**Light can also be slowed down to less than three hundred miles an hour in experiments. Photons and electrons etc. emerged probabilistically out of a plasma. For a while in the very early universe there was no speed of light.
[GF]I'd suggest that Einstein's motivation for constructing Special and General Relativity was probably religious, as evidenced in such remarks as the aforesaid disbelief in God as a gambler, or the famous "Subtle is the Lord, but he is not malicious!" I don't know if religious belief or emotions make him an idealist in the philosophical sense, though.
Einstein was troubled by the possibility that, as more and more sophisticated methods and instruments were brought to bear on the world, we would begin to get in the way of our own perceptions. Telescopes, computers, particle accelerators and so on are built according to elaborate assumptions about the physical world which may affect the results they obtain. "It is the theory that tells us what we can observe" was the way Einstein put it. To me, this seems opposed to the notion that ideas are what are really real, which is one meaning of _idealism_, and instead regards the material universe (God's handiwork) as the real and important item, in which ideas are only ancillary tools of perception.
**The power of observers to affect the observed, or generate whole new phenomena or entities via increasing technological sophistication makes the old idealist/realist quibble seem quaint. That space-time generated knowers of space-time and the concomitant "puzzle" of intelligibilty is something that was probably at the root of Einstein's religiosity which was a mixture of Spinoza and Kant. The physicist David Deutsch in discussing quantum computers and their future put it recently "if the laws of physics as they apply to any physical object or process are to be comprehensible, they must be capable of being embodied in another physical object. It is also necessary that processes capable of creating such knowledge be physically possible." Pretty pure Kantian sentiments to this bloke [also sounds like a recursive call function] and not too far from Einstein's ode to parsimony "nature is the realization of the simplest possible mathematical scheme". The unification of physics and computer science could quite possibly take us very far beyond Einstein's incredible ideas, with enormous economic and political consequences.
[GF]On the other hand, he hung out with Platonist Goedel. Maybe they argued about it.
**The best debates they had were when they argued over the US constitution and whether the man in the NYC ticker tape parade for the returning Korean war troops was MacArthur or an imposter :-).
Ian
"The space-time continuum? Even continuum existence itself? Except as an idealization neither one entity nor the other can make any claim to be a primordial category in the description of nature...We may someday have to enlarge the scope of what we mean by a 'who'" [John Wheeler]