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

The Cosmological Constant

  1. Sep 16, 2003 #1
    I started this thread in theory development again no reponse so I moved it here. Is it Cosmological or Universal Constant?

    Another related thought concerning the Cosmological Constant. Just as space time, dimensional space and time, is a characteristic of matter and formed as matter formed out of the expanding and thus cooling energy of the Big Bang, could the Universal Constant be a result of a characteristic of spacetime to tend to be flat rather than curved as does surface tension in a glass of water? As the universe expands or continues to inflate and is aided and driven by this tendency, The curvature of spacetime would decrease and thus the value of the Universal Constant would decrease to, or approach, 0 as the curvature of spacetime became more and more flat or nearly so.
    This may imply that once spacetime becomes flat as the universe continues to expand there would be no force acting to continue the expansion or to counter the force of gravity no matter how feeble it might be at that time and distance. Thus there would be nothing to keep the universe from contracting and forming the Big Crunch. Remember that regardless of how long the expansion continues or how vast the distances become the amount of mass-energy and thus gravity will remain the same and effect space time the same. There would be or is no escape velocity to attain and escape the universe or escape the inevitable Big Crunch for outside the event horizon of the universe there is nothing to escape from or escape to and nothing to effect anything within the universe itself or any of the internal forces at play.

    Again, I welcome any and all discussions on these thoughts. If you are able to show me completely wrong and off base and explain why or how to me I would appreciate just as much as any support. If I'm wrong or uninformed I want to know just as much as I want to know if any of this makes any sense or has any validity. Either way I can forget about it and go on to something else instead of being plagued by these thoughts all the time.
  2. jcsd
  3. Sep 16, 2003 #2


    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    It seems to me that you are thinking about space as a dynamic fluid arrangement----as if your mind were full of pictures of the expanding and flattening out and contracting.

    Such thoughts may constitute a mild addiction of sorts but they are not a plague----it is part of the human condition to appreciate the night sky and wonder about the world.

    I resent it when people think there is just one way to imagine these things and therefore claim that somebody else's way is invalid because it doesnt match theirs. Your way (with the surface tension and the flow impelled by a drive towards flatness) seems like it could make a good computer-animated film. It is a visual epigram or an idea with visual potential.

    I dont see how discussing these things will help you "forget about it and go on to something else".

    I can not criticize your mental imagery or tell you what to think but I can give you some advice at the personal level. I advise you not to tie Λ up into a neat package just now because it is one of those ideas whose growth (in intellectual history) will
    probably go beyond anything we can imagine right now.

    It seems likely that Λ whatever it is will turn out to be related to microscopic as well as macroscopic process and observation. It's participation in the observed acceleration of the large-scale expansion of space may be just the first drop in the bucket of what there is to find out----it may go on having unanticipated repercussions and influencing the thinking in various departments for several decades or even a generation.

    It could also go away!!! It could turn out that the supernova observations are in error and that Λ is zero after all
    (as was mostly assumed for 80 or so years up to 1998).
    The history of science has aspects of comic farce and this kind
    of thing, tho ridiculous, is possible.

    The present value as determined by observation is, IIRC, about
    half a joule per cubic kilometer. I have a terrible time remembering this for some reason. That absurd little half-joule per cubic click is virtually all we know about it too!
    If you are obsessed by "dark energy" welcome to the club. It has a lot lot lot to tell us and no one is going to figure it all out (IMHO)
    at this stage of the game.

    I'll tell you some Λ stuff I found out recently, in another post later.
  4. Sep 16, 2003 #3


    User Avatar
    Gold Member

    keep us hanging by a thread then, i it hate when one has
    to wait for the next episode:wink:
  5. Sep 16, 2003 #4


    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    No reason to keep you in suspense :smile: some articles I've been reading lately and trying to understand are
    "Quantum gravity with a positive cosmological constant"
    http://arxiv.org/hep-th/0209079 [Broken]
    by Smolin and follow-up that recently appeared by
    Amelino-Camelia, Smolin, Starodubtsev
    "Quantum Symmetry, the Cosmological Constant and Planck Scale Phenomenology"
    http://arxiv.org/hep-th/0306134 [Broken]

    The Lambda term (the cosmological constant) not being quite zero is what gives the quantization of GR an exact solution and correct classical or semiclassical limits----correct behavior at familiar scale.

    This is summarized on pages 3-7 without formulas (!) in
    http://arxiv.org/hep-th/0209079 [Broken]
    where it says for example at bottom of page 7

    "As the demonstration of a good low energy limit has been a key open problem, it is of some importance that the problem is solved for Λ not equal to zero. It is because of this that it can now be claimed that loop quantum gravity passes all the major tests required of a good quantum theory of gravity..."

    That is, it passes the tests in the case where the "dark energy" or cosmological constant is not zero. However astronomers have come up with some evidence that Lambda is indeed a small positive number which seems to be just the ticket. So I am trying to make sense of this. It does seem that Lambda is not just significant at very large scale (acceleratate expansion and all that) but may play a role at extremely microscopic scale and even eventually help determine how a successful quantum version of General Relativity must be built.
    Last edited by a moderator: May 1, 2017
  6. Sep 16, 2003 #5
    Thanks, marcus. I appreciate the humor and well as the links.
    Its not a neat package in my mind at all just a thought I came to when thinking about what could possibly cause it. Like a commercial jingle stuck in you head that you can't get rid of. Its all pure speculation on my part of course but it did and does make a pretty picture.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook