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Feynman's quote

  1. Jul 28, 2014 #1
    Isn't the above two statements contrary?

    From Feynman's quote, the atoms must be wiggling even at absolute zero. Thus we can expect the generation of electromagnetic radiation even at absolute zero. In contrast, according to wikipedia, generation of electromagnetic radiation is possible only if the matter has temperature greater than absolute zero.
    Last edited: Jul 28, 2014
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  3. Jul 28, 2014 #2


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    That moving charges generate EM radiation is a classical concept and at T=0 QM effects will be at work and everything will be in the ground state. By definition, no energy can be emitted from the ground state simply because there is no lower energy state for the system to go to. It is the same reasoning that stops the hydrogen atom from breaking down. If classical thinking would be applied as in "the electron moves around the proton" then it would radiate and eventually lose all its energy. Instead, a hydrogen atom in the ground state will not be able to radiate photons.
  4. Jul 28, 2014 #3


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    The wikipedia statement is incomplete. Moving charged particles emit radiation only if they can also reduce their energy by slowing down (because energy is conserved, and the radiation carries some energy away, the energy left behind must less than what we started with). If we're already at the lowest possible energy level, we can't radiate because we can't further reduce our energy.

    The Feynman statement is also incomplete, as no object can be cooled all the way down to absolute zero. We can get very close, but not all the way there (to see this, think about how we cool anything to a given temperature; we expose it to something even colder. There's nothing colder than absolute zero). Thus, there's always some minuscule amount of thermal radiation from the object; and the energy loss from this radiation is balanced by energy gain from equally minuscule radiation coming in from our equally cold surroundings.
  5. Jul 28, 2014 #4


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    You are making a fundamental logical mistake. The statement "if A then B" says that if A is true then B is true. It does NOT say what happens if A is not true. In particular, "B" may be true even when "A" is false.

    The statement "All matter with a temperature greater than absolute zero emits thermal radiation" says what happens if the temperature is greater than absolute zero. It does NOT say anything about what happens at absolute zero which what Feynman's statement is about.
  6. Jul 28, 2014 #5
    Be Cool alone!

    From the below source, I disagree that, to cool anything to a given temperature, we need to expose it to something even colder.

    Last edited: Jul 28, 2014
  7. Jul 28, 2014 #6
    Those guys use a method of laser/Doppler cooling, which also has a lower limit on how much energy/momentum it can force the atom to lose by emitting photons (called the Doppler cooling limit). I'm not sure if the lower limit of the method MIT used is calculated using the same Doppler cooling limit, or if there are other factors involved, but there you go.
  8. Jul 28, 2014 #7
    Lets fly with Hallsoflvy!

    Sorry, it is difficult to understand your "understanding" with the present bunch of words given. It will be useful for everyone, if you can increase the clarity. Everyone, atleast me will be waiting.:smile:
  9. Jul 29, 2014 #8

    Jano L.

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    For physics, in general good textbook is much more reliable than articles on Wikipedia. In this case, however, there is no problem with either statement. The quote from the Wikipedia only says that thermal radiation requires non-zero temperature. The movement Feynman talks about is called zero-point motion and hypothetical radiation it produces does not need to be thermal. There is a theory - stochastic electrodynamics - where similar radiation - the zero-point radiation - is not thermal, but has invariant temperature-independent character.
  10. Jul 30, 2014 #9
    Nugatory and Orodruin seems to be arguing that, the radiation (not mentioned properly whether it is thermal or not) can't be emitted.

    On the other hand, Jano L seems to be arguing that, the radiation ("hypothetical", but not thermal) is emitted.:confused:
    Last edited: Jul 30, 2014
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