Is it possible for photons to dissappear in vacuum.

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Discussion Overview

The discussion centers around the concept of photons potentially disappearing in a vacuum, as mentioned in a textbook on statistical physics. Participants explore the implications of this idea in the context of quantum mechanics and electromagnetic theory, raising questions about the nature of photons, vacuum states, and conservation laws.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • One participant questions the validity of the statement that photons can disappear into the vacuum, seeking clarification on the definition of vacuum and the implications of photons being quantized energy rather than "real" particles.
  • Another participant suggests that in high energy physics, photons are treated as real particles, while in statistical mechanics, they are seen as excitations of the electromagnetic field, implying that their disappearance refers to the system returning to the ground state with no excitations.
  • Some participants argue that a photon cannot disappear into a vacuum because it possesses non-zero momentum and energy, and such a disappearance would violate conservation laws related to energy and momentum.
  • One participant proposes that photons can disappear when absorbed by another particle, indicating that this process involves a change in the energy of the system.

Areas of Agreement / Disagreement

Participants express disagreement regarding the possibility of photons disappearing in a vacuum, with some asserting that it is not possible due to conservation laws, while others suggest that absorption by other particles accounts for this phenomenon. The discussion remains unresolved with multiple competing views.

Contextual Notes

Participants highlight the dependence on definitions of vacuum and the context of the discussion, such as statistical mechanics versus high energy physics. There are unresolved questions regarding the implications of photon behavior in different theoretical frameworks.

leoneri
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Hi, I am reading Introduction to Statistical Physics by Kerson Huang. On chapter 10 about Bose Gas, a statement intrigued me. He explains Photons.

"Photons are the quanta of the Electromagnetic field. They are bosons whose number is not conserved, for they may be created and absorbed singly. The Lagrange multiplier corresponding to total number is absent, and the chemical potential \mu is zero. This means that the particles can disappear into the vacuum."

I can't help but wondering myself if this is really true. If it's gone then where does it go? Is it disappear because Photon is a quantization of energy and not a 'real' particle? What is the definition of vacuum in this context?

From my Physics course, what I understand about EM field is that an exponential decay ~e^{-x} only occurs when there is material (and hence not vacuum) that absorbs the photons. While in vacuum, the field will oscillate harmonically ~~ e^{i x} and will goes on forever ...
 
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you can represent things in different contexts, for instance in high energy physics the photon is treated as a "real" particle just as everyone else.

Now in statistical mechanics, photons are excitations of the EM field as you said, and what "This means that the particles can disappear into the vacuum" only means that we also can deexcite the EM-field to the ground state - i.e. no excitations in energy and hence no photons - and the vacuum is just a fancy word for the ground state.
 
A photon cannot "disappear into vacuum". Each photon has a non-zero momentum and energy. Photon's disappearance would mean violation of both momentum and energy conservation laws.

Eugene.
 
meopemuk said:
A photon cannot "disappear into vacuum". Each photon has a non-zero momentum and energy. Photon's disappearance would mean violation of both momentum and energy conservation laws.

Eugene.

And angular momentum.

Torquil
 
It can disapear but it just means that it's absorbed by another particle. If you have changed the Energy of a system, you must have a particle scattered by that.
 

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