Theory Q: "Persistence of Light Inside an Impenetrable Sphere?

[shoook]

Hey guys, I have a theory question for you that may have been posed before but I can't find an answer to (not a school question):

There is a sphere with a completely impenetrable and reflective interior surface. A light in the visible spectrum is emitted from within this sphere. Because no light can escape from the spherical container, does the interior of this sphere stay lit forever?

Thanks for any help.

 

[zhermes]

Yup.

 

[Born2bwire]

Perfectly reflective and within the visible region I would say sure.

 

[Dr Lots-o'watts]

Except there is no such thing as perfect reflection. And even if it is 99.99%, light only stays there for nanoseconds because of its great speed, if it's a human-scale sphere.

 

[shoook]

Thanks for the input guys! Is there a known material that is "most reflective" to light? Is there a known material that is "most impenetrable" by light? Thanks again.

 

[zhermes]

mirror.

 

[Dr Lots-o'watts]

Thanks for the input guys! Is there a known material that is "most reflective" to light? Is there a known material that is "most impenetrable" by light? Thanks again.

It depends on the wavelength. If you choose a specific wavelength, a mirror can be designed to be as reflective as one can afford, for that wavelength, but it may be absorptive or transmissive to other wavelengths.

On the other hand, if you want a mirror that can reflect many wavelengths, metals are usually best for the visible range, but they all have some level of absorption, and reflection is not equal for all wavelengths.

As for most "impenetrable", again, this fundamentally depends on wavelength. See http://en.wikipedia.org/wiki/Attenuation_coefficient

 

[Phrak]

One online company claims to produce mirrors with better than 99.999% reflectivity in the 800 nm region of the spectrum. Going with the 99.999% number, it will take about 100,000 reflections for the energy to be reduced to 37%.

Put the mirrors in vacuum making a cavity 15 cm long having a round-trip time of one nanosecond, the storage time to 37% is 50 milliseconds. –that's longer than I expected.