Light trapped in a ball?

[Glaran K'erman]

I've always wondered this since I was a kid and figured someone here will be able to answer my question.

So lets say you have a hollow, perfect sphere with the thickness of the material being as thin as theoretically possible. Lets say this material is also perfectly reflective on the inside, reflecting every wavelength of light right off of it. What would happen if a small "hatch" were to be opened to allow a small bit of light in but was closed before any of it could escape. Now imagine the hatch closes to magically have no seams whatsoever making the inside of the sphere perfectly smooth. What would happen to the light?

[Captain Sierra]

Well, light reflecting off of something is never a perfect redirection of energy. Some of it is lost as heat in the material. Realistically I'd expect the light to dissipate as heat almost instantly after some bouncing.

Though, since you specify perfect reflectivity, I have no idea.

[Glaran K'erman]

That sir is the conundrum! Since heat is nothing more than infrared LIGHT, my theoretical material would (should?) ignore that.

[CalculusWarrior]

That sir is the conundrum! Since heat is nothing more than infrared LIGHT' date=' my theoretical material would (should?) ignore that.[/quote']

Well, there are three types of heat transfer (which KSP now models ), and radiation is only one of those. I believe the beam of light would jostle the molecules of the mirrors in an imperfect reflector, warming them up. Of course, you specify that this is a perfect reflector, so every photon is redirected.

In that case, I imagine that the beam would keep bouncing around until someone opened the sphere.

[lajoswinkler]

If the reflection is perfect, it would keep bouncing, but as there are no such things as 100% efficient energy transfers, it would be quickly consumed on heating up the ball material.

[sal_vager]

This might be better thought of in another way, like the energy in a universe, that energy cannot leave and no more can be added, but just as visible light might turn to infra red heat over time in a perfect mirrored sphere, so too does our universes energy become less ordered over time.

[RainDreamer]

Well, what is the environment inside the orb? Is it a perfect vacuum? I imagine if the photons bounce off impurities of the space inside the container, it could possibly be slowed down at one point.

[Glaran K'erman]

While I definitely get that the light would keep bouncing in the scenario, what woud happen to the characteristics of the light. How is the path of the light affected? Is it? Does the timing of the photons get altered in a way through the bouncing that this alters wavelength? Can the light exist in the same state indefinitely? All the questions!

Well, what is the environment inside the orb? Is it a perfect vacuum? I imagine if the photons bounce off impurities of the space inside the container, it could possibly be slowed down at one point.

Perfect vacuum

This might be better thought of in another way, like the energy in a universe, that energy cannot leave and no more can be added, but just as visible light might turn to infra red heat over time in a perfect mirrored sphere, so too does our universes energy become less ordered over time.

So the light "decays", so to speak, to a less energetic state over time?

Edited August 5, 2015 by Glaran K'erman

[CalculusWarrior]

While I definitely get that the light would keep bouncing in the scenario' date=' what woud happen to the [i']characteristics of the light. How is the path of the light affected? Is it? Does the timing of the photons get altered in a way through the bouncing that this alters wavelength? Can the light exist in the same state indefinitely? All the questions!

Well, if the light enters perfectly perpendicular to the far wall of the sphere, it will bounce back and forth between two points. Other entry angles will result in more exotic travel paths. I imagine that the beam will be scattered, as the mirror is not flat, and the photons will all want to converge on the centre of the ball. So eventually you'd just have random photons bouncing around with no semblance of order.

[Tex_NL]

Schrödinger's cat!

Without opening the sphere there is no way to know what's exactly happening inside and if the light is still there. But by opening the sphere the light, it is was still there, will surely escape.

[Glaran K'erman]

Well, if the light enters perfectly perpendicular to the far wall of the sphere, it will bounce back and forth between two points. Other entry angles will result in more exotic travel paths. I imagine that the beam will be scattered, as the mirror is not flat, and the photons will all want to converge on the centre of the ball. So eventually you'd just have random photons bouncing around with no semblance of order.

Yea should have clarified that they definitely don't enter perpendicular, that's be boring lol.

[CalculusWarrior]

Yea should have clarified that they definitely don't enter perpendicular' date=' that's be boring lol.[/quote']

So yeah, the beam will enter, start bouncing around, and scatter as it keeps going on, resulting in a photon soup of sorts. I can't imagine how the wavelength would be altered, as you generally need to pass through a material with a different refractive index in order for that to occur.

[Glaran K'erman]

Well thanks so far everyone, keep em coming!

[LordFerret]

{Imagining how Schrodinger's cat might or might not have played with the sphere of trapped light.}

[Darnok]

Or you can trap light in anything by slowing it down http://www.gla.ac.uk/news/headline_388852_en.html maybe someday we will be able to stop it.

Btw Schrodinger's cat thought experiment was created to show how stupid quantum physics concepts are, not to explain how it works

Edited August 5, 2015 by Darnok

[Tex_NL]

...

Btw Schrodinger's cat thought experiment was created to show how stupid quantum physics concepts are, not to explain how it works

It shows how you can only know the outcome by observing it. And the simple act of observing might change the outcome.

[LordFerret]

My observation has been that cats don't need to observe anything to play or not play with anything. lol

[lajoswinkler]

Schrödinger's cat!

Without opening the sphere there is no way to know what's exactly happening inside and if the light is still there. But by opening the sphere the light, it is was still there, will surely escape.

Quantum phenomena such as the one described humorously in that thought experiment are not applied to such macroscopic systems.

So yeah, the beam will enter, start bouncing around, and scatter as it keeps going on, resulting in a photon soup of sorts. I can't imagine how the wavelength would be altered, as you generally need to pass through a material with a different refractive index in order for that to occur.

If the reflectivity of the insides is perfect (albedo 100%), nothing would change. Of course, such surface can not exist because it would violate the basic laws of nature. Every photon bumping into atom, getting absorbed and then spitted out when the atom relaxes is subjected to energy conversion and that is never 100% efficient.

[Starwhip]

I've wondered EXACTLY this for quite a few years. Funny to see that someone else has been as well.

Interesting responses. I've nothing to offer that has not been said, frankly.

[Xannari Ferrows]

If the reflectivity of the insides is perfect (albedo 100%), nothing would change. Of course, such surface can not exist because it would violate the basic laws of nature. Every photon bumping into atom, getting absorbed and then spitted out when the atom relaxes is subjected to energy conversion and that is never 100% efficient.

"It takes energy to move energy."

-Entropy

[Glaran K'erman]

I've wondered EXACTLY this for quite a few years. Funny to see that someone else has been as well.

Interesting responses. I've nothing to offer that has not been said, frankly.

Great minds think alike...

Thanks again guys, good response but anyone want to throw anything out there technical or otherwise I'd like to see too!

[0111narwhalz]

If you want a visualisation of the first n bounces (where n is however many you have the patience to draw) I'm pretty sure an application like GeoGebra would expidite the process greatly.

[cantab]

If it was a single photon its frequency would remain unchanged and it would stay a single photon. I know that because I know from experience mirrors don't red- or blueshift the light they reflect.

However even if you could ensure the sphere wouldn't absorb the photon, there is always a chance of the photon quantum tunnelling through the sphere and escaping. Perfect, indefinite containment would seem to be impossible.

[spudman2]

Vsauce did a video on a similar topic.

[GeneralVeers]

EUREKA! I think I figured it out.

Even though the interior of the sphere is a perfect reflector, the light trapped in the closed sphere would still lose energy over time. Each impact by a photon would push against the sphere, transferring some energy from the photon to the sphere. This would either cause the sphere to recoil a minute distance (causing the sphere to encounter air resistance, thereby losing energy) or cause the casing of the sphere to distort slightly (causing friction between the atoms in the sphere, thereby losing energy).

End result: over time, the light would gradually decrease in frequency. But it would take quite a while.