I have a very long page titled "Einstein's Errors". Much of it is difficult (even for me after a lapse of seven years). Drawing on the work of some eminent scientists and philosophers, I expose what I believe to be crucial errors in Einstein's special theory of relativity (STR).
I recently encountered what looks like another error. This one is in Einstein's popular (short) book, Relativity: The Special and the General Theory (1920). In "III. Space and Time in Classical Mechanics" Einstein says this:
I stand at the window of a railway carriage which is travelling uniformly, and drop a stone on the embankment, without throwing it. Then, disregarding the influence of the air resistance, I see the stone descend in a straight line. A pedestrian who observes the misdeed from the footpath notices that the stone falls to earth in a parabolic curve. I now ask: Do the “positions” traversed by the stone lie “in reality” on a straight line or on a parabola? Moreover, what is meant here by motion “in space”?
This thought experiment is meant to illustrate the effect of the relative motion of observers on their perceptions of reality. But the thought experiment is flawed.
The flaw can be shown by a valid extension of Einstein's thought experiment. Suppose that there is a deep gorge between the footpath and the train track. The train track is at the same elevation as the footpath, but it is atop a high trestle that extends to the bottom of the gorge. Thus, when the stone drops, the observer on the train will see it "curve" toward the bottom of the gorge as the train (and he) move away from the point at which he dropped the stone.
Contrarily, if the observer on the footpath keeps his eye on the stone, he will see it drop straight down from the point of release to the bottom of the gorge.
This is a subtle but telling flaw. Einstein sometimes ventured in the wrong direction because of his penchant for thought experiments and analogical thinking. "Einstein's Errors" adduces many more -- and more egregious -- examples.