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Quantity of negative energy

  1. Mar 1, 2013 #1
    At what amounts can negative energy be produced by the Casimir effect? I know these are very small, but I am curious to know how small.
     
  2. jcsd
  3. Mar 1, 2013 #2
    Even though I have a good clue I still would like you to elaborate yourself what do you mean by "negative" energy?

    There is no such thing as negative energy, energy can only be greater than zero, otherwise you would do work backwards.
    Just like there is no negative mass, that's important to keep in mind.
    have you looked up wiki ? For starting this is pretty ok.

    http://en.wikipedia.org/wiki/Casimir_effect
     
  4. Mar 1, 2013 #3
    All that stuff is very speculative. I remember Kip Thorne talking about exotic matter in one of his popular science books. The idea was that it would take exotic matter with negative energy to stabilize a wormhole, and he mentioned that vacuum fluctuations can have such a negative energy. If you look up, exotic matter and negative mass you get short snippets on wikipedia. I think the idea is connected to negative pressure in the Casimir effect. So you say that in normal vacuum the pressure is zero, but the Casimir effect produces an attraction, therefore there is negative pressure between the plates, and I suppose you get some kind of estimate for the negative energy from the negative pressure times the volume between the plates, but that is a wild guess.
     
  5. Mar 1, 2013 #4
    Potential energies are often negative. Attractive field energies are negative. In the case of the Casimir effect, there is an attraction between two parallel plates, so this is a binding energy between the plates, which is negative.

    In some sense, the potential energy can be considered "not real" but merely looking at a subset of the energy of an object, whose total energy must be greater than zero. For example, we always refer to the energy of a bound electron in a hydrogen atom as having some negative energy. But of course, the total energy of the atom is positive, only the arbitrarily prescribed potential energy is negative.

    I don't think it's fair to say there's no such thing as negative energy, when negative energy is used all the time in university physics. Rather, a particular definition of energy: the energy needed to bring a particle and all its interactions into existence, is positive. This is presumably because the existence of a negative energy particle would render the vacuum unstable.
     
  6. Mar 2, 2013 #5
    Well I was thinking more in terms of theory because yes I agree there are many times when in calculations you get some sort of output that you call negative energy and in some frame of reference it may seem as negative but I believe the energy as property of a universe and all within it has to be positive.When something exists it has mass/energy it can have more mass less energy or vice versa but it has to have atleast some of those to exist at all that was what I was thinking.
    just like with temperature , there is a point of the lowest possible called absolute zero you can't go below it , temperature can only be positive or almoust zero but not below it.
     
  7. Mar 2, 2013 #6
    WMAP showed that the universe is very flat.
    http://map.gsfc.nasa.gov/universe/uni_shape.html
    But positive energy (matter, dark matter, photons, etc) bends space.
    If the universe is flat that means the amount of negative energy in the universe must be approximately equal to the amount of positive energy. It also means that negative energy is just as real as positive energy because it is able to bend space.
     
  8. Mar 2, 2013 #7
    I didn't quite understand the concept of the flat universe. If it is flat, then it wouldn't be (relatively) so distant to reach two sides of it (top and bottom). Is it so?
     
  9. Mar 2, 2013 #8
    Ok can someone please then explain , according to what frame of reference is that energy negative ?
    Or is it just negative by itself ? Then what characteristics it has that make it negative?

    gravity curves spacetime, dark matter tries to expand while gravity tries to hold together then what does this so called"negative "energy" does? Or is it just another term we use or some use to try to explain the things they can't yet understand?
    A little more insight please if you mentioned the word?

    Thanks.
     
  10. Mar 3, 2013 #9
    I thought about this.
     
  11. Mar 4, 2013 #10
    It should be possible to have a negative energy. Work can be negative (because it is Force times displacement, either of which can be negative), so the change in energy can be negative, which means you can have negative energy.
     
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