Does photon exist without velocity c ?

[cooper607]

hi,
recently i have been struggling with the concept if photon exists without traveling at velocity c ? i knew c is constant only when it travels trough space and when it travels through other medium with refractive indexes it does not exist at all .. is it true ?
how do scientists define why photons exists?
or what changes occur to a photon when it passes through other mediums except vacuum?
please help

 

[Naty1]

photons always travel a speed 'c'...they are born that way and die that way: instantaneously.
They don't accelerate and decelerate as do mass particles.

For a discussion try here:

https://www.physicsforums.com/showthread.php?t=687244&highlight=speed+light


From post #7 there:

According to wiki: "In a classical wave picture, the slowing can be explained by the light inducing electric polarization in the matter, the polarized matter radiating new light, and the new light interfering with the original light wave to form a delayed wave." (which is equivalent to using some tensor form of the permittivity).

And wiki also say: "In a particle picture, the slowing can instead be described as a blending of the photon with quantum excitation of the matter (quasi-particles such as phonons and excitons) to form a polariton; this polariton has a nonzero effective mass, which means that it cannot travel at c.

Alternatively, photons may be viewed as always traveling at c, even in matter, but they have their phase shifted (delayed or advanced) upon interaction with atomic scatters: this modifies their wavelength and momentum, but not speed.[97] A light wave made up of these photons does travel slower than the speed of light. In this view the photons are "bare", and are scattered and phase shifted, while in the view of the preceding paragraph the photons are "dressed" by their interaction with matter, and move without scattering or phase shifting, but at a lower speed.