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.

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.

Every American deserves to live in freedom, to have his or her privacy respected and a chance to go as far as their ability and effort will take them - regardless of race, gender, ethnicity or economic circumstances.

Never underestimate a child's ability to get into more trouble.

We have developed this unbelievable ability to deny. We have to. If we didn't, we'd go crazy.

To know how to hide one's ability is great skill.

It is the ability to take a joke, not make one, that proves you have a sense of humor.

The ability to deal with people is as purchasable a commodity as sugar or coffee and I will pay more for that ability than for any other under the sun.

Handcuffing the ability of states and localities to develop clean fuels in the cheapest possible way, using local resources, is not sound or sensible policy.

I realised from a very early age that God gave me a gift, and that gift was to run, and I wanted to use it to the best of my ability.

My vocal ability is very limited, but I'm fortunate in that I can write the songs around my vocal limitations.

The key to Operations at Wal-Mart is their ability to maintain the highest standards while at the same time getting things done with lockstep execution.

The test of a first-rate intelligence is the ability to hold two opposed ideas in mind at the same time and still retain the ability to function.

The Stones are a different kind of group. I realized that when I joined them. It's not really so much their musical ability, it's just they have a certain kind of style and attitude which is unique.

I liked his ability to deal with a lot of the negativity that surrounded him. Even though he was in a world that he didn't want to be in, he still saw the bigger picture.

We have the most flexible and adaptive economy. Making sure we sustain the ability of the American economy to perform well is really the priority of economic policy.

The system that enables the most people to earn the most success is free enterprise, by matching up people's skills, interests, and abilities. In contrast, redistribution simply spreads money around. Even worse, it attenuates the ability to earn success by perverting economic incentives.

Excellence is the unlimited ability to improve the quality of what you have to offer.

War should be the only study of a prince. He should consider peace only as a breathing-time, which gives him leisure to contrive, and furnishes as ability to execute, military plans.

Get that right, then- if you get the quality right, then the marketability or whatever; your ability to sell videos or your ability to earn money or whatever, will follow naturally. But try to be creatively lead rather than market lead. And that's important to me.

You have to open your mind. I like the ability to express myself in a deep way. It's the closest music to our humanity - it's like a folk music that rises up out of a culture.