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11 June 2011updated 17 Jan 2012 7:04am

“If we could prove string theory wrong, I would be thrilled!”

In this full Q&A, physicist Brian Greene talks about God, the multiverse and the theory of everythin

By Helen Lewis

For the Science Issue of the New Statesman, I interviewed Brian Greene, one of the most compelling and interesting advocates of string theory. The interview is now online but if you’d like a more in-depth look at some of the concepts we discussed, here’s the longer Q&A. In it, we discuss multiverses, extra dimensions — and the time Greene wrote dialogue for Third Rock from the Sun.

Why did you choose to write about multiverse in The Hidden Reality?

I think it’s the most exciting subject at the frontier of physics research today. It is a highly speculative subject but I don’t shrink from speculative subjects. I think they’re fascinating to explore and this one in particular — the possibility that there are other universes — has really bubbled up in the past few years and captured the attention of mainstream physicists, who have been searching for the unified theory.

We don’t know if these ideas are correct but they are sufficiently mathematically compelling that we’re taking them seriously. I wanted to give the general public a snapshot of some exciting physics that may be the gateway to a fantastically new view of reality.

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To what extent are these ideas becoming accepted now?

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I wouldn’t say “accepted” — that would be a bit strong. What I would say is that we all recognise that these ideas could be wrong . . . Our mathematical calculations bump into these ideas repeatedly from a variety of different angles. It’s not that we have some crazy idea about the universe that we’re trying to impose on these theories but, rather, the math leads us to this possibility.

That’s why we are willing to take these ideas seriously and investigate them. But, until there’s observational evidence or experimental proof, we won’t know if this math describes reality or is simply interesting math, which may be interesting to mathematicians but not to physicists.

Which strands of physics leads you to the idea of the multiverse?

Cosmological physics, unified theories, relativity, quantum mechanics, computational physics. In the book, I cover nine variations on the theme of multiverse proposals, because there are these different avenues that, when followed sufficiently far, take you to this idea.

If you like, I can give you some specific examples of how this happens. In cosmology, the big bang is a theory about how the universe evolved, from whatever caused the outward swelling of space to occur in the first place. We have been struggling for a long time to fill in a missing piece. What caused the outward swelling to start?

In recent years, a proposal has been slowly developed for what may have driven an outward swelling. But here’s the thing — when we study the math for that proposal, it naturally suggests that the big bang, that outward swelling, is not a one-time event. It may have been a many time event, with many big bangs in many different universes.

Our universe in that picture would be the aftermath of one big bang but there’d be other universes that resulted from those other big bangs. I like to think about it this way: our universe is one expanding bubble in a grand, cosmic bubble bath, where the other bubbles are other universes.

Different big bangs, temporally or spatially?

Both. It’s very hard to talk about time, when applied to the whole collection. We understand time in our universe. But how does time in our universe relate to time in the other universes and perhaps some more overarching notion of time that would embrace everything? We don’t know the answer to that.

So, when you say before or after, roughly speaking, I’m happy to say yes but if you press me really hard, I would have difficulty even defining before and after when discussing time beyond our little bubble universe. That’s a little mind-blowing!

You talk about examples where people have read The Elegant Universe and show up at your graduate class.

It’s not a common occurrence but it does happen . . . more often, it happens when people send me their manuscript. Not long ago, I got a manuscript from somebody who’d read The Elegant Universe and, for ten years, had been working in his basement trying to take the ideas to the next step.

He wrote how his wife almost left him because he wouldn’t come out of the basement — and the painful thing to me was, I think most people realise that these books are a translation from the mathematics to the ordinary language to give a feel for the ideas. It was heartbreaking.

The process of doing theoretical physics, how does it work?

Usually, it’s a fairly communal activity. For instance, I have a group of students, grad students, post-docs from the faculty, and we’re constantly at the blackboard discussing ideas, throwing things back and forth, reading papers that others around the world have posted into the archive.

Every morning, we go there to see what papers have been posted from the previous night. We read those papers, we think about how mathematical ideas there might be relevant to us, whether we can push somebody’s idea further. So it’s a very incremental process, with a lot of conversation and cross-talk happening throughout the world on these ideas. So the notion of the lone individual with the solitude of their own mind at their desk trying to figure out the universe is a nice romantic image but is usually not the way we work.

And when you talk and share ideas, do you talk in equations or do you find it useful to use metaphors?

It’s almost always in mathematics. Many of us do find it useful to have a mental picture of the mathematics. Personally, if my understanding of a subject is solely based on the equations, I feel like I don’t fully get it. I see the math — I understand the math — and that, ultimately, is what I’ll rely on to make progress and to gain further insight but I like in my mind to have a mental picture, a visualisation of what’s going on.

And, frankly, when I write these books, what I do is, I revert to those very mental images that I’ve developed over a long period of time of thinking about this material. I strip away the mathematics, put it in the end notes or don’t have it there at all. Then take the visualisation and try to develop them in a way that will be interesting, a story, a metaphor . . . something that will add life to the ideas that builds a bridge from the everyday to the exotic.

How do you put into language things we can’t even describe with maths yet?

That’s pretty tough. Often, even if we don’t have the full mathematical formulation of something, we have a mathematical trajectory. We understand certain mathematical ideas and we can see where they’re pointing; even if we haven’t developed the full rigorous math for where we believe we’re headed, the trajectory is often enough to build a coherent metaphor for where we’re going.

But there are some ideas, for instance . . . We all know that matter is made of atoms and molecules and one of the ideas I discuss even in this book is that we wonder whether space and time might themselves be made of molecules and atoms, of a sort; it can’t be the same molecules and atoms that make up tables and chairs but could there be a finer entity from which space and time are built? That’s a hard idea to get your head around but using the analogy with the ordinary matter, even though we don’t have the mathematical version of the story — that’s what we’re struggling now to comprehend — I think you can get the idea that if this table is made up of finer ingredients, could the environment that we’re immersed within be made up of finer ingredients?

A fabric of space-time itself?

That’s the language we use. And the question is how literal you should interpret that metaphor: is it a real fabric? Or is that just the poetic language we use to describe the environment within which we’re immersed? In many ways, the work of Einstein that we’re carrying on today suggests that it is a real fabric in some ways. It’s not as tangible as an ordinary piece of fabric.

When I try to grab space, it’s eluding me right now; whereas this isn’t eluding me, when I grab the lapel of my coat. But there are ways in which experiments have shown that space behaves very similarly to fabric. For instance, if you go near a spinning black hole, you can show with experiments that space seems to be dragged around the spinning black hole, much as would happen if I had a pebble and a vat of molasses. As the pebble spins, the molasses spin with it. The experiments show that space is enough of a real thing that it begins to spin, too.

Even in a vacuum?


I suppose that whole idea of gravity and the deformation that makes implies there is something to deform.

That is an even simpler version, absolutely. Right! The very image that you have — here’s the sun and the fabric sort of warps around it; if there wasn’t a fabric, what’s doing the warping? What is that thing that’s taking on a curved shape? And that is what drove Einstein to talk about the space-time fabric, the space-time continuum.

So I guess the overall lesson is, we’ve been fortunate that many of the ideas that have played a critical role in the advancement of understanding the universe have analogies in the everyday world, which, while imperfect to be sure — every analogy is imperfect — are at least pretty good at communicating the flavour of the idea.

So what is the point of knowing this?

My mom says: “Why aren’t you a doctor?” And I’m like “I am a doctor!” and she’s all: “No, no, not that kind of doctor, I mean a real doctor.” She reads my books, sort of, but she basically says they give her a headache.

I think that many of us, at one level or another, are searching for meaning. Why are we here? Where do we come from? Is there a purpose to it all? And I don’t think science can answer the purpose question. I don’t think science is well suited to providing direct pronouncements on meaning. But I do think that if you are investigating these issues, it’s critical to know where they’re taking place. What is this universe? How did it come into existence?

Maybe we can’t answer why it’s here but I think we can answer how it came to be. And how it will evolve. That, to me, is a vital part of being able to even start to think about meaning. The reason I get up in the morning is these questions and the progress we’re making is so exciting that that’s meaning enough for me. I feel part of why I’m here is to immerse myself in the mysteries and to contribute what little I can to unravelling them.

I think that journey — that view of science as a living, breathing, evolving, exciting journey, the drama of adventure and discovery, the journey from confusion to at least partial understanding — is a thrilling one. And these books can give you a snapshot of that process, which gives you a completely different feel from physics than what you’d get from a textbook.

My husband said The Elegant Universe is what got him through A-level physics. The idea that it wasn’t just about rote learning, it was about ideas and exploration.

Exactly. I’ve been saying a lot lately, more back home than here, that a big problem with our educational system in the US and perhaps here too, I’m not sure, is that in the classroom, we immediately focus in on the details. To solve equations, to balance reactions, know parts of the cell, largely because that’s the material that’s easy to test, and that’s what we do.

And I’ve been saying, and I feel so strongly, you’ve got to have a commensurate focus on the big wondrous ideas. How did the universe begin? How did light begin? How did consciousness begin? Those are the ideas that make one want to learn the details in order to perhaps make one understand those questions more fully, and we don’t do enough of that by any means.

In British schools, because testing is such a large part of how we teach, it perhaps becomes “here are three things you’ve learned and let’s find out if you remember them tomorrow” and it certainly does physics a disservice.

I’ve had the experience where I’m talking to kids, and I began to explain aspects of black holes, aspects of the big bang, aspects of quantum physics, and after five minutes, I find that their eyes open wide and they’re like, “That’s science?”

Because to them science wasn’t exciting, mind-bending ideas, it was memorising certain things so that they could regurgitate them on a test. And to me, I got to tell you, it’s heart breaking.

That a subject that could be the primary driver of imagination, the primary driver of interest in excelling academically, is so often viewed as the subject to stay away from. Boring, dry, dull, intimidating, who needs it? And that is a failure of the way we communicate the ideas.

There’s a big problem in this country that it’s very hard to get children to do what are seen as “hard” subjects, particularly as the focus is so much on grades, and grades get you into university. If you were going to do an arts degree like I did, why would you do a hard subject like physics which is going to drag you down.

You wrote a children’s book, could you tell me about that?

Well it’s a reimagining of the myth of Icarus which, I don’t know when, or if people encounter it here, but I came upon it at a pretty young age, and found it very distressing because in my naivety it was simply a story about a boy who was bucking authority, not doing what his father was saying and paying the ultimate price for that which seemed wrong to me.

And as I got older and became a scientist it seemed yet more off base because in order to have great breakthroughs and insights in science, you’ve got to go against what the elders are saying, you’ve got to be courageous and go off on your own, even into uncharted territory. That might me quite dangerous, but you don’t pay with your life.

The price you pay for great discovery is you and society often have to acclimate to a new reality, right? In the atomic age we learned how to split the atom, we learned how to harness nuclear power. We are obviously still struggling with that move into the nuclear age right now, obviously. The biological age — we learn how to understand DNA and the genome, and now we’re struggling how to figure out what to do with that knowledge.

That’s what happens, we have to acclimate to new reality. So my version of the Icarus myth, that’s what happens. The boy doesn’t go to the sun with wax wings, he builds a spaceship and against his father’s warning he flies to a black hole. And what happens at the black hole is purely scientific, not science fiction, not fantasy. To travel to a black hole, that is fiction today, but the real physics of Einstein’s general theory of relativity dictates what happens.

The boy spends an hour or two near the black hole on a joyride, going round the outskirts careful not to fall in. And what Einstein taught us is that time flows down over the edge of a black hole. So what is an hour for this futuristic Icarus, when he comes back and he wants to show his dad what he’s done, he learns quickly that 10 000 years have gone by for everybody else, because while time is running slow for him, it was running at the everyday speed for everybody else, so his dad is long gone, and he has to acclimate to this new reality.

And that to me is what the process of courageous exploration leads to. So that’s what the story is, and it’s a way in which young kids can actually learn a real piece of science, this time slowing at a black hole is real. But do it in a way where it’s emotionally compelling, because it’s a story, and it’s a story of exploration and loss.

And I read that you helped out with the dialogue on Third Rock from the Sun . . .

It’s true in the most minimal sense. There was one episode in which John Lithgow was growing tired of speaking physics babble without it meaning anything in physics so one of the writers, who I grew up with, wrote to me somewhat frantically, “Can you give us 18 words of real physics that might slot into this little moment so that John Lithgow is saying something real?” So I did — and the amazing thing is I don’t watch the show but, one day, years ago, I was channel-surfing mindlessly and I look at the programme and I see the equation of quantum thermodynamics on the blackboard, so I turn up the volume and it’s the words I wrote! It was one of my proudest moments!

Do you have a scientific hero?

Pretty much the one you’d think. The thing about Einstein is, almost everything that I do and almost everything that modern physicists do, in one way or another, leads back to Einstein. It’s kind of astounding.

We looked at the world one way in, say, 1900 and, by 1955, when Einstein left the scene, we looked at it a completely different way. The big developments — special relativity, general relativity, quantum mechanics — all are traceable back to Einstein in one form or another. And even today, as we seek a unified theory, we’re trying to put together general relativity and quantum mechanics, two threads that, if you trace them back, they end up with Einstein. So Einstein is a vital figure in everything that we’ve done.

And in terms of scientists working today, whose work do you find most exciting?

There are a lot of great creative physicists out there. Edward Witten from the Institute for Advanced Study has for a long time been the leader in pushing the frontiers of working unification.

So many of us revere him but it needs to be said because I’ve sometimes seen this reported in a slightly odd way, it’s not that way we revere Einstein the way some gurus of new age cults may be revered, or some religious leaders; no, we constantly are critical of everyone’s contributions, even Witten’s. We look at a given paper, we examine it from all different perspectives, we bang it around, we knock it, we try to break it, we try to see what aspects of it are pointing towards the new direction.

So we’re a highly critical bunch, a highly sceptical bunch. So when we have someone that we respect enormously, it doesn’t mean that we take in their pronouncements in some uncritical way. Not at all.

So you have standard model physics that is quite well supported and string theory is slightly more suggestive?

I would say hugely more. Again, let me just interject one thing, for you to ask me as you may: “Do I believe in string theory?” My answer is, “No, I don’t.” I don’t believe anything at all until it is experimentally proven, observationally confirmed. I do find string theory the most compelling approach to the search for a unified theory, for putting gravity and quantum mechanics together and that’s why I’ve spent time thinking about it. If you were to ask me, “Do I believe there are other universes out there?” — no, I don’t. Do I think it’s a compelling possibility that emerges from the mathematics and am I willing to take it very seriously and vigorously pursue it? Yes. But I won’t believe it until there is that observational, experimental support.

It’s an important thing to say that as a scientist you can’t believe anything without evidence. Or it’s not a question of belief.

That’s right. The better word is “confidence”. Because no matter how much experimental support a given theory may have, maybe you can confirm it on the 999th experiment, the 1000th experiment, but the 1001st might yield an anomaly! The results of that experiment might not agree with the theory and that shows that a theory that you thought to be correct wasn’t. And that’s common in physics; this is what happens.

Do you feel an emotional investment in it? What if string theory turned out to be a little cul-de-sac?

If we were able to show string theory wrong, and that is what science can do. It can’t prove something right, because again the experiments way down the line might suddenly deviate. But you can prove something wrong if you have experimental evidence that simply deviates from the predictions of a given theory, you wipe it out. If we could prove string theory wrong, I would be thrilled. And I don’t mean that in an offhanded way. My emotional investment is finding truth, making progress towards a deeper understanding of how the world works.

And if string theory is wrong, I would like to know that, I’d like to have known that yesterday. But if we can show it today or tomorrow, fantastic! We would push it to the side and that would allow us to focus our attention on approaches that have a better chance of revealing truth. So that’s where the emotional investment is. It’s not in any particular theory, it’s in contributing in whatever small way, to the journey that we’ve been on since the Ancient Greeks, and that’s what it’s about.

How do you balance your role between researching and communicating to a wider audience? Where do you see yourself more at the moment?

I definitely see myself more as a scientist who, every so often, steps outside of the research environment to bring a “report from the trenches”, if you will. My last book, The Fabric of the Cosmos, was seven years ago, in 2004, and my last television show, The Elegant Universe, was eight years ago. It has been a long time since I have stepped outside to do what I am doing now. It is virtually impossible, when you are in the last throes of writing a book and then out there discussing the book, to get any research done. For a good chunk of time, six months or so, you have to write the research off. But, when this periods ends, which will be relatively soon, I will go back and it will be a while before I come out in a significant making.

What area of research will you back to?

I work in String Theory which speaks to this possibility of other universes. The String theoretic version focuses upon the need for extra dimensions of space in String Theory, an idea that I have been working since I was a graduate student at Oxford in the 1980s. But the aspect that we are focusing upon now is: could it be there are many different universes, each with a different shape for the extra dimensions, and from that they will have each different physical features and properties. And we are trying to understand detailed phenomena like: “Can the shape of the extra dimensions change over time through quantum processes?’, that is one thing we are doing detailed calculus on. That is the arena in which my attention is scientifically focused.

I understand we need those extra dimensions to make sense of the maths. The maths of what?

The mathematics of String Theory falls apart if there are not these extra dimensions. It turns out that the maths requires that, left-right, back-forth and up-down [sic] — the three common dimensions — not be the only ones. The thing is, the maths does exactly not tell us what those extra dimensions look like. We believe they must be curled up and very small because we cannot see them, so this is a way to make this prediction compatible with our observation.

Our eyes only see the big dimensions, the ones that are accessible, but beyond those there are others that escape detection because they are so small. But the exact shape of the extra dimensions has a profound impact on things that can see like what the electron weighs, its mass, the strength of gravity, the strength of the electromagnetic force, all these features of the world that we measure in String Theory would be traced to the shape of the extra dimensions.

So a big challenge, for decades now, has been to figure out the shape of the extra dimensions and we were unable to nail that problem. We found candidate shapes, in fact a huge number of them. They are called Calabi-Yau manifolds. When I was a graduate student in Oxford, there were five known. My thesis took one of those shapes and did that mathematical analysis. The resulting physics did not agree with the observations but it was just a first test case. The problem was, when turned back to the list of shapes to look at the second, the list had grown. It was not longer five possible shapes, it was a hundred, then a thousand, then ten thousand.

Ten thousand is still potentially doable, it would keep an army of graduate students busy for a while trying to work out the consequences of these shapes, but the number of shapes continued to grow. Nowadays it has reached 10 [to the power of] 500 which is an unimaginably huge number. The number of particles in the observable universe is about 10 [to the power of] 80, this dwarfs even that. You would need far more graduate students than there are particles that make up the universe.

So what do you do? Some String theorists responded to this by saying: “I am out of here, I am going to work in something else. If you have some many shapes, each gives rise to different physics and you do not know which one is the right one so you are never going to to be able to make any definitive predictions.” Others, like me, have been saying: “Do not quit, it is early in the game, we need to develop the maths and that will hopefully give us ad equation that picks out one of those shapes as the shape. Then will study it and, if the predictions agree with what we see, great, if not, then we can discard the whole structure.”

A third group — which is what I focus on in the book — have suggested a more radical proposal. Those physicists have said: “Take seriously the failure to pick out one shape from the many, maybe that is telling there is no unique shape. Maybe the maths is really telling us that there are many universes where each of those shapes is in the limelight, where each of them gets its due.”

So the reason we have not been able to pick one out is that there is no unique special one. The only thing special about the shape in our domain is that the physics such that it allows our form of life to exist, stars, planets and galaxies, here. In those universes with different shapes, the physics is so vastly different that there are not any stars, planets or people. But that is the only thing that is special about this one: we can be here to think about these questions.

Does the idea that something happens in every possible universe have any implications on the concept of free will?

I think it does but I do not know that the philosophical ideas are that different from the ones that would emerge from Newtonian physics. Even in the Newtonian world, it is hard to see where there is free will.

When we look at the equations that have come down to us from the last few hundred years, those equations tell how they are now and how they will be in five minutes. Where does free will affect where they will be in five minutes? We do not see free will in the equations. I think that you and I are just particles governed by particular laws.

In Newtonian terms, it is very clear, there is no free will. The quantum mechanics comes along and people think that maybe that is where there is free will because, now, there is a fuzziness, there are many possible outcomes. Maybe free will enters there, but it does not, because, in the Quantum equation, there is still absolute determinism of what will happen in a probabilistic sense: the equations say, with absolute certainty, there is a 30 per cent of this, a 20 per cent chance of that, 50 per cent chance of that . . . Nowhere does free will come in into those equations either.

The only place where free will may still have a last fighting chance to emerge, is in something which we do not yet understand: how, in Quantum physics, do we go from this many possible outcomes to the one definite outcome that we observe. In that so-called Quantum measurement problem, which is still a puzzle, you could imagine that, maybe, free will emerge. I doubt it, but the standard free-willer could say that is where it will happen. In the many worlds approach to this world which I describe in this book, certainly there is no free will happening, as I can see it.

Every individual, when faced with five different choices, if each are allowed by the laws of physics, in quantum physics, each of those outcomes would happen. The individual would make all five choices, one per universe. And it would not be that the individual has had the choice to make one choice more real than the other, all of the choices would be as real as the others, they would take place in the different universes. There would not be any volitional choice involved in what happens.

Could you not at least say that I, in this universe, am tacking my own way through?

Not really, because you are following one trajectory of choices. It is not as though there was a place in the mathematics where your free will dictated that particular set of choices. You are knocked around by the laws of physics just like all your copies in the other universes.

Is there a moment you can pinpoint from which you were interested in this kind of subjects?

When I was really young — I was five — my dad taught the basic operations multiplications, which I found really exciting because it meant that you could do calculations that no one had ever really done before. They had not been done before because they were not interesting to do but, to me, to create a new sequence of numbers on a page from multiplying — my dad would set 30-digit-by-30-digit multiplication tables and I would buy huge pieces of construction paper, tape them together and spend the weekend doing these calculations — to me, it was so exciting to have an answer that no one had looked at before.

That is where my interest in maths took off. When I learned, later on, that math was not just a game — I remember, at some point soon after, when I learned multiplications, my dad asked me to calculate the number of inches between here and the Andromeda galaxy. That is a very straightforward calculation because people know how far away it is in light years. You just need to convert light years into miles, miles into feet and feet into inches, so it is just a sequence of multiplications. But, to get that number at the and look at it, I was like: “Wow, that is relevant to what is out there.” It hooked me for good, when that link to the real world was made.

Was your father interested in maths?

He was definitely interested. He dropped out of high school to be a musician. He was a singer, performer, composer, vocal coach. He liked to say that he had an “SPHD”: Seward Park High School Dropout, which is where he dropped out. But he was self-taught and because of that, his interest came from a very self-motivated place. He was constantly telling me about atoms and the universe and, in retrospect, some of that stuff was right, some was not, but it did not matter. It got me interested in the wider universe.

What was your experience of learning maths and physics at school?

I had some pretty good teachers: not all of them, but I can pinpoint a couple that recognised I had some ability and would give me work to do outside of the class: go home and work my way through various texts that they gave me to allow me to keep this enthusiasm and interest going. They were vital to me. When I was in seventh grade, I went to a public [as in state] school; I did not go to a specialised private school and I had exhausted what that public school could offer.

The teacher said: “Why don’t you go to Columbia University?” He wrote me a little note. I was this tall; my sister was three heads taller and she went with me. We just knocked on doors randomly and we would hand them this note. The note basically said: “Take this kid on, he is hungry to learn.” And most people we gave this to would say, “Oh, that’s nice,” and give it back.

They were busy, obviously, but one guy in the maths department — he was a graduate student — said, “Sure, come.” All summer, I met him every day and then I carried on during the academic year subsequently once a week. For no money — we did not have any money — but he just did this for the love of learning, the love of teaching. He took me to mathematical places that I would not have visited for five to ten years if I had just followed the traditional education. So it was a wonderful thing for me.

That’s wonderful because, without it, presumably, you might have just run into a dead end.

And joined some gang and just been a street thug. It is possible.

You present nine versions of the multiverse. Is there one that intuitively seems to you more attractive than the others? Is intuition a useful concept or should you struggle against it?

I think one of the big lessons of modern physics and certainly the idea of this book is that perception of the everyday world can be a very misleading guide the true nature of what is out there. And there is a way in which that is startling, because we all think we know the world!

On the other hand, if you think about it, when we were back there in the Savannah, trying to get our next meal, understanding the true nature of reality would not really have helped us. Would it have helped to know electrons can sort of be at two places at once in a quantum world? Would it have helped us to know about the nature of time near a black hole? No! We just needed where that antelope was going to be in five seconds so we can capture it and eat it.

Having said that, we need to inform ourselves by mathematics and observation and experimentation. That goes beyond our senses and that is what we are doing . . . So the yardstick that I would use is not really intuition but which of these proposals has the best chance of being tested in the shortest timescale. And, for that, I would place my focus on the brane multiverse — the idea that comes from string theory that we may be living in a giant, three-dimensional membrane.

The easier way of thinking about it is to suppress one dimension and thinking about it to make it more intuitive and imagining our universes taking place in a big slice of bread. The idea according to string theory is that there could be other slices of bread, other universes out there, maybe even nearby, all part of the big cosmic loaf. But we are not aware of these other slices of bread because it turns out that light cannot travel between them, so we a re blind to their existence.

However this is a testable idea — at least in principle — at the Large Hadron Collider, the big accelerator in Geneva, because when protons slam against each other at high speed, the maths shows that debris can be created that would be ejected off of our universe, off of our brane, off of our slice of bread. If that happened, how would we know? The debris would take some energy with it which means our detectors, which are on our slice of bread, would miss that energy and measure less energy than before. A missing energy signature that physicists are now looking for.

Presumably, the big problem with that is that something else could have taken the energy away.

That is the challenge and that is why the experiments get paid the big bucks. They have to be able to close all those loopholes.

The Higgs boson has been described as a “God particle” that would suddenly make everything clear. Is that not a bit simplistic?

No, I think it is a vital and important idea. It is not directly a force-carrying particle — that is not its claim to fame. The “God particle” concept comes from Nobel laureate Leon Lederman. I do not like that language; it is unnecessary to inject that perspective. That is my view on it.

The Higgs boson would be the smallest chunk of what we call the Higgs field. If these ideas are right, the Higgs field would be like an ocean that fills all of space, an invisible ocean. Right now, this room is filled with the electromagnetic field. The reason why I can turn on my cell phone, get my messages or log on to the internet is because these fields are here.

The idea of a field-filling space, much like steam fills a sauna, is not an exotic idea. It is true. The exotic idea for the Higgs field is that it is a new field that we have not yet seen. What would it do? If it is correct, if this field is filling space, the idea is that as matter tries to move through space, the Higgs field exerts a friction-like drag on particles, so as I am pushing an object, I feel it resisting my attempt to speed it up.

Normally, we say that is the mass of the object — the bigger it is, the harder it is to push it. But where does the mass come from? According to Higgs, it comes from this object, its particles, being dragged back by this molasses-like Higgs field, within which we are all immersed. So the Higgs field is meant to be the fundamental explanation for why particles have the mass that they do. And that is a drawl in the standard model of particle physics.

Has this research led you to reject the idea of “God”?

My view is that science only has something to say about a very particular notion of God, which goes by the name of “God of the gaps”: if you are trying to understand the world around you and science has not yet given an explanation for some phenomenon, you could step back and say, “Oh, that is God.” Then, when science does explain that phenomena — as it eventually does — God gets squeezed out because he is no longer needed to explain that phenomena.

But that is a very particular and simplistic notion of God. No matter what physics does, you can always say there is God behind it: God set up the rules the physics, God set the environment within which those rules play themselves out. Do I feel that we need that? No. Do I subscribe to it? I do not. But does physics rule that picture out? No it doesn’t.

I think the appropriate response for a physicist to is to say: “I do not find the concept of God very interesting because I cannot test it — I cannot rule it out in the traditional ways.” And what excites me and makes me want to go to my office is to work on things that I can test. For me, God is not that interesting but I do not think God is ruled out. That is a statement that’s unjustifiable.