Question about a photon's momentum.

[greswd]

When light travels in a medium, its speed is less than c.

Thus the lorentz factor is not infinite. Since photons have zero rest mass, does this also imply that the photons have zero momentum?

 

[Naty1]

The 'speed of light' in a medium is a complex subject that has been discussed at length in these forums. but individual photons still travel at 'c' in such a medium. the overall travel is slower than c. For example information transmission in fiber optic cable is a bit slower than in a vacuum.

Photons always have momentum.

In a medium there is a complex scattering and absorption interaction between photons , the phonons of of atomic structures such as lattices and atomic particles. There is a FAQ on this, but it is not so 'crystal clear' to me...and from another discussion:

Oh - hang on, found a FAQ:

https://www.physicsforums.com/showpost.php?p=899393

But see:
http://physics.stackexchange.com/que...-through-glass
http://physics.stackexchange.com/que...qed-snells-law
... many objections in the FAQ are addressed in these.

 

[harrylin]

[..] in a medium [..] the lorentz factor is not infinite. Since photons have zero rest mass, does this also imply that the photons have zero momentum?

Hi,

Light always propagates at c despite the fact that its effective speed is reduced in matter.
- https://www.physicsforums.com/showthread.php?p=4044159

Momentum of photon: p = E/c
- http://hyperphysics.phy-astr.gsu.edu/HBASE/Relativ/relmom.html