I think it’s safe to say that GR is the simplest of those theories, though. It’s not like, absent Einstein, folks would have come up with one of those other theories instead, and missed seeing GR itself.
I think there’s a qualitative difference in what von Neumann and Einstein did – von Neumann essentially introduced an abstract mathematical structure founding a formalism for QM, while Einstein introduced physically sensible postulates in order to give physical meaning to equations that were around as something of an oddity. The elucidation of what, exactly, von Neumann’s postulates mean in a physical sense is largely what the problem of interpreting quantum mechanics is all about – there’s no really intuitive notion of what Hilbert spaces or the Born rule are wrt physical reality, while ‘the speed of light is c in all inertial frames of reference’ has an immediate physical meaning.
Many people feel that it is such physically meaningful principles which are as yet missing from quantum mechanics, and work is ongoing on finding suitable candidates; there are some recent efforts by Hardy in deriving QM from five ‘reasonable’ postulates, and a general strategy is to impose epistemic restrictions of some kind – Rovelli, who also notes the connection between the interpretation of QM and what Einstein did for SR, and others formulate a kind of ‘principle of limited information’, which puts an upper bound on the information that is contained within any given physical system, which goes a long way towards reconstructing QM (but apparently doesn’t quite get there).
If Einstein and the other theoretical physicists had failed to come up with SR it would have been discovered experimentally. Particle physicists would have been clamoring to know why their accelerators were behaving so strangely.
It was a long, long time after Einstein before the particle physicists would have noticed anything. For it to take that long for SR to have been found by the theorists, you’d probably have to not only erase Einstein from the timeline, but dozens, maybe hundreds, of others.
Gunnar Nordström proposed a couple of metric theories of gravitation back in 1912 and 1913. While these models were erroneous in many details, they did follow the same general structure as general relativity. Other theories utilizing differential geometry of an underlying plenum were also advanced after general relativity, as the mathematics for topology had advanced sufficiently to develop these theories. Einstein’s development of general relativity, and friendship with David Hilbert, came at a very fortuitous time in mathematics; had Einstein been even a decade earlier he would not have had the tools available to develop general relatively Hilbert, for his part, became interested in mathematical description of physical mechanics only due to his association with Hermann Minkowski. Without Hilbert’s work, Einstein could not have formulated general relativity. With it, general relativity tends to naturally fall out of descriptions of metric space.
I don’t know if I’d go that far. Certainly Archimedes of Syracuse, Gottfried Leibniz, and James Clerk Maxwell were diverse in their fields of research and well ahead of their contemporaries in many salient points of their respective theories. The breadth of Einstein’s genius was impressive, but hardly without precedent, and I suspect many 20th century physicists demonstrated an equal degree of free and open thought, but without the opportunity for truly revolutionary invention. Andrei Sakharov, for instance, worked in a phenomenal number of fields, from nuclear weapon design and plasma physics to cosmology and particle physics, but a combination of the restrictions of the repressive regime under which he worked and the general circumstances of his life made many of his discoveries unrevealed or redundant.
Stranger
I said nearly unprecedented, not completely. There have been other scientists who had the same kind of breadth and depth as Einstein, but there haven’t been very many of them.
Well, maybe. Certainly Einstein put together all of the pieces in both special relativity and photoelectric phenomena (and later, relativity in relation to gravity) in an innovative way, but he also came about at just the time in which the tools and prerequisite theories became available, e.g. the failure to observe properties of a “luminiferous aether”, the Voigt transformations and Lorentz-FitzGerald geometric transformations, Boltzmann’s work in statistical mechanics, J.J. Thompson’s work on the mechanics of charged particles (particularly the electron), Poincaré’s work on relativity, et cetera. In fact, once it is laid out, special relativity is so simple and clean that it seems an almost a trivial result, and the theory of quantized light neatly resolved a sheaf of different problems in electrodynamics that had been troubling experimenters who had been stuck on “pure” wave theories since Fresnel and Poisson (and seemingly reinforced by Maxwell). The pieces were all in place for the discovery, especially Planck’s postulate, which despite being considered only a mathematical trick by its eponymous discoverer that allowed the theory to match observations, throws the quantized nature of fundamental mechanics right in your face. In retrospect, it is actually kind of embarrassing that it took someone so long to figure out the implications.
His later work on general relativity was strongly predicated on the development of the tensor calculus needed to describe the differential geometry of four dimensional manifolds. Without this, Einstein would never have been able to formalize any theory of relativity in a warped spacetime. With it, well, it seems irresponsible to say that it would have just fallen out, but the use of tensors in other contexts such as continuum mechanics is highly suggestive of a simple approach to gravitation. If Einstein hadn’t made the connection, it seems unlikely that someone else wouldn’t. Of course, the solutions for general relativity other than the most trivial conditions are very complicated, and most of the interesting results were discovered by physicists other than Einstein, His later career was marred by a distinct streak of conservatism that was guided by a rejection of the innate tenets of quantum mechanics, and a struggle to unify all physical forces into one model without fruit.
I don’t contend that Einstein was not brilliant; he clearly made some connections that others did not before him. I question just how unique he was as an intellect, versus just being in the right place at the right time to make those observations. I would argue that the work of less luminous but influential physicists such as Hermann Weyl, Boltzmann, Maxwell, Steven Weinstein, Niels Bohr, Werner Heisenberg, Erwin Schrödinger, John Stewart Bell, et cetera made equal contributions, albeit ones that are not stated in non-technical as simply as relativity or culminate in an equation as readily recalled by the public, and were not as self-promoting as Einstein.
Stranger