How can a Photon apparently transfer Momentum without any Mass?

In summary, a photon is a massless particle that still has energy and momentum due to its electromagnetic field. In relativistic physics, mass is not necessary for an object to have a momentum, and for a photon, the relationship between energy and momentum is given by ##E=|\vec{q}|c## where ##\vec{q}## is the momentum of the photon.
  • #1
KBon
Due to Compton - Scattering it seems that a Photon changes the Momentum of the electron, although it doesn't have any mass. How should I imagine this?
 
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  • #2
A photon is massless but has energy and momentum. It's the mode of an electrodmagnetic field, and you have
$$E=|\vec{q}|c,$$
where ##\vec{q}## is the momentum of the photon.

In relativistic physics you don't need a mass to have a momentum!
 
  • #3
Relativistically, the general relationship between energy, momentum, and mass is ##E^2 = (pc)^2 + (mc^2)^2## where p is the magnitude of the momentum. For a photon, m = 0 which gives vanhees71's formula, in different notation.
 
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1. How can a photon have momentum if it has no mass?

According to Einstein's theory of relativity, mass and energy are equivalent. Photons, as particles of light, have energy but no mass. However, they do have momentum due to their energy and their wave-like behavior. This is known as the photon's momentum-energy relation, which states that the momentum of a photon is equal to its energy divided by the speed of light.

2. How does the transfer of momentum by photons work?

The transfer of momentum by photons is known as radiation pressure. When a photon collides with an object, its momentum is transferred to the object, causing it to move. This transfer of momentum is very small, but it can have a significant effect on objects in space, such as comets and asteroids.

3. Can photons transfer momentum in a vacuum?

Yes, photons can transfer momentum in a vacuum. This is because photons do not require a medium to travel and can travel through empty space at the speed of light. This allows them to transfer momentum to objects in space even though there is no air or other material present.

4. How does the momentum of a photon compare to the momentum of a massive object?

The momentum of a photon is much smaller than the momentum of a massive object due to its small mass. However, photons can have a significant impact on objects in space due to their high speed and ability to transfer momentum through radiation pressure.

5. Is the transfer of momentum by photons a one-way process?

No, the transfer of momentum by photons can occur in both directions. When a photon collides with an object and transfers some of its momentum, the object will also transfer some of its momentum back to the photon. This is known as the momentum conservation principle, which states that momentum is always conserved in a closed system.

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