Can QFT adequately describe the elusive properties of photons?

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Discussion Overview

The discussion centers around the properties of photons and their description within quantum field theory (QFT) compared to quantum mechanics (QM). Participants explore the nature of the photon's wavefunction, measurement, and the implications of relativistic behavior on its properties.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants question the photon's equivalent of the electron's wavefunction and whether qualities of the photon can collapse into an eigenstate.
  • Others propose that the complex electromagnetic field (E + iB) serves as the QM analogy for a single photon's wavefunction, emphasizing that properties like position, momentum, and polarization are not necessarily fixed.
  • There is a discussion on the differences between the wave behavior of photons, described by Maxwell's equations, and electrons, which follow the Schrödinger equation.
  • One participant raises the issue of uncertainty in photons and queries how measurements affect the system, particularly regarding the concept of collapse and operators.
  • Another participant asserts that photons cannot be described by ordinary QM due to the non-observable nature of position for photons, suggesting that QFT is necessary for their proper description.
  • Some participants express that a foundational understanding of ordinary QM is essential before transitioning to QFT.
  • There is a contention regarding whether photons can be classified as electromagnetic waves, with differing opinions on their nature.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the nature of photons, their wavefunction, and the adequacy of QM versus QFT in describing them. The discussion remains unresolved with no consensus on several key points.

Contextual Notes

Limitations include the dependence on definitions of observables in QM and QFT, as well as unresolved questions regarding measurement and the implications of uncertainty in photon properties.

Gal
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What is the photon's equivalence of the electron's wavefunction? Can I measure qualities of the photon that will collapse into an eigenstate? What properties of the photon aren't fixed?
 
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Gal said:
What is the photon's equivalence of the electron's wavefunction? Can I measure qualities of the photon that will collapse into an eigenstate? What properties of the photon aren't fixed?
The photon is inherently relativistic and only properly described by quantum field theory. With that said, the QM analogy to the single photon's wave function is the complex electromagnetic field, E + iB. Google "photon wave function" and you will get quite a few references. And to draw the QM analogies further, neither position, momentum, or polarization are necessarily fixed.
 
Last edited:
Heinera said:
The photon is inherently relativistic and only properly described by quantum field theory. With that said, the QM analogy to the single photon's wave function is the complex electromagnetic field, E + iB. Google "photon wave function" and you will get quite a few references. And to draw the QM analogies further, neither position, momentum, or polarization are necessarily fixed.

The photon follows Maxwell's equation to form a wave according to the wave formula with velocity c. But this is fundamentally different from an electron's wave function that obeys the Schrödinger equation (first partial derivative in time opposed to second...) and that describes the probalistic state of the electron.
Where exactly is the uncertainty described in photons? How do I "measure" something and what "collapses" with respect to what "operator"?
 
Gal said:
The photon follows Maxwell's equation to form a wave according to the wave formula with velocity c. But this is fundamentally different from an electron's wave function that obeys the Schrödinger equation (first partial derivative in time opposed to second...) and that describes the probalistic state of the electron.
Essentially yes, so you should now go on to study quantum field theory, which is the proper theory for photons.
 
Gal said:
The photon follows Maxwell's equation to form a wave according to the wave formula with velocity c.
I would say not. The photon is not an electromagnetic wave, even if it has some properties of the em wave.

--
lightarrow
 
Gal said:
Where exactly is the uncertainty described in photons? How do I "measure" something and what "collapses" with respect to what "operator"?

Photons can't be described by ordinary QM because position is not an observable for photons (that position is an observable is a basic assumption of QM). It can only be described by QFT where the concepts you are alluding to above are much more nebulous eg in QFT even particle number isn't certain. Before moving onto QFT it would be wise to be reasonably conversant with ordinary QM. However once you are some good books are starting to appear that will allow you to learn QFT eg
https://www.amazon.com/dp/019969933X/?tag=pfamazon01-20

Thanks
Bill
 

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