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

QM calculation of vacuum energy

  1. Jun 12, 2008 #1
    If I came up with a theory that had predictions 100 times larger or smaller than experimental observation my theory would labelled rubbish by scientists.The quantum mechanical calcualtion of vacuum energy is 120 zeros at odds with experimental observation ( casimir effect).Why aren't people labelling quantum mechanics as rubbish?
    Last edited: Jun 12, 2008
  2. jcsd
  3. Jun 12, 2008 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    If that's all your theory can predict, then yes, it is totally rubbish. But if your theory predicts other things that actually WORK, and you are using the very effect of that theory right this very second, then how can it be labelled as rubbish?

    And it isn't widely accepted that such vacuum energy has THAT high of an energy density. There are fringe physics and crackpots that may think so, but we have seen from experiments on casimir effect that such an effect is extremely small and extremely difficult to detect, and that IS within what QM has predicted as well! I can show you MANY other nonsensical effects using many-body quantum mechanics. Does this make QM rubbish? No. You have to know that extrapolating QM in such a way requires significant assumptions and simplifications (example: mean field approximation). It is such simplification that can easily be at fault. Full, real phenomena are very seldom solved without making such assumptions.

  4. Jun 12, 2008 #3

    George Jones

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    As ZapperZ has already said, there is agreement between theory and experiment for the Casimir effect.

    Do you mean the difference between vacuum energy and observed cosmological dark energy? In this case, rough calculations, as given in, e.g., Carroll's general relativity book, lead to a discrepancy between "theory and experiment" of 120 orders of magnitude. Other calculations give different results, but usually there is a large discrepancy.

    Many people think that an accepted quantum theory that can be used for calculations is needed to explain this.

    A minority, e.g. Roger Penrose, think that a large change in quantum mechanics is needed.
  5. Jun 12, 2008 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    I don't really think this discrepancy is so weird. Remember that the construction of quantum field theories starts with the assumption that space-time is Minkowski space. This means that we're describing a universe where there is no gravity. The theories we construct in this way are in excellent agreement with experiments about everything, except this one thing that has no relevance whatsoever in a world without gravity.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: QM calculation of vacuum energy
  1. Energy in QM (Replies: 2)