Comment Curious (Score 1) 174
I read quite often that galaxies are moving away from each other at increasing speed.
In fact faster than light.
While special relativity constrains objects in the universe from moving faster than light with respect to each other when they are in a local, dynamical relationship, it places no theoretical constraint on the relative motion between two objects that are globally separated and out of causal contact. It is thus possible for two objects to become separated in space by more than the distance light could have travelled, which means that, if the expansion remains constant, the two objects will never come into causal contact. For example, galaxies that are more than approximately 4.5 gigaparsecs away from us are expanding away from us faster than light. We can still see such objects because the universe in the past was expanding more slowly than it is today, so the ancient light being received from these objects is still able to reach us, though if the expansion continues unabated, there will never come a time that we will see the light from such objects being produced ‘'today (on a so-called "space-like slice of spacetime") and vice-versa because space itself is expanding between Earth and the source faster than any light can be exchanged.
So that's confusing to me, wouldn't their mass increase as well and possibly lead to a massive attraction then collapse of the Universe back to the point prior to the Big Bang?
Or is it just the distance not the velocity relative to each other.
