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

Energy of gravitons

  1. Jun 21, 2004 #1
    What is the minimum amount of energy that a graviton is expected to have?
    And how much energy are all the gravitons in the universe expected to have in total?
  2. jcsd
  3. Jun 25, 2004 #2
    the minimum energy is zero because they are massless. I am not aware of any results involving the total energy of all the gravitons in the universe, and it is probably rather difficult to precisely define what is meant by the toatal energy.
  4. Jun 25, 2004 #3


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Not least because the graviton remains a hypothetical particle!
  5. Jun 26, 2004 #4
    It might be better if you ask the more tractable question: what is the energy expected from a gravity wave. :wink:

  6. Jun 27, 2004 #5
    I am not sure what sort of answer you expect. For a massive particle, the minimum possible energy it can possess is its rest mass, when the particle has zero velocity (if we ignore the problems associated with such states in quantum mechanics). But the graviton is expected to be massless. One might be tempted to say that the answer would be zero. This unfortunately poses a problem: a graviton of zero energy has no energy, momentum, or ability to interact with anything else. Such a 'graviton' would be a complete dud and it is not very productive to ascribe physical existence to such things. Mathematics tells us that "the smallest number greater than, but not equal to zero" cannot be defined. So there is no answer to your question: a graviton can have arbitrarily small energy, but (IMO) not zero. There is no relation(*) that fixes a minimum energy or a quantum scale for it (contrast, for example, angular momentum which can be proven in QM to be quantized in increments of h-bar/2).
    This question is similar to "what is the minimum energy of a photon?", which is equally undefined.

    (*): There is no agreed upon theory of quantum gravity and it is possible that some such theories may allow for that.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook