Greetings,
I have had an idea about what I call Perpetual Light for a long time now, and this is a good forum in which to discuss it.
If you had a hollow cube, with all 6 sides being perfect mirrors, and you somehow (magically?) introduced a brief light source inside, would the light reflect indefinitely? I have the feeling that thermodynamics is going to knock this one out of the ring, but gee, wouldn’t it be cool to show your friends? I think a sphere that is hollow and mirrored on the inside might even be a better construction for this.
Incidentally, the movie Hellraiser 4: Bloodlines shows the creation of perpetual light as a means to vanquish the bad guy with nails in his head…neat-o.
Please do what you can to lay this problem to rest once and for all…I’ve been chewing on it for years, and nobody ever seems to have any ideas.
Best,
JimmyD
“Condensing fact from the vapor of nuance”
The whole thing hinges on your “perfect” mirrors. Of course there is no such thing. Every (macroscopic) mirror reflects a little less light than it receives.
I added the “macroscopic” qualifier because I imagine it is possible to have a quantum-level mirror with no losses. Weird things happen in the world of the ultra-small.
Since light travels so swiftly a light ray performs about a zillion reflections in a few nanoseconds. Even if the mirror were 99.99% reflective all the photons would quickly be absorbed.
BTW, the problem of inserting a little flash of light is really not hard. How about a flashbulb in an electric circuit on a timer? Set the timer, close the box and – if it weren’t for those darned imperfect mirrors – perpetual light!
I thought of a clever new sig line last night, but I forgot it when I woke up this morning.
I still think a sphere construction would be optimal for this. However, the problem also comes in from the light source introduction: I like the idea of the light inside on a time, but there cannot be anything blocking the path of the light.
With perfect mirrors, could the photons bounce indefinitely? Is this some law of thermodynamics that would prevent that from happening? Somehow, a laser would have to penetrate the shell of the sphere and let it bounce.
Of course, how does one prove that the light is still reflecting?
Yes, there is a thermodynamic principle that will bite you no matter what. Every reflection will jostle the reflector a tiny bit. That’s the basis for the imperfect reflection – some energy goes into jostling the mirror. Another name for jostling molecules is heat. The second law of thermodynamics states, roughly, that all energy eventually ends up as heat.
Your description of a reflecting sphere is close to an actual device – a blackbody radiator. Take a hollow sphere made of a perfect absorber and drill a tiny hole in one side so you can see what’s going on. There will be some radiation inside – not light, necessarily, maybe infrared radiation. The radiation is absorbed by the walls of the cavity and then re-radiated. The radiation quickly reaches equilibrium, with as much being absorbed as emitted. The radiation in the cavity has a characteristic spectrum dependent only on the temperature of the cavity.
Other than the fact that it presumes a perfect absorber rather than a reflector, which turns out to make no difference, here is your perpetual light device. Of course it’s not really perpetual – any light that escapes through your peephole needs to be replaced.
I thought of a clever new sig line last night, but I forgot it when I woke up this morning.
It sure would be nice to show it to your friend’s but if they looked some of the light would have to impact their eyes (which aren’t perfect reflectors) and the light would be lost that way. It would only be perpetual if no one looked at it and no instrument measured it. And then your problem becomes explaining to people how something is perpetual when you can’t even prove it is happening.
