TERRY GROSS, HOST:

This is FRESH AIR. I'm Terry Gross. When my guest - when my guest Kitty Ferguson - I'm sorry. When Stephen Hawking was diagnosed with ALS, Lou Gehrig's Disease, at the age of 21, doctors expected he only had a few years left, but he went on to become one of the world's most famous cosmologists and physicists.

His book "A Brief History of Time" sold more than eight million copies. In 1980, at the age of 38, when he became the Lucasian Professor of Mathematics at Cambridge University in England, he could no longer walk, write, feed himself or raise his head. He said that although he can't move and has to speak through a computer, his mind is free.

This month, Hawking celebrates his 70th birthday. My guest Kitty Ferguson has written a biography of Hawking that describes his contributions to science, as well as the impact his illness has had on his life. It's called "Stephen Hawking: An Unfettered Mind." Her first book about him, written with his cooperation, was published in 1991. She's also worked with Hawking on his book "The Universe in a Nutshell."

Kitty Ferguson, welcome to FRESH AIR. Many of us who know that Stephen Hawking is really famous don't really understand what his contributions to science have been. So let me start by asking: What is he best known for in physics or in astrophysics?

KITTY FERGUSON: Well, if you ask his colleagues, his physics colleagues, they would probably say his discovery of what's called hot body radiation from black holes, that's known as Hawking radiation in more popular language, that's his biggest contribution and his most well-received contribution, and it's stood the test of time.

Also, he made a huge contribution by going out on the speculative edge of science in a way that's exciting and dangerous as a scientist. He's not always able to confirm what he suggests, but it's his willingness to do that and to take even a lay audience with him out there that I think is a huge contribution.

GROSS: So let me go back to the Hawking radiation. Can you describe what that is?

FERGUSON: Yes, this was a discovery that he made back in the '70s. It was very controversial at that time. When he first discovered, he couldn't believe it himself. He knew his colleagues were going to have even more trouble than he was having believing it.

You have to back up a little bit and say that the general opinion, the general discoveries before that, including his own, indicated that nothing could ever come out of a black hole. So a black hole could never get smaller. And then with Hawking radiation, he found that it could.

There are many ways to explain Hawking radiation, but one is just by the appearance of two particles right at the edge of a black hole. They part from one another, and then they come back together in an explosion. They annihilate one another.

But if one of them happens to fall into the black hole during the time when they're apart, then that allows the other one to escape out into space and appear as radiation from the black hole. That's really a very vague description of it, but that is Hawking radiation.

GROSS: And why is that important?

FERGUSON: Well, it's important because what happens in that little situation, is that the particle - we said there were two particles, one of them escapes, one of them goes into the black hole - the one that goes into the black hole has - is a negative particle, has negative energy. It's like taking a minus sign into the black hole while the plus sign goes off into infinity.

And in that way, it actually subtracts from what's in the black hole, and the black hole can get smaller. There's a big upshot to that, because as the black hole gets - and this was not discovered back when he first discovered Hawking radiation, this was a little later - what happens is that as this occurs and continues to occur, it's possible that the black hole will finally disappear entirely.

And then the big question is - and it's a very important question to physics - what happens to everything that had fallen into the black hole earlier? What happens to the star that collapsed to form the black hole? What happens to all that when the black hole disappears entirely? And does it mean that this stuff is actually - this information is actually completely lost to our universe?

And if it is, you know, it might not seem so important to you and me, you know, what's in a black hole, that's a fairly minor problem. But to physics that's a huge problem because if information can be lost from the universe, then that's a violation of a law that says it can't disappear. It means we can no longer predict, as science likes to predict things. It means that you and I actually lose our ability to count on cause and effect being something we can rely on in everyday life.

It's much more important than it might seem just to think of somewhere out in space, you know, information getting lost in a black hole. That's generally what Hawking radiation has meant. It means black holes can get smaller and disappear.

GROSS: Stephen Hawking has pursued what's been described as the theory of everything. What is that concept?

FERGUSON: Well, that's a concept that there should be some deep level of theory, of physics theory, one theory from which everything can be explained, one fundamental theory of everything. That's defined a lot of different ways, but - and sometimes they call it - they have what they call a unified theory, which just means that all the different forces of nature are unified. That's not a theory of everything.

A theory of everything has to even explain why the theory of everything exists. It's really a very far-out concept, but he has been predicting for most of his career that we will find it. First of all, he said we will find it within the 20th century. Now he very cagily says we will find it within the century, but there's a lot more time in this century.

However, recently - and this goes back to something I would love to talk about, which is that he does have a way of pulling the rug out from under his own theories and out from under his own findings. Just recently, he has decided that it's probably going to be impossible for anybody, ever, to find the theory of everything. And this is a huge turnaround. He thinks we'll come up with some theories that are sort of approximations, it'll take maybe six theories to explain it, but we'll never be able to know the underlying mysterious theory that would really explain the entire universe.

That's where he is right now, and that really is a turnaround.

GROSS: I think one of the things that has made Stephen Hawking so popular is that he's constantly investigating what the university - what the universe was like - university, yeah, through the university, he's constantly explaining, you're trying to explain what the universe was like at the very, very beginning, like what created the universe and what created this particular universe.

FERGUSON: That's right, yeah.

GROSS: Why does it have the particularities that it has?

FERGUSON: I think, too, that one partial explanation for his huge celebrity and his huge popularity is that he does deal with things right out on the borderline, you know, of human knowledge: the origin of the universe, black holes, does our - is our universe part of a labyrinth of universes and worm holes.

These are questions that are really right out at the edge, on the frontier between the known and the unknown, and the - possibly the unknowable. I love the phrase what John Wheeler, the American physicist, called the flaming ramparts of the world. And that's where Stephen Hawking goes.

And he takes - he tries to take us with him there on this adventure, and for him it is a huge adventure, and it's fun. And the ability to do that, even though he doesn't always manage to take us with him, it's - I think it's just mind-blowing, and it's wonderful. And I think that is part of the explanation for this huge popularity.

GROSS: I think part of the explanation, too, is that here he is, virtually paralyzed, there's really only a couple of muscles he can move because he has ALS, Lou Gehrig's Disease, and it's very advanced at this point. So, you know, he can barely move, but his mind is always thinking about, like, the largest cosmological questions that one can ask, and he's asking them on such an advanced theoretical level.

FERGUSON: That's exactly right, exactly, and also what I think really captures people is the fact that - is just the astounding good-humored dismissal of his disability. That's his attitude. I mean, it just seems unimportant to him. How important it really is I don't think anybody knows, but he just manages to dismiss it with a grin. It's incredible.

GROSS: One of the questions he's been considering is, what were conditions at the very beginning, when our universe first came to be. That seems like an impossible - unless you just want to say God created it, it seems like it would be so hard to answer that question, you know, in a scientific way. Like, what are some of the obstacles to actually understanding what's called the boundary conditions?

FERGUSON: Well, he actually set up one of the obstacles himself in his doctoral dissertation back in the late '60s. He discovered that the universe began in a singularity. A singularity means that everything we know about the universe and everything we might ever know about the universe, everything in it, was originally just a single point of infinite density and space-time curvature.

Now, you know the universe is expanding. We know that today. So if you run time backwards, and you allow the expansion to become a contraction, then it isn't so illogical or impossible to conceive of the fact that at some point everything was going to be in the same place. And that was the singularity.

Now that - a singularity is a dead-end for a physicist because at a singularity - and you also find them in black holes - but at the singularity at the beginning of the universe, all physical laws break down. Our ability to predict anything breaks down. You can't say what's going to emerge from the singularity. It could be any sort of universe.

You can't say what happened before the singularity. Presumably, time may have stretched back, but you can't know. It really is sort of a door slammed in your face.

But then in the early '80s, he and his colleague Jim Hartle came up with what was called the no-boundary proposal, and what they discovered or what they have proposed is that again, if you follow the universe backwards, and everything's contracting, eventually everything's going to be so small and so close together that it makes no sense to think of it in any other way except what we call quantum physics, which is the physics of the very small, atoms and molecules and particles.

So once you've got to that level, then something very odd happens, they say, and that is that the - what we think of as the time dimension, we have three dimensions of space and one dimension of time, I think most of us can get our minds around that pretty well, but what we think of as the time dimension would have been a fourth space dimension.

Now, that's impossible, don't even try to get your mind around it, you know...

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GROSS: Thank you.

FERGUSON: You know, that's what they say.

GROSS: Thank you for permission.

FERGUSON: There you are. But when that happens, then all the concept of chronological time, of past and present and future become meaningless: Time simply ends and becomes another space dimension. And when you do that, you can't go to the past anymore. You don't get the singularity; they say it's smeared away.

And the way he likes to describe that is as though you were traveling backwards on a globe of the Earth, when you get the South Pole, the concept of south no longer means anything. You don't say an airplane flew south of the South Pole. And so it's the same: Time becomes meaningless.

Now, you know, when you start to think about that, first of all, Hawking says that that relieves us of the need for a creator because there doesn't have to be a creation, you know, it just started, and it was all kind of all space dimensions, no time dimensions.

But what I find really interesting about that is it's not a new idea, it's an idea you find in the early Christian and Jewish philosophers, like Philo of Alexandria and Augustine. They both conceived of a universe in which time didn't exist outside of our creation. Time was part of the creation, and God exists outside of time in a sort of eternal now.

And it's the same idea. It's funny that it was not new to theology, not new to philosophy but very new to physics.

GROSS: In your mind, advanced physics and a belief in God do not contradict each other. In Hawking's mind, they do, I think.

FERGUSON: They do. It's hard to know what he really thinks. He likes to make these, kind of harsh, iconoclastic statements about religion and the afterlife. It's hard to know what he thinks because actually, he is a man who has a lot of intellectual humility.

I mean, you might not think that because sometimes he comes across as very dogmatic, very arrogant. But the very fact that he is willing to change his mind and his own physics so often, the very fact that he's willing to admit he's wrong and feels it's important that physicists will do that and are willing to do that, and his own vision of science, which is really the vision of science not as this monolith of unassailable truth, but as an ongoing self-correcting process.

All of this really smacks of a mind - that there is a humility before nature and what he can conceive of or what he can perceive as reality, which seems out of line with dogmatic statements about anything. And that's why those religious statements of his, or anti-religious statements, however you want to look at them, seem uncharacteristic.

He's out of his own field there, and it's not as though he has any expertise. He's out of his depth, really. But he does love to make those statements.

GROSS: That was interesting that you should say that you think he's just, like, out of his depth when it comes to religion.

FERGUSON: Well, I think, you know, he also tends to make political statements sometimes that people say he's out of his depth there. I remember one of my friends, Sir Brian Pippard, who is a physicist in Cambridge, said that scientists - and I can't quote him exactly on this - but many scientists, and he even included himself as being guilty of this, they know so much about their own field, and they're such experts that they feel that any area they talk about they must contribute, as he says, their penny's worth of wisdom to, when they don't really know what they're talking about.

And I think Hawking has to plead guilty on that.

GROSS: If you're just joining us, my guest is Kitty Ferguson. She's author of the new book "Stephen Hawking: An Unfettered Mind." It's a biography of the physicist and cosmologist Stephen Hawking. She helped one of his earlier books, which was called "The Universe in a Nutshell." Let's take a short break here, then we'll talk some more. This is FRESH AIR.

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GROSS: If you're just joining us, my guest is Kitty Ferguson. She has a new book that's a biography of Stephen Hawking and also an explanation of the science that he's been devoting his life to. It's called "Stephen Hawking: An Unfettered Mind."

And Hawking is a very well-known theoretical physicist and astrophysicist who also has a very advanced case of Lou Gehrig's disease, and he's basically paralyzed, with the exception of - what, Kitty, a couple of facial muscles that he can move.

FERGUSON: Just a muscle in his cheek right now, I think, is all he can move. But he can still smile. You know when he's smiling.

GROSS: What's it like to collaborate with somebody like Hawking, who is virtually paralyzed, and he can't talk back to you? He can't type out his answers. How does he communicate now?

FERGUSON: When I first met him was back in 1989, and at that time, he was communicating by using a little device that he held in his hand, more or less like a computer mouse that he could press. He can't type, but he could press this little device with one finger.

And what you do when you go to visit him, you don't sit across from him, you face his computer screen. You can see everything he's doing on it. And what you see on that screen is first of all a huge screen full of words, with the top of the screen highlighted and then the bottom of the screen highlighted and then the top: It goes back and forth.

And when he sees the part of the screen that has the word that he's looking for, he punches this little mouse. Then the screen changes, and we see lines of words scrolling down, and those are of course the words from that part of the screen. Then when he sees the word he wants, when the line he wants with that word is highlighted, he activates his little switch again.

Then the screen changes, and you see the cursor moving across that line of words, and when it hits the word he wants, he punches the device again. And then that word goes down to the bottom of the screen. And that's the way he builds up a sentence across the bottom of the screen. And when he gets the sentence completed, he makes some kind of a movement with his mouse-like device again, which indicates his voice, his synthetic voice should speak that sentence.

Now this all takes a long time, and it actually - it sounds simple. It's not simple. It moves at the speed of a video game, and very often he misses the word, or he misses the line, and then the whole thing has to start over. Now what that means is that working with him can be frustrating because very often, you know what word he's after.

You know, you know what word he wants to capture. But protocol says you do not second-guess him. You do not move ahead and say oh Stephen, I know what you're trying to say. You let him finish because he's going to finish anyway, he usually goes ahead and finishes what he has to say. It's just impolite, as it would be impolite to, you know, interrupt anybody talking.

GROSS: This would be hard enough if he was just saying get me some water, please, or...

FERGUSON: Yes, he does have a few phrases like that that he can select without having to select all the words, but yeah.

GROSS: But you're asking him about the nature of the universe. So, you know, to communicate on that level in the kind of laborious process that you've mention, that is really hard.

FERGUSON: It's really something. Now, when I went in to help him edit "The Universe in a Nutshell," this was back in 2000, the year 2000, I was actually hired by his publisher in New York, who was going to publish the book, and my - what I was supposed to do was help him make it simpler, help him make it easier to understand mainly by identifying places that were too difficult.

It was a very uneven book when I first saw it. There were passages which were just, you know, totally out there, you couldn't possibly figure out what they were unless you were a theoretical physicist of the highest order. And then there were other parts that were really quite simple.

But all this needed evening out. So first of all we communicated by email, which he can do. You know, it's slow, but he can do that. And then I went over to Cambridge and spent two weeks there in his office, and at this time, we - you know, you were facing his screen with his words and another screen, which had the manuscript of the book on it.

And I remember so clearly saying, you know, Stephen, I think that line, that's too difficult, you've got to find a way to say that more simply. And then he'd - there was a little clicking around, and the answer came: Seems clear to me.

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FERGUSON: And so I thought: Oh dear, this is going to be difficult. But then I looked over at him, and I saw this huge grin, and I could see OK, he's putting me on, you know. And we proceeded from there. And I would identify a paragraph or some words or so on, and then he would work on that to make it simpler.

And what I had done in preparation for this, you know, I had had the manuscript, and I had prepared alternate wording for these places, simpler wording or an analogy or something, you know. He never took my suggestions. That's why I say this is not a collaboration.

He never took my suggestions. He always did it on his own. It's his book. It's in no way a collaboration, and I wouldn't want to claim it was. All I was was the sort of guinea pig to decide, you know, is this going to be understandable, or could it be said more simply, and should it be said more simply.

I think it's very difficult for somebody who's thinking on his level - and it's not just Stephen Hawking but a lot of other people - to understand how simple things have to be for the rest of us to actually pick it up.

GROSS: Kitty Ferguson will be back in the second half of the show. Her new book is called "Stephen Hawking: An Unfettered Mind." I'm Terry Gross, and this is FRESH AIR.

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GROSS: This is FRESH AIR. I'm Terry Gross, back with Kitty Ferguson, the author of a new biography called "Stephen Hawking: An Unfettered Mind." Hawking is an internationally celebrated cosmologist and physicist who's virtually paralyzed as the result of ALS, Lou Gehrig's disease, which he diagnosed with at the age of 21. But as hawking likes to say, his mind is free. And he spent his life looking for scientific answers to some of the biggest questions like: how was our universe created?

Ferguson is also the author of 1991 book about Hawking and collaborated with him his book "The Universe in a Nutshell." Hawking celebrates his 70th birthday later this month. Like many scientists, he's waiting to see the results of experiments at the Large Hadron Collider, the world's largest particle accelerator, which is testing various theories of particle physics.

So without getting deeply into what's happening at the Large Hadron Collider, which is underground in Switzerland and is doing incredibly advanced research looking for the most minute of minute particles that will help explain a lot of things - how's that for a vague - there's what they're working on there - the discovery of the so-called Higgs boson, without getting too deep into what that is, is that likely to reinforce or contradict anything that Stephen Hawking has postulated over the years?

KITTY FERGUSON. SCIENCE WRITER: No, it's not. And it is interesting that, but, you know, Stephen Hawking loves to make these bets, betting whether Cygnus X-1 is a black hole, betting all these sorts. But he has placed a bet that the Higgs particle will not be found. And the question does come up, you know, why is he so concerned about this.

He doesn't have a competing theory to the theory which has the Higgs particle. Maybe we should just discuss a little bit what that is. One of the mysteries in physics is what gives elementary particles - that's electrons, quarks, things like that - what gives them mass? And mass, you know, we often define and mass as how many matter particles there are in an object. Well, that becomes a little stupid when you're talking about a thing that is just one matter particle itself. So there's another definition for mass, which is: the resistance you feel if you push against something; how much it resists any effort to change its speed or direction. And where does that resistance come from? Now that's the mystery that the Higgs particle would solve. Because Peter Higgs purposed something called the Higgs field that's supposed to permeate all of space and it acts kind of like molasses, drags on the particles as they try to move through it. And the stickier a particle is the more the molasses-like field is going to affect it and the more masses the particle appears to be. So that's what we're looking for, this Higgs field.

And the Large Hadron Collider, what it does is accelerate particles to nearly the speed of light and then slams them together in these head-on collisions, and hopefully in the debris of one of those collisions - just for a split second - a minuscule part of the Higgs field will break away and that will be the Higgs particle. That's what they're looking for. So far, they have pretty good evidence that they may have seen it, but it's not really definitive yet. But I really do think that within the next year we're going to find it.

GROSS: So if the Higgs particle is discovered what would that mean?

WRITER: Well, that would mean we would know then - or at least have a good indication - of where the elementary particles get their mass. There are some things like the speed of light, the masses of the particles, which it will be called arbitrary elements. You just can't get there by a theory. You can discover what they are by observation but that mass or at the speed of light, they're just a given and science likes to be able to explain why that's the speed of light, why things have these masses. They're always - they don't like to have things just out there without being able to explain them or predict them. So that's what the Higgs particle would do. It would give us that explanation for why particles, where particles get their mass.

Well, that does not seem, you know, like that does not seem like an earth-shattering question to most of us too, but to a theoretical physicist that's terribly important.

GROSS: Right. Stephen Hawking was diagnosed with ALS, Lou Gehrig's disease in his 20's. And he was symptomatic then, so this is like he's starting out his career as a scientist and he knows he has an incredibly serious, debilitating, degenerative disease. Did he consider giving up science at that point?

WRITER: I think he considered giving up everything at that point initially because he was given two years to live and he didn't really know what to do. He didn't know what to expect, how soon it was going to get worse, what would occur. And at first it did get worse a lot - very fast, even quicker than his doctors hoped and he had no idea that he had all these years ahead of him.

It's also interesting, and I think what's very poignant about this story is that at the same time he was coming to terms with his illness and at the same time he was struggling to begin his career, he was also in his courtship with Jane Wilde, the woman he married. That courtship took place in the context of all that struggle and it makes it a very, very touching story. And it's just so interesting to see how he came to terms with it.

He had to come to terms with it. What he says it wasn't courage. People call it courage; I just did what I had to do. And, of course, that in itself is a courageous statement. But yes, he did come through it and Jane came through it and they married and then the disease did slow down and he'll be turning 70 this month.

GROSS: Jane decided to early in their marriage to forego any idea of a career or anything. She figured she'd devote her life to her children, to taking care of her husband. And she attributed her ability to cope with her faith in God. And that created something of a conflict in the marriage. What was that conflict like? How much do you know about that?

WRITER: Well, I do know that she does - she did and she does - have, she's a very religious person - Anglican. And she does say that it was only her faith in God and a belief that her mother had taught her that good comes out of any - that good can come out of any sort of situation, no matter how deep and dark it is, that this sustained her through the years.

In the years when they were together he was not making such overtly aesthetic statements. They were more Agnostic. And at one point she even said that it's impossible - it's really impossible to know what his relation is with God because of what he's been through and his science and his belief that everything should be understood through mathematics. But many people even today say I'm not - some of his closest friends will say I don't know what Stephen really believes about God. He's just, he plays that sort of thing very close to the chest except for these occasional statements he makes to the media.

GROSS: Early in the marriage she gave up the possibility of a career to raise the children and care for him. But in the 70s, with the rebirth of feminism, she started to feel like she wanted more from life. So eventually she got some help for him, went back to school for her Ph.D. And 1977 she joined the choir of Saint Mark's Church and met the organist there, Jonathan Hilliard Jones. His wife had died from leukemia a year after they were married, and he and Jane became close and eventually that developed into a more intimate relationship. What was the agreement that they reached about their relationship? And what agreement did they reach with Stephen Hawking?

WRITER: Well, very little has been said about all that. But I do know that she was very honest with Stephen. She told him the situation - that as she puts it - Jonathan and she had developed a romantic relationship. Now evidently it was a platonic relationship for many years, but it was a romantic relationship. And his comment was is that he didn't mind as long as she went on loving him. Now that's a very ambiguous sort of statement but that's what he said. And that was all that was said as far as anybody knows. And they did all stay together because Jonathan was a huge help taking care of Stephen and helping with the children. He taught little Lucy piano lessons. He was just a huge help in that home.

I don't think anybody knows what Stephen really felt about that, whether he recognized that she had to have this help, that she really needed this not only help in the home but this emotional support and so on. I don't think anybody knows and he's not going to say and she's not going to say, and that's about all that can be said about it.

GROSS: Now she revealed this in her own memoir a few years ago, right?

WRITER: Yes, she did. That's she did. That's where...

GROSS: So you're not prying into something that, you know, whatever...

WRITER: No. No. I'm not a gossipy writer. And even things that I do know or have heard I don't necessarily put them in a book.

GROSS: But you write about it a little bit, so I have a couple of other questions about it.

WRITER: I do write about it. When I went into to talk with him, oh, a little or a year ago about this book and told him more or less what I was going to cover in it and ask him what he would like me to cover beyond that. And I felt, you know, we've got to talk about this problem of his private life and the fact that people have thought he was suffering some kind of physical abuse and some people thought it was from his second wife. That's nothing's been proved about that. But I thought, you know, I better ask him what to include. And I said what I'm going to do - because he can't not mention it in the book - is just mention that the subject came up, there was this controversy, there was this police investigation, but I'm not going to go farther than that. I'm not going to go out and interview people and find out the secrets behind it all. I'm just not going to do that. And he - that was fine.

This was not an authorized biography but he did give his blessing to my writing of it. And not everything in it is completely sympathetic to him, but it's, you know, it's I couldn't really just make it a, what you call it, an investigative thing.

GROSS: You mention that some people were concerned that his second wife might have been abusing him. And that's interesting story too because one of his nurses becomes, you know, intimately involved with him and he leaves his family for her. And you say you were just shocked when you first heard that because you thought that he was, you know...

WRITER: I was. Yeah.

GROSS: ...that Hawking and Stephen Hawking and Jane had had this like heroic marriage and he was breaking it up because you didn't know anything about the relationship that she had been having.

WRITER: No, that's right.

GROSS: Yeah. So what did his family - do you know how they reacted when he left for Elaine Mason?

WRITER: His children were really probably too young to react too much to it, or at least any way it...

GROSS: I see...

WRITER: ...has become public. Jane kept her feelings pretty much to herself about that too when they actually broke up. And it was so interesting to me that, you know, I was really a part of that Cambridge community there and knew so many people who were and nobody had talked about that. Nobody had said a word about the relationship - her relationship with Jonathan. Nobody had said a word about the possibility of a breakup until it happened. And that is so unusual in a tight-knit community like that, where, you know, gossip really spreads like wildfire. But everybody out of respect for them was just keeping their mouths shut. And indeed have since then too. What you know about the problems in their marriage and their marriage (unintelligible) comes from what they want to say about it. And other people, although yes, they'll talk privately about stuff, it's simply off the record. And it really shows a remarkable amount of respect for them. It's hard to explain why people have been so reticent about talking.

GROSS: My guest is Kitty Ferguson. She's the author of a new book about Stephen Hawking, the physicist and cosmologist and the book is called "Stephen Hawking: An Unfettered Mind." Let's take a short break here and then we'll talk some more. This is FRESH AIR.

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GROSS: If you're just joining us, my guest is Kitty Ferguson. She writes about the science. Her new book is about Stephen Hawking, the theoretical physicist and cosmologist who has had ALS, Lou Gehrig's disease since he was in his 20's. He's now about 70. And he's virtually paralyzed but he remains a great and active scientist. Her book about him is called "Stephen Hawking: An Unfettered Mind." And she also helped him edit an earlier book of his, which was called the "The Universe in a Nutshell."

So how has Stephen Hawking's physical condition changed from the time you first worked with him, which was in the '80s?

WRITER: In - about 1989.

GROSS: OK. To...

WRITER: That was when I first met him. Yes.

GROSS: To when you interviewed with him for this new book.

WRITER: Well, first of all, his communication has slowed down. He was doing about 15 words a minute then. Now he does one word may be in five minutes. This is a huge slowdown. He was at that time using the little mouse-like clicker in his hand. Through the years I noticed he changed hands. I guess maybe one hand became weaker and he changed hands. And then the last couple of times I've seen him he's been using his cheek muscle to control it, which also means one big difference to him. When he had the use of his hand he could drive his own wheelchair and he could bum around Cambridge and have a good time out on the streets scaring people by jumping out in front of cars and so on. Now he can't do that. He has always have somebody with him to push the wheelchair because that's not something - at least with the technology he has - that he can do with his cheek muscle.

GROSS: How do you control a computer with the cheek muscle?

FERGUSON: It's the same thing when he had the thing in his hand, you know, when he saw the word he wanted, he just gave it a little punch with his thumb or his finger - I forget exactly how it worked – and that chose the word. Now he just twitches that muscle and that does the same thing.

And that's one reason why things have slowed down, because that is not as easy to do.

GROSS: So his physical condition now is that he can – the only movement that he has is in a cheek?

FERGUSON: That's right. They're working right now on the technology to see if they can improve his communication. There are things – you can wear this sort of helmet that actually connects your brain into being able to control the screen. He seems very reluctant to do that and it's been one of the things that has characterized his whole way of dealing with his disease, is that very often he resists a change, even what might be an improvement in his communication or his, you know, ability to do whatever.

But he resists it because every time he makes a change it seems like a little bit of a concession and he fights those concessions, or what he sees as concessions, to the disease. So whether he will ever be willing to wear this helmet and try that out – because there are, you know, it's the possibility he might even be able to drive his wheelchair that way. Nobody knows exactly how this would work but there is the possibility. But he seems very reluctant to go to that right now.

GROSS: So Stephen Hawking is about to celebrate his 70th birthday and you're going for the celebration. What are you expecting it to be like?

FERGUSON: Yes. Well, it's quite a long celebration. There are 4 days of academic lectures and symposiums involving people from all over the world, absolutely top people. And then there will be one day that will involve four lectures on a popular level that the rest of us can all understand and a big evening party. And I don't think anybody knows yet exactly what will happen at that.

They had such a lavish party for his 60th birthday that I think they're having a hard time figuring out what can we do to top that for 70? You know, they had a Marilyn Monroe impersonator come in because he's always been really fond of Marilyn. And they had can-can dancers and it was just a huge celebration.

And I guess, you know, you say 10 years longer and maybe you'll live to 80 and they'll have to figure out how to top the 70th.

GROSS: Didn't he...

FERGUSON: But I think it's going to be spectacular.

GROSS: Didn't he crash his wheelchair into a wall right before his 60th birthday celebration?

FERGUSON: Yes, he did. Yes. And he was in the hospital, but the man who was in charge of that celebration, I was asking him a couple of months ago was there a moment when you just thought you were going to have to cancel the whole thing? He said, well, there was a moment. But he said then we found out that he was in the hospital; he was working on his speech for his 60th birthday so we knew it was going to go ahead.

GROSS: I mean, he broke his hip and he still...

FERGUSON: Yes, he did. Yeah.

GROSS: He still functioned. OK. Well, Kitty Ferguson, I really want to thank you for talking with us.

FERGUSON: Well, thank you for talking with me. This has been fun.

GROSS: Kitty Ferguson is the author of the new biography "Stephen Hawking: An Unfettered Mind." You can read an excerpt on our website, freshair.npr.org. Coming up, Maureen Corrigan reviews a new book collecting excerpts of diaries from the past 400 years describing life in New York City. This is FRESH AIR.

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