Synchronized Bosons and Entropy.

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    Bosons Entropy
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Discussion Overview

The discussion revolves around the relationship between bosons, entropy, and the implications of Bose-Einstein condensation (BEC) and laser operation. Participants explore how the behavior of bosons, particularly their tendency to occupy the same quantum state, interacts with the principles of entropy and thermodynamics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions how bosons occupying the same state does not violate entropy rules, suggesting that there may be more complex mechanisms at play.
  • Another participant explains that while the entropy of a BEC is low, achieving it requires cooling, which increases the entropy of the surrounding environment, linking this to the operation of lasers.
  • There is a discussion about the second law of thermodynamics and how the tendency of systems to reach their ground state relates to entropy, with examples involving excited states and photon emission.
  • One participant expresses uncertainty about the thermodynamics of lasers, particularly whether atoms are heated to achieve excitation, and how this relates to entropy changes.
  • Concerns are raised about the idea of more microstates being available when bosons accumulate in the same state, with a suggestion that this could lead to a decrease in entropy for the ensemble of laser atoms.
  • Another participant challenges the notion of "rules of entropy," asking for clarification on what specific rule is perceived to be broken.
  • There is a mention of the compatibility of quantum mechanics and statistical mechanics in the context of entropy, particularly in relation to blackbody radiation.

Areas of Agreement / Disagreement

Participants express varying degrees of understanding and uncertainty regarding the implications of bosonic behavior on entropy. There is no clear consensus, as some participants propose interpretations while others challenge or seek clarification on these ideas.

Contextual Notes

Participants reference the second law of thermodynamics and the concept of microstates without fully resolving the implications of these ideas in quantum contexts. The discussion includes assumptions about the behavior of systems under different conditions, such as isolated versus non-isolated systems.

dydxforsn
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How is it that the tendency for bosons to take the same state doesn't violate rules of entropy? I can understand why Bose-Einstein condensation wouldn't, because that's how the particles take a minimum energy state.

I know lasers work because the photons present encourage other photon involvement (excitation) because of this property of bosons. Is it that this ordered laser beam actually has an increased number of microstates? (that's my best guess) I'm only an undergraduate, so I'm assuming there's more "inner-workings" that I don't know of.
 
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According to the second law, entropy rises monotonically only in isolated systems. The entropy of a BEC is very low, but to achieve it, you have to cool strongly, therefore heating the environment and increasing the entropy there. The same is true for the laser.

In general, the tendency of a system to go to its ground state can be viewed as a consequence of the second law. If you have an ensemble of atoms in a given excited state and the "empty" radiation field (wich corresponds to T=0), the entropy increases if the atoms emit photons which then occupy states of the radiation field. On the other hand, if you have an ensemble of atoms in the ground state and a thermal radiation field, the entropy increases, if the atoms absorb photons until they reach thermal equilibrium. (as you've mentioned, entropy corresponds to the number of available microstates for a given macrostate)

What the ground state of a given system is, has nothing to do with entropy but is determined by QM. So there's nothing special about the boson case.
 
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"Rules of entropy"? I have never heard of such things, and I suspect that is what is causing you trouble. Why don't you tell us specifically what "rule of entropy" you think is being broken, and we can take it from there.
 
Thanks for the replys, but I still have some questions.

kith said:
According to the second law, entropy rises monotonically only in isolated systems. The entropy of a BEC is very low, but to achieve it, you have to cool strongly, therefore heating the environment and increasing the entropy there. The same is true for the laser.

Yes, I agree with that but I'm still not quite sure how it applies to the laser. (I don't doubt you I just don't know about the thermodynamics of a laser. Are atoms being heated to excite them?)

kith said:
In general, the tendency of a system to go to its ground state can be viewed as a consequence of the second law. If you have an ensemble of atoms in a given excited state and the "empty" radiation field (wich corresponds to T=0), the entropy increases if the atoms emit photons which then occupy states of the radiation field. On the other hand, if you have an ensemble of atoms in the ground state and a thermal radiation field, the entropy increases, if the atoms absorb photons until they reach thermal equilibrium. (as you've mentioned, entropy corresponds to the number of available microstates for a given macrostate)

That argument makes sense, except I think that the radiation field NOT being "empty" is what triggered laser activity which would be a tendency towards imbalance. This is my qualm.

kith said:
What the ground state of a given system is, has nothing to do with entropy but is determined by QM. So there's nothing special about the boson case.

See, I'm thinking that, that there is somehow (quantum mechanically) more microstates when the bosons accumulate in the same state than when they're not, which seems weird to me but possible. The only other explanation I can think of is like you said, there must be two systems and one's entropy must increase to account for a decrease in the entropy of the ensemble of laser atoms. I just don't think there should be any problem using the statistical mechanics idea of "entropy" in quantum processes.

Vanadium 50 said:
"Rules of entropy"? I have never heard of such things, and I suspect that is what is causing you trouble. Why don't you tell us specifically what "rule of entropy" you think is being broken, and we can take it from there.

Yeah, it may be. I'm operating under the idea that the microstates interpretation of entropy holds in quantum mechanics (systems tend towards the largest available number of microstates), as I've never heard of quantum going against statistical mechanical ideas of entropy, the subjects are frequently united when stat. mech. is used to explain blackbody radiation, etc.
 

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