Weinberg replies: I thank the writers of these letters for their thoughtful remarks. Alfred Goldhaber offers a fascinating speculation, that Einstein might have developed modern quantum mechanics by building on his 1905 introduction of the quantum of light. However, there would have been an obstacle in his path: a shortage of relevant data. By concentrating on atoms rather than photons, de Broglie, Bohr, Heisenberg, and Schrödinger were able to find guidance and confirmation from the huge amount of spectroscopic data already available to them. I can’t think of any way that the quantum theory of light itself could have found similar quantitative support from experimental data in the 1900s or 1910s.
Tom Cornsweet wisely reminds us that the published literature gives only a limited insight into the work of scientists. Real historians, unlike me, try to go deeper by studying diaries, letters, and personal reminiscences, but some aspects of the past can never be recovered.
As far as I have thought about the matter, I agree with Hans Ohanian about the synchronization of clocks. I have not emphasized this point when I have taught relativity theory, preferring instead to take Lorentz invariance as a starting point.
I do not know of any evidence that Einstein would have been content for God to play dice all the way, as suggested by Ravi Gomatam. Einstein did acknowledge the many successes of quantum mechanics, but as far as I know he always hoped that those successes could be explained on the basis of a thoroughly deterministic theory.
Ron Larson takes me to task for my “not-so-subtle knock on religion.” I certainly never intended my remark to be subtle. The reason that I did not mention religion is that I intended to knock reliance on any supposedly infallible authority—in other words, not only the attribution of infallibility to the Bible or Koran, but also to Das Kapital, Mein Kampf, or Mao’s little red book. I did not say that science gave Einstein guidance on public issues. The reason I said Einstein made no mistake on the issues I mentioned is not that I thought he was infallible, but that I thought he was right.
It is of course true, as Brian Hall says, that Einstein’s fallibility does not in itself show that religious prophets are fallible. My point was that, in recognizing that even Einstein was not infallible, we physicists set a good example. While it doesn’t prove anything, our example may have some beneficial moral influence. As to whether this sort of remark belongs in an article about Einstein, it seems to me that part of the justification of pure scientific research lies in the impact it has on the culture of our times. Anyway, some of us unpaid contributors to Physics Today take our compensation in the opportunity that publication gives us to express our personal views on one thing or another.
To answer Roger Newton, the difficulty that I find with quantum mechanics is that its rules tell us how to use the wavefunction to calculate the probabilities of various values of dynamical variables, but the apparatus that we use to measure these variables—and we ourselves—are described by a wavefunction that evolves deterministically. So there is a missing element in quantum mechanics: a demonstration that the deterministic evolution of the wavefunction of the apparatus and observer leads to the usual probabilistic rules.
Did Robert Brown study the motion of ink particles, and did they carry a significant electric charge, as Bob Eisenberg says? I thought that Brown chiefly studied pollen grains and dust particles, but whatever they were, I suppose the particles may have been charged, and if so, then the effect of electric forces on Brownian motion should be examined.
I may be missing the point of Robert Becker’s remarks, but I have never understood what is so important physically about the possibility of torsion in differential geometry. The difference between an affine connection with torsion and the usual torsion-free Christoffel symbol is just a tensor, and of course general relativity in itself does not constrain the tensors that might be added to any dynamical theory. What difference does it make whether one says that a theory has torsion, or that the affine connection is the Christoffel symbol but happens to be accompanied in the equations of the theory by a certain tensor? The first alternative may offer the opportunity of a different geometrical interpretation of the theory, but it is still the same theory.
