11. The Power of a Single ExperimentAs Norton alludes, Einstein's 1907 article and most modern textbooks introduce the Michelson-Morley experiment as being crucial to the development of special relativity. The papers that announced the discovery of the FitzGerald contraction, Lorentz transformation, local time, and spacetime geometry all explained these concepts as consequences of MMX.
The example of Einstein’s discovery of the light quantum will illustrate another popular myth about what powered Einstein’s discoveries. There is, in each case, a single, perplexing, powerful, decisive, crucial experiment. Only Einstein, it is said, was able to interpret the experiment correctly and arrive at a great discovery.
This myth is best known through the example of the Michelson-Morley experiment. Contrary to many reports, Einstein did not formulate the theory as a direct response to its null outcome. The mistake is an easy one to make. It was long standard for pedagogic accounts of special relativity to begin with an account of the experiment and jump directly to special relativity. The pattern starts with Einstein’s (1907) early review. It introduces the Michelson-Morley experiment and no others in its opening pages. Holton’s (1969) analysis of the myth is standard and includes numerous examples. To it, we should add that the null result of the Michelson-Morley experiment was unhelpful and possibly counter-productive in Einstein’s investigations of an emission theory of light, for the null result is predicted by an emission theory.
The null result could be explained by a light emission theory, or by a stationary Earth, or by an aether drag. So MMX alone did not prove special relativity. Other experiments cause the experts to reject those possibilities.
Einstein did not cite MMX or those other theories and experiments because his work was derivative. He was just giving a reformulation of Lorentz's theory, but not recapitulating Lorentz's theoretical and experimental arguments.
Einstein historians have to do a funny dance around this subject, because the relativity textbooks don't make any sense. They say that the MMX was crucial, and they say that Einstein invented special relativity, but Einstein denied that MMX had anything to do with his work.
There is a larger reason for denying the importance of MMX. Philosophers and science historians today are anti-positivists and they deny that scientific breakthrus are based on crucial experiments. Relativity was considered the first great breakthru of the XXc, so the postivist-haters need to have some way of saying that it was not driven by experiment.
It seems possible that someone could have predicted special relativity from abstract principles of causality, or from mathematical analysis of electromagnetism. But that is not how it happened. It was postivist analysis of experiments.