Can you "trap" light indefinitely? One of my fifth grade students wants to know if you can "trap" light. that is, can you let some light into a container and then seal it off, and let it out again some time later? I'm not a physics major so I wasn't sure at all, but instinct tells me "no". That's supposing you could even get it in a container and seal the container in the first place. At first I'm thinking you can bounce light off a bazillion mirrors and so why couldn't you just keep doing that, but then I realized you basically have to have all the mirrors set up already, since you could never keep up with the speed of the light, leading me to suppose it doesn't matter how far the light goes, what matters is how long it is preserved. So in that case, it may dissipate almost instantly. But then, there's the light from far away planets from a long time ago. So, light does in fact have an appreciable "shelf-life". Of course, this light was extraordinarily bright at the origin and is now extraordinarily dim. So, maybe your "light in a jar" would become so dim that you couldn't see it anymore extremely quickly. The most problematic thing of all, I think, would be that you would only have an instant of light, since you could only capture that last instant before sealing the container. Any light that had entered the container previously would have worked its way out almost instantly. Even if you could "collect" more than an instant of light, the instant you released the light, it would ALL come out at practically the same time. Well, it's all very impractical, but does the concept violate any laws? If not, what "practical constraints" would make the whole endeavor pointless? Please try to use basic language.