To attack the importance of the experimentum crucis (crucial experiment), some scholars (strangely and wrongly) cite the history of relativity. For an example, here is Pentcho Valev commenting on the Nature article:
Don't rely too much on the experiment. Experimental results can be interpreted so as to "confirm" the opposite of what was actually confirmed. For instance, in 1887 (prior to FitzGerald and Lorenz advancing the ad hoc length contraction hypothesis) the Michelson-Morley experiment unequivocally confirmed the variable speed of light predicted by Newton's emission theory of light and refuted the constant (independent of the speed of the source) speed predicted by the ether theory and adopted by Einstein in 1905 (nowadays the opposite is taught):It is true that the 1887 Michelson-Morley experiment could be interpreted to be consistent with an emitter theory or an aether drift theory, but the experts of the day had rejected those theories on other grounds.These efforts were long misled by an exaggeration of the importance of one experiment, the Michelson-Morley experiment, even though Einstein later had trouble recalling if he even knew of the experiment prior to his 1905 paper. This one experiment, in isolation, has little force. Its null result happened to be fully compatible with Newton's own emission theory of light. Located in the context of late 19th century electrodynamics when ether-based, wave theories of light predominated, however, it presented a serious problem that exercised the greatest theoretician of the day. Norton
But it is just wrong to say that Michelson-Morley had little force. The experiment was done following suggestions by Maxwell and Lorentz that it would be crucial. The length contraction was first suggested by FitzGerald in 1889 as a logical consequence of the experiment. Lorentz's relativity theories of 1892 and 1895 were explicitly created to explain the experiment. Poincare's criticisms of 1900 and Lorentz's improvement of 1904 were based on the accuracy of the experiment.
The most popular early relativity paper was Minkowski's 1908 paper saying:
But all efforts directed towards this goal [of optically detecting the Earth's motion], and even the celebrated interference-experiment of Michelson have given negative results. In order to supply an explanation for this result, H. A. Lorentz formed a hypothesis ... According to Lorentz every body in motion, shall suffer a contraction in the direction of its motion, ...It is a historical fact that relativity was developed with Michelson-Morley as the crucial experiment.
This hypothesis sounds rather fantastical. For the contraction is not to be thought of as a consequence of resistances in the ether, but purely as a gift from above, as a condition accompanying the state of motion.
I shall show in our figure, that Lorentz's hypothesis is fully equivalent to the new conceptions about time and space, by which it becomes more intelligible.
Einstein's 1905 paper gives an exposition in terms of two postulates that everyone agrees he got from Lorentz and Poincare. Maybe Einstein understood how those postulates depended on Michelson-Morley in 1905 and maybe he did not. Statements by Einstein and by historians are confusing on the matter. He did seem to understand later, as he said so in his 1909 paper. But it does matter when Einstein learned the significance of Michelson-Morley, because he was not the one who discovered the length contraction, local time, time dilation, constant speed of light, relativity principle, covariance of Maxwell's equations, spacetime geometry, and all the other crucial aspects of relativity. Those who discovered those things relied on Michelson-Morley, and that is a historical fact.
Modern philosophers reject the positivism of most scientists, and their foolish views depend largely on a misunderstanding of how relativity depended on experiment.