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information about the velocity of light from a moving source might be lost if the light passes through enough intervening transparent material before being measured. All measurements previous to the 1960s intending to verify the constancy of the speed of light from moving sources (primarily using moving mirrors, or extraterrestrial sources) were made only after the light had passed through such stationary material — that material being that of a glass lens, the terrestrial atmosphere, or even the incomplete vacuum of deep space. In 1961, Fox decided that there might not yet be any conclusive evidence for the second postulate: "This is a surprising situation in which to find ourselves half a century after the inception of special relativity." Regardless, he remained fully confident in special relativity, noting that this created only a "small gap" in the experimental record.
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effects of extinction on the measurement of the speed of light nullified much of the accepted evidence against it. So in 1964, while still a firm believer in special relativity, Fox decided it was necessary to critically reexamine all of the evidence against Ritz's theory. In doing so, he showed that most of the previous rejections of Ritz's ideas based on theoretical arguments were invalid, including all of those enumerated by
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His birthname was James Gaston Fox, James being the
English form of "Jacques", the name of his Swiss-born jeweller father. His parents called him Jacques, his friends called him Jack, and as a young man, Jack legally changed his name from James Gaston to John Gaston, to avoid inevitably being called
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was considered early on to be an alternative to
Einstein's special relativity. A key difference between the two is that under emission theory, the speed of light is expected to vary along with the speed of its source. Emission theory had long been disfavored by the 1960s, but Fox realized that the
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in his 1921 monograph on relativity. In addition, most previous experimental results disfavoring emission theory could be discarded as well, once extinction effects were considered, since the light (or other radiation) whose speed was measured was all actually re-emitted somewhere other than the
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Fox suggested that better experiments were possible, in order to close that "small gap". Since photons with higher energies will, on average, travel much farther in any material before being extinguished and re-emitted, experiments using gamma rays instead of lower-energy visible light or x-rays
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states that the speed of light is invariant, regardless of the velocity of the source from which the light emanates. The extinction theorem (essentially) states that light passing through a transparent medium is simultaneously extinguished and re-emitted by the medium itself. This implies that
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in nearby
Saxonburg. (The experiment with Filippas, noted earlier, was performed at this facility.) He served as head of Carnegie Tech's department of physics from 1955 to 1961. In 1962/63, Fox spent a sabbatical year in France at the
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would be dramatically less sensitive to the extinction problem. In 1963, along with T. A. Filippas (also of
Carnegie Tech), Fox examined 68 MeV gamma rays emitted in the forward and backward directions by
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original moving source. But Fox determined that his own work with
Filippas, as well as very current work done at the CERN laboratory using 6 GeV gamma rays from neutral pions moving at very close to
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In 2004, Alberto MartĂnez examined the rejection of Ritz's emission theory in favor of special relativity from a historical perspective. That work discusses Fox's findings at some length.
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at Los Alamos for the duration of World War II. In 1947, he married
Constance Sullivan of Victoria; they moved to Pittsburgh, Pennsylvania where he had joined the
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Jack Fox, as he was always known, was born in Biggar, Saskatchewan. He moved with his mother to
Victoria at age 13, and left high school two years early to attend
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Alväger, T.; Farley, F. J. M.; Kjellman, J.; Wallin, L. (1964), "Test of the second postulate of special relativity in the GeV region",
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to the then-current body of experimental evidence relating to both special relativity and emission theory.
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Fox, J.G. (1962), "Experimental
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Filippas, T.A.; Fox, J.G. (1964). "Velocity of Gamma Rays from a Moving Source".
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for his PhD, both in physics. He worked briefly in industry before going to the
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MartĂnez, Alberto A. (2004), "Ritz, Einstein, and the
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and the velocity of the source. Within our accuracy, the resultant sum is
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Fox, J. G. (1965), "Evidence
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Laboratoire Joliot-Curie de Physique Nucléaire d'Orsay
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team that created the then state-of-the-art 450 MeV
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