BBC The Next Big Thing

Sir Martin Rees is a Royal Society Research Professor and a fellow of King's College at the University of Cambridge. He also holds the honorary title of Astronomer Royal. He is a cosmologist and is trying to understand why the universe consists of the stars and galaxies we see around us, and how they've come to exist over the cosmic evolution that's extended up for fifteen billion years.

On what it would mean if we could understand where anti-matter went to:
The key question is why the universe does seem to consist of ordinary matter, all the stars and all the galaxies seem to be made of matter. If matter and anti-matter have been mixed up within our own galaxy for instance, then we wouldn't be here, because, during the course of stars forming and exploding, and mixing up the debris, it would all have annihilated, and when matter and anti-matter get together, they annihilate in a flash of energy we call gamma rays. So, we know that matter and anti-matter were separated very early in the universe, and that the anti-matter had somehow disappeared, and how this happened, is one of the mysteries of the early universe, along with why the universe is expanding the way it is, and why it contains the other ingredients we observe. So, it's a big mystery, why the universe consists of so many atoms but no anti-atoms.

On whether the universe was asymmetrical from the beginning:
Well, it might have been, the key question really is whether matter and anti-matter are completely conserved, or whether it's possible very occasionally, to create an atom of matter without the atom of anti-matter that goes with it. If it was completely conserved, then Fay would have to be right, we'd have to say the asymmetry that's present in the universe now, was there right from the beginning. I think that would be a rather difficult concept because, then we'd have to say, there's one enormous number in the universe, a number which is one followed by about eighty zeros, that's the number of atoms in the universe that we can see at the limit of our telescopes. And if we think the universe in a sense started off small, it's unappealing to imagine there has to be this, enormous number imprinted in it from the start.

So that's why I think most of us prefer the view, that perhaps, everything started off symmetrically, and there was somehow a slight favouritism, and a slight possibility to create matter without the accompanying anti-matter, and this lead to our universe, which is now dominated by matter not anti-matter. And as Graham said earlier, this favouritism need be only quite small because, our universe contains lots of radiation. For every atom in the universe, there are about a billion photons quanta of radiation, and we believe what happened is that, as the universe cooled down, we're talking now about when it was about a microsecond old, matter and anti-matter annihilated, and, for every billion antiparticles, there was a billion plus one particles.

So there were a billion annihilations, but one particle which was left over, and we are made, and the stars are made, of that one that did not find a mate to annihilate with as it were. It's a small asymmetry, and the mystery which has to await unified theory, is why the laws of physics did allow this small asymmetry to be imprinted very early on. This will have happened we suspect, much earlier than the time which we can simulate in accelerators, because accelerators, only allow us to understand the physics that prevailed after the first trillionth of a second. That may seem most of the universe, indeed it is, but if you think on a log scale, lots can happen at even earlier stages, and that's the era when the physics, must have lead to this Asymmetry in the universe.

On why the asymmetry in the universe has a tendency to produce matter, rather than anti-matter:
Well this really relates to a very deep question, which is the uniformity of the laws of nature, and it does seem that when we look at the light from a distant star or galaxy, and analyse the light with a spectrometer, the atoms which we infer to be there in that distant galaxy, are governed by just the same laws, as the ones we study in the lab. So it does look as though, at least all the universe we can now observe with our telescopes, was governed by the same laws, and the C P violation that Graham mentioned will probably prevail everywhere, and that suggests that whatever asymmetry favoured matter over anti-matter, would also prevail.

On whether anti-matter could be trapped in some way that made it inaccessible for annihilation with matter:
Well we'd have to ask how it got there, as we have good reason to believe the universe started off with the gas being fairly smooth, and no stars or galaxies forming, and of course, the problem with anti-matter, the problem with the spacecraft that's powered by anti-matter, is actually confining the stuff because, if it comes in contact with ordinary matter, it's annihilated in a spectacular way. So, the only way you could imagine anti-matter being confined, in some futuristic spacecraft or anywhere else, is if it's confined by some magnetic fields or something like that, so that you can stop it escaping, but keep it quarantined from ordinary matter.

On whether the laws of physics might have been different at very early stages:
Well it's partly a semantic point because, Graham's right in a seen in saying the laws of nature by definition apply everywhere, but the key thing is what they imply under extreme conditions. We're used to the idea that the more extreme conditions become, the more we have to jettison or modify our common-sense concepts. We have the spookiness of the quantum world, and the mysteries of space and time in black holes etc. So, we know that when conditions get very extreme, we have to give up some of our cherished common-sense notions, and I think the key question is whether the laws of physics as Graham would define them, apply to the ultra early universe, do allow the production of asymmetry or not. It's really a question of what the laws of physics are, at those very extreme times.

On whether there is a relationship between dark matter and anti-matter:
Well we're not sure, but we do know that the early universe must have contained not just the atoms that we're made of, they're just four percent, plus the radiation, which is the result of the annihilation of matter and anti-matter, but also dark matter. We suspect the dark matter, which is very important gravitationally for holding together galaxies, and clusters of galaxies, is made of some kind of particles, that are also a relic of the very early big bang, some sort of particles with no electric charge, that don't interact very much. But the big bang must have made these particles, which are very important in the universe today and, it just illustrates how, we are mystified, as to the basic ingredients as it were of our universe, and to answer the question of what the dark matter is, we need either to find it, by experiments, or to have a better understanding of particle physics. Because if we knew about the physics of high energies, and how particles crash together in the very early universe, we might know, whether they'll produce some kind of particle that would survive to make the dark matter. So, it's a nice link between the physics of the very large and the very small, and it's embarrassing that most of the universe is unaccounted for in this way, and it's in the form of dark matter, whose nature we are completely flummoxed about.

On the possibility of making dark matter:
I think some people think that a dark matter candidate is a so called super symmetric particle, which might be produced in the next generation of accelerators. So it's possible that it'll be produced but it's pretty unlikely.

On the security of the concept of the Big Bang:
Well I think most people would suspect that back to one second is fairly firmly established. The conditions back then are not all that extreme, they're rather like in the centres of stars, they can easily be assimilated in the lab, and we have very good evidence for what the universe was like then, which we can observe with high precision now. So I would say that back to one second, at least, the evidence is as good as what the geologists may tell you about the early history of the earth. Their evidence is less qualitative than we have about the early universe. But, when we get back, certainly into the first trillionth of a second, first ten to the minus twelve seconds, then we encounter a regime where, we have to be agnostic about the basic physics, because it's beyond what we can directly test. And so, here in a way the game changes because, we in astronomy and cosmology, are perhaps going to learn about the basic physics, because the universe is the only lab we can ever use, which tells us what conditions were like. So, in discussions of the early universe, trying to explain, where the dark matter came from, why there's no anti-matter, why the universe is expanding the way it is, we are, in a sort of symbiotic relationship with fundamental physicists because, we need their theories, and the only way their theories will ever be tested, may be in so far as they are corroborated by astronomical observations. So, there's a different type of interaction between, theories of the cosmos and the micro world, the inner space of atoms, and the outer space of the universe.

On when the universe is going to end:
As far as the universe is concerned, we can never make reliable long range forecasts of course but, I can be more confident than if you'd asked me five years ago. In that there's a strong reason to suspect, that the laws of nature, are such that the universe is going to go on expanding for ever, perhaps even at an accelerating rate, and that there will not be a big crunch. Now, of course, we could be wrong, it goes back to what we said about whether the laws of nature will apply in the distant future, there could be a change that would trigger a big crunch, but it looks as though the universe is expanding, and the expansion's even speeding up, not slowing down towards a halt, which would be the precursor of a big crunch. So, it does seem as though, the universe has an infinite future ahead of it , to quote Woody Allan, eternity is very long, especially towards the end, and there's plenty of time for all the stars to play out their life, and come to a terminal state, before the universe collapses on top of them.

On how to approach such abstract concepts as the early universe:
Well, you try and be as concrete as possible and to depend on observations, and my work depends on observations of galaxies and stars etc which, you can visualise in a fairly concrete way. But it's true that our common-sense notions must be modified drastically when we go down to the very small, the quantum world, or the very large. Fay has emphasised that when we get to the very tiny scale, even space itself has some complicated grainy structure. And in the early universe, we may have to stop our extrapolation back, right in the initial instance, because the whole idea of time breaks down. The idea of three dimensions of space, and clocks ticking away, may have to be generalised. Some ideas for quantum gravity, involve extra dimensions, and other deviations from common-sense. But then we do have to think in terms of mathematics but, what is amazing is how far we can go, with the laws that we understand here on earth. It's amazing, we can go back to the first tiny fraction of a second, and study a distant part of the universe through our telescopes and make some sense of it. So I think, what's amazing is how far we've got, not that we eventually come up against a barrier.

On quantum mechanics:
We do make use of quantum theory to make calculations on atomic physics, but there are mysteries. Someone once said that your average quantum mechanic is no more philosophical than your average motor mechanic, and that's certainly true. But nonetheless, the other side of that coin is that, although we use quantum mechanics, there are deep mysteries of a deep philosophical nature, which I'm sure we don't yet fully understand, and perhaps the deep understanding of those mysteries, will come when we link together, the quantum micro world with cosmology.

On whether he’s confident that we will ever will really understand, what happened at the start of the universe?
Well some people have to be confident or they wouldn't try and find out, if they don't try they certainly won't succeed. But we have to be open minded I suspect that maybe we will never be able to get a full understanding. Maybe the laws of nature, at their deepest level, are at a still deeper level than the ones we apply in our labs, and in our astronomy, and so we have to ask, to what extent are our brains matched to the deepest level of reality. It's amazing we've made so much sense, but we may come up against some inherent limitation eventually.

On how realistic the idea of a "theory of everything" is:
The phrase theory of everything is sort of hubristic and misleading in my opinion. Because, if we had such a theory, it will be the end of a certain quest, the one that started with Newton and went on through Einstein, to unify the laws, but of course the laws are just the rules of the game, and the way those laws are played out in or universe, and the way they have lead from the big bang, to the immensely complex cosmos around us of which we are a part, that's an unending challenge, and even if we have the laws then, that'll be what ninety nine percent of scientists will be doing. And so, it's the end of a certain part of science, but it's certainly not the end of science.

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