# Expanding universe

talzamir
Posers and Puzzles 13 Oct '11 13:00
1. talzamir
Art, not a Toil
13 Oct '11 13:00
Let's assume that a universe has at some point in its history started with all matter at the same point P. There was a huge explosion, and things started moving directly away from point P, in different directions and with various velocities. Keeping it simple, let's ignore gravity for now, and just say that everything just keeps moving in its original speed and direction.

Suppose an astronomer has for a while tracked the path of galaxies, and thinks that there is one that is special galaxy that didn't go anywhere. He wants to know if he lives in the one galaxy that did not move in the blast, and finds that indeed, all other galaxies move directly away from his own, at velocities relative to their distance.

Does that mean that indeed, his own galaxy is the special one?
2. 13 Oct '11 13:37
Originally posted by talzamir
Does that mean that indeed, his own galaxy is the special one?
No.

HTH; HAND; read an astronomy starter book.

Richard
3. forkedknight
Defend the Universe
13 Oct '11 15:301 edit
If the initial velocity and trajectory of matter is random and gravity does not exist, that behavior is exactly what you would expect when observing from any galaxy in the universe.
4. 13 Oct '11 16:39
No, in an expanding homogenous universe every galaxy will percieve itself as the unmoving galaxy with all other galaxies moving away.
5. talzamir
Art, not a Toil
13 Oct '11 19:09
I've read quite a few astronomy books, though I don't recall any of them explaining HTH or HAND. The "can you tell where all the particles are coming from" has sometimes proven useful in making a point about relative movement.

The explanations above are correct of course.