So the question came up after Sunday's run: has Einstein's theory of general relativity been proven? In other words, is it really still just a theory?
Unfortunately Brainiac still isn't answering his phone -- could he still be upset about that Wikipedia crack? -- and so in my own poor way I had to do the research myself. The conclusion may surprise you.
Einstein himself proposed three "tests" of his theory: 1) the perihelion procession of Mercury's orbit, 2) the deflection of light by the sun, and 3) the gravitational redshift of light. All three have by now been demonstrated beyond doubt, as well as many more newer tests. You can read all about it here.
But in fact we were asking the wrong question. Checking the Physics Forum (a very good U.S.-based forum backed by Scientific American magazine), I found this explanation by one of the boffins:
You don't seem to understand what a theory is. No explanation of
natural phenomenon can ever progress beyond the status of "theory". The
predictions of theories, if verified by experiments can be facts. Time
dilates in a gravitational field: FACT. Time dilates in a
gravitational field because mass bends a 4-dimensional
space time continuum: THEORY. See the difference? The second statement
can never be anything but a theory. Cause and effect is impossible to
verify experimentally (because its a relationship). It can only be
assumed based on repeated experiment, not proven. When people say
"Relativity is just a theory, not a fact" or "Evolution is just a
theory, not a fact", its painfully obvious they don't understand how
science works. Theory is as good as it gets. You do not progress from
theory to law. A law is just an assumed fact. The Law of Conservation
of Mass: We assume that mass is conserved. We cannot prove it. But
based on experience, it seems to be a reasonable ASSUMPTION. Theories,
do not become laws. Laws are assumptions. Theories do not become
facts. Facts are observations.
None of the three can be "promoted" into being one of the others, they
are seperate things altogether. Calling something a theory has nothing
to do with its merit or accuracy. The idea of the lumiferous ether is
still a theory, but is not given much credence. General Relativity is a
theory, and is widely believed to be a close approximation to the
. . . so now we know.