Massless Particles: Carrying Momentum?

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Discussion Overview

The discussion centers around the concept of massless particles, particularly photons, and their ability to carry momentum. Participants explore the implications of masslessness in the context of both real and virtual particles, as well as the relationship between energy, momentum, and mass in special relativity.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions how a massless particle can carry momentum, referencing a lecture on the interaction of charged particles via virtual photons.
  • Another participant challenges the premise by asking on what mathematical basis a massive particle carries momentum.
  • It is noted that both real and virtual photons, being massless, can carry momentum, with a distinction made between rest mass and 'relativistic' mass.
  • A participant elaborates on the relationship between energy, momentum, and mass as described by special relativity, specifically citing the equation E^2 - (cp)^2 = (mc^2)^2 and applying it to photons.
  • There is a reiteration that classical electromagnetic fields also carry momentum, suggesting a broader context for the discussion of momentum in massless entities.

Areas of Agreement / Disagreement

The discussion contains multiple competing views regarding the nature of momentum in massless particles, and no consensus is reached on the foundational questions posed.

Contextual Notes

Participants express uncertainty regarding the definitions of mass and momentum, particularly in the context of massless particles and the implications of special relativity. There are unresolved mathematical steps in the discussion.

Who May Find This Useful

This discussion may be of interest to those studying particle physics, relativity, or electromagnetic theory, particularly in relation to the properties of massless particles and their interactions.

matt_crouch
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In my lecture this morning i was told that charged particles interact by the exchange of virtual photons and that they serve as carriers of momentum and force. But it says that a photon is a boson with spin number 1, massless and zero charge.

The question is basically how can a massless particle carry momentum ?
 
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I would ask you: on what mathematical grounds does a massive particle carry momentum ?
 
It is irrelevant if it is virtual or not. Real photons are also masless, but they carry momentum. Massless = no rest mass, you are probably thinking about the 'relativistic' mass.
 
Elaborating a bit on what Dmitry67 wrote, according to special relativity, the energy, momentum, and rest mass of a particle are related by

[tex]E^2 - \left( cp \right)^2 = \left(m c^2 \right)^2.[/tex]

For a photon, [itex]m=0[/itex] and [itex]E = cp[/itex].

Even classical electromagnetic fields carry momentum.
 
George Jones said:
Even classical electromagnetic fields carry momentum.

And with the same relationship, if you considerf E and p as the energy and momentum densities of the fields.
 

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