What is the lifetime of a photon in a medium?

[docnet]

When light travels through a medium like water, it slows down and its speed is no longer equal to c. How does this affect the life time of the photon?

 

[Vanadium 50]

It doesn't.

 

[Nugatory]

Light traveling through a medium like water cannot be usefully thought of as photons moving through the water. The light is an electromagnetic wave, and we analyze this problem as a wave moving through the medium.

Photons only come into the picture when quantum mechanical effects are significant, and they aren't in this problem.

 

[Lord Jestocost]

When light travels through a medium like water, it slows down and its speed is no longer equal to c.

When light travels through a medium like water, it appears to slow down. The apparent "slower speed" is the result of the superposition of two radiative electric fields: the incoming light, traveling at speed $c$, and the light re-radiated by the atoms in the medium in the forward direction, traveling at speed $c$, too. In case one wants to understand the essential aspects of the phenomena, I recommend to read chapter 31 “The Origin of the Refractive Index” in “The Feynman Lectures on Physics, Volume I". (http://www.feynmanlectures.caltech.edu/I_31.html).