Absolute velocity

[badhorsey]

The speed of light is (generally) defined as an absolute limit of velocity. But is that relative to a stationery observer, or as a general velocity? Do we have any way of knowing what our current velocity is - with respect to the universe in general as opposed to the sun and our local system?

[vascop]

The speed of light is the same to all observers. There is no absolute frame of reference relative to which velocity is measured. All motion is relative.

[beso]

That is what Einstein's Relativity was about.

Indeed all measurement in Mechanics is relative except for one. The passage of time and the calculation of mass even change relative to the observer. The only measurement that is invariant from all frames of reference is momentum.

[Symmetryigr8]

We can estimate our current velocity with respect to the universe because of the isotropy of expansion. Simply put wherever you are in space it looks like everything is flying away from you, everything is moving apart from everything else. Red shift measurements allow the speed to be measured. For stationary bodies the red shift measured is also the same everywhere. Everything is moving apart from everything else at the same speed, weird huh?