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The end as we know it?

  1. Jan 23, 2009 #1
    hey my name is nick im very new to this kind of thing. i just had a few questions about the end of the known universe, dark energy and dark matter and how it will end the current universe.

    first of all i would like to ask a couple of my own questions.

    1. ok, so the big bang created or expanded the known universe?
    2. do we know where the center of the known universe is?
    3. if we dont than is it possible that due to the size of the of the big bang there could be an area in the universe that has unthinkable amount of gravity from wich not even light cannot escape creating an orbit for the universes many galaxies and therefore creating the illusion that the universe is expanding?(much like how our galaxy but on a larger scale)

    if i sound stupid in any way please correct me and if there is anyone out there that can help me that would be great. im very, very new to this so go easy on me.
  2. jcsd
  3. Jan 23, 2009 #2


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    No the big bang model does not go back to a moment of creation. At any point where you can run the model, the universe already exists.

    Have a look at Einstein-online's page on the big bang.
    Their page called "A tale of two big bangs" is especially worth reading.

    Yes indeed we do! We are at the center of that part of the universe which we can observe.
    The most distant matter from which we are now receiving is an estimated 46 billion lightyears from us in all directions. The observable part of the universe is a spherical volume with us at the center.

    We do, so your question doesn't apply.

    BTW coldfront, you might be interested by a chance to change your perspective a bit. Cosmology is a mathematical science which studies and tests mathematical models of the universe. It is not concerned merely with the "known universe" or the observable universe. That wouldn't work gravitationally, if that was all there is. Cosmology assumes a certain amount of uniformity, and models the whole universe. As normally modeled, the universe does not have a center.

    Matter is more or less uniformly distributed throughout space. So on average all space is more or less evenly occupied by matter (galaxies, gas, etc...). There is no empty space outside or beyond occupied space. Space and matter are in a sense coextensive.
    This leads to the simplest models that work gravitationally and fit the data.

    "Everything should be as simple as possible, but not simpler!" :smile:

    Here's a post with some good computer animation links:
    Last edited: Jan 23, 2009
  4. Jan 23, 2009 #3


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    Dark energy is a correction applied to the LCDM model. It's based on the Perlmutter supernova study. We had no reason to dream up this stuff before that came along. It does, however, explain some things that were not previously explained. Scientists have generally accepted it for those reasons.
  5. Jan 24, 2009 #4
    oh ok. cool. so if in a few years we find a way to see further using longer wave lenths than the we have now our moddel will change and therfore what now will change?

    sorry if wat im saying sounds stupid but one needs to ask the questions he does not understand to be humbled and patiant enough to start the basics. i will try to learn as much as i can about this subject and hopfully one day i can have a good understansing of of the questions i know ask. thankyou for the help.
  6. Jan 24, 2009 #5


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    Cosmologists have to live with a lot of uncertainty and gaps in knowledge. They do the best they can.

    Professional writing is full of ifs and buts---reservations---so reading it you are constantly made aware of how much is not known. And how many questions can simply not be answered at the present.

    But they do the best they can with the data and the instruments available.

    I'm a spectator. The way I see it, there's been dramatic progress in the past 10 years, since 1998. I don't anticipate any major revolution in the main overall model for the next 10 years, just more and more confirmation of the basic picture. And a better grasp of what underlies dark energy and what underlies dark matter.

    I don't expect more certainty about the ultimate dim-out, the dark chilly future, any time soon. I do however expect people to gain a better understanding of the conditions leading up to the start of expansion (the socalled big bang).

    The "end", supposing there is a well-defined end, is likely to remain unclear for a good deal longer than 10 years. After all it is 100s of billions of years into the future.
    The bigbang happened only 13-some billion years in past, it's closer to us in time, we have data on it. And better instruments all the time. So that's where I expect the exciting new understanding to come.

    Your pet idea of a huge concentration of mass at the other side of the universe is not consistent with observed spatial flatness.
    I also think it would mess up the observed pattern of expansion.
    It isn't needed to explain expansion---don't try to fix what ain't broke.

    On the other hand, there is this very slight acceleration in expansion. Some unevenness in the distribution of matter has been offered as a possible explanation of that. Several cosmologists have looked into it, notably a NewZealander named David Wiltshire. I think after several years of studying that possibility interest is waning. Our galaxy would have to be smack in the middle of a spherical region of low density. Too strange a coincidence.
    And there are other indications that the dark energy idea is right.

    But if you like the idea that uneven density could be the cause of acceleration then you can always hope that Wiltshire's idea will make a comeback, and of course it might!

    Coldfront, can your browser handle this animation?
    If you watch it, then I would expect some questions.
    Last edited: Jan 24, 2009
  7. Jan 24, 2009 #6
    thanks. so as the sphere gets smaller the galaxies do not. so if this was correct we would only see a vast blackness right before every particle in exsitance would discintergtrate into a singularity? but my assumption is that long before this happend all the stars and gasses that make up the universe would burnt out leaving a cold dark and lifless universe so there would be 2 ends. one of the living universe and one of the dead?
  8. Jan 24, 2009 #7


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    While technically accurate, it's also trivially true and utterly meaningless. Anywhere you go in the universe acts as a "center" if this is all you're going to use for the definition. So a better answer is just that there is no such thing.
  9. Jan 24, 2009 #8


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    I have to agree. The gist of the OP's question is not about the observable universe, it is about the whole universe, and whether there's a special spot at the "centre".

    There isn't.

    The balloon analogy, and the animated model in that link (http://www.astro.ucla.edu/~wright/balloon0.html) demonstrate that there is nowhere in the universe that is more central than anywhere else (remember, you only looking at the surface of the balloon, not the volume). Not one of those galaxies can call itself more central than another.
  10. Jan 24, 2009 #9


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    I guess because every ending is a start of a new begining, I don't see the multiverse or universe come to an end, it's like a game that keeps on going, there's a bloke who plays the pinball and every move construct a new universe.
    And in anyway, there are quantum fluctuations even in the vaccuum, even in the coldest tempratures, who knows what will trigger them to get hotter, perhaps an observer.
  11. Jan 24, 2009 #10


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    why would every particle disintegrate? :biggrin:
    what sphere are you talking about that is getting smaller?
    from where are you getting your ideas?

    There are several unreliable scenarios out there in the popular media for which there is either not much evidence, or no evidence at all. They grab people's imagination.

    In the professional research literature you won't detect much interest in exotic stories like "big rip". They are what is called speculative. Not worth discussing unless there's more evidence that they have something to do with realities.

    If you take a mainstream view, using the standard model of the universe that almost every working cosmologist uses---the best fit model---then the longterm future is not very exciting. There is no real end. Stars gradually burn out. I suppose if bio/robo organisms are then able to utilize dead stars they could gradually use them up--convert them to energy. The picture trails off into not-very-interesting science fantasy. The Dark, the Cold, and the Boring. Or else into some kaku-eyed multiversal kaku-land of the imagination.

    For a legitimate cosmologist's view there's an article by Larry Krauss. I'll get the link in case you want to read a non-speculative future picture.
    The Return of a Static Universe and the End of Cosmology
    Lawrence M. Krauss (1,2), Robert J. Scherrer (2) ((1) Case Western Reserve University, (2) Vanderbilt University)
    (Submitted on 2 Apr 2007)
    "We demonstrate that as we extrapolate the current LambdaCDM universe forward in time, all evidence of the Hubble expansion will disappear, so that observers in our "island universe" will be fundamentally incapable of determining the true nature of the universe, including the existence of the highly dominant vacuum energy, the existence of the CMB, and the primordial origin of light elements. With these pillars of the modern Big Bang gone, this epoch will mark the end of cosmology and the return of a static universe. In this sense, the coordinate system appropriate for future observers will perhaps fittingly resemble the static coordinate system in which the de Sitter universe was first presented."

    This is written for other scientists---not for the general public---and it is based on the current best-fit standard model of the universe, called Lambda Cold Dark Matter (LambdaCDM) which I believe it makes sense, as a newcomer, to focus on, rather than fringe visions.
    Last edited: Jan 24, 2009
  12. Jan 24, 2009 #11


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    Chalnoth and DaveC, please read my first post before you start criticizing.

    Chalnoth, you seem to disagree, or not to have read the post.

    The OP asked about the known universe. I take that to mean out to the limits of observation. The observable universe is meaningful and important in its own right, though certainly not the whole thing. Likewise the surface of last scattering, a significant related concept. It is simply false to say that "there is no such thing". It is not a "better answer" to oversimplify and mislead a newcomer.

    Good point! I think we all agree that the universe (at least as conventionally modeled) has no center. I am fond of the balloon analogy myself, and the Ned Wright animations. We should always make the point that in the analogy, all existence is concentrated on the 2D surface of the balloon, and we focus on the surface, not the volume, in the balloon analogy. That model universe is centerless and likewise its 3D analog, a hypersphere universe, has no center. There is no point in the 3D universe that is central. This point has been made in a number of PF Cosmo forum threads, and you make it very well!

    However the OP asked about the known universe. I believe it is an oversimplification, which can mire people in confusion, not to immediately distinguish between the whole universe (which has no center) and the observed part (which is obviously centered on the observer.)

    When people start talking about which speculative scenarios that appeal to them, or suit their fancy or agree with their philosophical intuition of how things ought to be, then we should probably just wish them pleasant fantasies and lots of happy fluctuations in their "vaccuums." There is at least one reproductive multiverse scheme that is falsifiable--that is testable with current means and has so far withstood testing. We don't have to accept irrational preferences and speculation. Would you agree?
    Last edited: Jan 24, 2009
  13. Jan 24, 2009 #12


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    The explicit distinction got sort of lost.

    No, but it is a better answer to determine what the newcomer meant to ask, rather than answering a question he didn't mean to ask. I think, considering the nature of his question, the "entire" universe is what he meant, rather than the "observable" universe.

    The OP didn't know that. That's why he asked.

    The distinguishment didn't come across very well. You said "Yes indeed we do! We are at the center of that part of the universe which we can observe." The rest sort of got lost in the "further reading" paragraph farther down the page. Considering that was the important bit to get across to the OP, it came across misleading.

    (This may sound like I'm raking you over the coals. That's not my intention. o:))
    Last edited: Jan 24, 2009
  14. Jan 24, 2009 #13
    thanks guys. i am sorry about how unclear and too simple my questions are but i only know what im am told by people who may not know what they are talking about on other forums before this and the small amount of wich is on tv(wich got me interested in the subject).
    i am very glad that you can give me a ligitemit cosmologist's view on things as im not interested in the most "hollywood" things but the most truthfull of way's, im here to learn. and learn i have thanks to the great deal of legitimate knowlege on this forum.
    i have tried to take in a huge amount of info in the last 24 hours(i will reread all of this many times) so i am sorry if i talk in circles or make no sence.:redface:
  15. Jan 24, 2009 #14


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    You do not need to apologize or feel unable to ask questions. You will lfind that people here will fall all over each other to answer your questions (as evidenced in this thread so far :biggrin:)
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