Naked Science Forum
General Science => General Science => Topic started by: Seany on 13/04/2007 12:00:00
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This one is one which I always wanted answered since about a year ago. I asked my dad and everything, but no one seemed to know. Since there are some great scientists here, I thought you guys could help out [:)]
There is a square DARK room, and the walls, ceilings floors, are all made out of mirrors. Even the door. I enter the room with a torch. I turn the torch on and turn it off about 3 seconds later. As soon as I turn the torch off, I leave through the door (made out of mirrors also).
Shouldn't the light ray just keep reflecting, reflecting, reflecting and reflecting? I understand that the mirrors aren't 100% at reflecting the light back, of course some of it would be absorbed by the mirrors. But for some time at least, wouldn't the light still carry on reflecting? Until the whole room is bright?
Assuming that the light stops as soon as I turn the torch off again, where do the light particles go? Do they just lose their energy? Then, what is this "light particle" without the energy of theirs? Just dust?
Thanks, if anyone can help, I've really wanted this question answered.
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Hi George! I see that you are online. Any help for this poor little fellow? [;D]
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Hi. Any guests out there watching this, please join in and help me out [:D]
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i think Richard Feynman address this in one of his books, check you school science library for books by him.
i think that it is a similar question to, do trees falling make a noise if nobody is there to hear it?
light being energy may stay bouncing around you mirrors but not for long. the energy will soon run out...or something like that
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Yes, the light would remain traveling it's merry way forever [;)]........however....I also asked a similar question about the nature of whether light runs out....I'll see if I can find it ...(it would be easy if the search facility worked ...lol..have I mentioned that ?)
However, onto your question....me is sure that imperfections in the glass will eventually cause the light to stop reflecting cos when it hits something...light dies !!...and it's really sad !! [:-'(].......and me suspetcs..this would happen very quickly !!...not enough time to boil an egg or even do a poo !! [;D]
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Hmm thanks Paul and Neil!
But, if the energy runs out.. What happens to the light particles then?
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This is exactly what I wanted to know !!..
This must mean that my mental age is more than 8.5 !!...it must be at least 13 ..YAYYYYYYYY !!!
I suspect it turns into something else !..George will explain...he's like....well good at that kind of stuff !!
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Yup, Georgey sure is.
Neil, I deleted my signature because "someone" thought it would make you go paranoid! I shall remain the "someone" secret though [:D]
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Yup, Georgey sure is.
Neil, I deleted my signature because "someone" thought it would make you go paranoid! I shall remain the "someone" secret though [:D]
That's fine about the signature my young chummy chum....I am paranoid enough without it anyway ..LOL [;D]......hmm..me wonders who that "someone" is ?...LOL !!
...you know...you're a breath of fresh air here !!...though..it's hard to keep up with ewe !!...I am well impressed with your typing speed..I gather you're the fastest in the school !!.
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Yeah.. I am pretty fast.. [:P]
It feels weird because my name is on every section as "Last posted".
And only 100 away till a full member! Woohoo!
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First problem I can see, in practice (if not in theory) is how do you leave the room without losing the light.
Light travels very fast, so unless the room was very large (or you can find light paths in the room that do not escape out of the door), it is likely that as soon as you open the do, light will escape out of it.
While you are yourself in the room, you too will absorb much of the light.
The air itself, particularly any dust or small droplets of moisture, will absorb light.
The other thing, even if you could obtain perfect mirrors, and the room was evacuated (so no air or dust within the room), and you could somehow exit the room without losing the light as you leave, is that you would still have quantum tunneling of the light, where very small amounts of the light will constantly be leaking out of the room. Although this is in some ways another way of saying the mirrors are imperfect, but it is not down to a flaw of limitation in the manufacture of the mirror, but is a physical limitation of nature no matter how absolutely perfect the manufacture of the mirror is.
All these things, when the absorb the light, will warm up from the energy of the light (as they warm up, they will then re-radiate some of that energy in the infra-red region - the exact frequency of emissions will depend on their temperature - if the temperature is low enough, it may not necessarily even be in the infra-red).
This is in many ways the same sort of question as to what happens to microwaves in a microwave oven if there is nothing within the oven to cook (both light and microwaves are just electromagnetic waves, and the inside of a microwave oven is a mirrored box, except for the opening where the magnetron introduces the microwaves, but unfortunately, that opening also lets out the microwaves back to the magnetron).
One interesting possibility would be, rather than simply a rectangular box, to have a box with lots of small reflective tubes in the wall, with tubules emanating from those tubes, ever smaller, in a fractal like manner. By this means you could create very long light paths within a still limited physical volume.
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Yes.. I can see the problems in it.
But still, what actually happen to the light particles when it lose energy, or energy is absorbed by other things?
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Light is an electromagnetic wave, just like radio waves, so its interaction with matter is at an electrical level, with the electrons in the atoms. The electromagnetic waves are absorbed by the electrons and increase the energy of the electrons in the atoms.
I suppose the even more interesting question is why do some materials absorb light, some are transparent to light, and some reflect light (the same is true throughout the electromagnetic spectrum – a material that will absorb light may be transparent to radio waves, or rarely, visa versa).
A lot depends on which energy states the electrons are allowed to be in, and this depends upon the quantum interaction between the electron and its environment (the atoms it is bound to, and in metals, where electrons have some freedom to move between atoms, the entire lattice structure). If the energy that the electron naturally has, when added to the energy it would obtain from the light wave, would place the electron in an illegal state, then it cannot happen, so the electron will not absorb that light wave. If the state of the natural energy of the electron and the light creates a new energy level that is legal for the electron, then it will absorb that light wave.
It really requires somebody more skilled in quantum physics than I to explain the whole thing in more detail than that broad outline.
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Ooo.. Quite confusing, but I think I get it.. a bit.
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would it change if you designed a mirrored box inside of a mirrored room. could you build in a torch(flashlight) for obsevation also covered by mirrors that would be mounted through said mirrored box with only lens exposed. Also have a hidden tiny camera to record the experiment whilst you are in the box!You could do it with a one way mirror rather then a camera, or is that type of mirror one that would not work at reflecting light back,? Say you have a mirrored cover that is manipulated from inside the box to close off the light from the torch rather then a switch as then when the lens was covered it would also be a mirror reflecting rather then absorbing the light and you would be inside said box so no obsorbtion there. Leaving no door to be opened allowing light to escape!
Would the outcome be the same, and again I still don't get where the particals go and how this works..LOL
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According to George here, he still thinks that it will someway or another be absorbed, even if the mirrors are 100% perfect, although that suggests that the mirrors aren't 100% perfect. Ok, I'm getting confused [;D]
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By the way Seany...I taught George everything he knows !!
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It's a strange world we live in; people actually do something very similar. If you use a small room with just 2 mirrored walls and let one of them leak slighty you have the setup for doing what's called "cavity ring down spectroscopy". This is used to measure very small absorbtions of light.
There's a Wiki article but it's not very user friendly. http://en.wikipedia.org/wiki/Cavity_ring_down_spectroscopy
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Thanks bored chemist! will check it out! Cause I am still baffled myself!
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Some small amount (typically around 0.1% or less) of the laser light leaks out of the cavity and can be measured each time light hits one of the mirrors
From Wikipedia. 0.01%, although the speed of light is immense, is a pretty darn low percentage. Surely, wont the light keep reflecting for atleast 10 secs?
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No,not even a second. Imagine how many millions of times a beam of light could travel backwards and forwards between two mirrors 100 metres apart in just one millisecond . And each time it bounces its losing energy as its absorbed by the mirrors and the air its traveling through.
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Ahh... OK. I understand now [;)] But, if we assume that the mirrors do not absorb ANY light, in an ideal world, then would it carry on going.. going.. going.. going.
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Ahh... OK. I understand now [;)] But, if we assume that the mirrors do not absorb ANY light, in an ideal world, then would it carry on going.. going.. going.. going.
If one had such unrealistic assumptions (not only that the mirrors do not absorb any light, but that they do not let any light out of the room), and assumed that between the mirrors the medium was perfectly transparent, then indeed light could keep bouncing around forever.
The problem is only that this scenario would not be the real world we live in.
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Yep. If there was such thing though, if I just turn on the torch for 1 millisecond, then the room would be bright in that 1 millisecond right>?
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Can you turn on and put out your torch in only 1 millisecond? I think that's impossible.
Why a torch, why not a lightbulb or laser?
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Yes, OK Ben. A lightbulb, laser, LED, sunlight, same thing. Just any source of light.
And I don't mean a torch as such, even a machine. A machine could easily turn on and off a source of light in only 1 millisecond.