The increase of disorder or entropy with time is one example of what is called an arrow of time, something that distinguishes the past from the future, giving a direction to time.

Mankind's greatest achievements have come about by talking and its greatest failures by not talking. It doesn’t have to be like this.

If the total energy of the universe must always remain zero, and it costs energy to create a body, how can a whole universe be created from nothing?

I have to speak through a computer... in my mind, I am free. Free to explore the universe and ask the big questions...

Real science can be far stranger than science fiction and much more satisfying.

For millions of years, mankind lived just like the animals. Then something happened which unleashed the power of our imagination. We learned to talk and we learned to listen.

My first popular book, 'A Brief History of Time,' aroused a great deal of interest, but many found it difficult to understand.