Transcript of a UK Science Television Program (10/23/00)

Einstein's Biggest Blunder

Programme transcript


Dr Joao Magueijo: We did something which most people consider to be a bit of a heresy. We decided that the speed of light could change in space and time, and if that is true then our perceptions of physics will change dramatically.

Narrator: At the dawn of a new century, a new theory is being born. It threatens to demolish the foundations of 20th century physics. Its authors are two of the world's leading cosmologists. If they're right, Einstein was wrong. It all began when Andy Albrecht and Joao Magueijo met at a conference in America in 1996.

Prof Andy Albrecht: This was pretty, exciting. Most of the key people were there and there were lots of debates about the contemporary issues in cosmology. Joao came up to me late one evening and had a very interesting idea.

Dr Joao Magueijo: This is total bullshit! It wasn't like that at all.

Interviewer: Joao how do you remember it?

Dr Joao Magueijo: I remember there was this conversation between the three of us, and then each one of us suggested something. I remember I suggested the varying speed of light and there was embarrassed silence. I think you two thought I was taking the piss at this point.

Prof Andy Albrecht: Maybe, possibly but

Dr Joao Magueijo: But then, oh he's actually serious, he's not laughing; then we started taking it more seriously.

Narrator: For most scientists the idea that the speed of light can change is outrageous; it flatly contradicts Einstein's theories of space and time. But recently astronomers have begun to realise that the Universe doesn't always behave as his theories would lead you to expect.

Prof Andrew Lange: We're making measurements which indicate that the Universe is filled with some kind of energy density and we don't understand this energy at all. It's unlike anything else in physical theory.

Prof Richard Ellis: And the surprise is that instead of the Universe slowing down, in fact it's speeding up.

Prof John Webb: It's certainly a very profound result for physics because it will be the first ever indication that the laws of nature were not always the same as they are today.

Prof Richard Ellis: Who knows what's in store? I think in some way it's a very exciting time: it's very similar to the revolution that was seen in physics at the turn of the last century. So here we are about to enter the new millennium with a whole lot of uncertainties in store.

Narrator: To understand what's at stake, we need to go back to that scientific revolution. It began here in Bern Switzerland in 1905. As the new 20th century dawned, the intricate mechanism of 19th century physics was beginning to show signs of strain. It was finally demolished, not by an established scientist, but by a patent clerk.

Prof Dave Wark: When Einstein started his career, we still lived in a Newtonian clockwork Universe. Space and time were simply a reference system. The metre was a metre anywhere you went,and time clicked at a constant rate throughout the whole Universe. It was unaffected by where you were, whether you were moving or not.

Dr Ruth Durrer: Time was considered as an absolute concept - the time would be everywhere the same, independent of the state of motion of somebody. That there would exist an absolute time which could be measured with a clock. This was the concept which Einstein smashed with his new thought.

Narrator: The tool that Einstein used to shatter the clockwork Universe was the speed of light. He knew that for 20 years scientists had been puzzled by an experiment which suggested there was something decidedly odd about the speed of light. In the 1880s two American scientists, Albert Michelson and Edward Morley set out to measure how the speed of light was affected by the Earth's motion through space. They set up an experiment with beams of light.

Prof John Baldwin: In this experiment there's a light source which is the laser, and one's splitting the laser beam into two, sending them in two directions at right angles, and measuring in a sense the relative speed of light along those two beams and recombining them. The pattern that you see is the interference between two beams and it's measuring the relative speed of light within those two beams.

Narrator: If the apparatus were static there'd be no reason to expect a difference between the beams, but in fact it's moving very fast indeed. Our planet orbits the sun at 30 kilometres a second. It also spins around its axis once a day so every laboratory on Earth is spinning through space.

Prof John Baldwin: Well at this time of day the Earth is moving in this direction through space round the sun. If we then waited six hours, the Earth would have turned and then this direction would be the direction of motion of the Earth through space; then in another six hours this direction would be back but reversed. So that by doing nothing you can just sit here and very, very smoothly the Earth takes you round and then you can just look at the stability of your apparatus.

Narrator: Michelson and Morley assumed that the planet speed would add to the speed of the light beams and their apparatus. So they expected to see a regular pulsing of the pattern every six hours as the Earth's motion added to the speed of light in first one beam and then the other.

Prof John Baldwin: The surprising thing of course was that the measurements showed that nothing happened, and no matter how they did it and when they did it and whether they waited a long time, all year even, still nothing happened. And that's the beauty of the experiment that if you can measure nothing very, very precisely then you've got something really important.

Narrator: The importance of this result was that it proved that you can never add to or subtract from the speed of light. This was a direct contradiction to what was supposed to happen in the clockwork Universe. When space and time are fixed, speeds must always add up.

Prof Dave Wark: In such a world one has a very simple rule for the addition of speed, the addition of velocities. In Einstein's example, if you're walking along a tram or a train, your speed, with respect to the ground outside, is just the sum of your speed walking along the tram and the tram speed with respect to the ground.

Narrator: But the Michelson, Morley experiment had proved that this was not true for light. Light leaves the tram at the speed of light and strikes the pedestrians at the speed of light and this speed never changes, no matter how fast the tram is going. But something must change as a result of the tram speed. Einstein realised that it must be space and time themselves.

Dr Ruth Durrer: Once you assume that the speed of light is the fixed thing, this will imply that space and time can no longer be fixed and that, for example, a moving clock which is moving with respect to you goes slower.

Narrator: So, viewed from the pavement, the speed of the light from a tram is not affected by its motion. Instead the watch, as the passengers are waiting, will run slow compared to a stationary clock. In a small two-room apartment a few yards from the clock tower, Einstein wrote up his radical theory of Special Relativity.

Prof Dave Wark: Advertisement for the unemployed Einstein offering

Dr Ruth Durrer: ...private courses in mathematics and physics for students. For some time he was unemployed; nobody wanted him. They thought he was too lazy.

Prof Dave Wark: I think they thought he was too troublesome. Does it say there how much he charges?

Dr Ruth Durrer: It says that test lessons are free.

Prof Dave Wark: Ok, I think I'll come by and have a test lesson.

Narrator: But Einstein's fortunes were about to change.

Dr Ruth Durrer: So it's 1905, he's 26.

Narrator: In that year he published several papers of which Relativity was just one.

Dr Ruth Durrer: Six papers if you count the PhD dissertation.

Prof Dave Wark: In one year. And each one founds a field of physics.

Dr Ruth Durrer: And each one is worth the Nobel Prize.

Prof Dave Wark: I wonder if he'd realised just how big a change he was making to the world when he wrote that down.

Dr Ruth Durrer: And that's the E=mc2 paper, which he published very shortly after that one.

Prof Dave Wark: Look how thin it is! Jesus! Three pages - if I could trade all of my lifetime publications for these three pages!

Narrator: But Einstein himself was not satisfied. The problem was that his theory of relativity broke down when gravity entered the picture and gravity was the dominant force in the Universe. Einstein realised that he had to take his notion of flexible space and time even further.

Prof Dave Wark: He had to give space-time actual properties, it was no longer just in an empty place where things occur, it was something that actually was interactive. So in his famous statement, mass tells space how to curve, the presence of mass actually curves space-time.

Prof Dave Wark: And in the flip side of that, his next part of this statement is: space tells mass how to move, so a mass moving through space-time now just follows the curvature induced on it by the presence of a mass.

Prof Dave Wark: And this solved an old problem from Newtonian mechanics: the Earth is going round the sun. The Earth feels a gravitational attraction to the sun. How does it do that? How does the Earth know the sun is there? What is the source of this instantaneous action at a distance? In Einstein's model there is no such instantaneous action at a distance. The mass of the sun simply curves space-time and then the Earth follows that curve. Just like this tram follows the tram line it is on in response to the local curvature of the tracks; it doesn't know if those tracks are going to curve some distance in advance; it doesn't need to know. It just follows the local curvature of the track.

Prof Dave Wark: Einstein realised that it wouldn't just be mass that would cause gravity, it wouldn't just be mass that curved space time.

Dr Ruth Durrer: Every form of energy, like heat or also pressure, reacts to the gravitational field.

Prof Dave Wark: There's nuclear energy many, many different types of energy and all of them cause space-time to curve the same amount, depending just on the total amount of energy present. Mass is nothing special in this regard.

Narrator: For 10 years Einstein searched for an equation to express this relationship between mass-energy and space-time. In the end it was stunningly simple. G = 8 p T. In five characters the Einstein field equation encompasses the structure of the entire Universe. It ranks as one of the supreme achievements of human thought.

Dr Ruth Durrer: When, as a student, you learn this theory you find it extremely beautiful and simple. But then if you think: how did he get it? How on Earth did he find out these equations? That's a miracle.

Narrator: But Einstein didn't stop. He set out to use his new equations to describe the entire Universe. It was a bold leap and immediately he ran into problems - problems which still remain.

Dr Joao Magueijo: Relativity was a great success at least until Einstein had the courage to apply relativity to the Universe as a whole. He invented cosmology, scientific cosmology, but at the same time he gave us a lot of problems which are still with us. Basically, the Universe as we see it doesn't want to behave according to relativity.

Narrator: Einstein's approach was based on a daring assumption. He knew that locally stars would distort space-time in complicated ways that would be too difficult to calculate. But he believed that if he stepped back far enough, all the matter in the Universe would look like molecules in a cloud of gas.

Narrator: The cosmological fluid. From this perspective, the shape of space-time would be uniform and simple enough to deal with. But when he began to calculate how the Universe would behave under the influence of gravity he got a nasty shock.

Prof Dave Wark: You look out in the Universe and you see what appears to be relatively stable: the unchanging stars. And in Einstein's era they thought the Universe was remarkably static. It looked the same over time. But in Einstein's solutions this couldn't be true.

Narrator: Einstein found that his equation predicted that all the matter and energy in the Universe would fold space-time back upon itself. Soon the Universe would meet a fiery end as all the stars and galaxies collapsed into an enormous fireball.

Dave Wark: And in order to prevent this, Einstein had to add a term which he called the cosmological constant.

Narrator: To Einstein this extra term, lambda, the cosmological constant, spoilt the beauty of his original equation. But he could see no other way to make the Universe stable.

Prof Dave Wark: Now this is a constant that gives space-time itself the property that it would tend to spontaneously expand, and so he added that constant in just the right amount so that this property of space-time to expand would exactly balance the property of the matter in the galaxy or in the Universe to collapse under its own gravity. So by exactly balancing these two, he could therefore make the Universe stable. Now it wouldn't really have worked of course because it's the stability of a pencil on its point. Even the smallest deviation - too small a matter of density, too large amount of density - would have made the Universe collapse or expand, so I don't really think he'd solved the problem.

Narrator: Einstein's problem was that, according to his theory, the Universe was inherently unstable; it should have collapsed or exploded long ago. It's a mystery that worries scientists to this day.

Part 2

Narrator: This is the echo of creation. Detune a television set and it will pick up microwave radiation from the edge of the visible Universe. When it' set out on its journey, it was orange light but over the 15 billion years it has been travelling the Universe, it has grown a thousandfold, stretching the light so that we now see it as microwaves. It warms us as it warms the entire cosmos, raising the temperature of space by 3 degrees. This signal is powerful evidence that the Universe is not unchanging as Einstein imagined but that everything we see around us was once part of an immense fireball. The first hints of that fiery beginning were found when astronomers started to look out into space beyond our own galaxy.

Prof Richard Ellis: The 1920s was an exciting time in astronomy because that's when the first large telescopes came on line and Edwin Hubble, an American astronomer, started looking at nearby stellar systems which we now call galaxies.

TV voice: Dr Edwin Hubble on a moveable platform lines up the massive telescope as he begins a cold night's work.

Prof Richard Ellis: And to his astonishment he found that they were very, very far away firstly, and secondly by measuring the light from these galaxies, he was able to see that they were moving away from us.

Narrator: To Hubble this could only mean one thing: the Universe itself must be expanding.

Prof Richard Ellis: It's a pretty profound discovery that the Universe is expanding because what that means is that at some point in the past, things were closer together. So if you measured density - the number of galaxies in a little box of space - then as you go back in time, the number that fit in a fixed box of space goes up and so the Universe becomes much denser and hotter. As one goes back in time, eventually you will come to a point which we call the Big Bang when the density was extremely high. And so the profundity of this discovery is that the Universe had a beginning: a Big Bang.

Narrator: If Hubble was right and the Universe had started with a cosmic explosion, then the force of this alone might be enough to counterbalance gravity's tendency to make the Universe collapse and die. Perhaps here was a way to make the Universe stable and solve Einstein's problem.

Prof Richard Ellis: You would have thought Einstein would respond positively to observations, but as is often the case, theorists completely ignore observations and so here was Hubble with a fantastic discovery - probably discovery of the century - and Einstein really didn't take any notice of it. So Einstein stuck to his static Universe, insisted on his cosmological constant to keep the Universe static, and it wasn't really until a meeting here in California between Hubble and Einstein in about 1932 that really there was a synergy between Einstein and the expanding Universe.

TV voice: And here he comes, down from the sun tower after a hard morning, looking a few million miles into his favourite space.

Narrator: Hubble, in the middle here, soon convinced Einstein that the Universe was indeed expanding. The cosmological constant which Einstein had introduced to hold up a static Universe against the force of gravity appeared to be unnecessary after all. With relief Einstein returned to the original form of his general theory of relativity.

Prof Richard Ellis: And it's at that time, or shortly after that, Einstein said that the invention of this cosmological constant was his biggest blunder.

TV voice: The construction is very ­ was very ­ skilful. You had to build up the outside and then put in the inside and then more outside and inside ­ it was a great piece of engineering

Narrator: But Einstein's optimism was premature. It has gradually dawned on cosmologists that the Big Bang doesn't in fact solve the problem with the Universe stability. For 21st-century physicists like Joao Magueijo and Andy Albrecht, the cutting edge of research is still the problem first identified by Einstein back in 1916.

Prof Andy Albrecht: If we can really make that connection, then it's the reason why people should want the speed of light to vary.

Prof Andy Albrecht: You'd think, with all the great success of the Big Bang, we'd be happy, we wouldn't be complaining. But there's a problem with the Big Bang, and the problem is we shouldn't be here.

Narrator: The Universe has been gently expanding for 15 billion years. That's allowed time for stars, planets and cosmologists to evolve. The problem is, it's almost impossible to get a gently expanding Universe out of the Big Bang. Either it expands too fast or it falls back in on itself. Either way the Universe could not last very long.

Prof Andy Albrecht: A good analogy is to think about throwing a rock in the air. You throw it up; you expect it to come back after a little while. You throw a little bit harder and it goes further; but eventually comes back. If you throw it hard enough ­ and no human can do this but NASA can do it with a space ship - you can leave the gravitational attraction of the Earth and fly off forever.

Prof Andy Albrecht: With the Universe there's this delicate balance. You throw the rock in the air ­ it keeps going. Is it gonna turn around? You don't know, it keeps going, it keeps going, you don't see it flying off, you don't see it turning around, it's balanced right at the end for year after year, thousands of years, billions of years. We're now almost 15 billion years, we still don't know - is it coming back is it flying off? That's what the Universe is like.

Narrator: With the ball it's how fast you throw it. With the Universe the key thing is the amount of matter and energy in the Big Bang. To produce gentle expansion, the density of this energy has to be precisely right.

Prof Andy Albrecht: How do we start this Universe out in such a special state? We have to take a number that describes the density of the matter in the Universe and get it right to a hundred decimal places. One after the other, if we get one decimal place wrong the whole thing gets out of whack. No physicist can stomach setting up a Universe in such a delicate way.

Narrator: Yet something set up the Universe in the right way. Some mysterious process made sure that matter and energy had everywhere the same critical density keeping the entire cosmos in perfect balance.

Narrator: Scientists call this the flatness problem.

Dr Joao Magueijo: So this is the flatness problem: it's the fact that the Universe is a bit like a pencil standing on its stick for 15 billion years.

Narrator: And it's even worse than that.

Andy Albrecht: The puzzle is that when you start saying OK, suppose at the beginning things were different and something could come along and adjust everything just the way you need it, you run into the following problem: nothing can travel faster than the speed of light.

Narrator: The Universe is very, very big. Bigger than we can imagine and bigger than we can see. There are regions of space so far away they are invisible because the light from them has not yet had time to reach us. In effect we are surrounded by a horizon; this horizon has been growing at the speed of light since the Universe began but beyond it are regions with which we have never had any kind of contact. Since nothing, not energy nor any kind of physical process can travel faster than light, nothing can cross the horizon.

Dr Joao Magueijo: The Universe is now 15 billion years old which means that the horizon is actually very large. Nowadays it's about 30 billion light years across. This doesn't mean that the Universe is only this size; of course the Universe is infinite. It just means the region we can see is this 30 billion light year region, and when the Universe is very young, it's still very big but conversely you see a smaller and smaller fraction because the horizon is smaller and smaller.

Narrator: To see what this means, imagine that we could travel back in time. We would see the Universe shrinking rather than expanding, but our view of it would shrink even faster because our horizon would be shrinking at the fastest possible speed: the speed of light. Galaxies that are visible today would have been invisible to us in the past, and to each other. So the early Universe was divided up into small islands, isolated inside their own small horizons. This picture of a disconnected Universe flies directly in the face of the idea of a single balancing process needed to solve the flatness problem. Confused? So were the cosmologists. The only way round this horizon problem was to assume that the entire region we see today started out so tiny it would fit inside a single horizon. This idea, called inflation, was first proposed by Alan Guth and then developed by Paul Steinhardt and his colleague Andy Albrecht. Today, their version of inflation is widely accepted among scientists but Andy Albrecht himself has never been wholly convinced by his own theory.

Prof Andy Albrecht: What we have to do to make inflation work is invent an entirely new form of matter that exists in the early Universe and then disappears so we don't have it around today. And I was always left with the nagging feeling that if you invent so much, is inflation really the right thing to invent? Or could nature have chosen something else?

Narrator: As a young researcher at Cambridge in the mid-1990s, Joao Magueijo was also sceptical about inflation.

Dr Joao Magueijo: Because inflation is the only thing available, people cling to it, just like to a lifeboat. To be a bit extreme, you could say, you could solve all these fine-tuning problems using divine intervention and I think inflation is a scientifically acceptable way to invoke divine intervention at some point.

Prof Andy Albrecht: I think that's a bit over the top but there's enough open questions that we really need to think about it.

Narrator: One day Joao saw that there might be a much simpler way to solve the horizon problem.

Dr Joao Magueijo: I realised that if you were to break one single but sacred rule of the game, the constancy of the speed of light, you could actually solve the horizon problem. And when you think back on it, it's just such an obvious thing that when Universe is very young if the light was very fast you could have a very large horizon. When the Universe was one year old the horizon would be one quick light here across to here, which could be as big as you wanted and of course you can connect the whole of your Universe if you do this.

Narrator: If early light was much faster, a single horizon could be big enough to encompass the entire known Universe. It was a bold idea, too bold.

Dr Joao Magueijo: This came at the time when I was a fellow of this college but it was also a stage in my career where I had to look for a job, I was about to finish my position here - not the time to go and pursue a very original idea. I was already quite controversial. I didn't need another thing that would be even more controversial. There were times when I saw myself selling the Big Issue outside St John's College! So I waited until I was on much safer ground.

Narrator: Joao found that safer ground when the Royal Society awarded him a rare and prestigious research fellowship. He joined Andy Albrecht's group at Imperial College. They started to work on Joao's idea together.

Dr Joao Magueijo: One day Andy just called me to his office and he said, 'Joao let's work on the varying speed of light here,' and he closed the door and made a big secret about it. He cleaned the blackboard afterwards; he was really afraid someone might steal the idea. Then gradually we just started putting more and more material together, trying to find more and more things about the theory.

Prof Andy Albrecht: You face the frontier, you face unknown questions and you argue about it and you have competing ideas and, after a while one is clearly the winner.

Dr Joao Magueijo: And you're really worried about something, it really is with you all the time, not just in your office. You go through phases in which you dream about your ideas, you sleep over your ideas you wake up tired. Well you need to cast things into equations in the end because this is what science is all about. It's about mathematical models not just theories, otherwise it's all very cranky. I think there is a very unique aspect of scientific discovery, there is a big adrenaline rush when you've spent months and months struggling with the problem getting it wrong and eventually you discover something and it's unique. I'm addicted to adrenaline in general but this one is unique.

Narrator: Joao and Andy were creating a completely new physics. As they explored this strange new world it began to dawn that perhaps they could solve more than just the horizon problem.

Dr Joao Magueijo: We got more than what we bargained for and this is really where the thing was massively rewarding. We found that we could solve the flatness problem as well and the reason for that is we realised very quickly there's no way we have energy conservation if the speed of light varies.

Narrator: In conventional physics, energy is conserved. It can be transformed but it cannot be created or destroyed. This is the principle of the conservation of energy and it means that the total amount of energy in the Universe is fixed. So the critical energy density the Universe needs must be established perfectly, right from the beginning.

Dr Joao Magueijo: Now if we change something as fundamental as the speed of light, which is woven into the whole fabric of physics, then of course you're breaking that principle: the Universe is different at different times. And you don't conserve energy. But then you realise this is exactly what you need to solve the flatness problem because you violate energy conservation pushing the Universe to the critical energy density. That is, you create energy if you have sub-critical energy density and vice versa. You take away energy if you have a surplus of energy density.

Narrator: In their theory, during the early Universe the speed of light was falling, which allowed the cosmos a built-in thermostat, creating or destroying energy so that the critical density was maintained exactly. Thus the Universe remained in balance for billions of years.

Dr Joao Magueijo: We were just trying to find an alternative to inflation as far as the horizon problem was concerned. We actually did not have hopes of solving everything. This was a gift we got out of it.

Narrator: Joao and Andy had set out to solve the horizon problem and stumbled upon a theory that solved the puzzle which had plagued cosmology since the time of Einstein. They had made a Universe that was inherently stable, held in balance by the creation or destruction of energy. A theory which predicted the Universe as we see it today. However it was still just a theory; proof could only come from the depths of space-time. But what astronomers found there would astonish everyone. Suggesting that the speed of light was also the key to the biggest mystery in cosmology: what happened before the Big Bang.

Part 3

Narrator: Long ago when the Universe was young, light itself travelled faster than it does today. The laws of physics were very different; that at least was the theory. The evidence could only come from the world's great telescopes. As they scan the far depths of space, astronomers also look back in time.

Narrator: In 1998 the British astronomer John Webb started to become interested in the question of whether the fundamental constants of nature could change as the Universe evolved.

Prof John Webb: We're using a technique which enables us to look back into the past to measure physics as it was a long time ago. So we're doing that using quasars.

Narrator: Quasars are the most distant objects we can see; they are thought to be primitive galaxies in the process of formation. But John Webb is not interested in the quasars themselves.

Prof John Webb: Quasars are just, as far as we're concerned for this study, very distant sources of light which shine through the Universe to us. In doing so, they intersect gas clouds along the line of sight and then we can study the physics of those gas clouds by looking at the way in which the light is absorbed. We can look at gas clouds relatively nearby, and we can look at them just about as far away as the most distant quasars. That means in terms of looking back in time almost 10 billion years, or something like that, an awful long time ago. So we're studying physics as it was when the Universe was quite young.

Narrator: When light passes through an interstellar gas cloud it collides with the electrons and the gas molecules. This creates a pattern of dark lines in its spectrum. What John Webb noticed was that this pattern looked different in the spectra from the most distant clouds. The inference was astonishing: either the electrons were different or the speed of light was greater in the distant past.

Prof John Webb: If it's correct, it's certainly a very profound result for physics because it would be the first ever indication that the laws of nature were not always the same as they are today.

Narrator: But far off in space and time an even more amazing discovery was waiting for astronomers: today cosmology is buzzing with news of the unexpected comeback of an idea discarded 70 years ago. Einstein's cosmological constant, lambda.

Narrator: For Joao it means taking his theory even further. He now believes the cosmological constant could be the link that connects changes in the speed of light to the origin of the Universe itself.

Dr Joao Magueijo: So Einstein has already endowed space-time with its own life, when he allowed space-time to curve, to have its own dynamics - and the cosmological constant was one step further - it was basically giving space-time its own energy so that even before he put matter into space-time, when we have vacuum, you have some energy density in this vacuum and this is what lambda is, and it has this very interesting property that essentially it makes repulsive gravity.

Narrator: Lambda produces gravity that pushes things apart rather than pulling them together and that seems to be what's happening to the Universe, something is blowing it apart.

Narrator: Ever since Hubble convinced Einstein that the Universe is growing, astronomers have been trying to measure its rate of expansion. The breakthrough came when they started to concentrate on exploding stars called supernovae. They thought that these would allow them to chart the gentle deceleration of the Universe. What they actually found was precisely the reverse.

Prof Richard Ellis: Now the question is, is the Universe slowing down as we would expect? The surprise is that instead of the Universe slowing down, in fact it's speeding up.

Narrator: Something is upsetting the delicate balance of the Universe, pushing the galaxies apart faster and faster. A new force in the vacuum of space.

Prof Richard Ellis: The acceleration as seen from the supernova data, of course, raises the amazing question of resurrecting Einstein's cosmological constant.

Narrator: It looks as if space-time is humming with energy. Buried in the equations of this theory, Joao has found a hidden link between this energy and the speed of light.

Dr Joao Magueijo: Well at some point we've found out two interesting things. One was that the energy in the cosmological constant also depends on the speed of light, and in particular if the speed of light drops, then the energy in the vacuum drops as well. And the second thing we've found is that this cosmological constant itself promotes changes in the speed of light - it can make it drop in value. So we have an instability.

Narrator: In Joao's theory, a change in the vacuum can cause a drop in the speed of light, but this in turn reduces the amount of energy the vacuum can hold, forcing energy out of it and into ordinary matter and radiation. Could this be the genius of the Universe? What happened before the Big Bang?

Dr Joao Magueijo: So in some of these scenarios in the beginning there is just a vacuum - but the vacuum is not nothing, it's actually the cosmological constant, this pull of energy in the vacuum. And in these theories, it is this energy that drives changes in the speed of light; it makes a drop in value. And what that does is that makes all the energy in the cosmological constant drop as well. It has to go somewhere. Where does it go? It goes into all the matter of the Universe, so it caused a Big Bang. So in this scenario it's actually this sudden drop in the speed of light - this change in the speed of light - that causes the Big Bang.

Narrator: In the beginning was the void. But the void was not nothing and there was light and the light changed. And so the void brought forth the world and the world was good, for it endured until men could comprehend it. But it will come to pass that one day the energy of the void will have pushed all things away, leaving nothing but the void. But the void is not nothing.

Dr Joao Magueijo: And you might think this is the end of the Universe, but of course in the picture of this theory it's just creating the conditions for another Big Bang to happen again - a sudden drop in the speed of light, another sudden discharge of all this energy into another Big Bang. So it is possible that actually our Big Bang is just one of many, one of many yet to come, and one of many which there were in the past already - maybe the Universe is just this sequence of Big Bangs all the time.

Narrator: Joao's bold challenge to the constancy of the speed of light has led him to a wholly new view of the cosmos. One in which the Universe no longer has a beginning and an end, but is eternal. An endless cycle of Big Bangs drawn from the vast reservoir of energy in the vacuum. And like every cosmologist before him, Joao has been guided by the theory that started it all: it is a measure of Einstein's genius that even when he was wrong, somehow he was right. What he called his biggest blunder may yet prove his greatest legacy.

Joao Magueijo: Well of course I respect relativity enormously and I have this feeling that it is only now that I have contradicted relativity that I really understand it. And it's actually just because I've gone against it that I'm showing my full respect to the great man. This is not at all trying to contradict Einstein, it's just trying to take things one step further. Eventually of course it will be nature that will decide whether this is true or not. I'm working on trying to find ways of deciding whether the theory is right or wrong. Some kind of experiment which will decide conclusively whether the varying speed of light theory is pure nonsense or not.