Relativity does not 'assume' anything....it predicts it.
SR & GR are the most proven principles in ALL of physics...we cannot ignore its predictions in favor of a personal world-view.
Relativity in no way "predicts" that the speed of light is constant -- it was developed because the solution to Maxwell's equations gives a constant c, and is completely built on this assumption! If anything you ought to be saying "Maxwells Equations prove that c is constant" -- which they don't.
suppose we exist on an infinitely large plane which is being curled into a tube at a rate much slower than our lifespan. we measure the interior angles of a triangle and they appear to within the accuracy we are able to measure to be 180*, so we say "the world is flat."
this does not prove that the world has always been flat or that the plane is not being curled into a tube, for 2 obvious reasons: 1) our measurements are inaccurate, limited by our finitely large measuring tools. 2) an observer sufficiently forward or backward in time would measure a convex or concave surface and if the rate of change of curvature were small enough compared to the scale of our lifespans, we would never see the change. In fact, even an abrupt change in curvature if occurring at a time well before or after we exist and take measurements might
never be seen by us. All we can say with certainty is that in our local timescale the plane appears to have no curvature.
Does this mean we have no business measuring triangles? Of course not! and the results of our measurements are useful for all sorts of predictions on our own timescale. Does verifying the interior angular sum of other triangles prove the plane is not slowly curving? Of course not! It only verifies that the local curvature (where we measure other triangles) of the plane is consistent. It shows nothing about the far reaches of the plane or the topology of the plane over very large timescales.
Computationally verifying that a graph is a straight line on some interval [a,b] doesn't mean it's OK to extrapolate the statistical parameters to intervals outside the range of data collection. Zoom in on the graph of log(x) near the y axis and it looks very much like a vertical line. If you're sufficiently close to x = 0 you can safely assume it's a vertical line. This doesn't prove that log(x) is a vertical line! It only means our approximation *works* on certain scales.
Is relativity "proven" ? Do you know why we have a separate "general relativity" theory? Because special relativity
does not work when we look at gravity. Do you know why we have the notion of "dark energy" and "dark matter" ? Because general relativity
does not work when we look at galactic structure.
Relativity is great, consistent in all experiments we can perform, but the scope of the experiments we can perform is on a very very small time scale, and we can only say with certainty that c appears constant within the scale of our ability to measure it. When we look at the formation of galaxies according to current theories about the development of the universe however, we find many things that don't fit. General relativity is commonly held by the scientific community as a theory that is needs replacing -- do you know why people are still looking for a GUT? why "string theories" and "manifold theories" get studied? Because General Relativity is insufficient (under many assumptions such as the invariance of physical constants) to explain observed phenomena on a cosmological scale!
what you are arguing is like having a wristwatch and comparing it's ticking to another clock presumed to be accurate for a minute or two, finding that as closely as you can count, it appears to match up, and extrapolating from your 2 minutes of admittedly imperfect observations that the wristwatch is accurate at any infinitely small scale and has been and will be accurate for all eternity! Believing that takes a certain faith, don't you think? Especially when it is pointed out to you that the wristwatches calendar is several days off and it shows AM when it ought to read PM ( here i allude to the whole "dark energy" bandaid patched onto our understanding of cosmological framework ).
verifying relativity
doesn't prove that any fundamental constant is invariant. It implies that on our time scales that the constancy of c is a safe assumption for which to do calculations. since you are arguing for an old universe, you ought to think a little deeper about very large time scales, the near absolute ignorance we have on a cosmological scale, and how dangerous it is to measure a molehill on earth and directly apply your measurements to Olympus Mons.
EDIT: spelling errors =D
