More Science Talk
Award-winning writer and physicist Graham Farmelo talks with podcast host Steve Mirsky (pictured) about The Strangest Man, Farmelo's biography of Nobel Prize-winning theoretical physicist Paul Dirac. Part 1 of 2. Web sites related to this episode include www.thestrangestman.com and http://bit.ly/dirac1963
Steve: Welcome to Science Talk, the weekly podcast of Scientific American posted on June 24th, 2010. I'm Steve Mirsky. This week on the podcast:
Farmelo: Today the modern theory of the early universe, [we all know] is in the first quillionth of a second, the universe was half matter, half antimatter, and then gradually matter wins out to speak better with not very much less antimatter, now by that light Dirac conceived half the early universe in his head.
Steve: That's physicist and writer Graham Farmelo. He is the author of the acclaimed biography The Strangest Man, the story of legendary theoretical physicist Paul Dirac. Farmelo is a senior research fellow at London's Science Museum and is adjunct professor of physics at Northeastern University here in the U.S. His book has won the 2010 Costa Biography award and the Los Angeles Times Book Prize in the Science and Technology category. Farmelo is spending the summer doing research at the Institute for Advanced Study at Princeton. He was kind enough to drop by the Scientific American offices on June 18th to talk about Dirac. Here's Part I.
Steve: Who was Dirac?
Farmelo: Paul Dirac was the greatest scientist produced by Britain in the 20th century and one of the greatest scientists of the 20th century. I have to say, though, he is one of the least well known. I mean, on his 70th birthday, C. P. Snow said of Dirac that he was the greatest living Englishman, Churchill having died, and the audience were nonplussed because most of them had never heard of him. So he is very much an anonymous figure outside that of the community of theoretical physicists.
Steve: Even an undergraduate taking [a] modern physics course can probably go through that course today without hearing Dirac's name mentioned.
Farmelo: Yes, I think that's probably true. They probably use some of the terms he invented like [eigen]function and various things like that; and some of his mathematics, for example, the equation with regard as the central driving equation of quantum theory, which we call Schrödinger's equation, which governs the behavior of the subatomic matter. And the version of that that is fully dependent on time and which most undergraduates will do it in their course, that was done independently by Dirac as well. But, it was Schrödinger who got the full credit for it because he was the person who came up with the first equation and generalized it but [Salam], one of Dirac's students, said that virtually everything in quantum mechanics apart from the very beginning of Schrödinger and Heisenberg, virtually everything Dirac did independently, he thought through in his own mind. [I mean] he really was one of the coinventors of the subject.
Steve: And what's really amazing is this work was done primarily on his own at a desk with a pencil and paper.
Farmelo: Yes, that's right. He was the classic loner, make no mistake. He needed other people in the sense that all scientists need them; you know, to verify his logic to pick him up, when he made slips and [what have you.] All scientists need that. But he hated working in teams. As you rightly say, he sat at his cheap school desk in his rooms at St. John's College in Cambridge and he worked alone, and that's how he wanted to do it. He didn't want to partake in all these debates the Bohr–Einstein debates and all this other stuff here, he just wanted to be on his own.
Steve: But he loved Bohr, and he revered Einstein.
Farmelo: Absolutely, he thought Bohr was the most intelligent person he had ever met; he thought Einstein was preeminently the greatest scientist of the 20th century and never changed his mind on that; [he] thought general relativity, not quantum mechanics, was the greatest theory conceived in the 20th century.
Steve: And he was a stylist. He was almost as much of an artist as a scientist.
Farmelo: Yes, I agree with that, I agree without in any way undermining the contributions of Schrödinger, Heisenberg, Pauli and the other[s], Dirac's work has a unique beauty to it, a unique logical force and concision, a beauty of notation, [an] elegance of conception. I mean, I love Freeman Dyson's phrase, I love the phrase Freeman used—which he coined right in front of me at the Institute of Royal Studies in Princeton; I remember him saying it to me—that what made Dirac's contribution special was more than anybody else, his contributions were like perfectly carved marble statues falling from the sky. And I think that is a great phrase. If you look at the other people, great, great physicists without a doubt but if you look at their contributions they somehow looked tentative, they looked somewhat messy. But, Dirac you can read them today, they look completely modern. And in particularly in his latter part of his career, I mean the stuff that he was doing for example on magnetic mono poles still not verified, that's an absolutely beautiful piece of science; fundamental today in the way that quantum, advanced quantum field theory is done.
Steve: But it is also the search for an aesthetic ideal also drove him. It was part of his parameters for success.
Farmelo: Well, I think what [you] say [is] very reasonable. In the book though I question whether that was actually the case when he was a young man. He certainly had that as he put it, "like a religion" as an elderly man that's not [in doubt.]
Steve: Right, you think that might be a little bit of revisionist history on his part.
Farmelo: Yes exactly. If you look [there are] very few mentions of beauty, which became his obsession. When he was young, he did mention it though. In a talk he gave as a graduate student he actually inserts the word beauty when talking about Einstein's general theory of relativity, theory of gravity; and he puts that in, so he was thinking about it. And in the book I trace this back to his school, his school days in Bristol where Sir. Henry Cole and others—Henry Cole invented the Christmas card in Britain; the first director of the V and A—he wanted beauty to be part of the education of young people. So Dirac was actually [saturated] in it, and it became, as you rightly say Steve, a big part of his approach to physics. But there is no, in my opinion, there is no evidence that when he was codiscovering quantum mechanics that he was driven by beauty in the way as, [you rightly say]; that he retro-interpreted his activities later on.
Steve: Yeah later in life he actually advises people to go for the beauty in their formulations, over experimental verification!
Farmelo: Yeah, he wrote that in Scientific American.
Steve: In 1963.
Farmelo: Yep, that was the article where he came out of the [closet] of the theoretician, if you can call it that, and wrote his first popular article. It was based on lectures he gave at Yeshiva, not far away from here. And those two phrases come up in that article, right. The one is that God appears to be a very fine pure mathematician. He got actually that line from James Jeans way back in the 1930s. I suspect he had forgotten he got it from there, [but] Jeans came up with that beautiful line, but he also said the phrase you just mentioned there, that it is more important for theory to be mathematically beautiful than for it to agree with experiment. He absolutely stood by that statement. And you'll know that to some degree, that is, if you like, a credo of perhaps the modern string [theorists], who invest a great deal in the mathematical elegance of the theory even though [there's not], at the moment, any direct evidence to verify it; so it's a lot of faith there that it is going to come good in the end.
Steve: Let's go back to his actual contributions to physics. If you think it's even possible, can we try to explain to people who might not be all that familiar with, I mean Schrödinger, they've heard of because of [he's] cat and Heisenberg they've heard of because of.
Farmelo: Actually Dirac's daughter told me they often visited the Schrödingers, and the one thing they didn't have was a cat.
Steve: Well, they might have had a cat, and…
Farmelo: I love that remembrance of Schrödinger, but sorry, [I digress].
Steve: They might have had an infinite number of dead cats.
Farmelo: Yes, yes, very true.
Steve: So we can't [know for] sure but there is no visible evidence of a cat. So, we have Heisenberg; [he] is famous, in general parlance, most people have heard of that uncertainty principle even if they don't know what it is. Dirac what actually was it that he did that was such an important contribution to the building of the edifice of quantum mechanics?
Farmelo: Alright, well lots of things. But perhaps, I can actually give the greatest hits. As you rightly say there began two theories of quantum mechanics: The Schrödinger one, where you look at things like electrons, subatomic matter, in terms of waves, you look at their behavior in terms of waves. There's also, the first one that come out was Heisenberg's, and he was looking at in terms of matrices, arrays of square numbers; complicated stuff and even Einstein, that gave him the heebie-jeebies,—can nature really [be this] complicated? So you have what looks like two completely different approaches to that theory. So, in a sense you have the same reality, [but] you are representing [it], if you like, there's Japanese and [there's] English, you might say perhaps. So you've got things that look very different but they're representations of same reality. Now after Dirac got his PhD, the first PhD in quantum mechanics, and after making a fundamental contribution that's the basis of micro electronics—we'll pass over that—when he went to Bohr's institute, where Bohr called Dirac the strangest man who ever visited that institute, what Dirac did was set up a theory that enabled you to go from one representation to [the] other: from Heisenberg's to Schrödinger's and back, right. And he called that theory his darling, and it was his favorite piece of work because he actually set out to do it, right. He thought these two things were pretty much the same, and he set [out] to do it, and he did it and he was very, very proud of that. Now the next thing he did which was he was one of the coinventors of quantum field theory. Now we all know about gravitational fields. We all, [you] know, [have an] intuitive [feel for it]—you know, the apple falling in Newton's garden pulled by a gravitational field. We all[know about] electrical magnetic fields. What Dirac was one of the first to do, independently of other people, was to show that the idea of that field could be quantized. You could introduce the quantum, the granular aspect to the concept of the field. So he was one of the inventors of the fundamental approach that physicists used to understanding reality now. But the biggest thing of all, though, [the biggest thing of all that he is] most famous [for] is his famous equation, named after him: the Dirac equation. Now why is that famous? [Well] what it is is an equation for the electron, the first fundamental material particle to be discovered. Now, what made that equation so special? Well, the first quantum theory—the one that we have just been talking about—was, had to be flawed because it was not consistent with Einstein's special theory of relativity, Einstein's theory of space and time that modified the Newtonian conception of the thing. And Einstein basically had this set of rules set [down] on special relativity that governed the way that a theory must behave [if it's to be in conformity] with nature. The flaw was that the quantum theory did not conform to that theory. What Dirac did, he married special relativity and quantum mechanics, and he was the first person to set out for the electron a theory that persisted with relativity and quantum mechanics. And he produced a beautiful—in Frank Wilczek's words an achingly beautiful—equation of the electron you can write on the palm of your hand. Now that's one thing. The reason why that was seen as a miracle at that time, and you could flutter all the cliché's of rabbits coming out of hats or what have you was that, first of all, Dirac did [it] on his own. There were dozens of people trying to do the same thing and flailing around in a very inelegant way. Dirac did it in such a way that he could announce that equation to his German competitors on four lines at the end of a letter, driving one of them into a depression that lasted years. Now what that equation did was something remarkable. The electron, physicists knew, had spin; you can think of it very vaguely, inaccurately but vaguely, like the earth spinning on its axis. That had been observed a few years before, but nobody understood what that meant. Spin drops out naturally like a golden egg, so to speak, from the Dirac equation likewise the magnetism of the electron also drops out at that equation. So not only do you have an equation that makes quantum mechanics relativistic, so to speak, but you instantly have an explanation for the spin and the magnetism of the electron. So, that's why [it was] seen as a miracle. Then perhaps even greater than that he used that equation, which had its flaws, but he overcame those flaws, and in what Heisenberg described as perhaps the greatest leap forward in 20th century physics, he deduced, purely from a mathematical point of view, not from experiment, he deduced the existence of the antielectron; the first example of what we now called antimatter, the flip side of matter, if you will.
Steve: It were these negative energies associated with his view of the electron and other people thought that those must be nonsensical.
Steve: And he stuck to his guns and said "No, somehow this is real" and he came up with an idea of a hole in the negative sea and it implied these antiparticles.
Farmelo: That's right, that's right. The paper where he comes up with this, which was a 1931 paper, which is an absolutely sublime piece of work—I might say, set against, the most terrible domestic [period]; his parents throwing things at each other, dreadful domestic turmoil back in Bristol—but out of this tragedy that was his private life came this foreseeing of the whole subject of antimatter, which is why Heisenberg praised it so highly. It's just [worth saying just] to give a sense of the grandeur of Dirac's intellect [here]. Today, the modern theory of the early universe we all know is: in the first quillionth of a second, the universe, was half matter, half antimatter, and then gradually matter wins out so to speak with very much less antimatter. Now by that light, Dirac conceived half the early universe in his head. It is an extraordinary thing that he did.
Steve: With the other half being there already.
Steve: So he [had] the whole thing.
Farmelo: But it was, but Heisenberg said: This changed everything. Now [of course it's] routine, [in] accelerate[r]s, in PET scanners—we use this stuff. But it was Dirac's mathematical imagination, that's the key thing. No experimenter came along and said, "Hey, Paul, I've got this thing here, what [do] you think this is?" Rather this came out of his mathematical imagination. I think it's such an important point.
Steve: The PET scan is positron emission tomography and the positron is the antiparticle to the electron.
Farmelo: That's right.
Steve: And that's used to image people's brains.
Farmelo: It is. You look at the electron-positron annihilation in the body and from that you can image what's going on inside the body without opening it up. In probing the fundamental laws of nature, we use matter–antimatter collisions and study [them]. So, it's a subject with enormous utility.
Steve: And he did all this by the time he was …
Farmelo: By the time, the antimatter was, if you like, verified, right—and that's what won him the Nobel Prize when he was 31 years old, just over 31—he was then seen as perhaps the world's leading quantum theorist; and when Einstein came to the States in 1933 to begin the Institute of Advanced Study in Princeton, the first person he wanted on the faculty with him was Paul Dirac.
Steve: And he is in some ways the antithesis of Einstein. Einstein is this media celebrity, the picture of the disheveled genius, and other than the fact that they both did some similar work alone…
Farmelo: Can I disagree with you.
Steve: Yeah, sure.
Farmelo: That's [one way in which] they were similar; Dirac's wife said that her husband was the second-worst-dressed man in the world, beaten only by Einstein.
Steve: Because his suits were shabby.
Steve: But he always did wear a jacket and tie.
Farmelo: Yeah, you're right.
Steve: But [it just was] the same jacket and tie.
Farmelo: Yeah, it just was the same one for 30 years.
Steve: Right. He bought an overcoat and wore it for the next 40 years.
Farmelo: He did, and just [up the road] here. Lord & Taylor I [think it was].
Farmelo: Yeah, he was still wearing in Tallahassee just before he died, probably it hadn't been cleaned.
Steve: On the colder days in Tallahassee.
Steve: So you mentioned that Bohr referred to him as the strangest man who had ever come through his lab, and that's the title of the book. Let's get into some of the roots of his strangeness and the diagnosis of his strangeness.
Farmelo: Yes, where do you begin? Every physicist, every PhD physicist at least, has to know about Dirac stories, and these are stories that tend to illustrate a very, very singular cast of mind, rectilinear in thought, very, very literal minded and great [taciturnity], [great] unwillingness to speak.
Steve: I mean, so literal minded that when his wife says, "What would you ever do, if I left you?" you know a threat that she is going to divorce him, "What would you say if I left you?" and his response is "I would say, 'Goodbye, Dear'."
Farmelo: Yes, that's right. That's right and certainly these things are always accompanied—you tell the story quite accurately—there was always a Dirac pause. And it lasted [incidentally] up to a minute, like Heisenberg said 20 minutes [at one point]. So, he would be going through, like kind of, mini world histories, all the different ways of answering the question, before he settled on the one that he would tell. And you rightly say Steve there, he thought there for 20 seconds before the logical answer which is he would say, Goodbye, Dear. The best example of the Dirac story occurred in States, I think the first time he came in 1929, when on his first visit to the United States, and he was on touring the Midwest. And when I began writing this biography I did not believe this story, I have to say. And that's true of many Dirac's stories; it's like that they transcend belief. And in this lecture, Dirac who was a very, very fluent speaker, the chair of the discussion turned to him and said, "After your lecture, Professor Dirac would you take questions?" And Dirac said, yes. There was a guy at the back, put his hand up and said "Professor Dirac wonderful lecture. I didn't understand the equation at the top right hand on the blackboard."
Steve: And there was silence.
Farmelo: There was total silence, after half a minute, chairman and everybody is getting very anxious and the chairman turns to Dirac and says "Would you like to answer the question?" And Dirac said "It wasn't a question. It was a comment."
Steve: Right, this really sums him up.
Farmelo: And he said that more than once. His great friend Leopold Halpern—who very, very kindly gave me hours of his time just before he died—one of my outstanding questions was did you ever ask Dirac about that and he said, "Yes I did, and Dirac said 'Yes, why is it funny?'"
Steve: So let's get back to Dirac's oddness and where it might have come from.
Farmelo: Yes, okay. Well for a regular person, the most striking thing about Dirac was he is taciturnity. He was very, very happy to go for days, even weeks, even among his family, without speaking. Now incidentally there are people who will tell you, and they're right, that he would in certain circumstances talk very fluently. In normal circumstances he was very, very quiet and he knew this. He collected in his papers, accounts of people who thought this was hilarious. So he knew that other people knew that he was regarded as a strange person. He knew that, and I don't think he was offended by that, but he was very aware that he was different from other people. And he put this down to his extraordinary upbringing. This was an R-rated upbringing by his account. He was one of three children of a couple in Bristol, England. His father was Swiss, his mother was a librarian in the Bristol city library. They had the most extraordinary family environment. In particular they hardly ever had people come in to their house for social reasons, they were basically excluded. Very few exceptions, they were just in there, in that house, in that hot house, and his father would drive them on because he would only speak to his children in French. At meal times—this is the really dramatic part, at least from outside; some[thing] Dirac told many close friends about, always in the same words—was at meal times the family was split in to two. His mother would be in the kitchen with his sister Betty and his brother Felix. His father would sit with Paul Dirac in the front room. In the kitchen they were speaking only English. In the front room his father would only speak to Paul in French. In fact, later on Dirac apparently told a reporter, a reporter noted, that Dirac as a young boy felt that men spoke French and women spoke English. I mean that's how extraordinary, it [transcends] belief, but that is part of a newspaper document at that time.
Steve: And young Paul would often get sick at dinner.
Steve: From the stress.
Farmelo: Well, he always had stomach problems, and like any other child he wanted to go to the toilet. Everyone does [that] at the dinner table. Now his father had this rule that any error at all in French would be punished by denying Paul his next wish. So you could imagine what happened at that dinner table. Now, it sounds beyond belief. His wife said in letters that existed in Oxford, I read to myself that this was happening, she says, everyday—being sick over his food, I mean just appalling. Now, I personally, I am not prepared to take that, as literal truth, because his wife was, in my experience [prone] to exaggerate. But I am quite certain that it was quite horrendous, what was going on there. And Dirac said, this is another point, that he was so scared of making these errors that he thought it was better to stay silent.
Steve: And Dirac confessed later in life that he [had] hated his father, he loathed him.
Farmelo: He did, he used that word.
Steve: And yet, he saved something that his father gave him was it a pen? I forgot, there was something in the book.
Farmelo: He did keep pictures of his father. He wouldn't have any pictures of his father in the house. He wouldn't have French spoken in the house. But he did, privately acknowledged although he did hate him, you're quite right, that his father who was driving him, right—not only to learn French which [as I said] he hated to speak—but he was driving him as a student to take work very, very seriously. And one of the pitiable things is his father kept this little book with P on the front. He was desperately trying to follow the career [of his] superstar son, right, and his son evidently would not even speak to his father.
Steve: Then later [there's] this very sad, touching anecdote about the father attending quantum mechanics lectures by another physicist to try to understand what Paul was actually up to.
Farmelo: That's quite right, that's right. And he said why don't you ask Paul; he said my son doesn't speak to me. That's quite right. I might say that, [for amateur Freudians], the death of his father is extraordinary because when he was cabled, when he was in the Soviet Union—which he was a lot because he was fascinated with Stalin and his project and he was out there a lot with his Soviet friends and colleagues—he heard about his father that he was dying, this was in 1936, and he flew home. So, he must have [cared] something about [him] [or perhaps] he wanted to be with his mother. But he flew home, and he missed his father there, and went to the funeral—incidentally more people attended Dirac's father's funeral than [attended] Diracs' funeral, because he was a big civic figure, very well known effective school teacher. When he came back from the funeral and the handwriting Dirac used in the letter to his girlfriend was the biggest handwriting he has ever used in his life. I have seen it, [held] the letter in my hand. Within ten days Dirac had ascended the tallest peak in Europe, Mount Elbrus, [and] he never climbed a peak as high as that again.
Steve: So there was something that had been liberated in him.
Farmelo: "I feel much freer now, and I am my own man"—[words to] that effect. He wrote those words; I've seen the letter. He really, that this man who was see[n] as one of the greatest physicists in the world [bar none] [had] felt under the heel of his father right to the end.
Steve: Through the end of the book you start to talk about, and it's a very dicey proposition, but an actual diagnosis of either autism or Asperger's syndrome for Dirac, and [why don't you] talk about what you think about that.
Farmelo: Well, I have to say that I certainly didn't begin the book thinking about this at all. But it occurred to me when you got someone of Dirac's singularity as a person that you have to at least look, from a modern sensibility, [at] the possibility that he was autistic. And what I decided to do was I spoke to experts in the subject. I consulted with them [about] what the definition of autism is. And if you look at that definition, then you'll know aspects of it, you know, this literal, very narrow-mindedness, they are unwilling to speak particularly as a child, there are several aspects to it that are very well known now. Every single one of those characteristics is fulfilled by Dirac and [in spades]. And that's why I believe that it would be, in my opinion, evasive not to come out and say that in my opinion he was very likely autistic. I think he was definitely autistic. But that said of course he is dead, and you could never be absolutely certain. And I have to say, to be absolutely meticulous about it for someone to be diagnosed for certain of autism, you have to be sure that they had these characteristics as a young child, and we don't have enough documentation to [do] that, so there is a logical loophole there. But I think it is very important to say this, because I don't think Dirac had a choice about that behavior, I think [the stuff about] [having] been driven into himself by his father, I don't buy that at all. So I mean it has an [import], so it is just not a frivolous label that one puts on.
Steve: So you think that he was autistic to begin with and then the family environment, just sort of, was overlaid on that situation.
Farmelo: Yes, yes, I mean, one of the things is very noticeable about Dirac is his extreme lack of empathy. Now, of course, there, like in every other psychological patient you could always find exceptions. Well I can given them, but mostly he was very, very devoid of empathy. Even sometimes even from his own family. Now, let me give you an example of this, something that I can't beget belief when I read it; that the abiding tragedy of Dirac's life—if you leave aside his father, although he is connected—was that he had this younger brother, excuse me, elder brother, whom he followed around. He followed him to study engineering.Very important part of Dirac's sensibility; he was trained as an engineer, not a mathematician, not a physicist. And he followed Felix to university and they were very close as brothers. And they diverged when they were in their teenage years. One could have many reasons for this. Probably one obvious one is that Dirac, Paul Dirac was the superstar, Felix was some[one] who struggled to get a degree. So you could imagine there are all sorts of fraternal tensions going on there. Felix desperately wanted to be a doctor and was forced by his father into a rather an ordinary career as a moderately successful draftsman. When Dirac was just coming up to the end of his PhD, it was in March 1925—when he [incidentally] wasn't speaking to his brother; he would walk on different sides of the street to avoid him—He got this letter from his Auntie Nel saying that his brother had killed himself. Felix had been found under a [holly] bush and had taken potassium cyanide and killed himself. Now Dirac never spoke about this subject extensively to the best of my knowledge, certainly not even to his wife. He didn't even speak to his daughters except for one moment when he opened a tin, a little tobacco tin, and showed them the picture of his brother shut it, and never said anything else. So, I think [it's] very reasonable [to say this was] an extraordinary trauma in his life. You know what he did [though], Steve? He said, an authenticated quote, that it was only that tragedy that revealed to him that parents were supposed to love their children.
Farmelo: Well, I said [when I read that], this is unbelievable: This guy had been around 23 years, and he said in a completely calm way but until then he didn't know that parents were supposed to love their children. I mean what do you do about that?
Steve: And much later in life, he talks about the fact that it was probably very difficult for Felix to have a young brother who so outshone him. But it's said with absolutely no feeling about it, just as a fact.
Farmelo: That's right, I mean, as a biographer when you write about Dirac, it's complicated because this character is crying out for interpretation right. And you have to do that as a biographer, but I think you have to be clear about what is fact and what is interpretation, and I tried very hard to do that in my book.
Steve: Yeah, and you're very successful. And the real paradox which—I am going to give away the end of the book—the very last lines of the book are about how, here's this man who is virtually incapable of emotion but one has to categorize his scientific philosophy as being one in which emotion, your aesthetic appreciation, is your principle guiding factor.
Farmelo: He was a physicist of feeling, that's absolutely right. And he said that if a physicist did not have that feeling about the beauty of theoretical physics, then he or she is in the wrong job. He felt that strongly.
Steve: Graham Farmelo's award-winning biography of Paul Dirac is titled The Strangest Man. We will back with part 2. Meanwhile, get your science news at www.scientificamerican.com where you can check out the In-Depth Report on personalized medicine in the genomic era. Follow us on Twitter, where you will get a tweet every time a new article hits the Web site. Our Twitter name is @SciAm. And Graham Farmelo is well worth following on Twitter. His Twitter name is Graham Farmelo. For Science Talk, the podcast of Scientific American, I'm Steve Mirsky. Thanks for clicking on us.