Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Expansion of galaxies

  1. Feb 11, 2006 #1
    man, after a long time i've got a question!

    Einstein proved that the universe is expanding but the the galaxies aren't expanding themselves, right? and i've also read an example given by one of the members saying that if u keep 2 or 3 coins on a rubber band and stretch it, the fabric of rubber band between the coins stretchs and the coins move apart but the coins don't stretch themselves. but the coins don't stretch because there is no space in them. they are so closely packed.

    but if you take a galaxy, there is space between every body. i,e; the space between the earth and mars or the earth and the pole star.

    so if the fabric of space is expanding, then even the galaxies should stretch right? because the space between each galaxy and between each matter in a galaxy, is the same.
    Last edited: Feb 11, 2006
  2. jcsd
  3. Feb 11, 2006 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    There is also space between the individual atoms of the coins. The reason they don't stretch with the rubber band is because the force between the atoms is strong enough to overcome any tendancy of the coin to stretch with the rubber band.

    With a galaxy, the individual stars are packed tight enough that the mutual gravitational attraction between them is strong enough to overcome any tendancy for the galaxy to expand.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?