Yes, in a mirrored room, the light fades away when you turn off the light switch. Let’s say you’re in a 12 foot wide room, and the mirrors are 99% reflective. Light travels a foot in a nanosecond, so every 12 nanoseconds, a wave of light will lose 1% of its brightness. After it bounces off the mirror 500 times, it will be reduced to only 1% of its original brightness. 500 bounces takes only six microseconds! Way too brief for you to detect it with your eyes and brain.
In fact, the filament of an incandescent bulb will get less bright when you turn off the electricity, on a time scale in the tens of milliseconds, thousands of times slower than the light fades by bouncing around. Even if you had a light bulb that shut off instantly, the switch would be the limiting factor - you can’t get a switch that interrupts a current flow in less than a millisecond or so (without spending thousands of dollars).
Actually, it’s pretty easy to shut off the current to an incandescent light quickly. A semiconductor switch (such as a triac, used in standard light dimmers) will turn off the current in a microsecond or two. To get down into the nanosecond range would require serious effort, though, at 120 volts and an amp or two (for 100-200W bulbs).
As you said, the filament will be glowing LONG after the current goes away, and the light has bounced around the room! Long, relatively speaking that is
If noise = sound, and sound = air pressure waves, then yes, the proverbial tree even makes a noise.
So really, it depends on what the definition of the word “is” is… Defining your terms seems to be the whole point of the exercise. In the context of noise = sound = longitudinal pressure waves in a material medium, one could claim that even if the tree didn’t fall, it still made noise (say, as its roots absorbed water), it’s just that that sound was too small to be heard.
Not that anyone seems to have noticed my previous post, but I should point out that I forgot to specify that the interior of the ball has to be a perfect vacuum (another minor inconvenience for someone to work out).
I don’t mean to hi-jack my own OP, but to hell with fading light, if you could invent that “perfect mirror”, given some peoples predisposition to vanity, wouldn’t you be a millionaire in about 10 fucking minutes!?
The answer to the tree falling in the woods question is: No. (I was there.)
As for the light question, when you turn off the light bulb, all the darksuckers come out instantly and devour the light. Either that or light is an illusion. The sun is 93 million miles away, the earth is lit up by the sun, but it is dark in between. The darksuckers at work again. :D:D
Nick:
Photons act as waves and as particles. As such, they can meet and not hit each other. Look at ripples in a full sink. You can put two fingers in at the same time, creating two different patterns of ripples. Where they meet, they will not ‘crash’, but will create an interference pattern. Just one of the interesting things about post-Newtonian physics.
Actually, no. Separate photons cannot stop or redirect each other, unless you count gravitational effects, which are completely negligible for our purposes. A photon can, however, interfere with itself, if it runs into itself. Yes, I know that sounds weird-- That’s the quantum mechanics that I warned you about. You see, in QM, if a particle has more than one possible path to follow, it will, in a sense, follow all of them at once. When it’s detected, it may become definite which path it followed, but in the meanwhile, it’s possible for the existence of those other paths to influence the behavior of the particle. This can cause the production of interference patterns, where some regions are dark and others are illuminated. The most familiar example of this is those rainbow glasses you sometimes see, that produce multicolored rays around light sources when you look through them. Each color has a different pattern of light and dark, and when you put them all together, you get those rainbows. Even in this case, however, energy is still constant, it’s just distributed a little differently. You have some regions that are twice as bright as they would be without interference, and some that have zero brightness, but the total brightness is always the same.
