padpowell@wateng.UUCP (PAD Powell) (12/03/84)
Seeing how we have covered large capacitors, frequency shifting, etc.,
how about something really interesting.
What is the speed of dark? This came up in an experiment when we were
fooling around with illumination. Given a light, and a room, how long
did it take to become "illuminated?" I was describing the problem to
my experimental animals, and then one of the kids said, "Yeah, that's
the speed of light, but what's the speed of DARK?" One then pulled out
a Garfield cartoon, where the same question was asked. O.K.- What is
the speed of DARK?
Patrick ("Ever have one of those sleepless nights?") Powelljj@alice.UUCP (12/04/84)
Well, I'm a bit curious as to how one defines dark. To define it as the absence of all light more or less requires that the temperature of the area be at absolute zero. Seems to me that I could extend that to require absolute vacuum, too, but I'm not sure, and in any case, it's moot. In accoustics, the "speed of quiet" so to speak, is defined by something called the T60 of the room. A room's T60 is defined as the time in seconds required for an impulse to decay by 60 dB, including all echos, etc. I suspect that a similar measurement could be designed for "speed of dark", although it seems that the greater absorbtion of materials coupled with the speed of light would lead to VERY short D60's (to coin a measurement) in all but the hugest of locations. Let's try a defination for "dark". I hereby propose that the threshold of "darkness" is calculated in the following manner: Consider a spherical shell, of interior radius 1 meter, with the interior of the shell representing a perfect black body. Consider that that shell is at exactly 373 degrees K. Measure, with a probe that has no effect on the EM radiation, the absolute EM spectrum at that point, averaged over, perhaps, 1 K seconds, and define that as the threshold of darkness. Then, any space can be said to be dark if no point in that space has any spectral line that exceeds that of the threshold, when measured by the same probe. Enjoy. P.S. One could also define D-time as the length of time that is required for a standard energy density (say that of daylight), to decay to the darkness threshold.
ltn@lems.UUCP (Les Niles) (12/10/84)
[] In article <alice.3140> jj@alice.UUCP writes: >... >I hereby propose that the threshold of "darkness" is calculated >in the following manner: > >Consider a spherical shell, of interior radius 1 meter, with the >interior of the shell representing a perfect black body. Consider >that that shell is at exactly 373 degrees K. Measure, with a >probe that has no effect on the EM radiation, ... > Sorry. Ever hear of quantum mechanics? There is no such thing as a probe that has no effect on the thing being measured. -les niles