- #1
mac_alleb
- 3
- 0
While planing some simple experiments us encountered such a problem: what is exactly photon momentum?
p_ph = ?
p_ph = ?
The photon momentum, ##p## is the momentum carried by a photon and is related to the energy of the photon by the equation ## E=pc## where c is the speed of light in a vacuum.While planing some simple experiments us encountered such a problem: what is exactly photon momentum?
p_ph = ?
Even classically, radiation carries momentum. That's why you get radiation pressure. The whole formalism is derived from the Lorentz forces which implies that E-M field carries momentum. In fact, the quantum field theory of photon arises from covariant quantization of vector potential and therefore photons carry quantized version of the classical E-M field momentum.
momentum is a vector .Then in which direction does the E-M field travel , say in the case of Cosmic Background Radiation, which is all around us?
It is not the E-M field that travels, it is the energy that travels. For free space, poynting vector is in the same direction as the wave vector and thus the direction of momentum vector. I am not expert on Cosmic background radiation, but I think they should have momentum, even on the ground of relativity. If you are in some random frame, it is likely that some of the photons are redshifted and some are blueshifted. For comoving fundamental observers, the radiation is isotropic, but that does not mean individual photon does not have momentum.momentum is a vector .
Then in which direction does the E-M field travel , say in the case of Cosmic Background Radiation, which is all around us?
The CBMR doesnt really have a direction - but recently there have been found small departures from uniformity that it is suspected to be left over from the early inflation phase of the universe.
So E = pc???
bolded by meActually, I just attended a talk by a scientist from Astronomy department. He was analyzing some data from a ground based telescope which potentially indicate CMB polarization by the inflatory gravitational waves. Unfortunately, the data is heavily affected by galactic dust and they are currently trying to salvage the actual signal.
But I am no expert on it. I do not know the details.
momentum is a vector .
Then in which direction does the E-M field travel , say in the case of Cosmic Background Radiation, which is all around us?
What direction does the microwave radiation in a cavity travel?
So, as easily seen, nobody knows what is photon momentum??