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Questions concerning Cosmological Constant

  1. Jul 21, 2012 #1
    I understand the begining basics of what it represents but how exactly does it tie into the inflation of space and what sort of energy is in a perfect vacuum?
  2. jcsd
  3. Jul 21, 2012 #2


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    The cosmological constant in Einstein's equations is simply a constant which (in absence of matter) causes a vacuum deSitter space time.

    Inflation caused by some inflaton matter field or "dark energy" as a source of accelerated expansion are mechanism caused by other (hypothetical) fields which mimic something like a cosmological constant. So instead of treating the constant as a constant it can be generated by the dynamics of other fields, it may vary in time which should explain why inflation had a beginning and an end etc. Both the inflaton and dark energy are more general mechanism than this cosmological constant.

    Current observations are in good agreement with the model of a simple cosmological constant.

    It is not known whether this constant is a constant to be introduced by hand (like Newtons constant), whether it can be explained by other fields or whether it is a constant + additional effects.
    Last edited: Jul 21, 2012
  4. Jul 21, 2012 #3
    Your question would be a sufficient basis for a lifetime career in cosmology..we have lots to learn!
    edit: And quantum mechanics, see next post.

    The cosmological constant remains rather mysterious as does dark energy and dark matter...Even Einstein got fooled initially. Tom's post captures many of the uncertainties. It is not perfectly 'settled science'....not that anything really is. What we observe is that the expansion of the universe is apparant, it's expansion has varied over time, and we are currently in a period of accelerated expansion.

    Read this recent discussion for some interesting insights:

    Expnding Universe Here

    I believe there is a bit of different usage in the discussion between the terms dark energy, cosmological constant, expansion and accelerated expansion in different posts....and a difference in their effects is explained. The Wikipedia discussion [DARK ENERGY] seems to me the equate dark energy and the cosmological constant.

    Note MarkM's post #18, and #34.....where the latter shows the relationship between vacuum energy and the cosmological constant. The cosmological seems to come along for 'free' with vacuum energy...also the 'ultimate free ride'....Whatever space is, it does not appear to be 'empty'.

    There are long discussions with these forums whether it is the mathematical 'metric' associated with our cosmological model [which describes distance] is all that is expanding or whether space itself is inflating/or expanding. Is iflation one time in one universe or eternal in an infinite number of universes? Is space a 'fabric' or just a geometric construct? Is space discrete or continuous or does that question not even make sense? All these have been the subject of discussions in these forums and are the subject of ongoing research papers.
    Last edited: Jul 21, 2012
  5. Jul 21, 2012 #4
    I kind of skipped that.
    Do you know what a 'perfect vacuum' is? I don't. But I do know there are a lot of 'different' vacuums...Wikipedia discusses them here:


    so the simple answer is: with every vacuum comes with some energy. I don't think anybody knows exactly what it is...but if so, somebody will correct me. One evidence MAY be the Casimer effect...but some think that has other origins.

    Let's just assume a good vacuum as in outer space. I think a 'perfect vacuum' would be in it's ground state, it's lowest energy configuration, but never zero. Quantum mechanics tells us that there are always fluctuations in fields and they are never quiescent, always bubbling....even though they may have zero average value. Space comes with some form of energy which is likely exactly what you are asking about. [Maybe one piece of that is dark energy??] One way to think about this is that at Planck scale, really,really tiny space and times, space and time get mixed up....there is always a 'froth'....an uncertainty. In fact Heisenberg uncertainty can also be utilized to described why there is always energy, variations in fields. But these theories do not REALLY describe exactly WHAT that energy is...only behaviors and rules we have come to observe.

    As a final perspective: space comes with horizons. Horizons 'cause' energy to pop out from 'nothing'....and even particles to appear! The Unruh effect and Hawking radiation are examples. If two observers are together, and one is inertial [free floating] and the other accelerating, they will count different numbers of vacuum particles and measure [ever so slightly different] temperatures!

    So space has 'vacuum energy' and expanding space [with horizons, like the Hubble sphere,for example] also comes with additional energy and particles [matter and radiation].
    As you can tell, lots more to learn here too.
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