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

Trivia question-about galaxies seen but now too far away to ever see in the future

  1. Sep 1, 2011 #1
    First a true-false question.
    Are the furthest visible galaxies presently incapable of any connection with us. That is, the light coming from them 'now', is incapable of reaching us, ever, and vice versa.
    If this is true, and I assume it is then has there ever been an estimate of where the present cut-off point is i.e. how many billion light years away is this sphere of visible, out of touch, galaxies.-trivia really.

    Upon reflection the true false answer would be false. Eventually the light would reach us but so red-shifted we couldn't detect it- if mankind still existed mega billion years in the future.
     
    Last edited: Sep 1, 2011
  2. jcsd
  3. Sep 1, 2011 #2

    Drakkith

    User Avatar

    Staff: Mentor

  4. Sep 1, 2011 #3
    Re: trivia question-about galaxies seen but now too far away to ever see in the futur

    Thanks Drakkith,
    the link was helpful, implying my first hunch was actually correct (if Wiki is correct). The galaxies that are now at this boundary position further away are seen by us in their previous closer location. It is this distance (the distance we see) that I was curious about. I.E. how much of what we see in our sky is already in a way out of reach by any means.
    mathal

    I just got started with the link in the wiki article -by Davis and Lineweaver and they provided the info I was after. All galaxies beyond a red-shift of 1.8 now 'out of touch' with us.
    Thanks again
    mathal
     
    Last edited: Sep 1, 2011
  5. Sep 1, 2011 #4

    Chronos

    User Avatar
    Science Advisor
    Gold Member

    Re: trivia question-about galaxies seen but now too far away to ever see in the futur

    But, they will never go 'poof' and vanish. They will merely redshift into oblivion.
     
  6. Sep 2, 2011 #5
    Re: trivia question-about galaxies seen but now too far away to ever see in the futur

    Wouldn't the quantized nature of light imply that there was some last photon emitted before a given distant galaxy receded beyond the hubble length? This would imply that there will be a final photon that will reach us and it will happen in finite time. After that, the galaxy will have vanished forever.
     
  7. Sep 2, 2011 #6
    Re: trivia question-about galaxies seen but now too far away to ever see in the futur

    Yes , slowly. All galaxies are slowly redshifting except Andromeda which is approaching us. Because of the accelerating expansion of the universe the future 'window' on the universe is limited to the light that can reach us. Over time all but Andromeda will wind up beyond our sight and reach.

    mathal
     
  8. Sep 2, 2011 #7
    Re: trivia question-about galaxies seen but now too far away to ever see in the futur

    You're both right. Whereas there will be final photons that can reach us their wavelength will be larger than the earth and unmeasurable. The process of disappearing is a long one. Technically, since you brought up the quantized nature of light, the galaxy will be out of reach when we can't measure it in any way. This might be used to change the bar of where the cutoff point is but I'm inclined to think this has already been taken into consideration.
    mathal
     
  9. Sep 5, 2011 #8
    Re: trivia question-about galaxies seen but now too far away to ever see in the futur

    The only way we could ever "see" the light of such galaxies would be if the universe were to change "direction" and undergo a collapse. At some point during the collapse, the energy from those distant galaxies would engage us, perhaps shortly before the big crunch occurred.

    Not that humans would be around to see that light. And not that I truly suspect a big crunch will ever occur due to collapse of our universe. However, that's the only way such light would ever reach our galaxy.

    Now -- permitting a science fiction scenario -- it's conceivable that humans may someday advance to the point that we create devices that allow us to "leap" to great distances across the vastness of the universe. If so, then we might leap to the outer galaxies that have expanded to places beyond our sight.

    Having reached the edge of our universe -- then what? I suspect that's where the real fun begins.
     
  10. Sep 5, 2011 #9
    Re: trivia question-about galaxies seen but now too far away to ever see in the futur

    Under the standard cosmological models, neither an open or closed universe has an "edge". In the open model, the universe is infinite and you can travel in any one direction with a superfast warp drive and pass unique galaxies that you have never encountered before for all eternity without ever reaching an end or seeing the same galaxy twice. In the closed model, the universe is like a 4d sphere where if you travel far enough in one direction you will return to your starting point. This model has no edge either. There are more exotic, outlandish ones, but they are way more constructed and the simpler models are assumed to be correct unless some evidence disqualifies them.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Trivia question-about galaxies seen but now too far away to ever see in the future
Loading...