Trapping Light

If you were to create a hollow sphere lined by a perfectly reflective surface with one small close-able opening, shine a small light in, and then quickly close the (reflective) opening before the light could exit, could you come back in some amount of time and find that the light is still reflecting around on the inside of the container?
- Aaron Cravens (age 17)
Champaign, Illinois, U.S.

As you are evidently aware, this isn't practical because materials don't reflect perfectly.  It's possible in principle, however.

Mike W.

(published on 05/07/2010)

Since you live around the University of Illinois at Urbana-Champaign, I thought I'd add the follow up that Prof. Kwiat of the physics department here does indeed "trap" light using highly reflective mirrors. There was an experiment where he needed to "hold" a photon for awhile before measuring it. Their lab used a mirrored 'box' that bounced the photon around long enough for them to later measure it when it came out of the mirror box. According to this paper, they "held" the photon for about 1 usec, which is a short time in human terms, but long enough for the electronics to setup the measurement they wanted to do on the photon. They also show how to design the box to hold the photon for almost arbitrary amounts of time given good enough reflectivity. http://research.physics.illinois.edu/qi/photonics/papers/SPIEDelayedChoiceQCrypt.pdf
- Kevin M (age 29)
Urbana, IL, 61801

Thanks,

Mike W.

(published on 05/08/2010)