I'm a CS graduate, not a physicist, so my question might be a bit silly, but I haven't found an answer in the internet yet.
I've read recently that the reason behind our observation that galaxies etc. seem to be moving away from us is because the space is expanding (and not that they are simply moving at high speed through the space).
The question is: what experiment or reasoning lead scientists to this conclusion - how one can tell if this is not simply a movement through space?
I've read somewhere an explanation, that it would be very peculiar that all objects are moving away from us, as we are not expected to be the center of the universe. But from my understanding of how velocity vectors addition/subtraction works, we would observe all galaxies to be going outward from us regardless of the original center of "explosion". So I guess this wasn't the best explanation/proof.
My personal problem with accepting the expansion idea, is that since objects keep their sizes intact (presumably to some forces keeping their atoms together) it should (?) provide the objects with more and more energy: consider a ball of gas which grows 1 meter in diameter and then "falls" back into it's previous size due to gravitation (or whatever other force) - it would heat up, and quite probably "bounce" again to the larger size, and oscillate like that for some period. (At least that's what I see on my simplistic 2-D simulations of balls).