside, the man cannot tell what is causing him to fall to the ground. CARROLL: Einstein realized that there is no way to distinguish between sitting in a gravitational field and being accelerated. These are equivalent situations JOHNSON: The fact that these two effects are equal, give the same result, means that gravity is acceleration. It's not just like acceleration; is the same. NARRATOR: It's a great advance. Einstein's theory of special relativity worked for motion at constant speed. By extending his ideas to acceleration, he could begin to formulate a new theory of gravity.

In 1912, Einstein lives in Zurich with his wife Mileva and their two young sons, Hans and Eduard. Academia had realized the importance of special relativity and his career had taken off. He is now a professor at the prestigious Swiss Federal Institute of Technology, but he dedicates as much time as possible to working on his theory. He needs mathematics that describes how objects move in space and time and soon realizes that the best tool for this job is a strange but powerful concept called "space-time." LEVIN: If I think about space, I know 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, because I also have toknow where you are in time. And so, if we start to think, to know everything about an event in the universe, I have to know not only its spatial coordinates, but also its temporal coordinates. I can start to think about where it is in space-time. NARRATOR: Imagine a camera filming an action, capturing each moment in time as a single frame. DIJKGRAAF: Einstein basically tells us, "Think about the film reel." So you have all these little images. Now, cut them one by one and stack them on top of each other, you will get this stack.

And if you go up the stack, you go up on time. And now stick them all together in one big block, and that block has space and time, and that is the space-time continuum. It's almost watching a movie, not frame by frame, but watching the entire movie at once. Now they would be sort of two strands rising in space and time, and they would be sort of like strands of spaghetti. In fact, we are all strands of spaghetti moving in this space-time. NARRATOR: Einstein feels that space-time is the natural realm in which his theory of relativity should develop.

But now he needs sophisticated mathematics. By his or my standards, Einstein was good at mathematics. He was Einstein. But he actually wasn't a mathematician per se. He did not prove theorems, he did not pore over mathematics books. He was physical. He did thought experiments. He thought about very tangible, concrete situations and what would happen. So when it came time to really pursue the absolute cutting-edge mathematics of his time, he needed help. NARRATOR: In college, Einstein had skipped geometry classes and let his friend Marcel Grossman take notes for him. Grossman had excelled in geometry and was now chairman of the mathematics department.

He suggests that Einstein use advanced mathematics in which the shape of space and time could be curved. CARROLL: Because spacetime has a geometry, he thinks to himself, "Well, maybe it's the actual shape of spacetime itself that's giving rise to gravity." NARRATOR: After months of work, Einstein has an extraordinary idea. "What if spacetime is shaped by matter and that's what we feel as gravity?" JOHNSON: Struggling to discover what causes gravity, Einstein has this great idea. It is simply that a mass distorts the shape of the space-time around it. So we get rid of this force of gravity and instead we have the curvature of space-time.

So in Einstein's universe, if space were empty, it would be flat. Nothing would happen. But as soon as you put the objects down, they warp the space and time around them, and that causes a shift in the geometry, so now things start moving. DIJKGRAAF: Everything wants to move as easily as possible through space and time. But Einstein tells us that mass sculpts space and time, and that the curved motion through this sculpture is the force of gravity. KNOX: We have a feeling that the reason I can feel pressure on the soles of my feet, that the reason things are going to fall when I throw them, is because there is a force that draws us towards the center of the land.

What general relativity tells us is that that's not the right way to think about what's going on there. What's really happening is that your natural path in space-time would take you to the center of the Earth, and what's actually happening is that the ground is getting in your way, pushing you up. CARROLL: When we look at it, we say, "Ah, the force of gravity." But Einstein says, "No, no, no, the curvature of space-time." NARRATOR: That's a surprising idea. Just as an ant can feel forces pulling it from left to right while walking on crumpled paper when it is simply the shape of a surface that dictates its path, Einstein saw that what we feel as the force of gravity is actually the shape of space. -time we are moving forward.

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 mistake, he continues working on incorrect ideas. NORTON: Just as Einstein goes to give the most essential equations of the theory, Einstein considers something like that and then says, "Oh, but these don't work," and then writes down the wrong equations. What follows is alternations of confidence and despair as he convinces himself that everything was fine with this theory, and then realizes that things are not so fine with the theory.

It's a long, dark period for Einstein as he struggles to come to terms with a theory that simply doesn't work. NARRATOR: Two years later, Einstein is in Berlin. At only 36 years old, he occupies one of the most prestigious positions in physics. But he's still struggling with his theory. ISAACSON: By 1915, he had reached the top of the profession. He is at the Prussian Academy and is a professor at the University of Berlin. But his marriage is falling apart, his wife and his two children have returned to Switzerland, so he walks around this apartment in Berlin almost alone.

NARRATOR: And now he has a competitor. Einstein had enthusiastically shared his ideas with the brilliant mathematician David Hilbert. Hilbert was so impressed that he decided to work on the theory himself. Einstein is now in a race to the finish line with one of the world's greatest mathematicians. KAISER: This takes place in a remarkably dramatic period of history. The First World War has begun to devastate central Europe. Einstein doesn't just work in the abstract; He is working hard while the world seems to fall apart. NARRATOR: In November 1915, Einstein is scheduled to present his work in a series of four weekly lectures at the esteemed Prussian Academy.

But he has a hard time formulating his ideas. In the midst of these challenges, letters arrive from his wife in Zurich pressing the issue of his financial obligations to his family and discussing contact with her children. When his lectures begin, his theory is still far from complete. The pressure on Einstein is enormous. SCHAFFER: He gave a lecture, revised it, and gave it again. He catches mistakes, correct them, go up to the podium, explain what he did wrong at the previous week's conference, correct it and then move on, and then do it again and again for four weeks straight.

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. NARRATOR: Somehow, he is able to focus on his theory with incredible intensity and advance it. He tests his equations on a problem that Newton's theory of gravity could not solve: the orbit of Mercury. Mercury's path around the Sun has an anomaly that Newton's theory cannot explain: it deviates slightly each time it rotates. Einstein calculates the orbit with his new equations. The answer is correct, exactly what astronomers had observed.

He had found the final equations for his general theory of relativity. CARROLL: You have to think about the arrogance of being Albert Einstein. He had already discarded Newtonian mechanics with special relativity and then embarked on his own little quest to incorporate gravity. And in the end, he reduces it to a prediction of a number that he had observed: the procession of Mercury's orbit. And miraculously, when the algebra pages come to the end, you get the correct answer. And suddenly, it's not just about playing with equations anymore; he realizes that this is how the world works. All this abstract nonsense is the correct theory of reality.

SCHAFFER: Einstein can finally present a successful theory. That is a triumphant moment, one of the great moments in the history of physics and, for Einstein, a victory against all odds, and he had won. NARRATOR: On November 25, 1915, Einstein presented 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 beauti

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y compact set of symbols. So the formula is really simple: G-mu-nu is equal to... NARRATOR: G for the shape of spacetime and T for the distribution of mass and energy.

So this very simple formula captures all of Einstein's general relativity. It is a beautiful and simple equation, but it requires a lot of work to unpack the symbols, the mathematical symbols, and see how in this very simple formula, all the geometry of the universe is hidden. It's kind of an acquired taste to see beauty. It is also a distinctive formula of Einstein. The true mark of his genius is that he combines two elements that actually live in different universes. The left side lives in the world of geometry, of mathematics. The right side lives in the world of physics, matter and movement.

So perhaps the most powerful ingredient in the equation is this very simple equal sign, these two lines that actually connect the two worlds, and it's quite appropriate that they're two lines because it's two-way traffic. Matter tells space and time to curve, space and time tells matter to move. NARRATOR: When Einstein presented his grand theory, few people understood it. He needed a way to prove to the world that the counterintuitive features of his theory were real. SCHAFFER: The general theory of relativity made predictions about things that seemed really strange. For example, the idea that light bends when it passes near a very heavy body.

Nobody had ever looked for that. Nobody had ever observed it. Einstein was desperate, desperate to get astronomers to do that test. NARRATOR: Einstein's theory predicts that when light from a distant star travels near the sun, the warped space around the sun bends the light's path. In May 1919, the English astronomer Arthur Eddington traveled to the African island of Príncipe to record images showing this phenomenon. KAISER: What Eddington had been able to do was take photographs of stars during a total solar eclipse, so that the moon blocked most of the sun's brightness and small points of light could be seen around the sun;

Otherwise, it would be lost in the glow, and Eddington and his colleagues were able to measure that the appearance of those stars had changed compared to where they would have been if that large mass of the sun had not deflected that light from far away. SCHAFFER: So Eddington was able to prove that Einstein's theory of general relativity is correct and a revolution in science has been achieved. ISAACSON: When eclipse experiments prove Einstein's theory correct, he rises to fame. Not only because it has explained a new way of seeing the universe, but at the end of the First World War, some British astronomers proved that the predictions of a German scientist were correct and made headlines around the world.

The New York Times says: "All lights point skyward, men of science are more or less anxious." This was back when newspapers knew how to write great headlines. But Einstein loves the fact that he is now an icon of science. NARRATOR: Einstein becomes a global celebrity, the icon of genius we still recognize today. SCHAFFER: The only person who was better known was Charlie Chaplin, and they got along like a house on fire. Chaplin said, "The reason they all love me" is because they understand everything I do, "and the reason they love you" is because they understand nothing you do.

Can you explain that?" And Einstein said... NARRATOR: But in 1930s Berlin, the Nazi party is gaining power. As a Jewish scientist, Einstein becomes increasingly caught up in political turmoil. KAISER: The theories of Einstein became a target. They were considered aesthetically repugnant to a kind of Aryan sensibility. So not only did people attack Einstein, the Jewish scientist, but there were also people who denounced general relativity. Nobel Prize-winning mathematician Albert Einstein visited California... NARRATOR: He begins to make trips to America, where he is received with open arms NEWSCASTER: Germany's loss, America's gain NARRATOR: And in 1933, he is. He settles in Princeton with his second wife Elsa, taking up a position at the Institute for Advanced Studies.

Today the Institute is directed by Professor Robbert Dijkgraaf: He was basically still very much alone, just as he was in Berlin, concentrating on his deep ideas and struggling to understand the universe. Of course, his office was here. NARRATOR: At the Institute, Einstein worked to unify his theory of gravity with the other laws of physics. DIJKGRAAF: With Einstein, you see this phenomenon that you see with many great scientists: that they climb this very high mountain and instead of celebrating their success, they have the privilege of seeing a much larger landscape, and they see all these mountains behind him. .

And I think he was very aware of how much there was still to be done. Until the last days of his life, he tried to push these equations and find a description of nature, of all nature, in terms of the geometry of space and time. NARRATOR: But general relativity was disappearing from mainstream science. Physics now focused on theoryquantum theory of atoms and tiny particles, a theory incompatible with Einstein's ideas, but which could be tested in the laboratory. Most of general relativity was then outside the scope of the experiment. When Einstein died in 1955, at the age of 76, his theory was considered to have little hope of being discovered in the future.

CARROLL: The best theories in physics always take us to places that the people who invented them did not imagine. And a truly wonderful theory like general relativity predicts all kinds of things that Einstein didn't conceive of. The theory has a life of its own. We currently understand general relativity much better than Albert Einstein. (engines roaring) NEWSCASTER: Space shuttle Discovery takes off with the Hubble Space Telescope, our window to the universe. NARRATOR: Today, 100 years after general relativity was first introduced... ASTRONAUT: Telescopes released, okay, thank you. NARRATOR: ...new technology is allowing us to explore the theory's most notable predictions: an expanding universe, black holes, ripples in space-time, and perhaps most bizarrely, the idea that not just space, but time itself is distorted by heavy objects.

To prove it, a team of physicists is carrying out a remarkable experiment. They are using two atomic clocks that are in almost perfect synchronization, accurate to a billionth of a second. The master clock remains at sea level as they carry the second clock to the summit of New Hampshire's Mount Sunapee. General relativity tells us that as we move away from the mass of the planet, time should speed up. After four days on the mountaintop, the test watch is taken to the laboratory for comparison. They there compare it to the sea level master clock. We'll put it on Channel A.

NARRATOR: Four days ago, they were dialing in unison. Master clock on Channel B. NARRATOR: But what about now? Are you guys ready? This is right here. The time interval counter will show us the time difference between these two clock ticks. 20 nanoseconds. You can see the time difference between them plotted here graphically from the clock that was on the mountain for four days and our master clock. NARRATOR: Gravity, the distortion of space and time, weakens as you move away from the planet's surface. Then, while the test watch was on the mountain, time sped up. They are now 20 nanoseconds, 20 billionths of a second, ahead of the sea level clock.

This is really amazing. NARRATOR: This time distortion has surprising consequences. The Global Positioning System, something we all take for granted, would not work without taking this into account. The engineers who built the GPS system we use every day to locate locations had to make sure it adjusted to the time difference between satellite clocks and ground-based receivers. If they didn't, the GPS would be off by six miles every day. JIM GATES: Your GPS units use the results of general relativity. When you're cruising in your car, maybe you should thank Uncle Albert. NARRATOR: Of all the general relativity predictions that new technology has allowed us to explore, there is one that seems straight out of science fiction: a black hole.

Everything we know in ordinary life is made of matter. But not black holes. Black holes are made of warped space and time and nothing else. A black hole is a spherical object, like a star or the Earth, with a defined boundary called the horizon through which nothing can leave. He then casts a shadow on whatever is behind him. It's just a black, black, incredibly black shadow. NARRATOR: This simulation shows the distortion of starlight around a black hole. Although Einstein knew that his theory predicted black holes, he found it difficult to believe that they actually existed 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 objects could be real. THORNE: It must be here somewhere, it's in one of these piles. NARRATOR: Kip Thorne made a bet with his fellow physicist Stephen Hawking over whether a strong X-ray source known as Cygnus X-1 was actually a black hole. THORNE: I think it's here. Yes, here we go, relativity, stars and black holes. Yes, there it is. So that's a copy of the famous bet. "Stephen Hawking bets a one-year subscription to Penthouse magazine against Kip Thorne's bet of a four-year subscription to a political magazine called Private Eye that Cygnus X-1 does not contain a mass black hole." about the Chandrasekhar.

Limit. He witnessed it on December 10, 1974." Stephen Hawking was terribly deeply invested in it actually being a black hole, so he made the bet against himself as an insurance policy that he would at least get something out of it. whether Cygnus It was absolutely overwhelming that Cygnus face turned red when I received it. NARRATOR: Today, we have evidence suggesting that there are millions of black holes in our galaxy alone, but perhaps the most profound prediction of general relativity is that our universe had a hot, dense beginning that We call the big bang. The discovery that distant galaxies are moving away from us and that there is background radiation permeating space provided evidence of the Big Bang and a growing universe.

SAUL PERLMUTTER: With this image of an expanding universe, natural questions arose. Is the universe slowing down as it expands? Is it so dense that it will one day stop and collapse? Will the universe come to an end? They seemed like good questions. NARRATOR: To find answers, in the 1990s, Saul Perlmutter and his team looked at exploding stars, called super

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e, to track the growth of the universe. PERLMUTTER: When we made the measurement, we found that the universe is not slowing down enough to stop. In fact, it's not slowing down at all; It's accelerating! The universe is expanding faster and faster.

NARRATOR: But what drives him? PERLMUTTER: To explain the acceleration of the universe within Einstein's theory of general relativity, we are considering an energy distributed throughout space that we have 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 matter in the universe to be in this previously unknown form of dark energy. So this is a lot to swallow, and you might imagine that at that point you should go back and revise your theory. The problem is that Einstein's theory is so elegant and predicts many, many, many digits of precision, that it is very, very difficult to propose any other theory.

NARRATOR: There is one final prediction of general relativity that has not yet been proven: gravitational waves. LEVIN: There are huge things happening in the universe, like black holes colliding or stars exploding, and they create these gravitational waves - ripples in the shape of space and time that travel through the universe at the speed of light. And right now, the space around me is being compressed and stretched by gravitational waves that have just arrived from, say, two black holes colliding a billion light years away. But the compression and stretch are so small that I can't detect them personally.

So what we're trying to do is build an instrument that can do that. NARRATOR: In Louisiana and Washington state, a vast experiment called LIGO is in the final stages of calibration. Laser beams traveling two and a half miles between precisely aligned mirrors are expected to measure the compression of space caused by gravitational waves. This could open a whole new window to the universe. For 100 years, general relativity has been proven time and time again to be correct. But Einstein himself knew that his grand theory had limits. It remains incompatible with the quantum world of small atomic particles.

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 is currently physics school. So here, people are still struggling with many of the same problems that Einstein would struggle with and they are still trying to capture the laws of the universe, from the smallest to the largest, in a single equation. And whiteboards are still the weapon of choice.

The world's greatest minds come here to work 24 hours a day, seven days a week, striving to understand the great mysteries of the universe. And I think we're still driven by the same dream: that at some point we'll be able to put it all into elegant mathematics. NARRATOR: 100 years after Einstein transformed our understanding of nature, the stage is set for the next revolution. CARROLL: When we finally move beyond Einstein, another singular genius might appear: someone who is struggling right now in a poor school in Kenya and about whom we know nothing. Or it could be 20 different people with 20 different points of view gradually building brick by brick to eventually discover a more comprehensive view that includes general relativity.

DIJKGRAAF: I think the most important thing you learn from Einstein is simply the power of an idea. If it's right, you know, it's just unstoppable. It is extremely encouraging that he was able with pure thought to solve the riddle of the universe. LEVIN: Once we had general relativity, the world changed completely. Our point of view on the world changed completely. I mean, the origin of the universe is a prediction straight out of general relativity. We didn't have that before. GATES: I often wonder what Einstein would make of today's theoretical physics. I think he'd really be saying, you know, "Keep going, he gets the story right, he gets the details right." DIJKGRAAF: You know, you have the huge universe and it obeys certain laws of nature, but where in the universe are these laws actually discovered?

Where are they studied? And then you go to this little planet and there's an individual, Einstein, who captures this. And now there is a small group of people following in his footsteps and trying to take them further. And I often feel, well, it's this little part of the universe that's actually reflecting on itself, that's trying to understand itself.