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What's a cosmic red-out?

  1. Aug 26, 2009 #1
    Can someone please give me a succinct definition/description of what this is? I can't seem to find any references to this by a Google search.

    I understand it's one of the several predicted scenarios of the fate of the universe dues to continued acceleration.

    Does this have any relationship to the collision of our galaxy and Andromeda in the future or the aftermath of this collision??

    What's the predicted expected time this is going to happen? I've read conflicting timelines from 6 billion years to 20 billion years.

    Thanks for your anticipated answers!

  2. jcsd
  3. Aug 26, 2009 #2


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    I've never heard of the term "cosmic red-out" before, and a Google search for it turns up this thread as the first result. Where did you see it?

    The scenario where the universe expands so quickly that increasingly smaller structures are dissociated is called "Big Rip": http://en.wikipedia.org/wiki/Big_rip. The authors of the Big Rip hypothesis calculated 50 billion years as the time we have left.

    As for our collision with Andromeda, no, the Big Rip has nothing to do with that. Galaxy collisions are common, as evidenced by the fact that we can see colliding galaxies with telescopes, and usually not dramatic. Interstellar space is so empty that collisions between stars is likely never going to happen.
  4. Aug 26, 2009 #3
    No, I'm not refering to the Big Rip although it was one of the scenarios cited as a predicted fate of our universe.

    I saw this term "Cosmic Red Out" in [an article by Michael S. Turner of the U. of Chicago] the recent September 2009 issue of Scientific American, the schematic cartoon on p. 42.

    Heck I might just e-mail him and ask.
  5. Aug 26, 2009 #4


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    I haven't read the article, but it sounds like the extrapolation of our current knowledge: in ~100-120 Gy, all matter except our local galaxy cluster will have left us. It will be seen approaching an event horizon, some 25 Gly (real distance) away, getting increasingly redshifted and unltimately invisible.
  6. Aug 26, 2009 #5


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    Just a quick comment on this side point on the Big Rip. The calculation is not really "how much time we have left". The "Big Rip" occurs if you have "phantom energy", which means dark energy with an equation of state having ω < -1.

    IF this is the case, then the implication is that the time from now until a singularity in which the whole universe is ripped apart is
    [tex]t_{rip} - t_0 \approx \frac{3}{2(1+\omega)H_0\sqrt{1-\Omega_m}}[/tex]​
    The calculation for ω = -1.5, H0 = 70 km/s/MPsec and Ωm = 0.3, gives about 22 billion years as the time we have left. But that is just a sample, for an arbitrarily chosen value of ω, which the authors acknowledge is way too negative.

    Empirical evidence places much stronger constraints on ω, and in fact it is unlikely to less than -1 at all.

    Reference: Caldwell, R. et. al. (2003) Phantom Energy and Cosmic Doomsday, in Phys.Rev.Lett. 91 (2003) 071301, also arxiv:astro-ph/0302506

    I shall correct the wikipedia article on this. Thanks for bringing it too my attention! (Added in edit: wikipedia updated: I'm "Duae Quartunciae" over there.)

    Cheers -- sylas
    Last edited: Aug 26, 2009
  7. Aug 26, 2009 #6
    sylas, can you answer my question(s)?

  8. Aug 26, 2009 #7


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    No, sorry. I've never heard of "cosmic red-out". Emailing the author of the article you saw is a reasonable approach, if there's an email provided.

    Cheers -- sylas
  9. Aug 26, 2009 #8
    I e-mailed the author already. I'll let you guys know after I hear back from him.
  10. Aug 27, 2009 #9


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  11. Aug 27, 2009 #10
    Alkemist, I believe that you've confabulated the "Big Rip" and red shift. As the Universe expands, things will move so far away from us that the light that makes it to us from them will red shift due to the Doppler Effect; giving everything a reddish hue.
  12. Aug 27, 2009 #11


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    That was my first thought too.
  13. Aug 27, 2009 #12
    I am familiar with what the "Big Rip" and heat death and redshift is.
    In the Scientific American article by Michael Turner, he describes the "Big Rip" and "cosmic Red-out" as two separate predicted outcomes of the universe.
    I'm yet to get a reply to the e-mail I sent the author.
  14. Aug 27, 2009 #13


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    Uh... correct. The Big Rip and heat death are two distinct ends to the universe. So I'm not sure why you're ruling heat death out.
  15. Aug 28, 2009 #14
    Oh. OK. So you're saying maybe the article was refering to "heat death" and "cosmic redout"?
  16. Aug 28, 2009 #15


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    I'm saying those are one and the same. But I'm just supposing.
  17. Aug 28, 2009 #16
    I just took a look at the article.

    Directly to the OP's question:

    It seems as if the author (Michael S. Turner) has coined a new term. He is not referring to a 'big rip' which is also noted on that diagram as something distinctly different. Turner is applying this term to the proposed situation in which acceleration continues and eventually the Milky Way/Andromeda/et al fusion galaxy will find itself alone in the observable universe. I am guessing that the use of the term 'red out' is designed to refer to the ever increasing cosmic redshift of extra-galactic bodies that ultimately leaves us as an island in the observable universe. The article and diagram actually seem pretty clear on this.

    Hope this was of some minor help

  18. Aug 28, 2009 #17
    I thought all along this was what the author was alluding to but I wasn't sure.

    I hope he responds to my e-mail to confirm.

    On another note - and once again, I'm a chemist not a physicist so pardon my ignorance - would said collision between the Milky Way and Andromeda increase the acceleration (of the now fused galaxies) leading to the "cosmic red-out"?
  19. Aug 28, 2009 #18


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    I don't see why it would.

    Perhaps the only reason the collision is mentioned is because, after hearing that galaxies are heading out-of-range, the first question to be asked will likely be: "Even Andromeda? I though it was headed toward us?"

    To which the answer is: "It is heading towards us, yes, and will collide. But other than that, the rest of the galaxies are going to yadda yadda yadda..."
  20. Aug 29, 2009 #19
    hmm ... makes sense.
  21. Aug 29, 2009 #20


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    The Bad Astronomer's book "Death from the Skies" gives a good account of the very long term history of the universe for the dark energy with ω = -1 (cosmological constant). The local group of galaxies is all gravitationally bound, and will not be separated. The merger with Andromeda is coming up soon, but in longer time scales we'll be combining with most of the other local galaxies as well. By 100 billion years (Phil's estimate) the local group will be one giant elliptical galaxy.

    As time goes on, we will no longer be able to see other galaxies. For astronomers in those times, the universe will appear to be one giant galaxy a few million light years across... and it is unlikely that they will have the evidence that would even allow them to infer the existence of other galaxies, or the expansion of the universe.

    After 100 trillion years or so, the stars run out of fuel. The galaxy will be a collection of white dwarfs, neutron star, black holes and various low mass objects. And this is just the beginning. Read this book. It's fun.

    Cheers -- sylas
  22. Aug 29, 2009 #21
    So basically what I said, lol.
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