Thread: invariant?

Bold mine...

Originally Posted by MisterMe

You appear to be intrigued by density. The density of ordinary matter is governed by its temperature and pressure. The Universe is inhomogeneous. It has a foam-like structure with the galaxies forming the cell walls of the bubbles. Local density is certainly not invariant. If the average density were invariant, then it would be as much fortuitous accident as fundamental law of the Universe.

It's interesting reading this bit while entertaining the thought that your Sig line would make Maxwell roll over in his grave...

Density is mass/volume or m/(x*y*z). When we are in motion relative to something, the apparent mass of it increases (in the old relativity definition of mass which does not mean rest mass) while the dimension in the direction that we are moving decreases. So its density goes up.

As for the OP, I'd have to say "none," provided #4 refers to the "Observable Universe."