STEPHEN HAWKING is one of the world's greatest physicists, famous for his work on black holes. His condition means that he can now only communicate by twitching his cheek (see "The man who saves Stephen Hawking's voice").

What has been the most exciting development in physics during the course of your career?
COBE's discovery of tiny variations in the temperature of the cosmic microwave background and the subsequent confirmation by WMAP that these are in excellent agreement with the predictions of inflation. The Planck satellite may detect the imprint of the gravitational waves predicted by inflation. This would be quantum gravity written across the sky.

Einstein referred to the cosmological constant as his "biggest blunder". What was yours?
I used to think that information was destroyed in black holes. But the AdS/CFT correspondence led me to change my mind. This was my biggest blunder, or at least my biggest blunder in science.

What discovery would do most to revolutionise our understanding of the universe?
The discovery of supersymmetric partners for the known fundamental particles, perhaps at the Large Hadron Collider. This would be strong evidence in favour of M-theory

If you were a young physicist just starting out today, what would you study?
I would have a new idea that would open up a new field.

What do you think most about during the day?
Women. They are a complete mystery.

To mark Hawking's birthday, the Centre for Theoretical Cosmology, University of Cambridge, is hosting a symposium entitled "The State of the Universe" on 8 January (watch live at ctc.cam.ac.uk/hawking70/multimedia.html). An exhibition of his life and work opens at the Science Museum, London, on 20 January