Interesting physics question..

[Joe]

In theory, if a little bit of light was released into a room completely made of 100% efficency mirrors (IE, it reflects the light back with 100% it's original strength, hence "in theory"), what would happen?

I'd think the light would continue to bounce from wall to wall for eternity, keeping the box lit up forever without requiring any energy, since the light itself is energy, not matter. However, over time, wouldn't the light itself succumb to gravity and fall to the bottom of the box? Or is it immune, since it's not matter? Would it's energy "wear out" over time and become dimmer, then black?

[Sidoh]

Energy is matter, matter is energy.  Haven't you heard of Einstein?  Electromagnetic waves are absolutely effected by gravity.  That's one of the reasons that dark matter is believed to exist.  Light from stars (and other cosmological objects) "bend" toward gravitational fields.  There are cases where the same object is seen twice in the sky because of this.

You're using the phrase "lit up" in a shady fashion here.  If the box is to be "lit up," that implies that there's something there to detect the presence of light, which would either mean that it's absorbing all or some of the light or that the light is dissipating or diffracting, which goes against what you're suggesting.

Also, this is really unrealistic.  It's closely analogous to asking what the world would be like without friction.  The world would be a very different place and inventing situations that are used in our world and applying them to the "new world" isn't very useful.  You'd practically have to reinvent Physics.

I know your normal reaction would be to say "but that's why I said 'in theory'," but there are dozens of things like this which are fairly obvious ("what if gravity didn't exist?").

[deadly7]

("what if gravity didn't exist?").

We'd all fly!

[Towelie]

It's closely analogous to asking what the world would be like without friction.

we would all be single cell organisms!

[Chavo]

Its often useful to explore physics theory with ideal (and impossible) situations to better understand a theory or a basic priniciple.  It is NOT useful to try to understand impossible conditions using impossible situations.

[iago]

If you had a 100% vacuum with 100% efficient mirrors, there would probably be light bouncing on the inside forever.

However, like Sidoh said, as soon as you put anything in the box (whether it's a person or a detector or whatever), it would absorb the light.

[Ender]

I believe the light energy would convert into different forms of energy over time (I'm not necessarily saying that all of it would...), and thus the light will dim very slowly. For instance, the photoelectric effect produces a current, which converts some of the light energy into electrical energy. (I'm actually a little unsure about this statement... since currents are caused by flow of electrons, not photons, but there certainly will be kinetic energy involved due to the photoelectric effect.)

And to add to what people have already said about your ideal conditions: although it can be helpful to consider ideal conditions to understand a principle, I'm not sure if you understand how crazy the universe really is on the quantum level... (e.g., one photon enters a double slit, two come out). There is no certainty. Look up Heisenberg's Uncertainty Principle.

[rabbit]

The light would eventually decay (much like a black hole does), and there would be nothing left but a box of mirrors.

[Joe]

The light would eventually decay (much like a black hole does), and there would be nothing left but a box of mirrors.

That, and iago's post, was exactly what the answer to my question was. Of course they seem to contradict themselves.

What I was going to say in response to iago's answer, if that's the correct one, is that by using that principle, that it's lit for eternity using no more energy than what it took to "turn it in", could we create extremely high-efficiency lighting? Obviously you need to be putting in more energy since some will be lost to light something, but couldn't we preserve more energy than we do with our current lighting strategies?

@UT: I can sort of see that point, but I like to come up with practical ideas by somewhat de-escalating impractical ideas.

[Sidoh]

No, absolutely not.  I'm sorry to be rude, but you don't have much of an idea what you're talking about.  If light is seen, energy is lost.  If light illuminates something, energy is lost.  If a bunch of photons bounced around in mirrors forever, they wouldn't ever light anything up.  It'd be useless.  I mentioned how this is impossible in my original post and iago agreed in his.

I don't know if you're trying to be vindictive by ignoring answers, but defeats the point of asking questions.  What practical ideas?  To reiterate what's already been said, it's useful to assume that imperfect reflection (or, to extend my analogy, friction) doesn't exist for the sake of approximations, but it's really silly to dream up routines that are contingent upon these obviously fallacious assumptions.  The "perfect mirror" doesn't exist just as the "perfectly smooth surface" doesn't exist.

[Joe]

You're right in saying I have no idea what I'm talking about. I don't. All I know about physics was learned in Freshman Science.

I wasn't trying to ignore the answers, but since rabbit's answer went against iago's answer, from what I understood, I figured that one of them had to be wrong.

I was just asking if this prinicipal could be implemented, without such efficiency in the mirrors or trapping of the light, to create a more efficient lighting apparatus. For example, think of how a floodlight bulb doesn't let light out the sides and therefore more energy comes out the top than your standard ceiling bulb. Some areas don't get lit, but the energy that would be used to light the useless areas is now lighting the useful area, so on a whole, you're better off.

[iago]

Sidoh is correct, it'll only work in an absolutely ideal situation, not in the real world. And as soon as you try to use it for lighting, the light escapes and you're left with a box as empty as your plans. Ha!

[Sidoh]

That's already used and has been for thousands of years.  It isn't even close to an application of what you're proposing here.