Physics Van 3-site Navigational Menu

Physics Van Navigational Menu

Q & A: What happens to the light in a closed box?

Learn more physics!

Most recent answer: 09/26/2014
Q:
Why can't you trap light in a box? Presumably the photons are still around when you close the lid, but it goes dark. I am really enjoying your site, even if most of it is over my head. Thanks.
- harriet
N.Z.
A:
You are right.   The photons are still there.   If the insides of the box were perfectly reflecting, like mirrors, the photons would just bounce around for a long time.   However, all surfaces have a certain amount of absorption that will eventually eat up the photons.  There is always a certain amount of thermal radiation in the box, but that is another story.

LeeH  

(published on 12/18/2009)

Follow-Up #1: Were do photons go when they die?

Q:
Ok so what happens to light when it dies ? Norm byproduct. is lead right so what I was wondering what is the byproduct of light?
- Bradley d Maddox (age 32)
Duncan ok
A:

Hi Bradley,

The ultimate fate of all photons is death by absorption.  In which case its energy is given up to that object which absorbed it.  For example photons from the sun that strike the earth are absorbed and warm it.  If a photon strikes a mirror or some thing similar it can be reflected with minimal energy loss. Now some photons are as old as Methuselah and seem to last forever like the remnant photons coming out of the Big Bang.  However, like Methuselah, they do age.  They start out nice and blue and energetic but wind up as red or even infrared or microwave in their old age, as observed by us, due to the red-shift caused by the expanding universe.

LeeH


(published on 09/26/2014)

Follow-up on this answer.