Oral History Transcript — Dr. Felix Pirani
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Felix Pirani; June 23, 2011
ABSTRACT: In this interview, Felix Pirani discusses topics such as: his family background and childhood; general relativity; P. A. M. Dirac; Peter Bergmann; Hermann Bondi; Alfred Schild; Carnegie Institute of Technology; Cambridge University; Bryce and Cecile DeWitt; Dennis Sciama; Riemann tensor; gravitational waves.
Rickles:The date is June 23, 2011. This is an interview with Felix Pirani conducted by Dean Rickles in Felix Piraniís home in central London. So thereís not much biographical information available, apart from the General Relativity and Gravitation piece. Thereís a little bit about your parents because they were pretty famous.
Pirani: Did you look them up? The family thing that one of my cousins did?
Rickles:The genealogy thing, I did, actually. That was very useful actually. So your father was Max Pirani. Now was he English or Australian?
Pirani: Australian, born in Melbourne.
Rickles:So theyíre both from Melbourne. Right, okay, so thereís an inaccuracy in something I read, because it said Max Pirani was English and born in England. And your mother was a Leila Doubleday, and she was also a violinist. So theyíre both from Melbourne, and so they moved about quite a lot, I can see, from the various recital programs and study tours and such that they did that was available online. So it would be nice if you could say a bit about their backgrounds and their academic credentials, and whether they had any leanings towards science or mathematics or anything like that.
Pirani: Right. Well, maybe I should tell you something about the family history.
Rickles:That would be even better, yes.
Pirani: Thereís a town which is now in Slovenia called Piran, it used to be called Pirano. This was a Venetian colony. And if you were from Pirano and you were gentile, your name would be Piranesi, like the painter. If you were Jewish, your name would be Pirani, or maybe Cohen Pirani. My great-grandfather in the Pirani line got married in the synagogue here, and it was the first marriage in the synagogue in Leeds, I think. Thereís a synagogue somewhere in the middle.
Rickles:He wasnít the other famous musician, musical Pirani?
Pirani: No. And he went to Australia, and my grandfather and his family were all born in Australia, and there are lots and lots of Piranis in Melbourne. My grandfather, my fatherís father, was a determined atheist, and paid no attention to customs that might interfere with his atheism, and brought up his children like that. He was a patent lawyer. My father had several siblings. One of them was severely damaged in World War I and died soon after. Another male died in 1989. Then he had two sisters, one of whom married aÖ Iím not sure if he was always military, but certainly a man known in the military called Cohen. If you look at the book called The Jews of Victoria, which I have somewhere if you want to look it up, he is described in that. And he was quite well off.
My father demonstrated his musical talent from a very early age. He would go to concerts with the school and play with the school where the concert was being performed. Iím not quite sure about all the details, but he was a pupil in New York of a musician called Max Vogrich about 1916, maybe a little earlier, and joined the Spaniard Army in the States during World War I.
Rickles:Oh, so he studied in America with Max Vogrich.
Pirani: He studied in America.
Rickles:Was that at Julliard or something?
Pirani: I donít think so, no. My father used to do things like play the piano for the background music in the movies, and I think thatís how he survived. And then I guess he went back to Australia after the War. Iím vague about the details. But by the early í20s he was here. And my mother was here, and she was a violinist. She was also very talented at an early age, and was known for having performed at a concert whereÖ
Rickles:Was this with Bruno Walter?
Pirani: Yeah, I was thinking that was the woman that the ice cream was named after. Iíll get to that. Iím bad on names nowadays. Anyhow, they met and they married in 1923, and had two children of which I was the first.
Rickles:And you have a younger sister?
Pirani: I have a younger sister who is now retired and lives in Oxford.
Rickles:Is she academic as well?
Pirani: She has a Ph.D. in History, and she was a schoolteacher for a while and then she was an inspector of schools, a school inspector.
Rickles:You were born in England?
Pirani: I was born in England, but I lived my teens in Canada.
Rickles:So you didnít spend any time in Australia?
Pirani: Well I did, actually; not much. About the time that World War II started, my father got a job, well it was another job doing music examinations in the commonwealth, and getting out of here at the beginning of World War II seemed to him a good idea. So he had some examinations to conduct in Canada, Australia, and New Zealand, and we went to Canada in April 1940.
Rickles:Hm, 1941 is when theÖ
Pirani: We went back to í41.
Rickles:So thatís already jumping quite a bit forward. So you would have been 12 by then. [Thatís right.] So were you already doing physics? Were you already mathematical by this stage?
Pirani: When I was about six, I was sent to a very broad-minded liberal private school. You must remember that the Education Act in this country was not passed until 1944, so the school system was pretty abysmal, and it was not unusual for middle-class people, if you want to use that expression, to send their children to private schools. So I was sent to this very liberal private school called King Alfred School, which is in Golders Green. There was also Paul Robeson Jr., and he was pretty much contemporary of mine. We took up smoking, and when my parents discovered what was going on they took me out of that very broad-minded boys and girls school and sent me to a much stricter boysí prep school in Swiss College called The Hall, which was a very different kind of school. I managed not to get beaten in the three years I was at The Hall. I went back last autumn to visit the place, just to see what it was like.
Rickles:Itís still a school?
Pirani: Itís still a school. Itís enlarged. The school hall has been divided up into sections, so that my memories were a bit disrupted, had been distorted. Anyhow, so I was educated at this prep school from the age of about 9 to about 12, which is when we left.
Rickles:Were there good teachers there? Were you reading physics things and doing math?
Pirani: You were doing pretty well everything, but of the classical school kind of things. You couldn't do both science and theatre, I think, and by some mistake of the rules I got into both science and theatre. But you didnít get much science anyhow; it was all very hypothetical. There was a good math teacher called Mr. Castle. There were a lot of good teachers.
Rickles:This was pre-War somewhat.
Pirani: Yes. When the War actually started, they sent me to another liberal sort of school that was a boarding school. They moved down to Sussex and I went to this boarding school in Petersfield called Bedales, which is known for having one of the royal family attend there more recently. And there it appeared from the reports, of which I do not think I have any copies now, but I was doing quite well at math. Then we went abroad, and I went to school in Melbourne and Christchurch, each for a term or two. That would be 1941, I guess. Then in í41 we went back to Canada, back to Vancouver when I was 13. And then something happened that had enormous effect on the rest of my education and social life.
Rickles:So 1941, so you went to Canada via Australia?
Pirani: We went to Canada and I didnít go school, or rather briefly, and then we went to Australia and New Zealand, and then back to Canada.
Rickles:And Iíve got Lord Byng High School.
Pirani: Thatís right; I went to Lord Byng High School. What happened there is that the guy who was responsible for taking in unorthodox people with unusual backgrounds gave me a math test and made me write an essay. When Iíd done that, he put me in the last year of high school, so at the age of 13 I was in the last year of high school.
Rickles:Yes, I found that very curious.
Pirani: Well thatís how it happened.
Did this happen to anybody else? Was it an odd thing, or was it sort of...?
Pirani: It was an odd thing. And then the next year I started going to the University of British Columbia.
Rickles:I found this; youíve probably seen this.
Pirani: Yes, Iíve seen that [laughs]. I have a copy of that somewhere. Iím embarrassed by what I said there.
Rickles:It is funny, though [chuckles]. Were you studying a range of subjects?
Pirani: Yes. You know what the North American universities are like. The first year I was doing math, physics, chemistry, economics, French and English. I remember writing an essay that I would now be embarrassed by where I criticized Eliot for his abstractness. ThenÖ how can I put this without seem very chutzpadik? I came top of the class in the first year, which provided me with a scholarship, which was a good thing because my parents were not in very good financial condition then.
Rickles:So was the scholarship to continue in Vancouver?
Pirani: I continued in Vancouver and I took the second year. And then my father got a job in London, Ontario starting up and running something called Music Teachers College, and we moved to London, Ontario.
Rickles:I think you probably have these as well; right [shows newspaper cuttings]? From different years in the same magazine.
Pirani: I donít remember that one, but maybe I have it.
Rickles:So in the time there you made an impression, because by this stage youíd left Vancouver actually, and they still have ďour former Felix PiraniĒ doing this. So did you start getting heavily interested in physics in Vancouver? Was that clearly going to be the direction, or were you just normally interested in science from earlier?
Pirani: No, it was a pretty broad sort of education. Now the Ontario high school system is a year longer than the other provinces, so I ended up in the second year at the University of Western Ontario when I started there in 1944 instead of the third year. Now I was beginning to concentrate on physics more.
Rickles:Were you doing a physics degree or anything? Was it an official degree plan?
Pirani: It ended up being a physics and math degree. And then I made a mistake and lost another year.
Rickles:Was that going to Oxford? [Yes.] Was that because — I know your father went there to do something. Was that related to your time at Oxford?
Pirani: No. I was at HertfordÖ shall I tell you about how that happened? [Yes.] Okay. In the summer of 1945 I hitchhiked from London, Ontario down to New York, which was not as dangerous as it would have been 40, 50 years later.
Rickles:So you were 16 or 17?
Pirani: 17 I was, yes. I went to visit some friends of my father, who lived actually in Connecticut but close to New York. And I was talking about science and physics and chemistry and whatever, and they took me to visit a friend of theirs who had a chemistry laboratory on the premises of her house near New York. She had a chemistry doctorate, and had had this lab built. Her grandfather was the general secretary of Sears-Roebuck, so that she was a wealthy sort of woman. Anyhow, my fatherís friends took me to visit her lab and to meet Ruth Alice Weil, and she said, ďUniversity of Western Ontario, whereís that? Why donít you go to a proper university?Ē And it turned out that I couldn't go to a university in the States in 1945 because Iíd just get drafted. So I said, ďWhat about Cambridge or Oxford?Ē That was where I made the mistake when I came back here at the end of 1945. Peace had been declared, but all the people going into the universities were people who had been in the Army since they were quite young. If they were quite young, then theyíd been through the school system here that gets you into Oxbridge, and they knew a lot more mathematics than I did at the age of 17. So finally with some effort they got me into Hertford, where my tutor was very nice and kind, but I just didnít fit. You know, I had a different background.
Rickles:Were you in math or physics in college?
Rickles:So were you just taking the normal first, second, and third year?
Pirani: The normal first year, or minus first year. You know, I didnít have the background in math that the other students entering Oxford would have had then.
Rickles:So did it give you a bit of shock?
Pirani: Yes, and after a couple of terms I went back to Canada.
Rickles:Were you inspired, though, once you got back toÖ?
Pirani: No. I just went back to into the course and finished doing the physics and math course that Iíd been doing.
Rickles:But you ended up with a gold medal in 1948. Also I noticed that you wrote a paper.
Pirani: Yes. I was looking at that yesterday. [Chuckles] Self-defense, so to speak.
Rickles:This is your note on the HartmannÖ
Pirani: Thatís right.
Rickles:On the Use of the Hartmann Formula with FosterÖ so who was A.W. Foster?
Pirani: She was my optics teacher. So that was my motivation. The magazine they sent it to was not like Physical Review. It was a teaching, whatís it called?
Rickles:That was American Journal of Physics, right?
Pirani: Yes, thatís right.
Rickles:So that must have been nice, writing your first real bit of research and getting it published.
Pirani: It was quite nice, yes. So then I got a degree there, a bachelorís degree. And did well enough that I could be recommended to Infeld in Toronto.
Rickles:The fact that you mentioned Infeld, were you already thinking about relativity?
Pirani: My father had been talking about Einstein for years, and I was indeed thinking about relativity.
Rickles:So what was your fate there at that laboratory? Do you remember what you did, briefly? Did you have any courses related to relativity?
Pirani: In Toronto, yes.
Rickles:But before that, before you went to Toronto.
Pirani: No, I donít think so.
Rickles:Did you actually do any self-teaching from any books? Of course Bergmannís book would have been out by then.
Pirani: Not that I recall. No, it was later. But Toronto opened up a brave new world. Alfred Schild was giving a tensor calculus course, and if I remember rightly, Infeld himself was giving the relativity course, and a guy called Stevenson was giving quantum mechanics. I only managed just to scrape through.
Rickles:So were doing masters there?
Pirani: I was doing a masters.
Rickles:Did that have a research component, or was it just courses?
Pirani: No, just courses. Then we went out to Vancouver in the summer of 1949 for the summer school, where there was Dirac talking about his theory and there was Homi Bhabha. Somewhere Iíve got a book, a text of the play that we put on at the end of the show, which had us taking the mickey out of those people. Like Dirac had this reputation for falling asleep in the course of lectures, ďIím Paul Adrian Maurice Dirac, and slumberís one thing I donít lack. Da-da-da-da-da, da-da-da-da-da, Iím often found flat on my back.Ē I donít think I have those sentences quite in the right order, butÖ
Rickles:Was that a public performance?
Pirani: Oh yes. If you want to know more about that, Iíll hunt around for the text. Someone sent it to me a few years ago.
Rickles:That would be nice to see. So did you go to this summer school precisely to see Dirac, or what that just coincidence?
Pirani: No, I went to the summer school because that was the thing to do. And Schild went as well. I got on quite well with him, although he was of course some years older than me. At the end of the summer school he was going off to Carnegie Tech up in Pittsburgh for a job there, and he said, ďWhy donít you come and be my first graduate student?Ē
Rickles:So thatís all pretty quick. But from 1948 you didnít really have any relativity really, and then in 1949 you kind of —
Pirani: I did quite well in his tensor calculus course. I really chewed that up. Do you know the book?
Rickles:I do, yes.
Pirani: Infeld and Schild.
Rickles:It was one of the few things I could afford as a student! Did you get any preparation from your Oxford courses?
Pirani: No, I donít think so; No, nothing at all. Maybe a bit of geometry, but classical geometry, not tensor calculus or differential geometry.
Rickles: So after the summer school, itís interesting, I mean presumably. Were you taught, did Schild have the insight that Diracís procedure could be used for quantizing gravity right away?
Pirani: Absolutely, and that was the thing that he wanted to do.
Rickles:He must have already been thinking about quantizing gravity beforehand.
Rickles:Did he ever discuss it with you, or mention, ďThis is an interesting problem,Ē before Diracís lectures at the summer school?
Pirani: If he did, I donít remember it. He certainly did after the Dirac lectures.
Rickles:So did you discuss it after summer school? Did you consider yourself together after summer school?
Pirani: Not a lot. It was in the air, you know.
Rickles:Was Bergmann there.
Pirani: I was just wondering that. I donít think he was.
Rickles:Iím curious as to howÖ
Pirani: How Bergmann got into it.
Rickles:Itís almost entirely the same idea, in many ways.
Pirani: Ted Newman ought to know how Bergmann got into it.
Rickles:Yes, in fact I should speak to Ted Newman.
Pirani: Havenít you talked to him yet?
Rickles:Yes, yes, but that was last spring, I think it was. I mean we should have spoken to him on our last trip. I should have mentioned we spoke to quite a few. We spoke to Anderson, and to Misner and Brill and Deser and Cecile DeWitt. We were supposed to speak to Suraj Gupta but he pulled out.
Pirani: How was Cecile DeWitt? How long since youíve seen her?
Rickles:A matter of months.
Pirani: Because weíve lost touch.
Rickles:She just got back from Vietnam ten days before we saw her.
Pirani: Who is ďweĒ?
Rickles:I was doing it with Don Salisbury. He was a student of Peter Bergmannís.
So back to the Vancouver lectures, so you donít know whether Bergmann were there. But do you remember anything of the nature of the discussions that you had with Schild?
Pirani: About how it could be done?
Rickles:Yes, about it might be interesting from the point of view of general relativity.
Pirani: Well that was clear. I think anybody who went to the lectures and knew about relativity would have heard about that.
Rickles:Did Dirac himself make any mention whatsoever about general relativity?
Pirani: Not that I recall.
Rickles:Itís not in the notes. Iím curious.
Pirani: Have you looked at the notes from the Dirac lectures?
Rickles:Yes. Thereís nothing on general relativity.
Pirani: Well youíve really been into it, havenít you?
Rickles:[Laughs] Well, thatís one of the main points that which the canonical approach kicks in, although Rosenfeld had something similar in 1930.
Pirani: Have you seen my Ph.D. thesis?
Only the Phys. Rev. piece.
Pirani: Do you want to see the thesis?
Rickles:Yes. I havenít been able to get a hold of it.
Pirani: Iíll dig it out. In fact Iíve picked out a few [inaudible].
Rickles:That would be great, actually. Iíve got my iPhone so I can take snaps, actually. Does it differ significantly from the Physical Review paper from 1950?
Pirani: Yes, itís longer. [Laughter] I was going to say, it did not have that merit of brevity!
Rickles:Okay, so then you go to Carnegie. Were you initially assigned to Infeld as a research student or anything?
Yes. As I recall, it had been made very clear to Infeld that Schild had invited me to Pittsburgh; not that Iíd made any initiative. And under those circumstances, it was okay for me to leave Toronto without a gray mark on my record.
Rickles:Were you already engaged in a Ph.D.? [No.] So you hadnít started it. [No.] Okay. So and then you moved to America. Was that strange? Did you mind going to America?
Pirani: Oh no. Iíd been living in Canada for eight years. But that did make a complication for my life which has persisted ever since, which is that because I was going to have a teaching position I had to have an immigration visa. And because I had an immigration visa, it made me eligible to be drafted for service in Korea. In order to avoid that embarrassment, I had to declare that I was an alien. You could escape from being drafted if you announced that you were an alien. What had to be done in writing Iím not sure, but I think I have the record of that. And by doing this, I lost the entitlement to American citizenship.
Pirani: Indefinitely. So that the last time I went to the States, which was in 1983, I had to go five times to the consulate, and ended up talking to a Vice Consul, to whom I made a list of all the organizations Iíve belonged to since I came back in 1951. And when he said, ďWhatís the New Left Club?Ē I said, ďOh, thatís a labor party Ginger Group.Ē
Rickles:So that was still persisting in the í80s?
Pirani: That was still persisting in the í80s. There was some file in Frankfurt that had my name on it. And I do not suppose that things have improved in the slightest since 9/11, so if I want to go back to the States my intention is to go to Canada and then see if I can get across the border, rather than get to JFK and be put back on the flight. [Laughter] But the chances of my going to the States are pretty small, nowadays.
So your Ph.D. topic, was that assigned by SchildÖ
Rickles: Öor did you choose it? So he said, ďThis is a good problem. Work on this.Ē
Pirani: Well, we worked on it together.
Rickles:Right. Did you have the approach worked out pretty right from the beginning?
Pirani: Looking for the first class and second class constraints. Iíve forgotten practically everything about them.
Rickles:I mentioned the Weiss method, by Paul Weiss.
Pirani: Yeah, that name did not convey anything to me. Is that somebody I used to know?
Rickles:Itís Weiss on the first page of the 1950 paper, and itís probably in your Ph.D. thesis as well I bet, because it was the method that Dirac used for quantizing Lorentz invariant field theory was by his method, the idea to take this arbitrary surface and you consider the data on the surface. That was his studentís work, Paul Weiss. And then in the 1950 paper, you mentioned that if we combine Diracís theory with Weissís theory, it turns out that you can use Weissís theory to quantize theories without a metric, basically, and amorphous spaces is the terminology he used, and topological space. So itís basically Weissís method thatís been generalized a bit. The reason why Iím curious about that, because Weiss is one of the people who was in the Canadian internment camps with Schild and Bondi, and then bizarrely, he spent some time in Ireland in Belfast I think, Queens, in Queens, and then he ended up working at General Electric in Syracuse, bizarrely, by the í50s.
Pirani: And did Josh know him?
Rickles:No, nobody knew. He disappeared, which is very strange that he ended up in Syracuse right next to Bergmann. And Bergmann mentions Weiss, and he said he basically took on Weissís method of quantization of field theory. So Iím just completely curious that nobody seems to know who this guy was, and he disappears, basically, despite being a student of Dirac and Bornís, and he had a Gottingen background, and had this paper that showed him referenced briefly. Dirac mentions it in his Canadian lectures, and then once again and then completely lost and he stops referencing him in all his later lectures.
Pirani: Shall we look at my thesis for that?
Rickles:Yes, yes, we can look for that. Iíll put money on the name of Weiss being in there.
Pirani: Incidentally, in sorting things out for you, I discovered some gaps in my CV. Like why do I have all this? Because I wrote the relativity article, but itís not in my CV.
Rickles:You did mention various entries in places, but not Ö
Pirani: Well that was supposedly a complete version of the CV, although it doesnít have this in it. [Looks in thesis.] Weiss, 36 and 38. Well he was considerably older, then. If Weiss was writing for Proc Roy Soc in 1936, he must have been born by 1911.
Rickles:He died in the 1980s, so he would have been quite a bit older than you, but not that much older.
Pirani: 17 years older than me, maybe more.
Rickles:So about Schildís age, then.
Pirani: Yeah, I forget exactly when Schild was born.
Rickles:But it is funny, because when you read —
Pirani: Itís in the second sentence! ďThis method is a generalization of Weissís and Diracís methods for quantization of field theory.Ē
Rickles:[Laughs] Right! And what I find strange is when you read Hermann Bondiís biography, he mentions that they were in these camps, and they were teaching physics and all the physicists were together, and he mentions that he learned relativity in these camps, basically. Weiss must have been amongst the physicists. He must have been. He was a Dirac student. He would have been there. He was at Trinity just before. It just seems strange that he disappeared. This is just my little hobbyhorse that Iím trying to understand.
Pirani: He was older than Bondi too, because Bondi was 1919, I think.
Rickles:I think Weiss was 1918.
Pirani: And heís writing papers when he is 18? [Yes.] Really? [I think so.] He must have been a sharp cookie. Heís written in Proc Roy Soc 1936.
Rickles:I think he was a little bit older there. He was around that time, though. If anything, something I find very odd is the disappearance of this guy, who obviously played some role in the development of canonical quantum gravity.
Rickles:Okay, so the paper with Schild, this must have been written really quickly, right? It was received in February 1950, so when did you start your Ph.D in Carnegie, do you remember? I mean itís in í49 right here.
Pirani: Yes. It must have been August or September.
Rickles:So this was written within a matter of months, which is interesting.
Pirani: The first paper was Schild and me, and then the second paper was with Ray Skinner, who died I discovered some years ago. He went off to teach in one of the western Canadian provinces.
Rickles:Yeah, you donít see his name popping up much after that paper.
Pirani: No, I donít think so.
Rickles:So, I think Iíve got it here, the presentation at the APS in the very beginning of 1950, or 1949 maybe. Do you remember going to that with Schild?
Pirani: Was that in New York? [Yes.] I donít remember that.
Rickles:New York City, February 2Ė4, 1950, annual meeting of the APS. Itís basically just... you probably wonít be able to read that. I assume itís the first presentation of the work. Is that right? Do you remember presenting it?
Pirani: It must have been Schild.
Rickles:What was the reception? I know there were letters going back and forth between Schild and Bergmann in... Was there any competition? Did you notice any competition between them?
Pirani: I think it was quite a competitive atmosphere.
Rickles:Iíve got a letter here from Bergmann, saying, ďDear Alfred, Itís hot off the griddle, pure Hamiltonian.Ē [Laughs] Can you see that okay?
Pirani: ďIím sending you the copies of our Hamiltonian on ditto paper. In all likelihood you would get that Hamiltonian from your formula by multiplying yours by the coefficient of the something. Notice that in your formulation as well as ours only one term contains them. There is right now little point in checking these arithmetical features.Ē
Rickles:So he saw it was pretty much the same thing.
Pirani: The same thing, yeah. But have you tried comparing the two texts to see if it looks the same, or is that hard work? I imagine that would be hard work.
Rickles:It is quite hard work. But I mean itís the same method. You got to adopt this parameterized formalism. I noticed in a letter you sent to Schild later on from Cambridge after Penfieldís paper, Hamiltonians without parameterization, when he showed that you could do the quantization without using parameterized formalism. Anyway, but you seemed to stick to this parameterized formalism. Do you remember why that might have been? [No.] Because I found it a bit curious. There are a couple of letters where Skinner is saying maybe we should drop this formalism. And you are saying, Ďwell Iím not sure, I still think thereís something good about the parameterized formalismí.
Pirani: Well, I have to say that after I got to Cambridge, my principal interest moved very much from quantization to cosmology quite quickly.
Rickles:Do you remember having any thoughts about the conceptual aspects of the approach to quantum gravity? Because thereís a bit where you end up with a zero Hamiltonian. Did you think this is rather odd; why is there a zero Hamiltonian?
Pirani: There was nothing left, it was all gone? Or was equal to zero.
Rickles: Well the fact that the Hamiltonian vanishes. Do you remember having any thoughts about the concept of energy? Did you later start thinking about similar ideas about energy? Energy as a pseudo-tensor. Did you sense there was something strange about it? I mean did any of this spring from the work with Schild?
Pirani: I donít remember anything about this. I do have much taste for the pseudo-tensor. In fact I wrote something somewhere about — you got my 1957 paper about radiation?
Rickles:The Phys Rev one? [Yes.] Yes, the invariant formalization.
Pirani: Thereís something in there about taking the pseudo-tensor and making sense of it by doing some kind of power expansion, taking a point and then doing the expansion in terms of the curvature tensor. You can turn the pseudo tensor into something to do with the curvature tensor, I think it was, but I really donít remember.
Rickles:Do you remember the reception of this paper? Were you speaking personally to anybody about this approach to canonical quantum gravity? To DeWitt or anything like that? Because they later did a similar thing, Bryce and Cecile did this interacting spinor field.
Pirani: I donít think I met Bryce until 1957. I may be wrong, but I donít remember that. I tell you what I can do at a certain point. I have my weekly diary back to 1952, so I could look through that and see whose names are mentioned.
Rickles:Yes, that would be great, especially quantum gravity related things. Thatíd be great, yes.
Pirani: Well it will say mostly about whom I met for lunch.
Rickles:And for beers, presumably [laughs]. Okay, so you only get the primary constraints in the 1950 paper. Were you aware of the problem of secondary constraints?
Pirani: Yes, Iím sure we were.
Rickles:And that was sort of the next problem. Was that a Skinnerís specific thesis topic?
Pirani: I donít remember.
Rickles:Did you interact much with Skinner?
Pirani: Yes. We sharedÖ we lived in a house with a number of other people, a large house off in the suburbs. So we talked quite a bit with each other.
Rickles:How many other Ph.D.s did Schild have?
Pirani: I think he just had the two of us then. He had me, and then he had Skinner. I don't know where Skinner came from. Do you know where he got his first degree?
Rickles:Iím not sure, actually. Iíve not really got any information on Skinner.
Pirani: Heís one of those people, of whom there are all too many now, where I say, ďI wonder what happened to so-and-so?Ē and I look them up on Google and it turns out that heís dead.
Rickles:Thereís not a lot of information. Lots of Wheelerís students are like this. In fact, finding the biographical information for that book I did with Cecile was very difficult, actually, because most of them disappeared after that conference and they left no record. Itís detective work.
Pirani: My copy is in shreds, or sheet by sheet, because several people wanted copies.
Rickles:Iíll send you a copy of the book, actually.
Pirani: Yeah? [Yes.] That would be nice.
Rickles:In fact I thought I did; I completely forgot about that. I sent a couple of copies out. Iíll send you a copy.
Pirani: It would be nice, but I donít promise to look at it properly.
Rickles:When did Schild leave for Westinghouse? Was that just a bit after you left? [Yes.] Did you notice any of the bad vibes there at the time? I know he left Carnegie Tech because he had issues with the head.
Pirani: I didnít know about that. If I did know about that, I repressed it and forgot it.
Rickles:Because Iíve got a couple of letters, and in fact I found his resignation letter in the Schild archives from the University of Texas, and he didnít like the head.
Pirani: Was Winnie helpful?
Rickles:I havenít spoken to Winnie, actually.
Pirani: Oh, it was Cecile DeWitt that you spoke to? [Yes.] Is Winnie still alive?
Rickles:I think she is, actually. Maybe in fact, thatís another. There are so many who I should speak to so much.
So weíll move on to Cambridge now. I noticed you visited Dublin before you went to Cambridge. In fact was this before you went to Carnegie Tech you had a visit to Dublin?
Pirani: I visited Dublin before I went to Cambridge?
Rickles:It looks like it.
Pirani: I was in Cambridge for three years with Bondi, and then I had a year in Dublin. I exploited the Canadian generosity to get a fellowship to take me to Dublin for a year.
Rickles:Royal Society of Canada research fellowship.
Pirani: That sounds right. There were two. That was one, and there was another one.
Rickles:Iíll see if I can find it — Iím sure I have a letter from Dublin from this year. Sorry. Oh well. So you donít recall being in Dublin.
Pirani: I donít recall being in Dublin before I went there to stay for a year.
Rickles:16th of January, 1950 Iíve got there. Hm. Okay. So how did the Cambridge decision come about, then? Had you met Bondi by that time?
Pirani: No. Schild and Bondi were in concentration camp together, actually. And then I was discussing with Schild what to do next, because I was imminently going to get my Ph.D. in the summer of í51. A few months earlier there had been Fred Hoyle on the front cover of Time, I remember, because of the steady-state theory, and Bondi and Gold were mentioned as well because there was the Hoyle theory and the Bondi and Gold theory of steady-state which were not really competitive, but alternative. I said oh it would be interesting, or words like that, to go to Cambridge, and someone said, ďWell I know Bondi.Ē So essentially Schild supported me applying to the Canadian whatever it was, fellowship, and wrote enthusiastically to Bondi, and Bondi got me into Trinity.
Rickles:So how come you did another Ph.D.? Was that just to get the funding?
Pirani: No, no, that was later. It wasnít clear that I was going to do another Ph.D. It was clear that I was going to do research.
Rickles:So it was just initially a post-doc.
Pirani: It was a post-doc. And I had two years of that, and then I won something called the Isaac Newton something or other, which gave me the third year, and then I got some more Canadian money to go to Dublin for a year.
Rickles:So that was in í54.
Pirani: í54 to í55. I went to Synge. His uncle was a famous playwright. It mattered in those days, I guess it still matters, he was a Protestant, and he was in the Institute for Advanced Study, which had been invented by the Prime Minister at the time some years before, Iím not sure of his name. But SchrŲdinger was the head of it. That was quite a place. Lanczos was there also, and Synge was there. About the only thing you had to do was to turn up for the morning coffee at 11:00. If you did that, thenÖ
Rickles:So I mean [???] wise then, what were you working — Well actually, I noticed that you applied for other post-docs as well, which I take it Trinity was your main first choice.
Pirani: Did I actually apply for other post-docs?
Rickles:At McGill, actually.
Pirani: Oh. I had forgotten that. Maybe I only got the Trinity one. Or did McGill offer me money?
Rickles:All I saw was a letter asking Schild for a reference, and Schildís reference, which was very good.
Pirani: I see. I donít remember. There was another university in eastern Canada that I applied to, the one in Hamilton.
Rickles:I think it is Queens.
Pirani: Well McGill is in Montreal.
Rickles:So you didnít have any personal contact with Bondi beforehand?
Pirani: I had no personal contact with Bondi. It was entirely thanks to them being in jail together.
Rickles:[Laughs] Internment camp.
Pirani: Internment camp.
Rickles:So what were you working on initially? I know in í56 you got this Ph.D. on the relativistic basis of mechanics. But what were you initially working on? On the steady state theory?
Pirani: I was doing whatever I liked.
Rickles:Do you remember what it was, though?
Pirani: Yes. There was some guy in Cambridge who had written a paper on an alternative relativity theory.
Pirani: No. McCrea was all right. Itís thanks to McCrea that I got to edit that book of Russellís, because he was too busy, so he said try Bondi, and Bondi said he was too busy, try Pirani. That was very nice. I actually got to meet Russell.
Rickles:I want to talk about that.
Pirani: [Retrieves materials] Oh itís Littlewood.
Pirani: And then I wrote a paper on the experience of the expansion of space on the gravitational field surrounding isolated bodies. Wonder what that was about.
Rickles:What date is that?
Rickles:And in fact, actually you did a kind quantum gravity paper on steady-state theory in í54, where you consider it to be connected to the neutrino [the gravitino], I think, where you tried to basically give an explanation for steady-state theory using more field theoretic...
Pirani: Yes, thatís right. And then the gravitino word was stolen from me many years later.
Rickles:Was that the first usage of gravitino? [Yes.] Oh, I didnít know that. Thatís interesting. Yes, the super-symmetry people took it.
Pirani: Thatís right. They didnít know. In fact Iíve been thinking of writing to the Oxford dictionary about that.
Rickles:Is it in the dictionary as — So who does it say coined it?
Pirani: Iím not sure that my — And it was that that put me on to — oh, and then I reviewed the — No, I read the review of a paper of, who was the guy who did the classification?
Pirani: The Petrov classification, yes. And I was reading the proofs of a book by Synge about special relativity where he said something about the geometrical characteristics of plane waves, and then boom! Connect Petrov, and it all comes out.
Rickles:So you had that insight. Was this in í54, or did it all happen at the same time as the McVittie?
Pirani: It all happened at about the same time, and I can remember now even about that time suddenly saying to myself, ďI understand GR,Ē being able to judge the significance of other peopleís papers, to see where the mistakes were, if there were likely to be mistakes, and all of a sudden to know what I was doing.
Rickles:Itís an amazing tour, actually. To be honest, I thought the work you did on gravitational radiation and the Riemann tensor; I thought that was just old news. I thought it had been known forever. It was only recently that I discovered that it traced back to that 1957 work. Itís amazing because itís just standard. Itís not mentioned or referenced. Itís just part of —
Pirani: Really? Is it still?
Rickles:Well, itís part of standard, just part of the standard way of doing general relativity now, isnít it? Thatís the interesting thing.
Pirani: I don't know.
Rickles:It is, yeah. So itís been absorbed.
Pirani: Well wait until we get to 1983. I found that paper. Can I just have a look at it? [Yeah.] Okay, Iíve found the right paper, found out what itís about.
Rickles:So what was the conclusion of that particular paper?
Pirani: It was in response to somebodyÖ You wouldn't like that freshened up a bit [refers to tea]?
Pirani: And who claimed? Oh, Einstein and Straus claimed that it didn't matter having an expansion space around a Schwarzschild solution, and what I noticed was that that depended on not having the cosmical term, the lambda term. Then I looked at Synge and OíBrien, whoever OíBrien was I don't remember. Synge and OíBrien had worked out the continuity conditions across a boundary, and it followed from this that if you have the cosmical term, the lambda g[?] term outside, you have to have it inside as well, and then it did affect that.
Mm-hmm [yes]. What was that written — oh, it says Trinity there.
Pirani: Yeah. Iím by myself, I guess. Okay, that was — I didnít know what that was about. And this is the remains of the paper on the Hartmann formula.
Rickles:Yeah, I do. I have a copy.
Pirani: But I think I need to do something with...
Rickles:So what was the working relationship like with Bondi initially? Was there kind of close immediate interactions, or?
Pirani: Well, we have very different backgrounds because his was astronomy, a good deal. His widow was an astronomer. He was very much into astronomy and equations of state and stellar evolution, and all kinds of things I didn't know, about and I was very much into tensor calculus — all kinds of things that he knew about but not closely.
Rickles:Well, he was an Eddington product, wasn't he, I suppose. Was he an Eddington student? I think he was.
Pirani: I don't know if he was an Eddington student, but he most certainly came from that area. So it was very fruitful for me because he knew a lot of things fluently which I didn't know.
Rickles:So was he kind of officially a supervisor straight away when you got to Trinity, or were you basically independent?
Pirani: No, he was officially my supervisor straight away.
Rickles:So did you have to specify your research project at the beginning?
Pirani: I don't think so.
Rickles:Did you completely abandon the quantum gravity stuff?
Pirani: I really did.
Rickles:Why? Why was that?
Pirani: I thought about it occasionally. I may have talked about it once or twice with a guy who later became famous for his mathematics at Trinity.
Rickles:Not Michael Atiyah.
Pirani: Yeah, Michael Atiyah, right.
Rickles:So do you remember the content of those? I know heís into topological quantum field theory, right? So I mean he basically uses quantum gravity to do mathematics, I suppose, so he blended them together. Was he interested in quantum gravity then? Was he already thinking about it?
Pirani: I don't remember.
Rickles:Was anybody thinking about it in Cambridge?
Pirani: I don't think so, not close up.
Rickles:Thatís a curious thing. I find it very odd because it seems like such an obvious problem.
Pirani: Well, I was trying yesterday to remember my conversations with Dirac, which werenít many, but I used to go to his lectures.
Rickles:Was he giving GR lectures by then?
Pirani: No, he was giving lecturesÖ
Rickles:Just from his book.
Pirani:Öturn the pages of his book. But I thought I ought to — they were not really for post-docs, but I thought I ought to listen to them. He was quite interested in what weíd been doing, I think. But I don't know that he actually got into it. I remember once atÖ was it Syracuse? Maybe it was at Syracuse giving a talk where I dismissed Diracís view of relativity, and this did not encourage my audience.
Rickles:Was that quite a bit later?
Pirani: Much later
Rickles:So were you doing much traveling while you were at Trinity? Did you go to Europe or were you pretty much — apart from Dublin, were you pretty much stationary?
Pirani: I don't think I went to Dublin until I went to Dublin to stay.
Pirani: Yeah. I wasn't traveling much.
Rickles:Maybe within England?
Pirani: My parents were living in London by then, so I was spending a lot of time in London. And I got married in í54 the first time.
Rickles:Still in Trinity by that stage.
Pirani: I was still at Trinity.
Rickles:So was that a student or a staff or somebody completely separate?
Pirani: No. It was somebody I met through Dennis Sciama.
Rickles:Okay. So you mentioned a trip to Rome. I showed you the letter, right, where you mentioned you had a trip to Rome, but maybe that was quite a bit later where you went with Dennis Sciama.
Pirani: Oh, I went with Dennis and somebody else. We were going to that meeting in Rome. That's right.
Rickles:I think it was inÖ was it an astronomy or astrophysics meeting?
Pirani: And Tommy Gold was there.
Rickles:Do you remember the year? Here it is. It was í52, actually. Yeah, yeah.
Pirani: We drove down with an astronomy student.
Rickles:Was it Bert someone? Malyka[?] Bert and Malyka? Keith Roberts.
Pirani: Do you know what happened to Keith Roberts? Iíve often wondered, because he went to work on nuclear weapons.
Rickles:Did he? I know a paper on Lagrangians, something like an objective approach to Lagrangians or something like that. And youíre right. I mean you mention in this letter, the one I showed you, that he was working on Weissís theory, actually. So I have that paper of his. So you keep mentioning Weiss all over the place. So I mean you were clearly traveling. í52 you come to this meeting. Do you remember what was being discussed there? So you would have just written the paper with Skinner and Schild on the secondary constraints.
Pirani: I think that was a general astronomical meeting. I don't think it wasÖ
Rickles:Did you give a talk?
Pirani: I doubt it. Letís see what all I can find about that. [Looks for materials.] It looks as though this damn thing has gotten out of order. Iíll see what I can do.
Rickles:I mean you mentioned Guptaís quantization paper as well in this letter. So you were still kind of reading quantum gravity stuff by the looks of it. It was Guptaís general one where he does the full theory, and youíre not very impressed with it.
Pirani: Well, it was later that I was going to Trieste. There was this quantum guy there running the place, this Indian guy.
Pirani: Salam! Bingo.
Rickles:So were you a convert to the steady state there? Did you think it was the right way to go at the time? [Yes.] Do you remember why?
Pirani: Yeah, because it pushed the creation out of sight.
Rickles:Thatís what I heard. Do youÖ You mentioned that you don't like black holes either. Is that for a similar reason?
Pirani: That was because I thought that the Schwarzschild solution was being over-interpreted.
Rickles:So how did Bondi and Gold react to your take on steady state theory?
Pirani: Well, it was fine for them to have aÖ
Rickles:Some extra ammunition?
Pirani: Yeah. And then I wrote that paper with the gravitinos in it, and the gravitinos wereÖ
Rickles:Thatís what Iím thinking of. What was their response to that paper?
Pirani: Well, the amazing thing was that whoever refereed it for the Royal Society let it through.
Pirani: Because it was pure cookery. I mean just having these negative energy things going out.
Rickles:Well, itís not that much different from Feynmanís kind of crazy approaches. [Laughs] So you also mentioned in a letter that there was an Eddington group. Was the Del Squared V Club, or was that a different thing?
Pirani: There were two groups, maybe not contemporaneously. Sciama had a lot to do with them. And at one point I was the secretary of one of them.
Rickles:The Eddington group.
Pirani: Was it?
Rickles:Maybe. I don't know. So you said it was basically for the non-subtractionists to go and talk together. You really didn't like their subtraction physics, it seems, at the time.
Pirani: I remember that I violated a convention by inviting somebody not from Cambridge to give a talk.
Rickles:Oh, right. In the Eddington group was this.
Pirani: No, that was in the Del Squared V Club. The Del Squared V Club was a general physics interest group, and the Eddington was, as you might suspect from the name, more oriented towards relativity. Excuse me.
Rickles:So before I go any further, is there anything that you think Iíve missed that might be interesting from the point of view of relativity and especially quantum gravity about your time in Toronto and Carnegie, around that time?
Pirani: Anything about relativity.
Rickles:That had an important role orÖ
Pirani: Well, what has not been spoken about enough is the relation between the Schild group and the Bergmann group, and I do not remember very well how that went.
Rickles:Was there a sense that they would — I supposed Schild didn't have aÖ you wouldnít really call it school by that point, because he was justÖ
Pirani: No, he really didn't.
Rickles:You and Skinner.
Pirani: It was me and Ray Skinner. I don't remember other people in the department who were particularly interested in relativity. There were people interested in geometry.
Rickles:I was going to say, was it the Applied Mathematics Department?
Pirani: No, it was physics.
Rickles:It was in physics. So was he teaching pure general relativity courses by that time? Do you remember?
Pirani: I think so.
Rickles:Wheeler wasn't into this by then, but did you have much interaction with Bergmannís group?
Pirani: We did have interaction with Wheeler later. It canít be, that can't be that much later.
Rickles:Maybe itís when you went back in to work for RIAS for a bit, and Chapel Hill, because thatís when the Stevens Institute thing got started.
Pirani: Maybe it was.
Rickles:Iíll come to that in a bit. But in the í50s when you were doing your canonical quantization stuff, there must have been some pool of ideas, because Bergmannís students were working on very similar topics and there was Anderson, 1950s, working on constraints in covariant field theories. Were you kind of going to each of those departments and giving talks or anything?
Pirani: Not that I recall. I remember meeting most of those guys, but I get muddled up between things which happened then and things which happened much later. Like when I was doing a year at Brandeis, and then the year at Northeastern or half a year at Northeastern when I re-met these people 20 years later. So Iím sorry not to be more overt about this.
Rickles:I suppose you did have a bit of experience of Infeldís school. I suppose he did have a school, and Schild was part of it and then you were maybe part of it. Did you know any significant differences between their approach and Bondiís approach? Or were they just working on completely different topics?
Pirani: It was different areas and different topics, really. Bondi, as I said, was much more astrophysical. And they were much more applied geometrical.
Pirani: Well, Schild. Infeld had a broad knowledge of all kinds of physics. He ended up going back to Poland to rescue Poland physics-wise, and I visited there in í57. Thatís when I established a connection with Trautman.
Rickles:That was í57.
Pirani: Thatís the first time I went to Poland, was í57.
Rickles:You must have done a lot of traveling in í57. So weíre still at Cambridge. You seemed to keep a foot in with the quantum gravity business, and also I think Iíve seen you mention in some letters that you think that the problem of gravitational radiation, classical problems are an essential preliminary to get to quantization. Was that still going on in your mind then or were you just interested in classical problems for the own sake?
Pirani: No, I think it was always in my mind that we have to get it all back together.
Rickles:Why, though? Did you have any sense that there was some necessity? I don't really expect you to remember your exact kind of thoughts that long ago. Was there any sense that it had to be resolved, the problem of quantum gravity, that it was a real physical problem?
Pirani: Well, I can't date the feelings.
Rickles:No, no, I know. Because I mean —
Pirani: Itís become so thoroughly understood nowadays that weíve got to have a theory.
Rickles:Because I know that Tommy Gold in the Chapel Hill conference was kind of saying, and Rosenfeld, ďWe don't necessarily need quantum theory of gravity. Thereís no physical reason and there might not even be any formal reason.Ē
Rickles: So was Tommy Gold there when you were there at Cambridge?
Pirani: Yes. And there was at least one semester when Bondi was away that Hoyle was my supervisor.
Rickles:Were you working with him on anything?
Pirani: No. I was going and talking to him once a week or so.
Rickles:Do you remember the nature? Was it basically steady state theory or other topics?
Pirani: Oh, I think I was probably talking about things I was interested in a good deal. Later on, Stan Deser and I and probably somebody else as well took Hoyle and Narlikar theory apart. Thatís much later, though. It was really confusing.
Rickles:No, but actually when did you — I know Schild started working on Whiteheadís theory. Isnít that kind of similar? Wasn't that an action at distance theory?
Pirani: I think that was later. That was after Iíd left Pittsburgh, wasn't it, when Schild was working on Whiteheadís theory? Because one of the things I failed to do in my time was to prepare an edition of Schildís some published papers after his death. We tried to do something with a lot of text of which a good deal was about Whiteheadís theory. Didn't manage it.
Rickles:Actually, there is a letter here from 1960 where you mention to Schild that youíve been looking into Whiteheadís theory of gravity.
Rickles:I presume possibly pre-Schild.
Pirani: Hmm. When was that? 1950?
Rickles:In fact, wasn't Synge interested in that as well? Didn't he do some work in that?
Rickles:Iím pretty sure. Are you absolutely sure you werenít in Dublin in 1950? I really want to check this letter. Maybe itís, I don't know, a squiggle on the zero and it should be a four. Iím not sure. Iíll check it when I get home, and if I find that itís 1950 Iíll email you a copy so you can see it.
Pirani: I just don't believe it.
Rickles:Okay. So weíll move to Dublin now, unless thereís anything else. Did you start thinking about the gravitational radiation work while you were still at Trinity, or was this in Dublin?
Pirani: Well, for that it would be a great help to know when the mass reviews about things were.
Rickles:I think they were í54. The McVittie one was I think í54. I actually have them on here somewhere.
Pirani: There was one issue where I think I reviewed about 50 papers one after another. Have you got that?
Rickles:Yeah. Almost every paper on gravity, actually, you seem to be the reviewer on. Do you still do —? When did you stop doing those, by the way? Those math reviews.
Pirani: I don't remember.
Rickles:I got into the habit of doing those as well.
Pirani: Oh, did you?
Rickles:Yeah. I still do them.
Pirani: It still happens, does it?
Rickles:Yeah. I like it. Itís good fun to find strange papers. Now what did I do with this? Letís see. There we go. Sorry. I do have them on here. Itís just rather a lot of documents on here. Letís see, Pirani as referee. So this 1955, the McVittie one. ďGravitational Waves and One-dimensional Einsteinian Gas Dynamics.Ē So you wrote: ďHere gravitational waves are said to exist when the field equations in empty space-time are shown to have solution g[?], which are time dependent and which are also solutions of the wave equation. Definition is not invariant and doesn't seem to have physical significance since the author has repeatedly to reject metrics satisfying these conditions which are either flat or can be transformed into time independent form or both.Ē
Pirani: Thatís right.
Rickles:And so they don't represent genuine gravitational wave solutions. Hmm. So that you think you identify that as the kind of trigger thatís —
Pirani: That would be one of the triggers, definitely. The other one was the Petrov classification.
Rickles:So did you manage to get a copy of the actual paper?
Pirani: The Petrov one?
Rickles:Yeah, because it was in a strange Kazan Journal or something.
Pirani: Yes, and I had somebody around here who helped to translate it, but he didn't do it very well. He wasnít interested. He wasn't knowledgeable about that kind of thing.
Rickles:So was Syngeís work basically at the same time? His classification ideas, they were about the same time as Petrov? Is that right, or were they earlier?
Pirani: I don't know when they were, but they were certainly in the book, and that was how I discovered them.
Rickles:Letís see. So í55. So you would have been at — How long were you at Dublin?
Pirani: I was there for a full year from maybe September to September, something like that.
Rickles:So you might have done that referee, that review, while you were at Dublin, you think?
Pirani: Quite likely. While I was at Dublin, Bondi moved from Cambridge to Kingís College, and that was how I got my job there.
Rickles:So in Dublin, what do you remember of your time in Dublin? So Schrodinger was still around. You mentioned Lanczos.
Pirani: He was very much around, and he had this student called Ludwig Bass, whom Iím going to be seeing again in August.
Rickles:So you have a paper, right, with him?
Pirani: We wrote a paper stimulated by, not by SchrŲdinger. What was the other guy?
Pirani: Yes, stimulated by Lanczos, we wrote this paper. Thatís right.
Rickles:Do you remember? I can't remember what it was on now.
Pirani: No. Maybe I can find it. [Looks for paper] This is the more complete version. ďThe Gravitational Effects of Distant Rotating Masses.Ē Itís about all those induction things, which nowadays I think are much better understood.
Rickles:So how did the Dublin position — was it just a post-doc again?
Pirani: Yeah. I think it was a Canadian one.
Rickles:I think it was. So did you apply there specifically to work with SchrŲdinger or with Synge?
Pirani: No, with Synge.
Rickles:With Synge, yeah. So what was it of Syngeís that you were impressed with at the time? Everything.
Pirani: Thatís a copy of that. Itís about classical paper of Thirring in 1918 is what that paper by Bass and me is about.
Rickles:Like frame-dragging effects?
Pirani: Yeah, thatís right.
Rickles:Lense-Thirring effects in here. Huh. So when was the Thirring paper? Had it just appeared?
Pirani: No, the Thirring paper was 1918.
Rickles:Really? Oh, there were two Thirrings right.
Pirani: And Lanczos told us about it, and then we worked on it. Bass ended up in Brisbane. Heís still there, by the way.
Rickles:So actually, didn't you send a letter to Einstein while you were in Dublin? Is that right?
Pirani: Was it in Dublin? I sent a letter to Einstein.
Rickles:It was on Machís principle, right?
Pirani: Machís Principle and I got an answer, and I gave it to a secretary to type out and to photocopy and I never got it back. So the text is published, but I do not have the letter.
Rickles:I wonder if itís in the Einstein archive. It might be.
Pirani: Both what I wrote and what he wrote have been published. But the actual letter I didn't get back from the secretary. She mislaid it or something.
Rickles:So were you arguing against a particular understanding of Machís principle or just arguing against Machís principle?
I was in favor of Machís principle until I got talked out of it by a guy who went to Texas. Heís of Austrian background and his name begins with R... Rindler.
Rickles:Oh, Wolfgang Rindler. Is he Australian?
Pirani: Austrian, I think. Yeah, I think Rindler talked me out of Machís principle.
Rickles:Was Rindler Cambridge? No, he was Oxford, right? I think he was Oxford. Anyway, but you wrote your really famous paper ďOn the physical significance of the Riemann tensorĒ in Dublin, is that right? Did you write that in Dublin? Am I getting the dates right?
Pirani: Yeah, I think that probably looks right. I had it in my hand not many minutes ago, butÖ I had two papers chosen for Golden Oldies now. Do you know about Golden Oldies?
Rickles:Yeah. Well, "The physical significance" one, that was obviously a Golden Oldie. What was the other one?
Pirani: No, it wasn't that one. They havenít chosen that.
Rickles:ďThe physical significance of the Riemann tensor?Ē
Pirani: Oh no, the one about gravitational radiation, the invariant formulation, which I thought was a good paper. What was ďThe physical significance of the Riemann tensorĒ about?
Rickles:So you used these orthonormal tetrads. Well, itís basically an extension of Syngeís idea, and Eddingtonís idea that you use the geodesic equation, and you look at a relative acceleration. Well, everythingís in the Riemann tensor basically, and this tells you about the relative accelerations, and this is how you get the physical picture of general relativity. Which again, I thought that was standard relativity. Itís what you learn in every text now. So I was surprised to see that it went back to this paper. I thought it was just the way you do relativity! So thatís why itís a Golden Oldie.
Pirani: I see. Okay.
Rickles:In fact, isnít that what you spoke about at Chapel Hill?
Pirani: Oh, thatís possible.
Rickles:The same kind of topic. Do you remember what kind of topics you were discussing with SchrŲdinger? What were the interactions like in Dublin?
Pirani: Well as I said, you have to turn up for coffee at 11, and then you talk to everybody.
Rickles:Did people interact much? Were there regular seminars and these kinds of things?
Pirani: There were regular seminars. It was quite a small group. I would have said there were only five or six of us, apart from the three more senior guys. Some of the people from Trinity College Dublin used to come over sometimes.
Rickles:Who was that? Do you remember?
Pirani: No. It might come up.
Rickles:Have you never sort of been taken up by quantum mechanics and looking more at quantum mechanics, because SchrŲdinger would have been doing his — 1954 was when he was doing his Dublin lectures on the interpretation of quantum mechanics.
Pirani: Was it?
Rickles:Yeah, theyíve been published as well. They were unpublished; theyíve now been published, about particle statistics and his interpretation of the wave equation.
Pirani: If it was 1954, I must have gone to them.
Rickles:You don't remember those?
Pirani: No, I started there in autumn. What part of 1954 did he give the lecture?
Rickles:I can't remember.
Pirani: I don't remember him giving a lot of lectures.
Rickles:Were his main interests at that time interpreting quantum mechanics, or completely different?
Pirani: I think that was his main interest, yes.
Rickles:And you werenít drawn into it at all?
Pirani: Moderately, but I was never very good at quantum mechanics. In fact, I taught it at Kingís College once or twice and probably not very well.
Rickles:Just quantum mechanics, not quantum field theory.
Pirani: Quantum mechanics. I don't think I ever could have taught quantum field theory.
Rickles:So the 1950 paper you wrote is very formal quantization as well, isnít it? Itís just to promote to commutators andÖ [Yes.] Okay, letís see. Ah, so yeah. In fact, you had an interview with Daniel Kennefick, right? This was a while back. He was writing a book on gravitational waves. So he mentions that you were also inspired to do this work on classification of gravitational fields when you were proofreading Syngeís book. So was this happening at the same time as you were reviewing Petrovís thing? So it all luckily conspired?
Pirani: I don't think I reviewed Petrov. I read the review of it.
Rickles:Oh, you read the math review that somebody else did?
Pirani: Yes, thatís right.
Rickles:So it was kind of a lucky coincidence that all these things came together.
Pirani: Absolutely, absolutely.
Rickles:Did you know about Eddingtonís earlier work using these kind of invariant methods and whatnot?
Pirani: What, about 137 and all that?
Rickles:Oh no, no, this is slightly different. The idea that the Riemann tensor was the thing to focus on.
Pirani: I don't think I did know.
Rickles:Yeah, because it dropped out of fashion.
Pirani: But I did discover much later a paper that somebody had written a few years before 1957, around 1950, and if I had seen that paper, I would never have dared to write mine because there was such a lot of overlap.
Rickles:What was it?
Pirani: It was a paper on gravitational fields and something about Riemann tensors. But I don't remember his name now. It was just an awful lot of common sense. It fell out of sight. Whatever he did, it fell out of sight totally.
Rickles:So were you aware of controversy at the time about gravitational radiation not being real?
Pirani: Yes. Bondi would always do this thing [shakes fists]. Dipole radiation is whatís real.
Rickles:Oh, thatís what he thought, that it was dipole, not quadrupole?
Pirani: That it was a quadruple reaction that is real. I mean. This is the quadruple variant; itís not the dipole. Yes.
Rickles:So the difference is Eddington used these methods and he thought he had proved that they werenít real, across gravitational waves werenít real.
Pirani: Is that what heíd done? I don't remember.
Rickles:Well, because he said for similar reasons that you brought up, you thought they were artifacts of the coordinate system. The title of this guyís book who interviewed you a while back is —
Pirani: Kennefick. [Yes.] I have had some correspondence with him recently.
Rickles:Itís a very nice book that he wrote, actually, and he uses Eddingtonís favorite famous phrase that gravitational waves propagate at the speed of thought, i.e. they don't exist; theyíre just figments. Itís a really nice book, actually.
Okay. Any other things we should say about your time at Dublin?
Pirani: I became a father for the first time. That was quite a significant thing for me.
Rickles:Did it have a big impact in a positive way or a negative way as well?
Pirani: At the time it was very positive. My daughterís name is Abigail.
Rickles:Hence the book.
Pirani: Sheís forgiven me for using her name so much in fiction. She lives in Glasgow now.
Rickles:I see. So what did your wife do? She was able to just move with you, no problem, to Dublin?
Pirani: Yes. She was writing and has been writing ever since. She was reading and writing. She was really an English literature person. In fact, she used to get irritated with me because I didn't know enough about some of the literature things that she thought significant, like F. A. FrankÖ
Rickles:Who am I thinking of?
Pirani: FrankÖ oh well, it will come. We were divorced later, and then I was married and divorced again. And then I had a 20-year relationship with an Italian woman to whom I wasn't married, and she died six years ago.
Rickles:Do you think it affects your work?
Pirani: Not a lot. My second wife was very annoyed because she thought she would understand what I was up to within a reasonable time, and I told her she was never going to understand what I was up to.
Rickles:Okay. Was there any other traveling or were there any conferences that were significant during theÖ
Pirani: During the Dublin period? Yes, there was a conference in Dublin, an astronomical conference.
Rickles:Was that organized by Synge or by you?
Pirani: No. It was organized by the Dublin Observatory guy, whose name escapes me. But I did a report on it daily for The Irish Independent I see.
Rickles:Hmm. Was it an international conference?
Pirani: Very, yes.
Rickles:Were people speaking on general relativity, or just specific astrophysics results in astronomy?
Pirani: Well, one of my news reports was ďUniverse Is Expanding at a Slower Rate.Ē It was thought that the universe was about two billion years old, and that was a problem because it was thought that the Earth was about five billion years old. Jupiter can send out radio waves. You can have this.
Rickles:What is that?
Pirani: This is the longÖ
Oh, with everything so I can see —
Pirani:Öread with nearly everything. I printed it out for you.
Rickles:So do you remember who attended that? From overseas, Iím thinking of.
Pirani: Iím pretty sure Tommy Gold was there. I don't think Bondi was there. But lots of Americans.
Rickles:American general relativity people or was it mainly just astrophysics?
No, it was mainly astronomy people. Shall I look at the — Iíve got another one of these which has the newspaper sort of things in it.
Rickles:That would be good.