Could we store light forever?

Chris Smith asked materials scientist, Rachel Oliver, to shine a light on this question from listener R. Middleton...

Rachel - The difficulty is storing the light without absorbing it; so you can do that in a thing called a "cavity". In the simplest sense, a cavity could just be two mirrors and you reflect the light backwards and forwards, and backwards and forwards. We can make cavities that will store light, but probably not for very long, so fractions of a second might be the amount of time that we could store a single particle of the light that I was talking about earlier. So you can store information in the form of light and there are ideas for using that, but the problem is the storing part not the information part.

Chris - So if you had a box which is entirely mirrored on its interior, and you put some light in there, would it not just ricochet around forever in the box?

Rachel - Your problem is the "entirely mirrored". You don’t ever manage to make a mirror which is 100% reflective that always bounces back the light. They’re always going to absorb some of the light as well, or some of the light's going to leak out of the box. So, in your theoretically perfect mirrored box, yeah you’re doing great. But actually making one of those is so difficult that the word "impossible" is probably quite relevant!