Center of momentum frame with photons?

In summary, it is possible to have a unique frame in which a photon and a massive particle have opposite momentums, as long as the velocity of the particles in the CM frame is redefined. This is due to the Doppler shift changing the energy and momentum of the photon as reference frames are changed.
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Is it possible to have a center of momentum frame in a system with a photon and a massive particle?

If you were to do so in a system with two massive particles, this would involve redefining the velocity of the particles in the CM frame. E.g. if A moves towards B with speed 2v, in the CM frame, A and B would move towards each other at v.

Since the photon will have speed c in all frames, is it possible to have a unique frame in which the massive particle has momentum -E/c (where E is the energy of the photon)?
 
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  • #2
Yes, it is possible. Remember that as you change reference frames the photon will red-shift or blue-shift. The Doppler shift will change the energy and therefore the momentum of the photon. There will be a unique frame where it is opposite that of the massive particle.
 

FAQ: Center of momentum frame with photons?

What is the center of momentum frame?

The center of momentum frame is a reference frame in which the total momentum of a system is equal to zero. In this frame, the net momentum of all the particles in the system is cancelled out, making it a useful tool for studying collisions and interactions.

How does the center of momentum frame relate to photons?

In the center of momentum frame, the total momentum of a system is equal to zero. This includes the momentum of photons, which have a momentum even though they have no mass. In this frame, the momentum of the photons is balanced out by the momentum of other particles in the system, such as electrons or protons.

Why is the center of momentum frame important in studying photon interactions?

The center of momentum frame allows scientists to simplify the analysis of photon interactions. By cancelling out the momentum of the photons, the focus can be placed on the interactions between the photons and other particles in the system, without having to take into account the photons' momentum.

Can the center of momentum frame be used for any type of interaction involving photons?

Yes, the center of momentum frame is a useful tool for studying any type of interaction involving photons, such as scattering, absorption, or emission. It allows for a simplified analysis and can provide valuable insights into the underlying physics of these interactions.

How is the center of momentum frame calculated?

The center of momentum frame is calculated by finding the reference frame in which the total momentum of a system is equal to zero. This can be done using the principles of conservation of momentum and energy, and taking into account the masses and velocities of all the particles involved in the system.

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