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Interview of Charles W. Misner by Eline V. A. van den Heuvel on January 14, February 8, and May 11, 2020.
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
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Physics Graduate student Eline V. A. van den Heuvel (University of Amsterdam) interviews Professor Emeritus of Physics and Senior Research Scientist at the University of Maryland Charles W. Misner. After obtaining his BA at the University of Notre Dame in 1952, Prof. Misner continued his education at Princeton University, where he completed his PhD in Physics under supervision of Prof. John. A. Wheeler (1911-2008) in 1957. In the spring semester of 1956, Prof. Wheeler fulfilled the Lorentz professorship at Leiden University, the Netherlands, accompanied by his student Misner. Prof. Misner discusses this trip, focusing on his personal experience and his work on the Already Unified Field. He also discusses Wheeler’s relativity work and possible motivations for Wheeler to go to Leiden. The remainder of the interview deals with the many-worlds interpretation of Dr. Hugh Everett, a friend of Misner and former a PhD student of Wheeler, and Misner expresses his disappointment in how the physics community has treated Everett.
I’ve seen some documents from Wheeler, and one is a letter from the Dutch physicist Sybren de Groot to John Wheeler. In this letter, he [de Groot] was asking if Wheeler wanted to fulfil the Lorentz Professorship at Leiden University.
I was wondering if you can remember how Wheeler responded to this invitation.
Well, I haven’t seen the letter. I don’t know how he would have responded, but he certainly did respond and accept, because he then ended up, after I don’t know how many levels of negotiation with the Lorentz Institute—what was the name of the man who wrote him?
Sybren de Groot.
OK. But anyway, once he was committed to going there, he talked the Institute into letting him bring three other people, and those three were Joseph Weber, myself, and Peter Putnam. In early February- whenever the spring term was—or the winter term was over at Princeton, we set out. I think all of us—maybe Weber came independently, but Peter Putnam and I were on the S.S. United States, a large ship that took us across the Atlantic. I then, after disembarking at Le Havre, I guess shepherded by Wheeler maybe, got brought on to Paris where I remember the Wheelers taking me to dinner somewhere. That was John and Janette. And then after that, we went separately, I guess, to Leiden, where—I believe Peter Putnam must have arrived before I did. And anyway, he had found a suitable place for me to stay, which was on the Pieterskerk Square. And so I ended up with a room above this restaurant, which was an Indonesian restaurant run by a woman from—from Luxembourg, I think. Anyway, so it ended up that having tried to learn a little bit of Dutch while I was in Princeton, before this—because I must have had months’ notice of this, and there was a Dutch student in Princeton who tried to teach me a little of the Dutch language.
Do you know who this student was? Who this student was? The student in Princeton?
I may have it written down somewhere. Somewhat Rini. But—and she was probably in Princeton as an au pair, working for some family in Princeton. I’m not sure exactly of that.
OK, but she was not a student there?
She was not a student.
But anyway, so then it turned out that as I was staying in this room above the restaurant run by a Luxembourg woman, and she had hired a young Luxembourg girl to work there, and so I found it much easier to just converse in French—
—than to try to use my Dutch.
[laugh] Yeah, yeah. I can certainly see that.
Because I had had some fairly good French education. Not very strong; I never got in a situation where I had to listen to many—or try to respond to Native Frenchmen. But these two clearly were, and so it improved my French a lot, but didn’t do much for my Dutch.
Yeah. [laugh] Who needs to speak Dutch when you speak English and French? I was wondering— I’ve seen the letter in which Wheeler asks the Leiden people, de Groot, if he can bring you and Joe Weber. Was this a pre-condition for him for going to Leiden, or who came up with this idea?
Why does he want to bring us along? OK. Joe Weber, who is now remembered by everyone involved in the detection of gravitational waves as sort of the person who provoked the development of that now new arena of astronomy, namely gravitational wave astronomy—he wasn’t doing it with the point of view of astronomy, which later was the focus, as LIGO was built 50, 60 years later. But he was determined to try to understand gravitational waves. He wanted to get into gravity. Somehow he had been on a sabbatical year originally at Princeton, at the Institute for Advanced Study, where in the Fall of ’55 he would have talked with—while he was at the Institute for Advanced Study, he would have talked with Wheeler about wanting to get educated in gravity. And Wheeler was not deep into the stage yet of studying gravity himself. But anyway, so—and then so Wheeler encouraged Weber to come with him to Leiden, which he did. And I was an active student of Wheeler’s just having begun that fall. I think that’s right. And when Peter Putnam got involved in it, I’m not sure; but he was a student of John Wheeler’s for maybe ten years earlier, as an undergraduate. And Wheeler knew him and respected his unique ways of looking at things and convinced him to come back to university and try to work on a Ph.D. So he was also brought along. I don’t know whether the [Lorentz] Institute was aware they were getting so many people, but they did find a very large room with four desks in it for Wheeler and the three of his attendees. And they gave him a second room which he went to, to work on nuclear physics. I don’t know much about the exact work in nuclear physics he was interested in, but maybe Jim Griffin, whom you’ll talk to in a week or so, will know more about that. But anyway, I didn’t interact with him at all on the nuclear physics side. Weber was there too —and very soon focused on gravitational waves, which at that time were in question whether Einstein’s theory even actually had gravitational waves as one of its components. Einstein had thought so, but that was based on his work with an approximation to his equations for the general relativistic form of gravitation. And so some of the mathematically inclined people were worried whether even though there seemed to be waves if you make that rather drastic approximation to the full Einstein theory, they weren’t sure that, if you went to the next level, there would still be gravitational waves there. So it was a question that was quite alive theoretically at that time. There was almost no gravitation as active experimental or observational physics at that time. It had simply dropped out of the scope that most physicists were willing to spend time on throughout the ‘30s and the ‘40s. Of course, half of the ‘40s were taken up by World War II, but when people came back from that, almost all of them thought that the new technology would be used primarily for studying elementary particles. But Wheeler—who of course had a great career up to that point, most of it in nuclear physics working on the atomic bomb during World War II. And then a couple years just before I arrived in Princeton, he was very much involved with the development of the H-bomb. So I think probably the year—I suppose—well, he had closed up—he was in the process of closing up his work with this Project Matterhorn, I think it was called, which was done at a special facility out a few miles away from the center of Princeton along Route 1. And let me see. I guess I arrived in Princeton in late ’53, Spring of ’53, and I began worrying—focusing on a thesis in the—I arrived, yeah, in the summer of ’53. First classes at Princeton that fall. And then in ’54, in September, at the end of the summer, I was looking for a thesis advisor and ended up deciding that Wheeler was the most attractive one for me, even though I had done some other very mathematical work with Wightman the previous year. But so Wheeler, however, in that previous year before I began formally working with him, was teaching for the first time a general relativity course, and he was doing that as his way of studying the field. He always tried to think of teaching as a way of—where the teacher studies, where he learns a lot by trying to present it to other people. And even after he knows a lot, he likes to work with students—this is John Wheeler—likes very much to work with students because he feels they bring a much broader viewpoint than he would come just out of his own past experience. Mostly they come with questions he might not have thought of asking. So anyway—
Yeah, so by this time that the four of you were going to Leiden, he just entered relativity. He starts to teach this course in ’53. And then when he goes to Leiden, he’s also going to teach a course about relativity?
So here at this moment, was he still using the course to learn, too?
Oh, I think so, yes. In our letters setting this up along with Jim Griffin and so forth, there was a little bit of confusion. Jim Griffin is, as he says, Wheeler’s last nuclear physics Ph.D. student, but I am not the first gravity Ph.D. student that Wheeler had, that was Arthur Komar.
And he got his degree a year before I did and did not come to Leiden. He was working on somewhat different parts of—well, he was just finishing up writing his thesis, I think, while we were in Leiden, probably. So he went on to, I just learned recently, a fellowship for a year in Copenhagen, which would have been the year after—had it starting just at the end of the summer, at the point where Wheeler and I were returning to Princeton. And then following that year, Komar went to Syracuse where he spent substantial time. He worked there with Peter Bergmann and has ever since that time been considered much more a student or a much more associated with the kinds of activities in gravity that Bergmann did rather than those that Wheeler was leading. So he was frequently identified as part of the Peter Bergmann group working on gravity rather than being active in interacting with Wheeler the way his other students did from then on.
So how old were you at the time you got this invite to go to Leiden? You were a Ph.D. student?
I was born in June of ’32, so I guess that makes me 24.
How was it for you that you got invited to the Netherlands?
Well, it was entirely due to Wheeler. He was going there. He, I think, valued me for my mathematics background. In fact, in his autobiography, which he wrote with the help of Ken Ford, he says that I got my bachelor’s in mathematics at Notre Dame, which is incorrect. I went to Notre Dame in the Fall of ’49 when I graduated from high school, at age 17 I guess. And at the end of three years, because I was—well, at Notre Dame, I was taken under the wing of Arnold Ross, who was I think the chairman of the math department there at that time. But he always was looking out for bright, mathematically inclined students, and got quite famous for that after he—starting then and continuing mostly later to Ohio State. He ran summer schools for high school-aged students to do abstract mathematics. He would bring students at that age together and let them work full-time, living on the campus of the university, and spending hours every day listening to lectures or arguing with each other or writing up their homework assignments. And a typical homework assignment, as I can remember it, that later very much impressed me, was a statement with the challenge, “Prove, disprove, or salvage.” In other words, if this statement is a theorem, prove it. If it’s a conjecture which you can show is false, show it. If it seems interesting, maybe you just need to change the statement a little bit into one that can be proven. And so that’s the salvage part.
[laugh] That sounds like hard questions. [laugh]
Well, that’s a hard question. Most of them were questions on number theory because he could get down to interesting questions quickly with the students that way. And then the main thing he was teaching was how to think about mathematics. Not how to accept known knowledge, but how to—
Not reproduce, but really think.
Right. So anyway, getting back to me in Princeton, I came—Ross had taken me under his wing at Notre Dame, saw that I had already learned a lot of calculus by looking at my father’s old calculus books from the 1910s, and so he got—let me skip a year or two of the conventional mathematics for students there.
Oh my. [laugh]
That was the days when you did pre-calculus for a semester before you even started calculus. In college! And so I would skip all that and got immediately into some more advanced calculus. And that meant I had a lot of tools to get better at physics, so immediately I skipped the first year or so of physics. And throughout that, Ross kept feeding me with good mathematics. But I decided that I wanted to be a little bit closer to reality, so I kept—I switched out of chemistry just weeks after I got there and met Ross. But I decided rather than being a mathematician, I’d rather be a physicist and use the mathematics for something. So I was a physicist there. I graduated from Notre Dame after three years’ work. They made a special exception for me because I didn’t have the course requirements---I had skipped all the courses the first year. But they made that decision late and they wanted me to stay around for another year, so I stayed another round, my fourth year at Notre Dame. And that year, I took essentially all graduate courses. Well, I had already taken some, I guess, even before that. And so when I arrived at Princeton—in the Fall of ’53, that would be—I found that I had already had at Notre Dame all the courses that were, so to speak, unofficially expected of first-year graduate students there. So I just started doing some research and reading and so forth and didn’t take many courses. And then passed my qualifying exam, as they call it, so you’re ready to start a research project. So that meant that I did that. Wheeler, because I had all this background—and part of the first year I spent at Princeton was talking with mathematicians, close friends who were mathematicians, they had this tearoom in the math department, where physicists and mathematicians would meet every afternoon, very informally. Nobody had to go in any particular number of times and so forth. You saw lots of people there. And so I also continued my higher-level math work, thereby being told what to read by mathematicians. [laugh] So when I got to Wheeler, he essentially looked at me as someone who could bring more fancy mathematics to gravity than he knew. And that was true. He had drawn pictures of wormholes. He talked about if space is curved, maybe it’s curved enough to allow that sort of weird geometry. But he probably had no idea that you could ever find how to, were after a relatively short time with him, after all the mathematicians I had, I came to know, well, that was only—that was—it was only after I absorbed and explored what’s called the initial value problem. Those are the conditions that have to be satisfied before you could even start evolving the Einstein equations to say what comes next. So I eventually got to the point where I realized that it was entirely possible that one could prove rigorously that solutions corresponding to Wheeler’s picture of a wormhole did exist. The Einstein equations allowed solutions that looked exactly like that, although I didn’t do the details of that and publish it until a few years later. But that was the sort of thing that was on my mind, and the kind of things that I knew how to talk about that made Wheeler be attracted to see what I could do working with him on some fancy mathematics introduced into relativity.
So he had those big ideas, and he needed someone good with mathematics. And that’s where you came in the picture?
That’s right. That’s where I fit in, yeah.
How was this visit to Leiden? How was this for your career? You were young. You had just started your studies with Wheeler.
Well, it was a great way to get started. It turned out that, well, I interacted not so much with Peter Putnam except sort of socially, because his—he was intrigued in various parts of relativity that didn’t appeal to me at all, namely Eddington’s theory and whatnot. But between Weber and Wheeler and I, we talked a lot about gravitational waves and things like wormholes and getting clear in our minds how to think about strongly curved space-time. That’s what Wheeler was really after. All the previous work on gravity—well, the cosmology—well, I guess there were two things that didn’t—cosmology and the Schwarzschild metric were two of the things that were known as related to physics. The Schwarzschild metric played a role in being able to analyze the motion of the planet Mercury, which didn’t—was known to better accuracy than Newtonian theory could show. But apart from those two things, like the waves and so forth, most of what was being done in relativity—the bending of light and things like that—was being done by saying, well, you could almost do these things in Newtonian theory, and to get to do them correctly, you have to add a little bit of Einstein’s equations. So it was mostly done by adding a little bit of Einstein’s equations to things you could already imagine existing in Newtonian viewpoints. And Wheeler said no, these equations don’t just allow a lot of strange coordinate systems; they allow strange curvatures. If gravity is the curvature of space-time, let’s look at it when it’s really curved, not just when it’s curved a little bit.
He didn’t just make some corrections to the Newtonian model, but he did something new?
Yeah, he wanted to get something new and extreme out of it. So he was looking in that direction, and I was working with him on things like that. It turns out there were actually two things going on there that I got involved in. One was how to think about and do things with strongly curved space-times. And one other reason that Wheeler liked this wormhole idea is you could imagine that in a classical picture, there could be electric lines of force that would go in one side of the hole and come out the other side, and then, to a distant observer, it would look like a negative charge one place and a positive charge another. So he was saying, well, maybe we can do without particles. He described later in his career that—he said—he wanted to see if all of the physics could be described in terms of particles. And eventually, he was giving them up and say, well, maybe it’s all in terms of fields. Of course, Einstein had that goal, too. But people weren’t paying attention to him because he was just doing it in ways that didn’t work out. And much later, after a jaunt with gravity, Wheeler said maybe everything is quanta in some more general sense, than just particles or fields. But anyway, he was on this kick for a while to see how much we can do only with fields, without the particles, because this wormhole idea says you might have things that look like particles from a distance but aren’t. They’re just curved space-time with fields running through them.
Can you tell me something about how far Wheeler got with his ideas of the Einstein-Rosen bridge for spin without spin? So he had geons for mass. He had wormholes for charge?
Right. Geons—right. Geons I can tell you about. Spin, I can’t say much for. He did have students working on that [Dieter Brill perhaps], but I don’t think that got as far as, say, you can get somewhere with just electric fields. But the two things that I worked on there—one of them looked initially as not gravity but I got into it because of gravity, and that was Wheeler always wanted to add to the classical gravity you could get from Einstein’s equations, where I could maybe dig in and see the behavior of curved space-time and Maxwell’s equations and so forth. But one of my roommates, Hugh Everett, had pointed out to me that there was a textbook by [laugh]—names always]—
—are hard, yeah.
—[Rainich] which had shown that half of the Maxwell equations could be expressed—if the Maxwell fields were the only fields besides gravity in a model universe, half of Maxwell’s equations could be stated entirely in terms of their gravitational effects. So Everett pointed this out. [Diversion regarding Everett QM:] Because Wheeler wanted to do quantum gravity—he had been talking to Bryce DeWitt [CWM: I don’t think I ever heard about DeWitt by the time I was in Leiden. See Wheeler’s notebooks to date when they first interacted], encouraging him to think about these things, too—and he wanted to think about a wave function for the universe. But standard quantum mechanics then said, well, quantum mechanics has to separate the world according to Bohr’s approach to it, into the quantum view and the classical view. You have to have a classical instrument to record the results of an experiment, but you have to have a quantum idea that predicts the probability of what you should get. But you can’t—under that viewpoint, you can’t have a wave function for the universe because there’s no one to observe it. Because it’s outside the universe. I mean, in a lab, you could have your equipment here and you’re outside as a classical object, or your equipment is various meters that are clearly classical objects, and they can record what’s going on microscopically, that you try to predict quantum mechanically by assigning wave functions to the things that get involved, and predicting the probabilities and checking it. Well, so Wheeler—this idea that Everett came up with said, well, maybe you should just assume that the Schrödinger equation of quantum mechanics is always working. That when you do an experiment, if you include the observer in what’s in your description of what’s going on, then you don’t have to let the wave function collapse when the experiment is done. It’s this famous Schrödinger cat picture, where Bohr would say OK, you’ve got this cat in a box so it can’t be observed, and there’s some mechanism that will randomly, with certain probabilities, touch off a poison gas to kill the cat.—but until someone opens the box and looks, you don’t know whether the cat is alive or dead. And Everett said, well, look, that means you’re ignoring the Schrödinger equations. If you just include the recording equipment in the wave function, you end up that the robot that opens the box and records what’s there simply is part of the quantum mechanics. There’s one universe where the robot writes “dead cat,” and another one where it writes “live cat.” And so if you accept that view of how to do quantum mechanics, why then, of course, you can have a wave function for the universe, except that you don’t know anything about the other universes that got the other answer to all the questions. So that was going on, and Wheeler was interacting with Everett, who was trying to write his—so that’s why Everett gets into gravity, because it provides background that says it is possible or reasonable to talk about the wave function of the universe. We just have to take this other very unreasonable bit of stuff, of multi-worlds. So Wheeler was attracted to that. On the other hand, he also felt he owed a lot of his bringing up in physics to Bohr, and he really respected Bohr. So during that year, he was trying to negotiate that Bohr would look at or have one of his colleagues look at some of these ideas that—where Everett was putting out.
Because Everett’s studies were not really being taken seriously in the beginning?
No, no. I have to—I didn’t pay much—well, I knew Everett. I understood what he was doing. I didn’t like his view, but I didn’t know anything wrong with his logic. So I just said, “Well, that’s his problem. I’ve got other things to do.”
But then a few years ago, I got a clue as to how I could have a different view of Everett, namely get the answer I want without saying Hugh made mistakes. I’ll give you a copy of that paper [Phys. Scr. 90 (2015) 088014 (6pp)] that I published in a special volume of the Swedish journal of physics in honor of Dick Arnowitt, whom I worked with soon after what we’re talking about. Anyway, I can give you that. But that was in the background. [End of diversion re Everett QM] And then there was this other thing of the already unified theory of—why can’t I remember the name?
Wasn’t it [George] Rainich?
No. Oh, yeah, right—yeah, that’s it. I think that’s it, yes. So there was this—he had had a textbook that showed that half of Einstein’s equations could be—have a—the Maxwell equations in a universe that only had Maxwell or gravity, half of them could be stated entirely in terms of gravitational concepts. And so Everett quite independently of this other project had pointed this out to me and said that maybe you could find a way to get the other half of Maxwell’s equations out of gravity, and that would probably intrigue Wheeler. Which it did. So Wheeler got intrigued by that because that would be an example of pure fields, and as he put the name, already unified, in the sense that he could write entirely—in terms of curved space-time and the properties of curved space-time, you could write something that included the Maxwell equations. So he set me to work on that, which went alongside all the other physics he was doing like gravitational waves where he talked about other aspects of gravity. So I worked on that and solved it. Then it was discovered [Peter Bergmann told Wheeler] that Rainich had also solved that problem. He just didn’t bother to put it in his book. And so then I had to go back and write something I had started years—in my first few weeks with Wheeler, of trying to think about how to use the Feynman action-at-a-distance —Feynman sum over histories -- to do something with quantum gravity. So I wrote that up for a thesis, but it never got anywhere. But it got me out.
[laugh] So you worked on this already unified field theory. It appeared to be done and ready, so then you had to go back to Feynman’s sum over histories to get your research done.
Right, yeah. So I did that. Everett was somewhat the same. When he wrote up a big long paper about his ideas, and Wheeler couldn’t sell it to Bohr, he got a much-reduced paper that he could call his thesis and somehow get through. And so he got his Ph.D., but he was—he had many interests, particularly in game theory, where he had a very—a big career and was highly recognized there. But he never intended to become an academic—some people say he—because people didn’t pay attention to his thesis, he didn’t—he had to go off and work in the industry. Well, that’s completely wrong. He never had the slightest interest in being an academic. And the reason for that was purely economic. He knew what people got paid in industry, and he knew what they got paid in universities, and he wasn’t going to go for the low pay. So he was never going to try to get an academic position. Three or four years after graduating, he was probably getting up to where he was getting paid more in the government than Wheeler was being paid at the university. But he was also a person full of many faults, which killed him, because he drank too much, ate too much, et cetera, et cetera. But he did live long enough to see people begin to take his work seriously about 30 years after he wrote it.
Poor guy. [laugh]
Right. He was not around when they had the 50th anniversary of his thesis. There were two large conferences that invited people from around the world to each of them, to look at and argue about Everett’s view of quantum mechanics. There was even a BBC program. Did you ever see that?
I have not.
It’s probably available somewhere. Anyway. There is also a Peter Byrne biography from Oxford UP and collected works from Princeton UP.
I would like to—yeah, so let’s see. This question is maybe a little bit more hard to answer, but do you know what Wheeler expected to find in Leiden? Because Leiden has— in the beginning of the 1900s, it had a big history, actually, with general relativity. Einstein was often around there. Or did he maybe want to work with specific people? Or was he more looking for having some time off to work with his team, to work with you?
I would think it’s more likely that last. I mean, he liked Europe. He had been at the Bohr Institute soon after his Ph.D. He had been in Paris four times. And when he got called back to work on the H-bomb, he had to break off a year sabbatical in Paris, where he knew his wife would enjoy and run off. So I think it was more that there was a chance to concentrate on his research, be a little closer to Copenhagen, and let his family—well, during that year, only one of his children came with him. That was Alison. She was a schoolgirl at that point, and she came with him. But the other two children were in college, and so they stayed in the United States during that semester at Leiden. But anyway—
But he did consider Europe a suitable place for his wife and his children?
Yeah. So I’m sure his wife enjoyed it very much. If she had her choice, she probably would have gone to Italy, but there wasn’t that much good science there then.
But she did love Europe, and he was very happy with his times in Europe, so he wanted to—that was an opportunity for him. And I guess he felt that he could—it’s only a semester. He could still work with me and Weber. And so the prospects of getting something done—I think he may have also felt that it was going to give him a chance to finish his nuclear physics project. I think he didn’t succeed in that, probably. I suspect he was trying to write a too-comprehensive paper, and by the time he got near enough to finish it, everything he needed to say there had been said by other people. So I think that that was just—I don’t think he spent a lot of time on it when he was there, but I remember seeing—in that office he had, he had various posters up on the wall where he had prepared the presentation of graphs of this, that, and the other thing, from the nuclear physics days. But I never got any detail on that. I didn’t want to.
[laugh] You were like, “Let me deal with gravity.”
Right. Like I didn’t want to really argue about Hugh Everett. I just said, “Well, he’s a bright guy, and I’ll let somebody else worry about it.”
So by this time, too, Wheeler was working on relativity. He was also still doing some work in nuclear physics. What was his main interest?
Well, when he came back to the—his main interest was, I think, getting gravity to be recognized as an important part of physics. It had been ignored as just a playing ground for mathematicians for a couple of decades. Nobody had very much good to say about Einstein’s efforts to do unified field theories. He didn’t attract any followers—of note, anyway. But Wheeler felt that with all the new technology—because Bob Dicke at Princeton was already talking about making experiments and observations on gravity, so the technology that had grown up during the Second World War and soon thereafter was clearly going to offer some new opportunities. Wheeler didn’t know exactly what. I doubt he would have thought that detecting gravitational waves was one of the first things because as Einstein had pointed out, it’s hard to think of anything that would produce a strong enough wave to ever be seen. But nevertheless—so one of Wheeler’s projects there that did not take place in Leiden but I think was on his mind then is to redo the structure of neutron stars. He eventually had a crop of people doing—because if you want to describe what’s possibly known about the possibility of neutron stars, which were not known to exist in the universe, but there was a conjecture that they could. The white dwarfs were known to exist, and it was known that they came from the collapse of stars, and neutrons, but they had a maximum mass. You couldn’t get collapse to a white dwarf for masses bigger than about one or two solar masses. And so the question of neutron stars—but Wheeler liked that question because it brought his nuclear physics into play. That meant that physicists who would not be inclined to read anything about gravity might be willing to read about neutron stars because they would see their work or somebody else’s work that they understood well on the structure of the nucleus of the atom. They could see that kind of work going on by someone who’s well known and highly respected for being an expert in those fields. So it brought a cachet of wider approval to think that gravity is a part of physics that shouldn’t be totally ignored. And he has said various places that he had thought about getting interested in gravity for many years but he never did anything with it because he always thought he did his best work when he works with students, and he said during the ‘30s or the ‘40s that if he worked with a student on gravity, the student would never get a job. [laugh] Because no—in fact, Princeton wouldn’t have supported gravity if they had any choice, for decades after that. I mean, after Wheeler—Wheeler tried I’m told many times to get the physics department at Princeton to appoint a tenure-track or a serious—or eventually the possibility of giving tenure to somebody who worked in gravity, and they just wouldn’t. People who were later very well-known were supposedly on his list of people to invite and maybe give a tenure position to. For me, they—I had an assistant professorship a couple of years after my Ph.D., and when it came time to renew that, they renewed it, but for the first time in all my years there, they did not give me a pay raise. And so I took that as a sign, correctly, that they did not want to waste any of their precious tenure faculty budget on gravity. They wanted to do other things like condensed matter and elementary particles.
But Wheeler was allowed to teach a general relativity course.
They couldn’t kick him out at that point.
They couldn’t kick him out?
He had tenure on the basis of his nuclear physics work. By that time, he had been president of the Physical Society. He was widely recognized as being important. So they didn’t object to him getting money from the federal government to explore gravity, as long as it wasn’t their money.
[Allen] Shenstone, the chair of theoretical physics—Wheeler asked him if he could teach a course on general relativity. But Shenstone could also have said no, right?
Oh, yeah, but that would go against—I mean, it doesn’t cost the university anything to let him do what he wants, and he’s got such a reputation, why not let him do what he wants? So I don’t think that was any question that he would do that.
OK. I was wondering—so when Wheeler is thinking about neutron stars, he’s thinking about the collapse of heavy stars. The gravitational collapse.
But he was not studying the gravitational collapse; he was just studying the endpoint. What kind of static non—no longer active objects that were at the density of the nucleus.
So was he there only studying neutron stars, or also singularities—gravitational singularities?
That was on his mind, yes. Although a surprising thing for me was that although it’s clear from other work he did he was worried about the gravitational singularities—and this famous paper by Oppenheimer and Snyder from the late ‘30s, where they described the collapse of a very highly idealized and simplified chunk of matter into a black hole, except that it wasn’t known as a black hole, and they didn’t describe it as that. They said the matter collapses to a singularity, and on the outside, the star never stops moving. The collapse just slows down. And so they—that’s the title of their paper—” Continuing Gravitational Collapse.” So they did not have any picture of a black hole at that time. They just had a picture of a slowly collapsing piece of matter that could be seen from the outside. And so that gets to be a few years later before that picture is straightened out. And maybe if we want to go a couple of years past Leiden, we can talk about that.
I would prefer for now to stay with Leiden.
Only one thing that I was wondering was that I was just wondering if this thinking about singularities, gravitational singularities—if that did have anything to do as well with his view of particles, as particles can also be seen as point particles.
No, I don’t think he thought of that singularity as point particles. He certainly was—he didn’t like the idea that gravity could produce a singularity. His hope was that if you introduced quantum mechanics, there wouldn’t be a singularity. That was his hope. So he did this work on neutron stars just to attract the attention of physicists who respected his work in neutrons to think about gravitation physics. And he was very slow to accept the idea that larger masses than could collapse into a neutron star could do something else. Because something else he thought of was collapsing to a singularity, and he didn’t like that. So that’s one of his pushes for quantum gravity was to see whether it would avoid the singularity.
So the quantum mechanics takes over, and it doesn’t have to collapse any longer?
OK. Yesterday, I went to Niels Bohr Library & Archives, and there I actually read a letter from Joe Weber, and he’s describing the time in Leiden—it’s actually from—it’s called a family gathering.
I also read a letter from you. But in the letter from Weber, he says that Wheeler was very busy, that he had lots of visitors. Do you know who all those people were?
No, I don’t think so. I don’t. I doubt that I could remember much of that. I know that Peter Putnam was interested in people and he got to know—I think it was Ehrenfest’s widow, and introduced Wheeler to her, and Wheeler was very pleased with that interaction. And—
There wasn’t a lot of collaboration between people from Leiden and Wheeler’s group?
No. Not on gravity. I don’t remember—there were people that talked to him frequently, but I think they were mostly on the nuclear physics side. He must have, by that time from his brief period in Paris, have known of Lichnerowicz because he referred me later to Lichnerowicz’s book on gravity as a good place to study. But I don’t remember Lichnerowicz. I think I would have noticed if Lichnerowicz had come to visit. Much more likely was that Wheeler could run off for a day or two to Paris and him see [Yvonne] Choquet-Bruhat for his—she was a student of Lichnerowicz who was known to Wheeler because she was invited to that 1957 Chapel Hill conference, just a year after we came back from Leiden. But again, I don’t think she came to Leiden. And who else could have been there? Mercier from Switzerland. I probably didn’t—the name probably didn’t even ring a bell to me at that time. And Møller from Copenhagen, I would have, I think, known if he had come, but I’m pretty sure he didn’t. Because Wheeler, I think, did go to Copenhagen just for a few days or a week or something during that spring in Leiden.
And of course Regge, if I am pronouncing it well? Regge?
How do you spell it?
Like this. They wrote a paper—
Regge. Yes, sorry.
He’s Italian. Yes, he did. He was there. Yes, Wheeler had met him first at a conference in Rochester, New York, I think, which held conferences on particle physics. And he was such a bright guy that whomever he was working with in Italy arranged for him to be in the United States at that time, and he was introduced to Wheeler. And then by the time we were in Leiden, Regge was on his way back to Italy. But Wheeler had got him started on a project to check the stability of the Schwarzschild solution. And Regge has described that maybe Wheeler—also saying that Wheeler was always interested in things that you find very hard to teach to physics students when they’re young, which is that you don’t just start by filling in equations. You start by trying to figure out what’s happening and what you’re going to do. Well, Wheeler, after all his experiences saying that he had apparently written a paper about checking for the stability of the Schwarzschild solution. That is, if such a piece of curved space-time existed, would it stay there, or would some random thing knock it over, and it would disintegrate? So that was to be settled—he wrote this paper outlining how to go about the problem, and turned that draft of the paper over to Regge and said, “OK, this is how I think it would work. Give it a try. Fill in the equations. [laugh] Because I haven’t written any. And we’ll see what we can do.” Well, Regge was clever enough to be able to handle that, and they developed a technology for analyzing the stability to the lowest order. It’s called linear stability. Figured out all the technology needed for that. But, as I would later say to one of my students, they didn’t at that time know how to treat the region of space-time approaching what we now call the horizon, which was then called the Schwarzschild singularity. So they made their best guess at how to do that, and they came up with the conclusion they wanted—that Schwarzschild curved space-time was, in fact, immune to minor disturbances. So a few years later, after Finkelstein had shown to me and the rest of the world what’s really going on at the so-called Schwarzschild singularity, now called the horizon—so I had one of my first students when I went to Maryland redo that work of Regge and Wheeler because then we knew what the answer was. How do you treat the field to say that this is a black hole? That the fields can fall in, but they can’t come out. That was not part of the thinking that Regge and Wheeler knew. And it turns out, when we set the students on it, there was no useful computer mathematics or things like that. You had to do everything by hand, and they were very long difficult calculations. And it turns out that my students found several errors in those.
Right. So they had to get corrected, too. And then they published this. Well, two of them started working on it. One of them, due to my immaturity of a mentor, didn’t finish a thesis. If I had him later, I would have found a way to do it, because he did a huge amount of work and then he didn’t get something that satisfied him as a thesis and he went off and did other things. But anyway, eventually this Regge-Wheeler work was redone with the equations corrected, and the boundary condition, as it’s called, at the R equals 2M singularity or horizon. And Vishveshwara, known as Vishu, did that paper, and after he left with his Ph.D. for that, he worked for a while at NASA in New York, where they declined to renew his fellowship for a second year which is normally completely standard because they said he wasn’t doing anything worthwhile. And among the things he did there that were considered not worth renewing his fellowship for was a paper that was cited in the first LIGO paper—
Oh, wow. [laugh]
Because he had shown that after having done this business of how the black hole would behave if it’s perturbed, he said, well, how could you perturb it? Well, he had the technology for handling gravitational waves. He said, well, let’s throw a gravitational wave at it and see what happens. And he found out that if you have a pulse of gravitational waves that are very small, they just fall into the black hole. If they’re very big, it’s too small for them to see; they just go past it. But if they’re right in between, they hit it and set it ringing, and it rings and damps away like a bell. And that’s known as the ringdown of a black hole. And that was seen in the first detection of black holes, and they cited his paper. The one he got kicked out of [laugh] his job for.
[laugh] That’s a bit like Everett.
Yeah. [Except that Vishu was cultured and respectful, and lived to see his work confirmed and applauded.]
So another person—besides Regge, Griffin came too, you said, to visit Wheeler in Leiden, but they did—
No. Not—you’ll have to ask him. I don’t believe he came, because he was in Copenhagen. I mean, he could have come, but you have to ask him. I don’t remember it.
I will ask him.
Oh, yeah. It’s [Arthur] Komar I’m thinking of, didn’t come until a year later. He was in Copenhagen then.
OK, but I will ask him if he did come then.
Our exchange of letters recently suggests that he wasn’t quite sure whether he went to Copenhagen or if Wheeler came to Copenhagen.
Maybe I can trace it back.
And tell him where he was! [laugh]
I’m also going today to John Archibald Wheeler Papers.
Oh yes, in Philadelphia.
So I can probably—if he’s not sure, trace it back. You said before that there wasn’t so much collaboration on the general relativity research with people from Leiden and Wheeler’s group.
But I have seen in one of the relativity notebooks from Wheeler that he has been in the house of Fokker, so I guess he knew Fokker. He was working in Delft at the time.
I see. OK.
Do you know anything about that?
I don’t know. No.
That’s OK. Then I might find some letters maybe. [laugh] So the group didn’t have—oh actually, your paper with Wheeler that has been written in Leiden, Classical Physics as Geometry— in the acknowledgments, Schouten appeared.
And also I’m not sure if I pronounce it right, but Géhéniau—two mathematicians.
Can you spell that last one for me? [pause] Géhéniau?
He was from Brussels.
OK. I didn’t remember it spelled that way, but that is—yes, that’s a name I know. I’m not aware that I’ve ever met him.
OK. And neither Schouten?
OK, I’ll move on. Let’s see. This is also a bit of a harder question to answer, but in the letter of Weber that I mentioned before, Weber says that Tolhoek who was a Leiden physicist— That he wanted to discuss, and then he literally says “problems of physics and society” with Wheeler.
Do you know what that’s about? Is that nuclear energy or—?
No, Wheeler had a very wide set of interests, and certainly nuclear energy would be one. But he was interested in finding the broadest sort of philosophical attitudes that people would bring with them when they worried about the real world. And so it could have been much wider things than that. I don’t know whether he would have worried about the political attitudes of people, or—I just don’t know. But given the opportunity, he would talk to artists and novelists and other such people. So he had very broad interests.
OK. Because when he was in Copenhagen with Bohr, the first time, I guess it was in ’38, —I’m not totally sure—that’s the time of Hitler’s rise.
Hitler was starting to rise well before that. He started in ’33 or something.
So did Wheeler feel—did feel some sort of guilty about that? I think that they saw that happening but that he didn’t do anything about that.
That’s right. Wheeler—well, that’s a place where Wheeler and Putnam had something in common. Each of them felt that they had lost a brother in World War II, and John felt in a sense guilty thinking that if—somehow if he had paid more attention to Hitler when he was in Copenhagen, he might have earlier gotten into the atomic bomb business. I have no idea about that. I know he did distinctly say in his autobiography that he felt that if only he could have somehow managed to get the atomic bomb produced a few months earlier, maybe the war would have stopped early enough that his brother wouldn’t be killed. And Putnam also lost a brother, but he was too young to be able to have any influence on it. He couldn’t feel guilty about it, but he felt certainly unhappy about society getting into the stage where they have to deal with Hitler.
But might it be that in a way, Wheeler also felt some sort— that he also felt that he wanted to help Europe and the Netherlands, like after World War II period?
That there was some sort of moral aspect for him going to Europe and talking to people about the—?
I think that’s true.
That’s what I would think as well, but it’s hard to verify.
There’s one thing—that is the development of nuclear power for society. And I don’t have any recollection of Wheeler ever showing an interest in that or the dangers associated with it. It wasn’t as though he said, “Well, at least we can bring one thing out of the atomic bomb that’s useful to everybody. We can make cheap power.” Which was thought to be the case in those days. But I never saw him having activity or comments about that.
In the time that you were in Leiden, Wheeler visits the International Conference on Nuclear Reactions in Amsterdam.
I see, OK.
And there he gives a talk. It’s called Fission. Can you recall anything about that? Was he asked to go there? Did he want to go there? Like whose idea was it to go there, and was his talk influential, important?
Oh, well, I think he probably would have been very happy to go there. I don’t know whether they had to give him an invitation or whether he just talked to them and said, “Can I give a talk?” I’d have no idea which it could have been. But I can well imagine that they could come searching for him. Because essentially he was the—he and Bohr had together published this or at least written—I forget to what degree it was published—this liquid drop model of the nucleus that could give some insight on how fission could take place. So because he had spent his entire war years worrying about the details of fission and how to produce fissionable material—I think that was his principal assignment during World War II was to develop this Hanford fission facility to—I guess it was primarily to produce plutonium. But anyway, he was the originator with Bohr of some important early ideas about fission, and he continued to be an expert on it by doing some of those important things, including working with people with a more engineering background to make sure that when they built these facilities to try to make plutonium, or I don’t know, that they gave enough extra capabilities for the cases where they might have guessed wrong on something. So there was supposed to be one famous case where they were expecting a given arrangement of materials to go spontaneously into fission, and it didn’t happen where they thought it should. And because he had insisted on these extra facilities, they were able to just let the thing get a little denser, and it worked. And later on, they figured out that, well, we had the cross-section of some capture process either left out or mis-guessed. So anyway, he had done very detailed and important work on making sure you could have fission and control it, as well as make bombs.
So related to this conference, when de Groot asked Wheeler if he wanted to fulfil the Lorentz professorship, Wheeler asked him if he can teach a relativity course, and then de Groot answers something like “OK, you can do that, however, we also need you to give a seminar for everyone.” So also for the experimentalists. And then he gives a seminar about nuclear models. But this is also I guess then just a natural thing to do for him because he just—yeah.
That’s right. I mean, he knew so much about it, and he knew that there would be many more people interested in that than were interested in gravity. Because by that point, his work on gravity had not yet made much of an impact.
Can you say something about how well the relativity course was visited and how the seminar was visited? Did a lot of students show up there?
I have no idea.
OK, you weren’t there?
I didn’t go to either of those.
OK. [laugh] The idea that I get from reading letters and everything is that Wheeler wanted to do general relativity, he takes his own group, and that your group worked productively on that, but that the Dutch wanted his nuclear knowledge. That was actually what the Dutch were seeking.
That sounds very plausible to me. As I say, if they had the chance—Princeton would not have hired him again if he would—
[laugh] —look for a job there. To do gravity. They would have happily hired him to do fission.
Until gravity became—
Yeah. But that took another ten, 20 years.
Yeah. I’ve asked a lot of the questions I had. Something more that I wanted to know is can you recall how Princeton, how Shenstone responded to the fact that Wheeler wants to go to Europe again? Was it easy to go a half-year somewhere else, or was it something he had to—
I would think it was easy, but I don’t really know. I was a graduate student. I don’t give advice to the chairman. Or get asked for advice by the chairman.
[laugh] I can see that. This is also a bit more of a vague question. Can you remember any, let’s say Cold War events, happening during this period, or other political stuff that influenced your time being there?
I don’t think there was anything that would bother my time there, no. [pause] I don’t know. To me, at that age, I was quite young, and you know, I had grown up in the Midwest in the United States—Michigan and Pittsburgh—and to me, the Atlantic Ocean was far away. I probably never actually got to the Atlantic Ocean until I had been at Princeton for a couple of years when somehow, on some occasion, I would get that far. So going to Europe—when I was in high school, I assumed that Europe had been decimated by World War II, and I’d never see any of these stories people used to tell about how great times were in the ‘20s and so forth, and Europe was a marvelous place then. And I thought it had been destroyed, and I’ll probably never see it; too bad. [laugh]
So I would think that once I got to Paris and so forth, I was so over-awed by the fact that so much was going on, especially as I travelled around a bit in Holland, to see Rotterdam trying to grow itself out of all the devastations and so forth. It never occurred to me to worry about getting across to Russia or so forth. That was just still beyond even dreaming about or thinking about it. It was just a fact that that’s there and we’re not there.
It was not really in your mind back then.
One question—Did any long-term contacts emerge from this visit in Leiden, with Dutch people or—?
With Dutch people?
Or other European people that you met there?
I’m trying to see how—well, certainly there arose an inclination to explore Europe more. So Leiden was the spring semester of ’56, right?
And so ’57, I had finished—I got my Ph.D. There were all these papers in the, I think roughly January Reviews of Modern Physics that was—at least half a dozen papers by Wheeler and his students reflecting a lot of work that was done in Leiden. As well as Everett’s thing. And my thesis is actually, in total, published there in that issue.
Right. That was one of the reasons I liked to work with Wheeler—because he didn’t think a thesis had to be long [laugh] and he managed to get me through on a 40-page one or something like that. But it did certainly give me an inclination that I would like to see more of Europe, so that in the summer of ’57, just after my Ph.D., I went intending to go with my younger brother, who at that time was studying in Rome to become a priest. And I purchased a scooter, and the two of us planned to travel around in Europe for the summer. But then a conference in Copenhagen, small workshop, was organized in Copenhagen by Stan Deser, who had been there for that year probably on a sabbatical or something, postdoc, whatever it was. Christian Møller helped organize things, but it didn’t do any harm that Stan Deser was I suppose married at the time, or probably courting, Oskar Klein’s daughter. Anyway, he was there and got together a handful of people to work on quantum gravity, mostly, and I was invited there. So that occupied the first few weeks of that summer, so my brother had to pick up the Lambretta—in probably Rome, and I couldn’t get down to meet him until a couple of weeks later, where we went down and met in Florence and then travelled around Europe and drove eventually up the Rhine, left the country through Saarland. So that was a big adventure and left me not so much with times to ties to colleagues anymore, but on that visit to Copenhagen, I met the woman who would become my wife two years later.
Oh, that’s sweet. [laugh]
Was she from Copenhagen?
She grew up in Copenhagen, had lived all her life there. Had been in the United States on some years of college study in North Carolina before I ever met her. But I met her in Copenhagen and we hit it off just enough to keep in touch for the next couple years until I got a fellowship to let me go back to Copenhagen and court her seriously and get married.
And did you get married in Copenhagen?
Yes. Right. So that was great. And had close ties to Europe through now family in Copenhagen. But the one thing, going to Copenhagen that year meant that if I was serious, I should learn some Danish. It turned out I couldn’t keep Danish and Dutch separate in my head. So I had to suppress the Dutch to be able to learn Danish.
I have asked my questions.
Well, then, I think I would like to tell you a couple of things that are loosely tied to Leiden. First was the question of the Oppenheimer-Snyder paper. I was surprised that although Wheeler was obviously aware of it, he never mentioned it to me. He was worried about singularities and things, but I never—I had to wait for Sam Treiman to mention—just meet me in the hall and say something about it. And I said, “Oh, I don’t know about that.” I won’t look at it. So just surprised he had me so saddled off in some corner of his work that he didn’t mention that work to me.
Do you know why he did that?
Well, he was busy with other groups of students worrying about the neutron stars and things like that. And he knew I wasn’t about to get into nuclear physics. But on the other hand, this relationship of the curved space-time, wormholes and so forth, and what’s going on with the Schwarzschild solution that he did all this work with Regge on meant that he was fully aware of all these things. But then it appeared a couple of years later, after that, that David Finkelstein, who was at the Institute for Advanced Study on a sabbatical or something or fellowship, whatever it was, he wanted some mathematical advice on things like curved space-time and came to me. And I was able to answer his question rather quickly because I had been studying a lot of mathematics after I got to Princeton, even as well as physics. So I showed him how to think about light cones tumbling around in curved space, and he took that idea up and applied it to the Schwarzschild solution and found a way to describe what’s going on, not near R equals 2M but at R equals 2M. That place was originally called the Schwarzschild singularity. And the title of his paper was I think something like—anyway, he used the phrase—that thing that had been called singularity was the— unidirectional membrane, he called it. The later language says it’s the horizon. But anyway, that was in my mind the first time that I knew about how to think about what’s going on not just outside the collapsed matter, the way Oppenheimer and Snyder did this continuing collapse, and where the Russians called those things “frozen stars” because the matter would go down and then freeze in the sense that it would go down asymptotically as you’ve tried to watch it from a distance. And this said, no, you can talk about from the Einstein equations. You can talk about what’s actually going on right at the R equals 2M. And Oppenheimer and Snyder knew how to talk about the collapsing chunk of matter, but they didn’t do anything about what was beyond that once it was smaller than that 2M. And so this was the first time that the whole picture fits together. And so I regard that as the birth of the black hole. Now various pieces of that had been known. I’m sure there were others who—well, in particular, when we were writing that MTW book, we introduced that, and Wheeler wanted to call Finkelstein’s metric the—[pause]—the what shall we call it—the—no, I just lost that astronomer’s name. Eddington. He called it the Eddington-Finkelstein metric. Well, as I later discovered, Eddington wasn’t the first one. The paper we cited to when I finally got around to reading it said that [Edmund]Whittaker has written the following metric. He would like to explain why it gives the same answer as Einstein got. Because Whittaker had done it in a different theory than relativity. And so it was really the Whittaker metric, but now what was going on there, except that R equals 2M was not a singularity. But they didn’t notice that. They weren’t interested. Because R equals 2M for the sun is a radius of about a kilometer or two. And they were talking about Mercury’s orbit. Well, they never thought that there could be an object in the universe that was that small. So didn’t pay any attention, even though the metric they wrote down, to any mathematical insightful person, was clearly not singular at R equals 2M. But they didn’t pay attention. And I think probably other people had noticed that it was not really a singularity, but no one put it so clearly as Finkelstein in saying, “This is a one-way. You can fall in, but you can’t get back out. Even light.” But you can describe what’s going on there, not—and also inside. What the light does after it gets inside. Well, I showed that to Wheeler after Finkelstein showed it to me, because Finkelstein had used the work we did together as a clue for how to get there. But he hadn’t yet published the paper. He was writing it or—and I went to Wheeler and said, “Hey, here’s this great insight into what’s going on at the so-called Schwarzschild singularity.” And he said, “You know, I’ve heard something like that before. I think I was having lunch with Kruskal at Matterhorn.” This classified place. But there were two halves of it. One of it was to get thermonuclear power, and the other was to get H-bomb. They were both classified at that time. So the people who worked in one couldn’t talk physics to the other. So they would meet at lunch and talk about something else. And that was general relativity.
Oh, that’s interesting.
Right. So Kruskal had sketched out on a paper napkin at the table his ideas of how you would think about the Schwarzschild metric. So Wheeler looked it up in his notebooks, found it. Just the year or two before, he had got that little message from Kruskal, but he didn’t do anything more with it. And so but one thing he did do was say, “Well, since Finkelstein’s got you convinced that we now know what’s going on there, Kruskal had the same—had an equally good metric, except all I’ve got is a few notes in my notebook, but I think it should be published.” So Wheeler wrote a paper based on that note in his notebook and sent it to the Physical Review as a paper by Kruskal. Kruskal at that time was on a sabbatical in Europe, so Wheeler said, “Well, if I wait for him to answer my correspondence, it will take forever. I’ll just write the paper and let him—” And so Kruskal didn’t know Wheeler had written this paper until he got the proofs from the Physical Review.
[laugh] He was wondering, what?
Here’s this paper on—you know, you used to get long sheets [galley proofs] before they paginated—broke them down into pages, so you could do all the corrections necessary if there were any. And so he tried to say, “Well, no, Wheeler, you’ve got to put your name on this.” And Wheeler said, “No, no, I didn’t do any of it. I just wrote down the things you told me.” Well, he did a lot more than that. He used this as a way to advertise wormholes, not to advertise black holes. He didn’t do anything about pointing out the black hole part of it seriously, but he did a lot about showing the wormhole ideas.
From which year was this article?
I can find it for you later when you get back. I can start digging through things. Around—well, I don’t know, maybe around ’62. I’ll have to— [David Finkelstein, Phys. Rev. 110, 965; May 1958]
So anyway—but then I think I only realized much later—I set a student to the job of redoing the Oppenheimer-Snyder collapse now that we understood what the geometry is at R equals 2M, but because I can’t draw neatly and the Kruskal picture was easier to draw than the Finkelstein picture, I let the student work with the Kruskal picture. They’re both—the parts that are used in describing the collapsing of the star are the same geometry in both of them, but Kruskal’s simplified sketching, because of the light-cones 45 degrees everywhere. And the Finkelstein view of it is more insightful because it lets you see that the whole process becomes stationary. It stops moving. And you can’t see that in the Kruskal, that it comes to rest. And so, unfortunately, this has overwhelmed most of the—because it got done that second way and was cited in MTW, it has sort of overdone the fact that Finkelstein’s really was the insight that led to black holes. Kruskal was just a way I had of sketching it that was easier for me to do sketches. So I’m always disappointed that Finkelstein doesn’t get more credit for having been the first one to let people think seriously about black holes.
You just mentioned that at the Project Matterhorn, during their lunch breaks, people were talking about GR because they couldn’t talk about what they were actually doing. Were there more people talking about GR? Was it common? Do you know that?
Well, no, I don’t know. You could look for that—if you can find that in Philadelphia, Wheeler’s diaries in Philadelphia, he undoubtedly would have had other notes from various lunches there. I don’t think general relativity was the only thing they talked about. But they couldn’t talk about what they—because one was on the plasma side, and the other was on the fission side, or the fusion side. They couldn’t talk to each other about their work, and so they talked about whatever. Maybe they talked about children. Maybe they talked about things here or there or the other place. But anyway, among the things they talked about came up at some point relativity. Maybe more often than once; I don’t know. So that has to be probably—
Yeah, I will try I can find more about that.
I can let you get your notes. I’d have to get my computer out and dig things up to get you the actual references, but we can do that when we’re not talking. So I can get that straighter for you.
That’s nice. Do you have anything else more you would consider interesting for me?
Well, of course, the whole idea that Weber was—we got to know each other originally there in Leiden, and he was doing things that eventually bore on gravitational waves. After that summer was over, he focused more strongly on gravitational waves and decided to actually think what you’d have to do to detect a gravitational wave. At that time, he was a professor in the electrical engineering department at the University of Maryland. But after he got a couple of years into this business of gravitational waves—well, one thing, he wrote a textbook, a very nice, good textbook, which has all the essential things in it for gravity. And then he was trying to—he was building machines that he hoped could detect gravitational waves, but at the least they would put a limit on how strong the gravitational waves running around the universe are. So it was because of him that I eventually moved to Maryland. As I said, when I was up for renewal of an assistant professorship at Princeton, and they sent this signal that I would never make tenure there, I went looking for another job, and one of the places I went to was Maryland. And I went there for two reasons. One, that Weber was there. And that was the—apart from Princeton where Dicke was doing things on experiments, that was essentially the only place in the world where you could find people thinking about experiments in gravity. So I went there. In fact, one of my first students there is Vishu. V-I-S-H-U is the abbreviation for his name [C. V. Vishveshwara]. He was one of my first students at Maryland, and he had been a graduate student at Columbia, and he told his mentor there [Robert W. Fuller] who was someone who knew Wheeler well that he wanted to work on gravity for his Ph.D. He was told by this professor or faculty member at Columbia, “Well, if you want to do that, you shouldn’t do it at Columbia. You should go to Maryland because apart from Princeton, they’re the only place that has both theory and experiment.” So that’s by the time I got to Maryland in early 1963. So that’s — well, that’s only, what, that’s only eight years after Leiden.
Yes, that’s pretty quick.
And then, of course, Weber a few years later declared that he thought he had detected gravitational waves. And there had been enough taking gravity seriously by Dicke’s work and the work on the redshift—at MIT—that one could get somewhere in that field. And so Weber claimed to have discovered some gravitational waves, and a few dozen people thought that, well, that’s worth looking into, and so they spent a few—or in many cases several—months trying first to understand gravitational waves from the theory, because at that time, most people had never even had a course in general relativity. That wasn’t offered many places. So they had to get out the books and learn about it, and then learn about relativity and gravitational waves. And then several of them tried to repeat Weber’s work or improve on it, and neither case showed any results. So the consensus changed. People thought that Weber had not interpreted his data correctly and that he had not detected gravitational waves. But they could! Because they were better than him. [laugh] So they set to work! And it turned out that these people who by that time had taught themselves general relativity by trying to repeat Weber, by that time, they were able to go, and it only took—instead of a couple of dozen people, it ended up to take a thousand. And instead of a few hundred thousand dollars, it took a billion dollars. But anyway— it was harder than Weber could have thought. But they all say, OK, yeah, this field would never have gotten off its feet—maybe ten years later, it would have started—if Weber had not gone through this uproar. And if it came ten years later, many people believe it never would have succeeded. Because, add on ten years to when they discovered it, and you’ll find that the political situation is such that there would not be a half a billion dollars to finish the job. It never would have been done.