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Universe expansion question

  1. May 9, 2012 #1
    Why assume that the universe is expanding by observing that the space between our galaxy and distant galaxies is expanding. For example, what if our galaxy and distant galaxies are moving in the same direction, but our galaxy is moving faster than the distant galaxies we have observed. Resulting in the distance between to grow.

    I have been thinking about this for some time. Please reply.
  2. jcsd
  3. May 9, 2012 #2
    Okay. According to this theory, in one direction, we'll be, um, moving faster (I suggest you look into a layman's understanding of Special Relativity to understand why this has no meaning :wink: ), and the galaxies will appear to be moving away from us.

    But in the other direction, according to your theory, shouldn't galaxies be slowly moving towards us on average?

    General Relativity alone is enough evidence for the expansion of the Universe, the observation that faraway galaxies are moving away from us just supports the theory.
  4. May 9, 2012 #3
    Tyah, welcome to the forum!

    Like Whovian said, the expansion is uniform in all directions. This was discovered by Edwin Hubble, using the redshift of light from distant galaxies. When he took a measure of the redshift of this light, he discovered Hubble's Law - that there is a linear relationship between the distance to a galaxy, and the redshift of its light. This is implies that space is expanding - distant photons traverse larger amounts of expanding space.
  5. May 9, 2012 #4
    thank you. Your replies have been very helpful
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