Q: What was Einstein wrong about?Of course Einstein made mistakes. There is a whole book on Einstein's Mistakes. Here is Weinberg's essay on Einstein's mistakes.
Weinberg: Oh, a number of things. One of the reasons I wrote that essay was to show the spirit of science that even the -- we recognize that even the greatest -- Einstein was certainly the greatest scientist of the twentieth century, and one of the greatest of all times -- could be wrong about things and we are capable of pointing that out. Einstein's work is not a sacred text that we are forbidden to depart from.
Weinberg is a big-shot physicist, and his opinion of Einstein should be taken seriously, but I think that he idolizes Einstein for faulty reasons. Here is Weinberg's 2005 praise for Einstein:
Most advances in the history of science have been marked by discoveries about nature, but at certain turning points we have made discoveries about science itself. These discoveries lead to changes in how we score our work, in what we consider to be an acceptable theory.No, it was Poincare who clearly articulated the Principle of relativity as applying to all of the laws of physics, and the Lorentz group as a symmetry group. These were published before Einstein wrote anything about relativity, and Einstein's famous 1905 paper lacks these ideas. These are even Poincare's terms, not Einstein's, and everyone accepts them as Poincare's terms. Poincare takes the ideas further, and searches for laws of physics that are invariant under the Lorentz group. He was years ahead of Einstein. So while Weinberg praises the importance of "symmetry principles as a valid basis for physical theories", that is what Poincare did with relativity, not Einstein.
For an example look back to a discovery made just one hundred years ago. As you recall, before 1905 there had been numerous unsuccessful efforts to detect changes in the speed of light due to the motion of the earth through the ether. Attempts were made by Fitzgerald, Lorentz, and others to construct a mathematical model of the electron (which was then conceived to be the chief constituent of all matter), that would explain how rulers contract when moving through the ether in just the right way to keep the apparent speed of light unchanged. Einstein instead offered a symmetry principle, which stated that not just the speed of light but all the laws of nature are unaffected by a transformation to a frame of reference in uniform motion. Lorentz grumbled that Einstein was simply assuming what he and others had been trying to prove. But history was on Einstein’s side. The 1905 Special Theory of Relativity was the beginning of a general acceptance of symmetry principles as a valid basis for physical theories.
This was how Special Relativity made a change in science itself. From one point of view, Special Relativity was no big thing — it just amounted to the replacement of one 10 parameter spacetime symmetry group, the Galileo group, with another 10 parameter group, the Lorentz group. But never before had a symmetry principle been taken as a legitimate hypothesis on which to base a physical theory...
Lorentz did just grumble that Einstein was simply assuming what he and others had been trying to prove. Lorentz said that Einstein postulated what he (Lorentz) and Poincare had proved. Again, there cannot be any serious doubt about it. Einstein's famous 1905 paper start by saying that he is postulating Lorentz's 1895 theorem of corresponding states, without mentioning the 1904 improvements. Poincare's 1905 relativity paper proves the Lorentz invariance of Maxwell's equations, but Einstein's 1905 does not, and merely postulates what Lorentz had proved. This is all explained in my book.