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I know that thermally excited materials "act as atomic oscillators" which can oscillate in a continuous range of frequencies, producing light in said frequencies. But in my searches, the nature of the oscillators isn't clear.

Are these quantum harmonic oscillators (i.e. each atom is a quantum oscillator)? If so, how is the frequency distribution continuous? And why is the energy of quantum oscillation related at all to the thermal energy distribution (Boltzmann distribution)?

In summary, what's the exact mechanism by which blackbody radiation is produced?

side question: I've read about the Bose-Einstein distribution for the blackbody spectrum, but don't understand much. How does that fit in here?

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marked as duplicate by Rob Jeffries, John Rennie quantum-mechanics Jul 19 at 5:33

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Are these quantum harmonic oscillators (i.e. each atom is a quantum oscillator)?

You need to distinguish between the hot atoms of the blackbody and the electromagnetic radiation in free space.

The hot atoms are hard to describe quantitatively. Instead, the electromagnetic vibration modes in free space (the blackbody cavity) are easier to describe, and they can be treated as harmonic oscillators.

If so, how is the frequency distribution continuous?

When analyzing the electromagnetic waves within a finite volume $V$, you find a spectrum of discrete frequencies. (Think of the standing waves inside a rectangular box.) Only in the limit of an infinitely big volume ($V \rightarrow \infty$) you get a continuous spectrum.

And why is the energy of quantum oscillation related at all to the thermal energy distribution (Boltzmann distribution)?

The electromagnetic radiation is in thermal equilibrium with the hot atoms of the blackbody. Both have the same temperature $T$.

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  • $\begingroup$ So if the atoms themselves are not the oscillators, how are they producing radiation? It is a causal relationship, right? The whole cavity thing never really made sense to me, because it doesn't seem to describe the interaction between the atoms and the EM field that allows them to equilibriate thermally in the first place. I guess that's the idea I was trying to get at: what is that interaction and how does it produce a continuum? $\endgroup$ – user3125721 Jul 18 at 22:31
  • $\begingroup$ The cavity thing is a way to circumvent all these messy details. In general, I believe the oscillations are largely atomic-motions, which carry the electron clouds with them; these atomic motions are due to thermal fluctuations. The accelerating electrons in the atomic clouds then generate an EM field, which is emitted and/or is reverberated in the cavity. The details of the emission, and the absorption and equillibration within the cavity, would vary with the materials. In general materials are NOT black-bodies, after all. $\endgroup$ – PhysicsTeacher Jul 18 at 22:39
  • $\begingroup$ The atoms emit/absorb photons to/from the cavity. This is the interaction between wall and cavity. Because the wall are many atoms coupled to each other, their emission/absorption spectrum is nearly continuous. $\endgroup$ – Thomas Fritsch Jul 18 at 22:40

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