On Sunday, November 11, 2018 at 8:36:43 AM UTC-7, Gary Harnagel wrote:

Astronomy and meteorology allow observation under many different
conditions and as time passes, the data mount up. Astronomy is also
aided by controlled physics and chemistry experiments in laboratories
and then ASSUMING that those conditions apply elsewhere. We know
that relativity applies throughout the solar system because we have
actually performed experiments with spacecraft. We ASSUME SR and GR
work all the way back to the Big Bang, but maybe they don't.

Well, for one thing, we can analyze the spectra of light from the stars. We
assume that the same pattern of lines stands for the same element in a distant
star, so we can tell what is in those stars - but the fact that we _are_ seeing
the same patterns of lines indicates that some of our laws of physics must be
working out there.

The fine-structure constant, which got its name from some characteristics of
spectral lines, is a ratio involving the speed of light, the inertial mass of
the electron, and the force exerted by its charge. So those spectral lines are
the result of physics.

And, of course, absent evidence to the contrary, that the laws of physics are
the same elsewhere and in the past is the most reasonable starting assumption.
It can be re-evaluated when we run into trouble.

John Savard