Understanding the Paradox of Photon Momentum: Electromagnetic Force Revealed

In summary, the conversation discusses the concept of momentum in relation to electromagnetism and the properties of photons. It is noted that the classical electromagnetic field has momentum and the photon, as the quantum mechanical minimum unit of this field, also carries momentum. This may seem paradoxical due to the photon's mass of zero, but it is explained that in relativity theory, particles can have momentum and energy even with zero mass. This is supported by the equation E^2 = (pc)^2 + (mc^2)^2, where for photons this can be simplified to E^2 = (pc)^2. Finally, the conversation touches on Planck's constant and classical physics in relation to momentum and energy.
  • #1
scilover89
78
0
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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  • #2
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.
 
  • #3
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?
 
  • #4
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.
 
  • #5
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.
 
  • #6
So for photons this equation can be written as:
E^2=(pc)^2
 
  • #7
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.
 
  • #8
Yeah, you are thinking in terms of classical physics.
 
  • #9
Strafespar said:
Yeah, you are thinking in terms of classical physics.

5 year old thread
 

1. What is the concept of photon momentum?

Photon momentum is the measure of the energy and momentum carried by a photon, which is a unit of electromagnetic radiation. It is described by the equation p = h/λ, where p is the momentum, h is Planck's constant, and λ is the wavelength of the photon.

2. How is the electromagnetic force revealed in the paradox of photon momentum?

The paradox of photon momentum arises from the fact that photons have no mass, yet they possess momentum. This paradox is resolved by understanding that photons carry energy, and according to Einstein's famous equation E=mc², energy and mass are equivalent. Therefore, photons have momentum due to their energy.

3. How does the understanding of photon momentum impact our understanding of light?

The concept of photon momentum helps us to understand that light is not only a wave, but also a particle. This dual nature of light is fundamental to many phenomena in physics, such as the photoelectric effect and the Compton effect.

4. Can the paradox of photon momentum be explained by classical physics?

No, the paradox of photon momentum can only be explained by quantum mechanics. In classical physics, momentum is always associated with mass, so a massless particle like a photon would not have momentum. However, in quantum mechanics, the concept of momentum is extended to include particles without mass.

5. How does the understanding of photon momentum impact other areas of science?

The concept of photon momentum has implications in various fields such as astrophysics, where the momentum of photons is crucial in understanding the dynamics of stars and galaxies. It also plays a significant role in the development of technologies such as solar panels and laser technology. Additionally, the understanding of photon momentum has led to advancements in quantum computing and cryptography.

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