Question

what is the speed of dark?

if the speed of light equals c. what is the speed of dark

Answer 1

Imagine the following thought experiment.

The earth receives light from the sun. The light , with it's finite speed takes about 8 minutes to reach the earth (approximately)

Now, let us say that the sun continuously kept emitting small photons of light and then at a certain time , call it t=0, the sun vanished.

No more photons are emitted.

Now, the previously emitted photons would keep reaching earth. The last photon every emitted would take 8 minutes to reach earth from the sun.

Then, the earth would suddenly become dark. (after the last photon came to earth)

Thus, it took dark 8 minutes to reach earth from the sun. Thus, the speed of dark is equal to the speed of light.

This is because if it takes a time t= x/c for a light signal to reach us, then it also takes a time t= x/c for the stopping of a light signal to reach us. Dark is just the cessation of a light signal.