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

B Who turned out the lights?

  1. May 27, 2016 #1
    Since the universe is expanding and all objects are getting farther and farther away from earth, won't there come a time when all of the objects we see will have gotten far enough away from the earth that we can no longer see them and it will appear to us that the universe has gone dark?

    In reality all of the objects will still be there just outside our vision...is that correct?

    tex
     
  2. jcsd
  3. May 27, 2016 #2
    The light still can go to us, can't it? No matter how fast the object goes away, if it emits the light, or reflects the light, then it can reach anywhere possible. So we still can see them?
     
  4. May 27, 2016 #3
    I read that there is a mid range outside the no visibility distance where light can still catch up and cross the sphere so we can see it but that eventually even the distance and recession speed will be too much for even that to happen. I think.

    For example, what about the light from a star 500 billion light years away (if there can be such a thing)...hypothetically, will we ever be able to see that light?
     
  5. May 27, 2016 #4

    Bandersnatch

    User Avatar
    Science Advisor
    Gold Member

    Yes, there will come such a time when only what's currently in the local group of galaxies will remain visible in the practical sense.

    Here's a bit more elaborate answer I once gave to a similar question:
     
    Last edited: May 27, 2016
  6. May 27, 2016 #5
    I think not. Because in Hubble law, everything which moves more than c to us, we can't see them.
     
  7. May 27, 2016 #6
    So, the local group is not affected by Hubble Flow?
     
  8. May 27, 2016 #7

    George Jones

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

  9. May 27, 2016 #8

    Bandersnatch

    User Avatar
    Science Advisor
    Gold Member

    In general, gravitationally bound structures are not affected by the expansion. Clusters of galaxies are the largest such structures, and the local group is a cluster of galaxies that also happens to include Milky Way.
     
  10. May 27, 2016 #9

    Chalnoth

    User Avatar
    Science Advisor

Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted