Results 1 to 8 of 8

Thread: Lights Out

  1. #1
    Join Date
    Mar 2008
    Posts
    31

    Lights Out

    With the universe expanding at accelerated rates faster than the speed of light, have astronomers found stars disappearing from sight? One would think that objects on the edge of the observable part of the universe would become un-observable.

  2. #2
    Join Date
    Jun 2004
    Posts
    6,011
    Not so much stars as whole galaxies... Yes. gone.

  3. #3
    Join Date
    Dec 2004
    Posts
    14,782
    Two problems: 1) We can't see anything at that distance clearly enough
    yet to be able to observe such events. Bigger and better telescopes are
    still allowing us to see galaxies that are farther and farther away. Those
    galaxies are hard to see because their light is so extremely dim. The
    expansion just makes it get even dimmer. 2) It takes time. If we watch
    a galaxy at the edge of the observable Universe for a few hundred years,
    we will probably be able to see its redshift increase. We might see the
    peak brightness shift from the middle infrared to the far infrared. Another
    thousand years of watching, and we will see the peak brightness shift
    into the shortwave radio band. Another few thousand years, and it will
    have shifted into the longwave band. It takes time.

    And as Mark said, only galaxies or quasars are visible at such distances.
    Individual stars can only be seen in the nearest galaxies, even with the
    most powerful telescopes, except for supernovae, which for a short time
    can be as bright as an entire galaxy.

    -- Jeff, in Minneapolis

  4. #4
    Join Date
    Dec 2008
    Posts
    581
    There is a theory, which I only recently heard about, that states that light from a superluminally receding object can get to us and the analogy is an ant on a rubber rope of which one end is tethered (representing us) and the other being stretched (the greater the distancefrom us the more space expands). Even though the ant/photon initially moves backward it progresses to a point where relative to where it started it is accelerating back less and eventually will get to a place where it can start making up ground (although it will have gone backwards up to that point). I'm pretty sure that this would only apply if initial accelaration were only very slightly faster than c. I didn't tink of this theory and can see holes in it.

    Anyhow, if this were the case then I suppose a galaxy that becomes unobservable at the edge of the Hubble Volume may come back into sight after some time when its plucky photon finally gets to us.

  5. #5
    Join Date
    Jul 2005
    Posts
    18,079
    The idea that we receive photons from objects that are now, and have always been, receding from us faster than light is actually part of the standard model of the Big Bang.
    If the expansion of the Universe were slowing down then we could expect the Hubble distance (the distance at which objects recede at lightspeed) to keep increasing, so that increasingly distant photons would be able to make progress in our direction, and we'd therefore be able to see increasingly more distant objects.
    If the Universe's expansion continues to accelerates, then we have the possibility that the Hubble distance will shrink: in which case photons from objects we can currently see may end up on the far side of the Hubble distance, so that distant objects drop permanently out of sight.

    Grant Hutchison

  6. #6
    Join Date
    Nov 2008
    Posts
    460

    Great Paper

    I am really not one to comment as I barely understand it. Even so, this paper has done wonders for my overall understanding of modern cosmology.

    Enjoy!


    http://www.mso.anu.edu.au/~charley/p...neweaver04.pdf

  7. #7
    Join Date
    Jun 2004
    Posts
    6,011
    I have just had a good look at this link, http://www.mso.anu.edu.au/~charley/p...neweaver04.pdf
    Thank you m74z00219.
    Well constructed as that argument is... I do not except it as factual.
    I am of the view that the currant view might diminish with the acceleration rate continuing to increase.

  8. #8
    Join Date
    Feb 2007
    Posts
    1,602
    Quote Originally Posted by astromark View Post
    I have just had a good look at this link, http://www.mso.anu.edu.au/~charley/p...neweaver04.pdf
    Thank you m74z00219.
    Well constructed as that argument is... I do not except it as factual.
    I am of the view that the currant view might diminish with the acceleration rate continuing to increase.
    That article reflects the current mainstream view of cosmology. Is any of cosmology "factual"?

    And yes, as time goes on in an accelerating universe, our view will diminish. You seem to imply that the article and that view are incompatible?

    Here is the scientific paper, by the same authors, that the article was based upon:

    Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe

Similar Threads

  1. Lights in the Sky
    By Fraser in forum Universe Today
    Replies: 0
    Last Post: 2012-Mar-12, 02:10 AM
  2. How Many Lights?
    By Graybeard6 in forum Off-Topic Babbling
    Replies: 8
    Last Post: 2010-Oct-18, 05:49 PM
  3. lights in the sky...
    By Sabeth91 in forum Space/Astronomy Questions and Answers
    Replies: 6
    Last Post: 2009-Jan-09, 02:56 PM
  4. lights in the sky...
    By Sabeth91 in forum Life in Space
    Replies: 0
    Last Post: 2009-Jan-07, 03:04 AM
  5. sky lights
    By Grand_Lunar in forum Space/Astronomy Questions and Answers
    Replies: 24
    Last Post: 2006-May-22, 07:40 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •