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Scalar-tensor theories of gravity: some personal history. (English) Zbl 1169.83005

Guzmán Murillo, Francisco S. (ed.) et al., Gravitation and cosmology. Proceedings of the third international meeting, Morelia, Michoacan, Mexico, 26–30 May 2008. Melville, NY: American Institute of Physics (AIP) (ISBN 978-0-7354-0614-8/pbk). AIP Conference Proceedings 1083, 34-46 (2008).
(Jordan)-Brans-Dicke theory is one of the most prominent relativistic non-Einsteinian theories of gravity. One of the fathers of this theory, Carl Brans, now presents his view to the history of this theory.
From the abstract: “From a perspective of some 50 years or more, this paper reviews my recall of the early days of scalar-tensor alternatives to standard Einstein general relativistic theory of gravity. Of course, the story begins long before my involvement, going back to the proposals of Nordström in 1914, and that of Kaluza, Klein, etc., a few years later, so I include reviews of these seminal ideas and those that followed in the 1920’s through the 1940’s. This early work concerned the search for a unified field theory, unifying gravity and electromagnetism, using five dimensional manifolds. This formalism included not only the electromagnetic space-time vector potential within the five metric, but also a space-time scalar as the five-five metric component. Although this was at first regarded more as a nuisance, to be set to a constant, it turned out later that Fierz, Jordan, Einstein and Bergmann noticed that this scalar could be a field, possibly related to the Newtonian gravitational constant. Relatively little theoretical and experimental attention was given to these ideas until after the second world war when Robert (Bob) Dicke, motivated by the ideas of Mach, Dirac, and others, suggested that this additional scalar, coupled only to the metric and matter, could provide a reasonable and viable alternative to standard Einstein theory. This is the point of my direct involvement with these topics. However, it was Dicke’s prominence and expertise in experimental work, together with the blossoming of NASA’s experimental tools, that caused the explosion of interest, experimental and theoretical, in this possible alternative to standard Einstein theory. This interest has waxed and waned over the last 50 years, and we summarize some of this work.”
From the text: “In 1957 I was a first year graduate student at Princeton who was very interested in the applications of topology and bundle theory to the differential geometry of general relativity, motivated largely by lectures of Charles (Charlie) Misner. Looking for a thesis topic I approached Charlie with the idea of incorporating and extending bundle theory further into general relativity and even quantum theory. Perhaps this might have developed into an early form of gauge theory. Misner thought this was too abstract, and besides, he knew that Bob Dicke was looking for a theorist to provide some formalism for his ideas, motivated by proposals of Mach, Dirac, et al. So, he suggested I approach Bob for some thesis ideas. Somewhat reluctantly, being very experimentally challenged myself, I nevertheless worked up the courage to approach Bob. To my great relief, Bob was very kind and tolerant of my experimental incompetence. He even invited me to the regular meetings of his experimental group. They were very kind and forbearing of a dumb theorist who did not know a vacuum tube from a screwdriver. More significantly though, Bob took me aside in private meetings. He pointed me to the works of Dirac, Sciama et al. (but we were unaware of Jordan’s work at this time), and suggested I try to formulate a set of equations generalizing SET to allow for the almost quaintly paradoxical idea of a ‘varying gravitational constant’. This resulted in my PhD thesis of 1961. During the writing I discovered the work of Jordan et al. on this topic and almost quit writing. However, I was encouraged to continue, giving what I hope was sufficient and appropriate credit to Jordan and his group. From this thesis, Bob and I published the first paper on our version of this subject in 1961. Of course, these theories ought properly be called ‘Jordan-Brans-Dicke’, (JBD), but unfortunately many papers disregard Jordan’s ground breaking work and refer to it simply as BD. Remo Ruffini has shown me a letter he received from Jordan decrying the lack of credit he (Jordan) was receiving during the explosion of interest in ‘scalar-tensor’, ST (a more neutral term) theories. I really believe that much of the reluctance to credit or investigate Jordan’s work was due to his apparently strong, and perhaps even enthusiastic, membership in the Nazi party. But, back to the origins of our version. Among other things, Dicke pointed out to me that Einstein himself was strongly motivated by the ideas of Mach.”
For the entire collection see [Zbl 1157.85001].

MSC:

83-03 History of relativity and gravitational theory
85A40 Astrophysical cosmology
83D05 Relativistic gravitational theories other than Einstein’s, including asymmetric field theories
01A70 Biographies, obituaries, personalia, bibliographies
83E15 Kaluza-Klein and other higher-dimensional theories
01A60 History of mathematics in the 20th century
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