It is all right to make mistakes; nothing is perfect because with perfection, we would not exist.

Someone told me that each equation I included in the book would halve the sales.

Life on Earth is at the ever-increasing risk of being wiped out by a disaster, such as sudden global warming, nuclear war, a genetically engineered virus or other dangers. I think the human race has no future if it doesn't go into space. I therefore want to encourage public interest in space.

It often happens that I have an idea, but then I try to fill in the intermediate steps and find they don't work, so I have to give it up.

When I get to heaven I'm gonna find the guy in charge of the weather and kick his rear.

Time travel was once considered scientific heresy, and I used to avoid talking about it for fear of being labelled a 'crank.'

Think of our DNA. In the last million years, our DNA hasn't changed at all. It's really much the same as it was in the jungle, a million, two millions years ago. But in the last 200 years, our destructive capacities have increased many, many millions of times over. Why don't we see intelligent signals from outer space? Because in all likelihood, once the civilization reaches the point our civilization has reached, it destroys itself.