Amount of energy required to change path of a photon

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Discussion Overview

The discussion revolves around the amount of energy required to change the path or trajectory of a photon, particularly in the context of single particle interference experiments. Participants explore the implications of using a magnetic field to alter a photon's trajectory and whether energy transfer is involved in such a process.

Discussion Character

  • Exploratory, Debate/contested, Conceptual clarification

Main Points Raised

  • One participant questions the energy required to change a photon's path by an infinitesimal amount, suggesting that electromagnetic energy might be needed to shift the photon from one interference fringe to another.
  • Another participant asserts that using a magnet to change a photon's path would not be effective, implying a limitation in the interaction between magnetic fields and photons.
  • A different viewpoint posits that changing the trajectory of a particle, including a photon, does not require energy transfer, as only momentum is altered in elastic scattering.
  • One participant acknowledges that the photon's landing position changes based on whether which-way information is available, raising the question of whether this change necessitates energy transfer.
  • Another participant reinforces the idea that deflecting a particle does not change its energy, suggesting that energy cannot be transferred in this context due to conservation of energy principles.

Areas of Agreement / Disagreement

Participants express differing views on whether energy is required to change a photon's path, with some arguing that it is not necessary while others question the implications of interference and which-way information. The discussion remains unresolved regarding the energy dynamics involved.

Contextual Notes

Participants reference concepts from quantum mechanics and conservation laws, but the discussion does not resolve the assumptions about the interaction between photons and magnetic fields or the implications of interference on energy transfer.

San K
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What is the amount of energy required to change path/trajectory of a photon by an infinitesimal amount?

In a single particle (double slit) interference, the photons land up on one of the interference fringes. (when no-which-way)

If we were to place a magnet to try to slightly change the path of the photon, (say from one of the fringes to a blob in-between)how much of the electromagnetic energy would be required? (relative to the one quanta of energy of the photon)

alternatively

are there any energy effects involved in (single particle) interference?

...the path of the photon is getting changed (after all, atleast per some of the interpretation of QM) from fringe to no-fringe co-ordinates
 
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The amount of energy needed to change a trajectory of a particle is zero - in elastic scattering, only momentum is changed, not energy. I think in principle this should also hold for a photon.
 
Thanks JTbell and Sonderval.

The photon lands on a different x-coordinate when we do which-way, than when we don't.

The photon's path is being changed.

To change the path of something isn't energy (transfer) required?
 
If you simply deflect something its energy is unchanged. Therefore no energy /can/ be transferred, by conservation of energy.
 

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