Leonard Susskind

At some point we have to give up and say that's just the way it is. Or, not give up and push on.

There is a philosophy that says that if something is unobservable -- unobservable in principle -- it is not part of science. If there is no way to falsify or confirm a hypothesis, it belongs to the realm of metaphysical speculation, together with astrology and spiritualism. By that standard, most of the universe has no scientific reality -- it's just a figment of our imaginations.

I did not come from an academic background. My father was a smart man, but he had a fifth-grade education. He and all his friends were plumbers. They were all born around 1905 in great poverty in New York City and had to go to work when they were 12 or 13 years old.

I'm afraid I am a bit of a technophobe - a nineteenth-century man caught in the twenty-first century. But there is one piece of technology that I would especially welcome: a device to automatically balance restaurant tables on all four legs so that they don't rock back and forth.

I have a funny mental framework when I do physics. I create an imaginary audience in my head to explain things to - it is part of the way I think. For me, teaching and explaining, even to my imaginary audience, is part of the process.

You are a victim of your own neural architecture which doesn't permit you to imagine anything outside of three dimensions. Even two dimensions. People know they can't visualise four or five dimensions, but they think they can close their eyes and see two dimensions. But they can't.

I'm not going to argue with people about the existence of God. I have not the vaguest idea of whether the universe was created by an intelligence.

Life is fragile: it thrives only in a narrow range of temperatures between freezing and boiling. How lucky that our planet is just the right distance from the sun: a little farther, and the death of the perpetual Antarctic winter - or worse - would prevail; a little closer, and the surface would truly fry anything that touched it.

Unforeseen surprises are the rule in science, not the exception. Remember: Stuff happens.

Space can vibrate, space can fluctuate, space can be quantum mechanical, but what the devil is it? And, you know, everybody has their own idea about what it is, but there's no coherent final consensus on why there is space.

Why is there space rather than no space? Why is space three-dimensional? Why is space big? We have a lot of room to move around in. How come it's not tiny? We have no consensus about these things. We're still exploring them.

Extra dimensional theories are sometimes considered science fiction with equations. I think that's a wrong attitude. I think extra dimensions are with us, they are with us to stay, and they entered physics a long time ago. They are not going to go away.