There could be whole antiworlds and antipeople made out of antiparticles. However, if you ever meet your antiself, don't shake hands! You would both vanish in a great flash of light.

It is tribute to how far we have come in theoretical physics that it now takes enormous machines and a great deal of money to perform experiments whose results we can not predict.

We think we have solved the mystery of creation. Maybe we should patent the universe and charge everyone royalties for their existence.

The real challenge is to work out what aliens might actually be like.

Computer viruses are alive.

I put a lot of effort into writing 'A Briefer History' at a time when I was critically ill with pneumonia because I think that it's important for scientists to explain their work, particularly in cosmology. This now answers many questions once asked of religion.

Speech has allowed the communication of ideas, enabling human beings to work together to build the impossible. Mankind's greatest achievements have come about by talking, and its greatest failures by not talking. It doesn't have to be like this. Our greatest hopes could become reality in the future. With the technology at our disposal, the possibilities are unbounded. All we need to do is make sure we keep talking.