Sometimes we see stories about searching for the origins of high energy particles called cosmic rays. These are massive particles like protons, which have been accelerated by something in deep space to nearly the speed of light. The usual suspects are black holes, neutron stars, supernovae, and other exotic phenomena. The puzzling thing is that some of these particles seem to have traveled great distances, farther than thought possible without losing momentum (slowing down by bumping into things like photons).
What I wonder is whether the human perspective on Earth is far too biased. Einstein’s theory of special relativity says that there is no preferred rest frame in the universe. A fast moving particle is moving fast relative to us, but it is equally valid to say that the particle is at rest, and it is we who are moving fast relative to it.
If indeed there is no preferred rest frame in the universe, shouldn’t there be a uniform distribution of velocities for distant galaxy clusters? Because of the strong influence of gravity, galaxies within a cluster would be bound to move together. But galaxies that are not close enough together will move independently. Wouldn’t one expect that two galaxies separated in space and time by 12 billion light years have an equal probability of moving at any speed between zero and c relative to each other?
However, indeed our picture of the universe seems to be of a relatively organized structure like a web of filaments, possibly with a flow in a particular direction. It is far more accurate to describe the structure as static than it is to say that it is randomly moving with a uniform distribution of velocities. This means there is a definite bias for a rest frame, where the relative motion of the large scale structure of the universe is minimized. Am I wrong?