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mac_alleb
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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.mac_alleb said: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.
Johan0001 said: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.Johan0001 said: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?
bhobba said:The CBMR doesn't 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.
mac_alleb said:So E = pc?
bolded by meZealScience said:Actually, 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.
Johan0001 said: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?
bhobba said:What direction does the microwave radiation in a cavity travel?
mac_alleb said:So, as easily seen, nobody knows what is photon momentum??
Photon momentum refers to the amount of momentum that a single photon carries. It is a measure of the photon's motion and is directly proportional to its frequency and inversely proportional to its wavelength.
According to Einstein's theory of relativity, the speed of light is constant and independent of the observer's frame of reference. This means that the momentum of a photon, which is directly proportional to its frequency, is also constant and independent of the observer's frame of reference.
Yes, photon momentum can be observed indirectly through its effects on objects. For example, when a photon strikes an object, it imparts some of its momentum to the object, causing it to move. This can be measured using instruments such as a photometer or a spectrophotometer.
In quantum mechanics, momentum is a fundamental property of particles, including photons. The concept of photon momentum helps to explain various phenomena, such as the photoelectric effect and Compton scattering, which cannot be explained by classical mechanics.
Yes, just like momentum is conserved in classical mechanics, photon momentum is also conserved in interactions and collisions. This means that the total amount of momentum before and after the interaction or collision remains the same.