Bryce DeWitt on Quantum Gravity and String Theory

Last night a preprint appeared on the arXiv from beyond the grave, an undated manuscript entitled Quantum Gravity, Yesterday and Today, found without any indication of its purpose in the files of Bryce DeWitt, who passed away in 2004.

DeWitt devoted much of his career to the question of how to quantize the gravitational field, beginning back in 1948 when he was a student of Julian Schwinger. He has some interesting comments about the dramatic changes over the years in popularity of research work on GR and quantum gravity:

Most of you can have no idea how hostile the physics community was, in those days, to persons who studied general relativity. It was worse than the hostility emanating from some quarters today toward the string-theory community. In the mid fifties Sam Goudsmidt, then Editor-in-Chief of the Physical Review, let it be known that an editorial would soon appear saying that the Physical Review and Physical Review Letters would no longer accept “papers on gravitation or other fundamental theory.” That this editorial did not appear was due to the behind-the-scenes efforts of John Wheeler.

DeWitt gives some history of his important work on the quantization of gauge theories, which culminated in working out a functional integral method to handle to all orders the ghost terms that Feynman had shown to be necessary. He describes a 1955 offer from the Glenn L. Martin Aircraft Company to fund his research in hopes that it would lead to an antigravity device, one that he didn’t accept. Instead, the Air Force supported his research during the period he was unraveling the story of ghosts, support that ended in 1966 when they finally realized that gravity research was not going to lead to magical results. With the termination of his grant, he could no longer pay page charges to the Physical Review, delaying the publication of one of his papers by a year.

He also has some interesting comments about the DeWitt-Wheeler equation:

… intensive work was carried out in those years on canonical quantum gravity, culminating in an equation that bears my name along with that of John Wheeler who was the real driving force. Research on the consequences of this equation continues to this day, stimulated by work of Abhay Ashtekar, and some of it is quite elegant. But apart from some apparently important results on so-called “spin foams” I tend to regard the work as misplaced. Although WKB approximations to solutions of the equation may legitimately be used for such purposes as calculating quantum fluctuations in the early universe, and although the equation forces physicists to think about a wave function for the whole universe and to confront Everett’s manyworld view of quantum mechanics, the equation, at least in its original form, cannot serve as the definition of quantum gravity. Aside from the fact that it violates the very spirit of general relativity by singling out spacelike hypersurfaces for special treatment, it can be shown not to be derivable, except approximately, from a functional integral. For me the functional integral must be the starting point.

He ends the paper with positive comments on string theory:

In viewing string theory one is struck by how completely the tables have been turned in fifty years. Gravity was once viewed as a kind of innocuous background, certainly irrelevant to quantum field theory. Today gravity plays a central role. Its existence justifies string theory! There is a saying in English: “You can’t make a silk purse out of a sow’s ear.” In the early seventies string theory was a sow’s ear. Nobody took it seriously as a fundamental theory. Then it was discovered that strings carry massless spin-two modes. So, in the early eighties, the picture was turned upside down. String theory suddenly needed gravity, as well as a host of other things that may or may not be there. Seen from this point of view string theory is a silk purse. I shall end my talk by mentioning just two things that, from a nonspecialist’s point of view, make it look rather pretty.

The two things he has in mind are the ability of a single string diagram to sum up a lot of Feynman diagrams, and the use of orbifolds to make possible topology-changing transitions.

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11 Responses to Bryce DeWitt on Quantum Gravity and String Theory

  1. Shantanu says:

    This is interesting. Were you planning to attend the emergent gravity workshop at MIT in August?
    also did not know that Olaf Dreyer(who primarily works in LQG) is now at MIT.

  2. Brandon DiNunno says:

    If you found this particular article to be interesting, you should see all of the amazing things in Bryce’s documents. Hopefully Cecile and I will be able to get a few more out to the public very soon.

  3. Marcus says:

    on internal evidence I would date the manuscript roughly around 1995. it refers to something “forty years ago” and cites a 1955 publication. Can someone more knowledgeable say whether circa 1995 makes sense?

  4. Professor R says:

    “Most of you can have no idea how hostile the physics community was, in those days, to persons who studied general relativity.”

    Peter: coming from such a reputable source, that’s an astonishing statement. It makes me wonder whether it really is true that the American schools are more suceptible to trends that their European counterparts…

    For example, I do know that at the Dublin IAS in the fifties and sixties, all the quantum hotshots started their careers with serious research in GR as a matter of course (not least due to the presence of Synge). For example Dad’s first book was on GR, not QFT (see General Relativity; Papers in Honour of JL Synge, ed O’Raifeartaigh OUP 1972).

    Actually, if you don’t know this collection, you might find it a treat – it has papers by Lanczos, Sciama, Penrose, Chandrasekhar and Israel, among others!

  5. Robert says:

    Thank you for the link to this first-hand view, by one of the founders, on the history of quantum gravity.

  6. Peter Woit says:


    Thanks, will look forward to more. Maybe you can set up a web-site…


    Thanks for the info, but my interest in quantum gravity is limited enough that I wouldn’t travel to such a conference.


    At least in the US, I think GR was considered somewhat of a backwater, with the leading institutions and physicists pretty focussed on the particle physics that was coming out of dramatic amounts of accelerator data. Much of the fundamental work on gauge theory ended up being done in Europe and the Soviet Union, with DeWitt one of the few doing this in the US. As he notes, it’s funny that the US during the late 80s and 90s then swung to the other extreme and became completely focussed on (one idea about) quantum gravity.

  7. Dr. E says:

    I recall Wheeler characterizing the heavy focus on particle physics as “ino-itis.”

  8. Indrajeet says:

    Hi Peter,
    This is just to draw to your notice that Willis Lamb has passed away on 21st. More here:

  9. RZ says:

    “Given the fact that the vertex function in diagram 1 contains over 175 terms and that the vertex functions in the remaining diagrams each contain 11 terms, leading to over 500 terms in all[…]”
    I suspect that there is a typo there, and there actually were 110 terms.

  10. wb says:

    “Most of you can have no idea how hostile the physics community was, in those days, to persons who studied general relativity.”

    I can certainly confirm that in the ’60’s Chandrasekhar warned prospective students. “GR is outside the mainstream of physics. That is okay for people at my stage of a career. But as a young person you need to consider whether you want to work outside the mainstream.”

  11. Shantanu says:

    Peter and wb, I thought that 60s and 70s were the golden age of black hole physics. I did not know that GR was outside the mainstream.

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