Relationship between Planck Distribution and Quantization of Energy

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Discussion Overview

The discussion revolves around the relationship between the Planck Distribution and the quantization of energy, particularly in the context of black body radiation. Participants explore the implications of Planck's law in addressing the ultraviolet catastrophe and the nature of energy exchange in quantum theory.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants suggest that the Planck Distribution is necessary to explain the ultraviolet catastrophe and implies that energy emitted by a black body has discrete values.
  • Others argue that a black body emits a continuous range of frequencies and challenge the notion that the distribution equation suggests quantized energy values.
  • One participant connects the concept of quantized energy to the equation E=nhv, questioning how the integer n relates to the distribution equation.
  • A later reply discusses the thermal equilibrium of radiation in a cavity, emphasizing that classical physics leads to the UV catastrophe due to the assumption of continuous energy exchange.
  • Another participant explains that in quantum theory, each mode can only exchange energy in discrete portions, leading to a finite total radiation energy and resolving the UV catastrophe.
  • There is a question raised about whether quantum theory limits the number of modes that can exchange energy, contrasting it with classical assumptions of infinite modes.

Areas of Agreement / Disagreement

Participants express differing views on whether the Planck Distribution implies quantized energy values, with some asserting it does while others maintain that black body radiation is continuous. The discussion remains unresolved regarding the implications of quantum theory on energy exchange and the nature of modes.

Contextual Notes

Participants reference concepts such as thermal equilibrium, the equipartition theorem, and the nature of photons, but there are unresolved assumptions regarding the definitions and implications of these terms in the context of the discussion.

HelpMeGodWithPhysics
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TL;DR
I got stuck with the correlation between Planck Distribution and Quantization of Energy.
I came to understand that Planck Distribution is necessary to explain UV catastrophe. With that necesity in the background, the distribution equation eventually suggests that the energy emitted by black body has discret values. But I wonder how that's related to E=nhv. I understand that "n" also implies the discrete energy values but how does "n" ultimately contribute to deriving distribution equation? I might need a mathematical explanation.
 
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HelpMeGodWithPhysics said:
the distribution equation eventually suggests that the energy emitted by black body has discret values

No, it doesn't. A black body emits a continuous range of frequencies (energies).

HelpMeGodWithPhysics said:
I wonder how that's related to E=nhv

Where are you getting the ##n## from?
 
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As indicated, to me, it sounds like this experiment shows that energy is quantized or has discrete amounts when it's tranferred and Planck Distribution is an explanation for that.
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The crucial point is that radiation in a cavity comes to thermal equilibrium through interaction with the walls of the cavity. Kept at constant temperature, the radiation must come to thermal equilibrium at this temperature, which means that the rate of absorption and emission of radiation energy are the same. In the classical picture each mode of the radiation field (i.e., the solution of Maxwell's equation harmonic in time with (angular) frequency ##\omega##) can exchange any quantity of energy, but this leads to the validity of the equipartition theorem, i.e., each mode would contain on average ## k T## of energy, which clearly leads to the UV catastrophe since you have infinitely many modes.

According to QT (i.e., in this case quantum electrodynamics) each mode can only exchange an integer number of energy portions of the size ##\hbar \omega##, i.e., you can excite only an integer number of "photons" of each mode. Together with the Bose nature of photons, which is due to the integer spin of 1 of the em. field, you get Planck's radiation law, which leads to a finite total radiation energy ##\propto T^4##, i.e., it solves the problem with the UV catastrophe.
 
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vanhees71 said:
i.e., each mode would contain on average ## k T## of energy, which clearly leads to the UV catastrophe since you have infinitely many modes.

(i.e., in this case quantum electrodynamics) each mode can only exchange an integer number of energy portions of the size ##\hbar \omega##, i.e., you can excite only an integer number of "photons" of each mode.

So is it safe to say that according to QT, it limits the number of mode that can exchange energy rather than allowing infinite number of mode of energy exchange so that the total radiation energy becomes finite rather than infinite?
 

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