Why can't light be in black color?

[zinq]

You can define anything you want (that makes sense); such definitions are not "wrong".

In mathematics, a hole in a space is a very precise concept, that most certainly exists.

There is nothing wrong with defining darkness as the absence of light.

But do no confuse it with light, which carries energy and wavelength, can be a wave or particle, etc. Dark could be defined as the zero element in the (portion of) the infinite-dimensional Hilbert space that comprises all possible light rays. But it is different from the nonzero elements, in that it doesn't "carry" any information, since it doesn't "go" anywhere.

IF we wanted to make sense of "the speed of dark", that might actually make sense: Suppose we are continuously shining a light at a screen at a distance D away. Suddenly we turn of the light source; assume for simplicity that the light emission stops instantly. Then if as usual, c is the speed of light, the screen should stop reflecting light at a time equal to D/c later. So in this sense the speed of dark is the speed of light.

 

[Drakkith]

IF we wanted to make sense of "the speed of dark", that might actually make sense: Suppose we are continuously shining a light at a screen at a distance D away. Suddenly we turn of the light source; assume for simplicity that the light emission stops instantly. Then if as usual, c is the speed of light, the screen should stop reflecting light at a time equal to D/c later. So in this sense the speed of dark is the speed of light.

Now take that light source and sweep it across the screen. What is the maximum speed of the shadow/light spot across the screen?

 

[zinq]

Sure, no maximum, but that's not dark "moving". Because, in no sense is the shadow at one location the "same" as the shadow at another location. Nothing moved, so no speed is relevant.

 

[Grinkle]

What is the maximum speed of the shadow/light spot across the screen?

Musn't it be c, since we could never measure with any experiment that it were faster?

 

[Grinkle]

If dictionary.com is an acceptable reference, then below citation should resolve the question of whether black is a color. ;-)

noun
20. the color at one extreme end of the scale of grays, opposite to white, absorbing all light incident upon it.

 

[Drakkith]

Musn't it be c, since we could never measure with any experiment that it were faster?

Sure we can. Place two light sensors on the screen some distance apart from each other and then sweep the light across them. You'll find that the difference in the time that one sensor goes on/off and the other sensor goes on/off can be anything from 0, corresponding to just pointing the light source directly at the sensors and turning it on or off, all the way up to any value, corresponding to how fast you sweep the light source across the screen.

Sure, no maximum, but that's not dark "moving". Because, in no sense is the shadow at one location the "same" as the shadow at another location. Nothing moved, so no speed is relevant.

The only stuff that moved was the light on its trip from the light source to the screen. But that's not any different from your example. It still makes little sense to talk about the speed of darkness.

 

[davenn]

Get real Dave! Read a book called The Shadow Club by Roberto Casato. It should make you more careful with such assertions.
A hint: before claiming that an entity exists or not, you should analyse its nature.
Would you say that a hole in the ground does not exist? Or a hole in a semiconductor?

back off Jon .. stop being obnoxious !

 

[Drakkith]

I think this thread has gone on and off topic long enough. Since the original question has been beaten to death as well, I'm locking this thread. Anyone interested in the 'speed of dark' or something else in this thread can start a new one.