# Refraction and Special Realitivity

Hello, new comer to realitivity here.

My friend and I were wondering if when light refracts if the photons temporarly convert back into partial mass.

Through my understanding of e=(mc^2)/sqrt(1-v^2/c^2) it appears as if they would, but since photons have an infinite amount of energy backing them up, then is it even possible for them to even reach a stage of having mass?

edit: sorry for my bad grammar, english has never been my strong point.

## Answers and Replies

JesseM
Science Advisor
Hello, new comer to realitivity here.

My friend and I were wondering if when light refracts if the photons temporarly convert back into partial mass.
A photon can never have mass, but it is possible for a photon to convert into other particles which do have rest mass. I don't know exactly what happens when light refracts, but see post #4 here for a good discussion of why light slows down in a medium like water, basically involving the photons being repeatedly absorbed and re-emitted.
haloshade said:
Through my understanding of e=(mc^2)/sqrt(1-v^2/c^2) it appears as if they would, but since photons have an infinite amount of energy backing them up
No, photons only have a finite amount of energy--keep in mind that the "m" in that equation is the rest mass, which would be zero for a photon, so the equation just gives the undefined answer 0/0. To find the energy of a photon you have to use the quantum equation E=hf, where f is the photon's frequency and h is planck's constant.