Jaydan Aguirre

2022-07-14

Can an "absolute" frame of reference be determined by measuring the compression of light?
General relativity tells us that there is no absolute frame of reference (actually, it tells us that all frames are relative, which is close but not the same as there is no absolute frame).
Special relativity demonstrates that there is an absolute: the speed of light.
Notwithstanding the impracticality of the issues, is it possible to determine an absolute frame of reference based on minuscule difference in the wave length of light (measured by doppler shift)?
In effect, can we measure our (Earth's) compound frame of reference by measuring the doppler shift / compression of light in our own frame of reference. Or would any relativistic compression be undetectable within that same frame of reference? Or would it be practically infeasible?

Marisol Morton

Expert

Technically, doppler shift for light happens due to relativistic time dilation, so it is subtly different than acoustic doppler shift. It cannot therefore be used to determine an absolute reference frame.
That doesn't mean there isn't one. Spacetime as we know it is formed by the big bang, so that might be an absolute reference frame if only we can figure out how to detect it. Unfortunately, we can't, and in a very real sense the Big Bang happened everywhere, since all of space was compressed to a tiny point.

nidantasnu

Expert

By compression of light you mean the Doppler shift?Then yes you can measure your speed relative to the light source by comparing the Doppler shift in different directions.
It's been used for a number of different radio positioning systems - but it only gives you a motion relative to the light sources

Do you have a similar question?