[Thomas Merrigan]

Tom Merrigan  asked the Naked Scientists:
   
What happens to the reflection of light initiated in the centre of a perfectly spherical mirror with nothing to absorb the light?

What do you think?

[Bored chemist]

If there's nothing to absorb the light it's hard to see what emitted it.

[AllenG]

Saying that light could be trapped in a spherical mirror then two things are going to happen.  1.) The mirror is not going to be 100% reflective and the light will be absorbed. 2.) Light diminishes by the square of the distance traveled, so even if the mirror was perfectly reflective the light would still grow dimmer as it bounces around in the sphere.

[Madidus_Scientia]

Light diminishes by the square of the distance traveled, so even if the mirror was perfectly reflective the light would still grow dimmer as it bounces around in the sphere.

Yes, the light at any one point diminishes with distance, which makes sense because there's basically more points. But this would be irrelevant inside a hypothetical perfect mirror sphere.

[Bored chemist]

"even if the mirror was perfectly reflective the light would still grow dimmer as it bounces around in the sphere. "
No it wouldn't, where would the energy go?

[Thomas Merrigan]

Question clarification:  The inside of the sphere is completely spherical and has, had its center, a flash bulp with vaporizes once it flashes like a camera light flash.  There is no where for the light to leave.  Unfortunately, there is not an apparent way on the outside to determine the results.  i envision the light TRAVELING AT THE SPEED OF LIGHT, indefinitely bouncing off all the other photos which are bounced back to the center.  Would the photos simply dissipate overtime by continuing bumping into other photos, or would it be a sort of perpetual light machine, neither increasing nor increasing as the light waves continue to richochet off one another.

[Madidus_Scientia]

If the mirror reflected 100% of the light, then yes the light would remain trapped. However, no mirror is that efficient. If the diameter of the mirror sphere was 1 metre then it would bounce around 299792458 times per second. So even if the mirror was 99.99% efficient, it would still dissipate very quickly.

[Bored chemist]

If you have something in the sphere that absorbs, but only slightly, and a mirror that leaks light out slightly then you have the conditions for doing this.
http://en.wikipedia.org/wiki/Cavity_ring-down_spectroscopy

[Madidus_Scientia]

How reflective is the most reflective mirror we can make?