At the age of 21, the British physicist Stephen Hawking was found to have amyotrophic lateral sclerosis, Lou Gehrig's disease. While A.L.S. is usually fatal within five years, Dr. Hawking lived on and flourished, producing some of the most important cosmological research of his time.
In the 1960s, with Sir Roger Penrose, he used mathematics to explicate the properties of black holes. In 1973, he applied Einstein's general theory of relativity to the principles of quantum mechanics. And he showed that black holes were not completely black but could leak radiation and eventually explode and disappear, a finding that is still reverberating through physics and cosmology.
Dr. Hawking, in 1988, tried to explain what he knew about the boundaries of the universe to the lay public in "A Brief History of Time: From Big Bang to Black Holes." The book sold more than 10 million copies and was on best-seller lists for more than two years.
Today, at 69, Dr. Hawking is one of the longest-living survivors of A.L.S., and perhaps the most inspirational. Mostly paralyzed, he can speak only through a computerized voice simulator.
On a screen attached to his wheelchair, commonly used words flash past him. With a cheek muscle, he signals an electronic sensor in his eyeglasses to transmit instructions to the computer. In this way he slowly builds sentences; the computer transforms them into the metallic, otherworldly voice familiar to Dr. Hawking's legion of fans.
It's an exhausting and time-consuming process. Yet this is how he stays connected to the world, directing research at the Center for Theoretical Cosmology at the University of Cambridge, writing prolifically for specialists and generalists alike and lecturing to rapt audiences from France to Fiji.
Dr. Hawking came here last month at the invitation of a friend, the cosmologist Lawrence Krauss, for a science festival sponsored by the Origins Project of Arizona State University. His lecture, "My Brief History," was not all quarks and black holes. At one point, he spoke of the special joys of scientific discovery.
"I wouldn't compare it to sex," he said in his computerized voice, "but it lasts longer." The audience roared.
The next afternoon, Dr. Hawking sat with me for a rare interview. Well, a kind of interview, actually.
Ten questions were sent to his daughter, Lucy Hawking, 40, a week before the meeting. So as not to exhaust her father, who has grown weaker since a near-fatal illness two years ago, Ms. Hawking read them to him over a period of days.
During our meeting, the physicist played back his answers. Only one exchange, the last, was spontaneous. Yet despite the limitations, it was Dr. Hawking who wanted to do the interview in person rather than by e-mail.
Some background on the second query, the one about extraterrestrials. For the past year, Lucy Hawking was writer in residence at the Origins Project at Arizona State University. As part of her work, she and Paul Davies, a physicist at Arizona State, started a contest, "Dear Aliens," inviting Phoenix schoolchildren to write essays about what they might say to space beings trying to contact Planet Earth.
Q. Dr. Hawking, thank you so much for taking time to talk to Science Times. I'm wondering, what is a typical day like for you?
A. I get up early every morning and go to my office where I work with my colleagues and students at Cambridge University. Using e-mail, I can communicate with scientists all over the world.
Obviously, because of my disability, I need assistance. But I have always tried to overcome the limitations of my condition and lead as full a life as possible. I have traveled the world, from the Antarctic to zero gravity. (Pause.) Perhaps one day I will go into space.
Q. Speaking of space: Earlier this week, your daughter, Lucy, and Paul Davies, the Arizona State University physicist, sent a message into space from an Arizona schoolchild to potential extraterrestrials out there in the universe. Now, you've said elsewhere that you think it's a bad idea for humans to make contact with other forms of life. Given this, did you suggest to Lucy that she not do it? Hypothetically, let's say as a fantasy, if you were to send such a message into space, how would it read?
A. Previously I have said it would be a bad idea to contact aliens because they might be so greatly advanced compared to us, that our civilization might not survive the experience. The "Dear Aliens" competition is based on a different premise.
It assumes that an intelligent extraterrestrial life form has already made contact with us and we need to formulate a reply. The competition asks school-age students to think creatively and scientifically in order to find a way to explain human life on this planet to some inquisitive aliens. I have no doubt that if we are ever contacted by such beings, we would want to respond.
I also think it is an interesting question to pose to young people as it requires them to think about the human race and our planet as a whole. It asks students to define who we are and what we have done.
Q. I don't mean to ask this disrespectfully, but there are some experts on A.L.S. who insist that you can't possibly suffer from the condition. They say you've done far too well, in their opinion. How do you respond to this kind of speculation?
A. Maybe I don't have the most common kind of motor neuron disease, which usually kills in two or three years. It has certainly helped that I have had a job and that I have been looked after so well.
I don't have much positive to say about motor neuron disease. But it taught me not to pity myself, because others were worse off and to get on with what I still could do. I'm happier now than before I developed the condition. I am lucky to be working in theoretical physics, one of the few areas in which disability is not a serious handicap.
Q. Given all you've experienced, what words would you offer someone who has been diagnosed with a serious illness, perhaps A.L.S.?
A. My advice to other disabled people would be, concentrate on things your disability doesn't prevent you doing well, and don't regret the things it interferes with. Don't be disabled in spirit, as well as physically.
Q. About the Large Hadron Collider, the supercollider in Switzerland, there were such high hopes for it when it was opened. Are you disappointed in it?
A. It is too early to know what the L.H.C. will reveal. It will be two years before it reaches full power. When it does, it will work at energies five times greater than previous particle accelerators.
We can guess at what this will reveal, but our experience has been that when we open up a new range of observations, we often find what we had not expected. That is when physics becomes really exciting, because we are learning something new about the universe.
Q. I'm wondering about your book "A Brief History of Time." Were you surprised by the enormous success of it? Do you believe that most of your readers understood it? Or is it enough that they were interested and wanted to? Or, in another way: what are the implications of your popular books for science education?
A. I had not expected "A Brief History of Time" to be a best seller. It was my first popular book and aroused a great deal of interest.
Initially, many people found it difficult to understand. I therefore decided to try to write a new version that would be easier to follow. I took the opportunity to add material on new developments since the first book, and I left out some things of a more technical nature. This resulted in a follow-up entitled "A Briefer History of Time," which is slightly briefer, but its main claim would be to make it more accessible.
Q. Though you avoid stating your own political beliefs too openly, you entered into the health care debate here in the United States last year. Why did you do that?
A. I entered the health care debate in response to a statement in the United States press in summer 2009 which claimed the National Health Service in Great Britain would have killed me off, were I a British citizen. I felt compelled to make a statement to explain the error.
I am British, I live in Cambridge, England, and the National Health Service has taken great care of me for over 40 years. I have received excellent medical attention in Britain, and I felt it was important to set the record straight. I believe in universal health care. And I am not afraid to say so.
Q. Here on Earth, the last few months have just been devastating. What were your feelings as you read of earthquakes, revolutions, counter-revolutions and nuclear meltdowns in Japan? Have you been as personally shaken up as the rest of us?
A. I have visited Japan several times and have always been shown wonderful hospitality. I am deeply saddened for my Japanese colleagues and friends, who have suffered such a catastrophic event. I hope there will be a global effort to help Japan recover. We, as a species, have survived many natural disasters and difficult situations, and I know that the human spirit is capable of enduring terrible hardships.
Q. If it is possible to time-travel, as some physicists claim, at least theoretically, is possible, what is the single moment in your life you would like to return to? This is another way of asking, what has been the most joyful moment you've known?
A. I would go back to 1967, and the birth of my first child, Robert. My three children have brought me great joy.
Q. Scientists at Fermilab recently announced something that one of our reporters described as "a suspicious bump in their data that could be evidence of a new elementary particle or even, some say, a new force of nature." What did you think when you heard about it?
A. It is too early to be sure. If it helps us to understand the universe, that will surely be a good thing. But first, the result needs to be confirmed by other particle accelerators.
Q. I don't want to tire you out, especially if doing answers is so difficult. But I'm wondering: The speech you gave the other night here in Tempe, "My Brief History," was very personal. Were you trying to make a statement on the record so that people would know who you are?
A. (After five minutes.) I hope my experience will help other people.