If God doesn't exist, why did the concept of his existence become almost universal? Basanta Borah, BASEL, SWITZERLAND
I don't claim that God doesn't exist. God is the name people give to the reason we are here. But I think that reason is the laws of physics rather than someone with whom one can have a personal relationship. An impersonal God.
Does the universe end? If so, what is beyond it? Paul Pearson, HULL, ENGLAND
Observations indicate that the universe is expanding at an ever increasing rate. It will expand forever, getting emptier and darker. Although the universe doesn't have an end, it had a beginning in the Big Bang. One might ask what is before that, but the answer is that there is nowhere before the Big Bang, just as there is nowhere south of the South Pole.
Do you think our civilization will survive long enough to make the leap to deeper space? Harvey Bethea, STONE MOUNTAIN, GA.
I think we have a good chance of surviving long enough to colonize the solar system. However, there is nowhere else in the solar system as suitable as the Earth, so it is not clear if we would survive if the Earth was made unfit for habitation. To ensure our long-term survival, we need to reach the stars. That will take much longer. Let's hope we can last until then.
If you could talk to Albert Einstein, what would you say? Ju Huang, STAMFORD, CONN.
I would ask him why he didn't believe in black holes. The field equations of his theory of relativity imply that a large star or cloud of gas would collapse in on itself and form a black hole. Einstein was aware of this but somehow managed to convince himself that something like an explosion would always occur to throw off mass and prevent the formation of a black hole. What if there was no explosion?
Which scientific discovery or advance would you like to see in your lifetime? Luca Zanzi, ALLSTON, MASS.
I would like nuclear fusion to become a practical power source. It would provide an inexhaustible supply of energy, without pollution or global warming.
What do you believe happens to our consciousness after death? Elliot Giberson, SEATTLE
I think the brain is essentially a computer and consciousness is like a computer program. It will cease to run when the computer is turned off. Theoretically, it could be re-created on a neural network, but that would be very difficult, as it would require all one's memories.
Given your reputation as a brilliant physicist, what ordinary interests do you have that might surprise people? Carol Gilmore, JEFFERSON CITY, MO.
I enjoy all forms of music--pop, classical and opera. I also share an interest in Formula One racing with my son Tim.
Do you feel that your physical limitations have helped or hindered your study? Marianne Vikkula, ESPOO, FINLAND
Although I was unfortunate enough to get motor neuron disease, I have been very fortunate in almost everything else. I was lucky to be working in theoretical physics, one of the few areas in which disability was not a serious handicap, and to hit the jackpot with my popular books.
Does it feel like a huge responsibility to have people expecting you to have all the answers to life's mysteries? Susan Leslie, BOSTON
I certainly don't have the answers to all life's problems. While physics and mathematics may tell us how the universe began, they are not much use in predicting human behavior because there are far too many equations to solve. I'm no better than anyone else at understanding what makes people tick, particularly women.
Do you think there will ever come a time when mankind understands all there is to understand about physics? Karsten Kurze, BAD HONNEF, GERMANY
I hope not. I would be out of a job.