As for the forces, electromagnetism and gravity we experience in everyday life. But the weak and strong forces are beyond our ordinary experience. So in physics, lots of the basic building blocks take 20th- or perhaps 21st-century equipment to explore.

I wouldn't have thought that a wrong theory should lead us to understand better the ordinary quantum field theories or to have new insights about the quantum states of black holes.

String theory is an attempt at a deeper description of nature by thinking of an elementary particle not as a little point but as a little loop of vibrating string.

There was a long history of speculation that in quantum gravity, unlike Einstein's classical theory, it might be possible for the topology of spacetime to change.

In Einstein's general relativity the structure of space can change but not its topology. Topology is the property of something that doesn't change when you bend it or stretch it as long as you don't break anything.

Having those extra dimensions and therefore many ways the string can vibrate in many different directions turns out to be the key to being able to describe all the particles that we see.

As far as extra dimensions are concerned, very tiny extra dimensions wouldn't be perceived in everyday life, just as atoms aren't: we see many atoms together but we don't see atoms individually.

You have that one basic string, but it can vibrate in many ways. But we're trying to get a lot of particles because experimental physicists have discovered a lot of particles.

Spreading out the particle into a string is a step in the direction of making everything we're familiar with fuzzy. You enter a completely new world where things aren't at all what you're used to.

Even before string theory, especially as physics developed in the 20th century, it turned out that the equations that really work in describing nature with the most generality and the greatest simplicity are very elegant and subtle.

Technically you need the extra dimensions. At first people didn't like them too much, but they've got a big benefit, which is that the ability of string theory to describe all the elementary particles and their forces along with gravity depends on using the extra dimensions.

Quantum mechanics brought an unexpected fuzziness into physics because of quantum uncertainty, the Heisenberg uncertainty principle.

On the other hand, we don't understand the theory too completely, and because of this fuzziness of spacetime, the very concept of spacetime and spacetime dimensions isn't precisely defined.

As of now, string theorists have no explanation of why there are three large dimensions as well as time, and the other dimensions are microscopic. Proposals about that have been all over the map.

It's indeed surprising that replacing the elementary particle with a string leads to such a big change in things. I'm tempted to say that it has to do with the fuzziness it introduces.

One of the basic things about a string is that it can vibrate in many different shapes or forms, which gives music its beauty.

But the beauty of Einstein's equations, for example, is just as real to anyone who's experienced it as the beauty of music. We've learned in the 20th century that the equations that work have inner harmony.

If I take the theory as we have it now, literally, I would conclude that extra dimensions really exist. They're part of nature. We don't really know how big they are yet, but we hope to explore that in various ways.

As for the forces, electromagnetism and gravity we experience in everyday life. But the weak and strong forces are beyond our ordinary experience. So in physics, lots of the basic building blocks take 20th- or perhaps 21st-century equipment to explore.

The theory has to be interpreted that extra dimensions beyond the ordinary four dimensions the three spatial dimensions plus time are sufficiently small that they haven't been observed yet.

So when you ask me how string theory might be tested, I can tell you what's likely to happen at accelerators or some parts of the theory that are likely to be tested.

I don't care about movies. I tend to play badminton once a week.

I have a tendency, more than most other physicists, to try to figure out everything all at once, before I publish. And even to try to figure out everything in my head, without pencil and paper.

I just think too many nice things have happened in string theory for it to be all wrong. Humans do not understand it very well, but I just don't believe there is a big cosmic conspiracy that created this incredible thing that has nothing to do with the real world.

I'm actually, for the most part, a complete agnostic politically.

If you are a researcher, you are trying to figure out what the question is as well as what the answer is.

One very important aspect of string theory is definitely testable. That was the prediction of supersymmetry, which emerged from string theory in the early '70s.

Quantum mechanics brought an unexpected fuzziness into physics because of quantum uncertainty, the Heisenberg uncertainty principle. String theory does so again because a point particle is replaced by a string, which is more spread out.

Regardless of any deviations, it was clear I was supposed to end up in math and physics.

We know a lot of things, but what we don't know is a lot more.

We must support initiatives that provide clear, concrete measures and milestones that our troops need for defeating the insurgency, building up Iraqi security forces, and handing over Iraq to the Iraqi people.

In other words, I have no truck for anyone who goes out and does an eclectic building.

We believe that peace is not just signed papers, but rather a contract between generations for the building of a more promising and less threatening future.

Belief in oneself is one of the most important bricks in building any successful venture.

Living at risk is jumping off the cliff and building your wings on the way down.

When I say artist I mean the man who is building things - creating molding the earth - whether it be the plains of the west - or the iron ore of Penn. It's all a big game of construction - some with a brush - some with a shovel - some choose a pen.

Nature is my manifestation of God. I go to nature every day for inspiration in the day's work. I follow in building the principles which nature has used in its domain.

So I rang up a local building firm, I said 'I want a skip outside my house.' He said 'I'm not stopping you.'

We have a group of friends of the museum who try to raise, if they can, periodically something to help us. Of course, the main thing about a building like this is its upkeep. It needs central heating and it needs central air conditioning.

Rather, it is through conciliation and compromise that we are building a fair Iraq, a just state for all its peoples.

For the next century, the Republicans have agreed that we will promote the dignity and future of every individual by building a free society under a limited, accountable government that protects liberty, security and prosperity for a brighter American dream.

I smuggled the camera, it was no problem to smuggle the camera there. And I took 60 photos, two films, during the time when there was no one in the control room, in the building.

Well, by the end of the millennium, five, six months from now, we hope to somehow manage to move into a new location where we have the whole building, so we can devote space to all our activities.

The anger that appears to be building up between the sexes becomes more virulent with every day that passes. And far from women taking the blame... the fact is that men are invariably portrayed as the bad guys. Being a good man is like being a good Nazi.

Building one space station for everyone was and is insane: we should have built a dozen.

There are some who are scared by unity and by building a country on the basis of ideas.

I don't think so, in that Virgin is already a global brand. Brands like Amazon have had to spend hundreds of millions of pounds you know, building their brands, whereas Virgin is already well-known around the world.

Man is a fire-stealing animal, and we can't help building machines and machine intelligences, even if, from time to time, we use them not only to outsmart ourselves but to bring us right up to the doorstep of Doom.

For the first time in history all the major countries in the world are pushing together to reach this goal... building something in space that is really for all humankind.