When was your first in-person encounter with Hawking?
The first time I met Stephen personally, he was visiting Harvard while I was a postdoc there. Other students and postdocs tended not to talk to him because it was very hard. For one, he was a legend, a monumental figure. Someone once described their legs going queasy in his presence, and I know the effect. Your breath seizes up. But also, because he had to communicate through a speech synthesizer, the regular ebb and flow of conversation—the long sentences and interruptions and fast-paced exchange of ideas—was not there. You had to really think about what you wanted to say to get the most out of the conversation, and then wait for him to compose his response, letter by letter, with small motions of a finger.
Once you got to know him well, a thing you dared to do was go stand behind him and read his screen and try to anticipate what he was going to say. That would save him from typing the rest of the sentence. Our conversations, which would be about all manner of things, were very interesting and fun. He had an excellent sense of humor.
What are some moments you and Hawking shared that stand out in your mind?
One thing about Hawking that really stands out to me is the sheer dedication he showed to his work every day. One of the times I visited him in Cambridge, he had a severe cold and yet he still showed up to work. And, if you went to look at his screen, you would see that he always had papers from the physics paper archive on there. He wasn’t shopping for shoes or reading the news; he was reading these papers.
And that didn’t mean he wasn't well informed about the world. When I introduced him to my wife, Heather Sharkey, also a Penn professor and a historian of the Middle East, they ended up having a 45-minute conversation about colonialism and the Sudan. He was a feisty conversationalist and had strong opinions about everything. I didn’t always agree with some of the ways he wanted to solve physics problems, but he was always completely focused in conversation and talking with him was an extremely intense experience—an intellectual workout!
How would you describe Hawking’s impact on the field of physics?
His impact on the field was transformative. He developed many famous theories, one of the most influential being his identification that black holes act as thermodynamic objects. This means that, though they’re supposed to eat stuff up, they actually glow as though they’re hot because of the effects of quantum mechanics. And, if you leave a black hole alone, this glow causes it to slowly radiate energy and eventually evaporate away. You can think of it as a lump of coal that is slowly burning down to nothing. This leads to the potential paradox that the information about what made the black hole gets destroyed in this thermal glow.
This paradox poses a challenge to the foundations of modern physics. The two pillars of physics in the 20th century are general relativity and quantum mechanics. Hawking showed that when you put these together, at least in the obvious way, you have a contradiction. It is such an important mystery that, since then, generations of physicists have used this paradox as the central problem that they seek to solve. And to do this, they have built all kinds of auxiliary tools. So there’s an enormous part of the edifice of modern theoretical physics that has been aimed at answering why black holes do not destroy information and other theories posited by Hawking.
And how would you describe Hawking’s influence on the general public and their conception of science?
Hawking was, in some sense, the romantic ideal of a scientist from the point of view of the general public. Here was a man who was disabled in the physical world and yet was able to sit there in his wheelchair dreaming up deep truths about the universe. I think that’s what people imagine the intellectual life to be.
In a sense, it’s a dramatization of what I think of in general as the human condition: we are really constrained by our physicality. We have to eat, find shelter, all these ties that bind, and our ability to construct theories of the universe is limited by our mortality. But I think people would like to believe that their inner lives and ability to seek truth is transcendent. Hawking inspired that feeling.
If people could take away one or two things from Hawking's life, what would you hope that would be?
His courage and determination. Not only in his personal life, but in his scientific life, too. He dared to ask questions that other people didn’t or thought they couldn’t answer. And he was determined to keep pushing until he solved them. Those are the two most important traits for a scientist, and they are very important traits in life as well.
