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

Quantum vacuum nothing or sea of energy

  1. Nov 7, 2012 #1
    I always thought that the quantum vacuum was absolutely nothing. But I have heard that the quantum vacuum is not nothing and contains energy although it is the lowest state of energy. I am not talking about the fluctuations rather I am talking about the vacuum itself. Also do quantum fluctuations have causes or do we adopt an in deterministic interpretation??
  2. jcsd
  3. Nov 8, 2012 #2
    The vacuum in QFT is a superposition of different field configurations. You can compare it to the ground state of a harmonic oscillatorin the following way:
    Consider one fourier component phi(k) only.
    phi(k) is the classical amplitude of the field. It corresponds to the x-coordinate in teh ground state of the H.O.
    In the H.O. ground state, the x component has a probability distribution that looks like a Gaussian function - there is a prob. to find the particle at position x given by this distribution.
    The same holds for the field amplitude: There is a gaussian distribution to measure any field amplitude, centered at an amplitude of zero and falling off to larger values.
    Similar to the zero-point energy in the H.O., this non-vanishing of the probability for an amplitude that is not zero gives you a zero-point energy.
    For the full vacuum, you have to consider all possible k-values, this is why you get very large (unphysical) values for the zero-point energy.

    Quantum fluctuations are a slightly different thing - in a free field theory, there are no fluctuations (there can't be because the vacuum is Lorentz invariant, so there is no reason for a fluctuation to be "here" and not "there"). In an interacting theory, you can imagine that the interaction "measures" the field amplitude and thus "realises" a fluctuation; exactly in the same way as you could measure the particle in the H.O, ground state and realise a non-zero position. Similar to the measurement problem, there is no way to determine the actual outcome of such a "field measurement".
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook