Some advice: keep the flame of curiosity and wonderment alive, even when studying for boring exams. That is the well from which we scientists draw our nourishment and energy. And also, learn the math. Math is the language of nature, so we have to learn this language.

If all our common-sense notions about the universe were correct, then science would have solved the secrets of the universe thousands of years ago. The purpose of science is to peel back the layer of the appearance of the objects to reveal their underlying nature. In fact, if appearance and essence were the same thing, there would be no need for science.

The best theory comes from string theory, which states that dark matter is nothing but a higher vibration of the string. We are, in some sense, the lowest octave of a vibrating string.

I vowed to myself that when I grew up and became a theoretical physicist, in addition to doing research, I would write books that I would have liked to have read as a child. So whenever I write, I imagine myself, as a youth, reading my books, being thrilled by the incredible advances being made in physics and science.

It would take a civilization far more advanced than ours, unbelievably advanced, to begin to manipulate negative energy to create gateways to the past. But if you could obtain large quantities of negative energy-and that's a big "IF" - then you could create a time machine that apparently obeys Einstein's equation and perhaps the laws of quantum theory.

It's pointless to have a nice clean desk, because it means you're not doing anything.

Once confined to fantasy and science fiction, time travel is now simply an engineering problem.