Understanding the Paradox of Photon Momentum: Electromagnetic Force Revealed

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Discussion Overview

The discussion centers around the concept of photon momentum within the framework of electromagnetic force. Participants explore the relationship between mass, energy, and momentum, particularly in the context of photons, and whether the notion of photon momentum presents a paradox given that photons are massless.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants assert that momentum can be categorized under electromagnetic force, with photons as the carriers, questioning the existence of a paradox.
  • Others argue that the classical electromagnetic field possesses momentum and that photons, as quantum mechanical units of this field, also carry momentum.
  • Concerns are raised about how photons can carry momentum despite having zero mass, referencing the classical momentum formula p=m*v.
  • One participant introduces the equivalence of energy and mass through E=mc^2, suggesting that moving energy must carry momentum regardless of classical mass.
  • Another participant clarifies that in relativity, particles can have momentum and energy even with zero mass, citing the relationship E^2 = (pc)^2 + (mc^2)^2.
  • Further elaboration on the equations specific to photons is provided, including E=hf and p=f/h, along with classical field momentum equations.
  • Some participants suggest that the discussion is rooted in classical physics, indicating a potential divide in understanding between classical and quantum perspectives.

Areas of Agreement / Disagreement

Participants express differing views on whether the concept of photon momentum is paradoxical, with some asserting clarity and others questioning the implications of masslessness on momentum. The discussion remains unresolved with multiple competing views present.

Contextual Notes

Participants reference various equations and principles from both classical and quantum physics, indicating a reliance on specific definitions and interpretations that may not be universally agreed upon.

scilover89
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Momentum can be categorised under electromagnet force, and electromagnetic force carrier is photon. But photon have momentum. Isn't this paradoxical?
 
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The classical electromagnetic field has momentum. The photon is the
quanum mechanical minimum unit of this field, and it also carries this
momentum.

There is no paradox.
 
Mhh, how can it carry momentum if it has mass of zero? Momentum is p=m*v. Or is here the meaning of the quantum mechanical operator?
 
According to E=mc^2, energy and mass are eqivalent in this case.

Moving energy must carry momentum. It does not require the
presence of a classical mass.

A compressed spring is a little heavier than a loose one. If they move at
the same speed, the compressed one has more momentum.
 
Sterj said:
Mhh, how can it carry momentum if it has mass of zero? Momentum is p=m*v.

No, in relativity theory it's possible for a particle to have momentum and energy even though it has zero mass. The general relationship between mass, energy and momentum is

[tex]E^2 = (pc)^2 + (mc^2)^2[/tex]

Set [itex]m = 0[/itex] and you have [itex]E = pc[/itex] which in fact has been verified for electromagnetic radiation.
 
So for photons this equation can be written as:
E^2=(pc)^2
 
Sterj said:
So for photons this equation can be written as:
E^2=(pc)^2


Yes. E=hf, p=f/h where h is Planck's constant, when you are talking about
photons. For classical fields, momentum/m^2=ExH/c^2, energy/m^2=ExH.
 
Yeah, you are thinking in terms of classical physics.
 
Strafespar said:
Yeah, you are thinking in terms of classical physics.

5 year old thread
 

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