Does Electrical or Magnetic field attract photons?

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Discussion Overview

The discussion revolves around the interaction of photons with gravitational, electric, and magnetic fields. Participants explore concepts related to the nature of photons, their mass, momentum, and how they are influenced by gravity and electromagnetic fields.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants assert that photons are not attracted by electric or magnetic fields due to their lack of charge polarity.
  • Others question the implications of gravity on photons, discussing whether they have mass and how gravity affects them.
  • A participant mentions that in Newtonian gravity, photons are considered massless and not affected by gravity, while in General Relativity (GR), the concept of gravitational influence is tied to stress-energy rather than mass.
  • There is a claim that gravity does not "pull" photons but rather bends space, allowing photons to travel along curved paths without acceleration.
  • Some participants argue that photons possess energy, which contributes to their momentum, despite being massless.
  • A later reply introduces a relationship from relativistic mechanics that connects energy, momentum, and mass, specifically for massless particles like photons.

Areas of Agreement / Disagreement

Participants express differing views on whether photons are influenced by electric and magnetic fields, with some asserting no attraction while others suggest a weak gravitational interaction due to the mass-energy of the fields. The discussion remains unresolved regarding the implications of gravity on photons and their momentum.

Contextual Notes

Limitations include the dependence on definitions of mass and energy, as well as the unresolved nature of how gravitational effects on photons are conceptualized within different frameworks (Newtonian vs. General Relativity).

Ozgen Eren
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I have heard that photons are attracted by gravity. Does this apply to electrical or magnetic fields?
 
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No because photons have no charge polarity.
 
Yeah that makes sense. Do you know with what acceleration gravity pulls them? They ought to have some sort of mass to have a finite acceleration in response to gravity's force?
 
In Newtonian gravity, which is wrong, photons are massless and are not affected by gravity. In GR, the gravitational "charge" is not mass but stress-energy, and for the a photon this is not zero.
 
Gravity does not "pull" them. Gravity bends space and the photon continues on a straight path through curved space. Photons are never accelerated, only the frequency is affected, which confirms they have no mass.
 
jerromyjon said:
Gravity does not "pull" them. Gravity bends space and the photon continues on a straight path through curved space. Photons are never accelerated, only the frequency is affected, which confirms they have no mass.

Okay so how can they have a nonzero momentum?
 
Because they have energy.
 
jerromyjon said:
Because they have energy.

Having energy does not imply having momentum, any object in rest has potential energy and zero momentum.
 
What does a photon at rest have?
 
  • #10
If you simply asked if photons are attracted by EM fields, I would simply say no, and that would be the end of it. But since you specifically mention gravity, the answer is yes (for a certain definition of "attract"), very weakly, since electric and magnetic fields have mass-energy and generate a gravitational field. In Gaussian units,
##E=\frac{1}{8\pi}\left(\mathbf{E}^2+\mathbf{B}^2\right)##
 
  • #11
Ozgen Eren said:
Having energy does not imply having momentum, any object in rest has potential energy and zero momentum.

Photons are not at rest. They are moving at c and have energy and momentum. Yes, they are massless, but this does not prevent them from having momentum, you just need to use different laws with them, not the laws that govern bodies with mass.
 
  • #12
jerromyjon said:
Gravity does not "pull" them. Gravity bends space and the photon continues on a straight path through curved space. Photons are never accelerated, only the frequency is affected, which confirms they have no mass.
Ozgen Eren said:
Okay so how can they have a nonzero momentum?

In relativistic mechanics, the general relationship between energy, momentum and mass is E2 = (pc)2 + (mc2)2, where m is what some people call "rest mass". (Physicists generally call it simply "mass".) For a photon, m = 0 so E = pc or p = E/c.
 

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