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Why isn't energy quantised

  1. Aug 18, 2013 #1
    If mass is quantised and energy is mass why isn't energy quantised. It seems that it's possible to have arbitrarily small amounts of energy.

    Then if energy does not need to be quantised, then what is the need for a graviton, when gravity is described as a curvature of space?
     
  2. jcsd
  3. Aug 18, 2013 #2

    Bill_K

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    Mass is not quantized, physorguser. There is no reason to believe it is. For example if it was quantized there would be a smallest mass that every other mass was an exact multiple of, a "quantum of mass", and there is not. The electron's mass is 0.510998928 MeV while the muon's mass is 105.6583715 MeV. It's clear that one is not an exact integer multiple of the other.

    As particles go, the electron's mass is pretty small, but the mass of some of the other particles is much smaller still. Neutrinos have nonzero mass: the value is not yet known but believed to be 1 eV or less. A hypothesized particle called the axion may even have a mass as small as 10-6 eV.
     
  4. Aug 22, 2013 #3
    Gravitons arise naturally in string theory, they weren't inserted into it. They're a way of describing gravitional phenomena particle-wise. Gravity's still described as a field, as it is in GR, but just a virtual particle field, like electromagnetism, instead of space time curvature. So gravitons are to gravity as photons are to EM. You don't lose anything describing gravity this way.
     
  5. Aug 23, 2013 #4
    One thing to remember is that quantization is not coming from the nature of energy/mass itself, it's coming from the surrounding constraints, a.k.a. boundry conditions. Take the (kinetic) energy of the electron as an example, in free space it's not quantized and can have any value. However, once it becomes bound to an atom it will be subject to periodic boundry conditions (orbits were the wavefunction doesn't interfere constructively disappear), and this causes the electron energy to now be descrete, i.e. quantized.
     
  6. Aug 24, 2013 #5
    Yes, but what I have trouble comprehending, is that it's fine that gravity can be described as a field of virtual particles like the EM field, but when gravity is described as a curvature of space-time, does that mean that spacetime and the virtual field of gravitons are the same thing in a different form or two different things. Or only one thing but with two different descriptions like how Schrod's wave mechanics and Heisenberg's Matrix mechanics were both describing one reality.

    OK thanks, that's cleared that up.
     
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