Weird question about light

[Junghalli]

Suppose you had a chamber with wall made out of perfect energy barriers. No energy can get in or out of the chamber. Say it's sort of like a Thrint stasis field minus the time delation effects. In this chamber you have a lightbulb. You turn the light off.

If you were in the chamber, would it go dark? Or would it take a while for the light to decay to heat, and you'd still be able to see for a while after the light was turned off?

Just a weird thought experiment that's been bugging me for a while.

[Lord of the Abyss]

Not a physicist, but my guess :

If done as stated, it would go dark immediately, because your body would absorb the light. If you covered yourself with a similar reflective field, it would stay light until it decayed to heat, but you'd be blind and unable to see it. Covering everything but your eyes would make it go dark a little slower, but I doubt you'd be able to detect the difference.

[Plushie]

What if the energy barriers were, instead, perfect mirrors? Or near perfect, anyway.

[Master of Cards]

What if the energy barriers were, instead, perfect mirrors? Or near perfect, anyway.

is the area full of air or a vac
in the first the light will bounce around slowly expanding because of heating the air and the second bouncely for a long time

[Dooey Jo]

One has to remember that if the chamber isn't huge, the light will bounce many millions of times per second. So even if the photons manage to stay in the visible spectrum for a "long time", that time will most likely not be long enough for a human to notice any difference. And if the human is in the chamber itself, then she definitely will not notice anything, unless she somehow is also reflective, but in that case she wouldn't be able to see anything.

[Braedley]

It depends a lot on the reflection coefficient of the barrier. If it doen't have a coefficient magnitude of 1 (it can't be any greator) then it will get very dark very quickly. And possibly very cold too. For that reason, we should also consider whether this barrier itself releases energy into the electromagnetic spectrum, because that will skew the results.

[TheBlackCat]

It depends a lot on the reflection coefficient of the barrier. If it doen't have a coefficient magnitude of 1 (it can't be any greator) then it will get very dark very quickly. And possibly very cold too. For that reason, we should also consider whether this barrier itself releases energy into the electromagnetic spectrum, because that will skew the results.

It can't get any colder than the surrounding environment. If the barrier is perfect, all energy would be trapped and the temperature would either remain constant or increase if a person is inside. If it isn't perfect, everything inside the barrier would move towards thermal equilibrium with the outside as energy passes across the barrier, so it would either move towards the temperature of the outside environment if there is no one inside or move towards a temperature somewhere above the outside environment if a person is inside. If the barrier was somehow a rectifier the temperature would decrease, but probably pretty slowly because radiative heat transfer is much less than conductive or convective heat transfer.

[Braedley]

It depends a lot on the reflection coefficient of the barrier. If it doen't have a coefficient magnitude of 1 (it can't be any greator) then it will get very dark very quickly. And possibly very cold too. For that reason, we should also consider whether this barrier itself releases energy into the electromagnetic spectrum, because that will skew the results.

It can't get any colder than the surrounding environment. If the barrier is perfect, all energy would be trapped and the temperature would either remain constant or increase if a person is inside. If it isn't perfect, everything inside the barrier would move towards thermal equilibrium with the outside as energy passes across the barrier, so it would either move towards the temperature of the outside environment if there is no one inside or move towards a temperature somewhere above the outside environment if a person is inside. If the barrier was somehow a rectifier the temperature would decrease, but probably pretty slowly because radiative heat transfer is much less than conductive or convective heat transfer.

A reflection coefficient of 1 or -1 would be a perfect barrier, in which case the energy would be absorbed by the surrounsding air, and the room would get dark fairly quickly, but would stay relatively warm, and you'd be dead from lack of oxygen before it'd get too cold. But it would still get cold as long as you are using energy (to think, move around, etc.).

If the reflection coefficient does not have an overall magnitude of 1 (it can be complex btw), then there are two options: unreflected light can either be 1) transmitted through the barrier, or 2) be absorbed by the barrier. Since it's stated in the OP that EM waves cannot penitrate the barrier, this rules out 1. If energy absorbed by the barrier is then channeled someplace else (admittedly not a certainty) then the total energy in the chamber will gradually decrease until there's absolutely none left.

In any case, my studies into this general field haven't progressed far enough to totally deal with this problem. We have only studied the interface of "simple" materials (linear, homogeneous and isotropic), of which this barrier certainly is not.

[TheBlackCat]

But it would still get cold as long as you are using energy (to think, move around, etc.).

No, humans don't absorb energy from the air or from electromagnetic radiation. The energy they use comes from oxygen and materials in their body. The chemical potential energy in those molecules does not contribute to the temperature of the room, but as soon as you use it the energy is released as kinetic energy as you move, heating up the chamber.

If energy absorbed by the barrier is then channeled someplace else (admittedly not a certainty) then the total energy in the chamber will gradually decrease until there's absolutely none left.

That is assuming the barrier only absorbs energy and does not emit it. It would effectively be a black hole or other infinite energy sync. That would make it a rectifier. Otherwise it will only absorb energy until it reaches thermal equilibrium, at which point the energy emitted will match the energy absorbed and the temperature would stabilize.

[Braedley]

But it would still get cold as long as you are using energy (to think, move around, etc.).

No, humans don't absorb energy from the air or from electromagnetic radiation. The energy they use comes from oxygen and materials in their body. The chemical potential energy in those molecules does not contribute to the temperature of the room, but as soon as you use it the energy is released as kinetic energy as you move, heating up the chamber.

Uh, yes we do absorb energy from various wavelengths in the EM spectrum. We'd all be pastey white if we didn't absorb portions of the UV spectrum. There's also a reason that there are regulations governing the acceptable levels of EM radiation that an employee can be exposed to in industry. If we didn't absorb any EM radiation, there'd be no need for these regulations. Also, how do you think a microwave oven works?
I'll have to concede for the time being on the potential energy stored in molecules part, though, as moving around will produce heat. However, if the barrier is a net absorber of energy, then you are still dead because the total energy within the barrier will continue to be constant or decrease, like I said in my previous post.

If energy absorbed by the barrier is then channeled someplace else (admittedly not a certainty) then the total energy in the chamber will gradually decrease until there's absolutely none left.

That is assuming the barrier only absorbs energy and does not emit it. It would effectively be a black hole or other infinite energy sync. That would make it a rectifier. Otherwise it will only absorb energy until it reaches thermal equilibrium, at which point the energy emitted will match the energy absorbed and the temperature would stabilize.

Se above, although I do suppose that a nominal gross energy output aside from reflection can be expected. But that will still be offsided by the absorbtion.

[TheBlackCat]

Uh, yes we do absorb energy from various wavelengths in the EM spectrum. We'd all be pastey white if we didn't absorb portions of the UV spectrum. There's also a reason that there are regulations governing the acceptable levels of EM radiation that an employee can be exposed to in industry. If we didn't absorb any EM radiation, there'd be no need for these regulations. Also, how do you think a microwave oven works?

All the mechanisms you just listed convert EM radition into thermal energy (except for UV, which usually is converted into thermal energy but sometimes causes chemical reactions). That would make the room warmer. Besides, there is nothing in the room that emits significant levels of UV, microwave, RF, optical, or anything else besides IR radition.

Se above, although I do suppose that a nominal gross energy output aside from reflection can be expected. But that will still be offsided by the absorbtion.

Only as long as the energy contained the barrier is less than the energy in the chamber. Unless the barrier is effectively a black hole, sooner or later it has to reach thermal equilibrium with its environment. No normal matter can absorb infinite amounts of energy from an environment that has finite energy available. As the energy contained in the barrier increases, the energy difference between the barrier and the chamber decreases so the energy it absorbs decreases and the energy it emits increases. Eventually the energy absorbed by the barrier will equal the energy emitted by the barrier and energy will stop flowing. That is thermal equilibrium.

[Neko_Oni]

Well every time a photon hits a wall it reflects with no change in energy. If it hits normal matter it might get absorbed and coverted into heat. So my guess is the room goes dark very quickly as all the light rapidly shifts out of the visible spectrum.