Does dark travel at the same speed that it takes for light to disappear or move on? Or does it have its own metrics entirely?
In: Physics
There isn’t technically a “speed of dark” at all. Darkness is the *absence* of light, it is not in an of itself a thing, therefore it can not have a speed. The word “dark” describes the concept of not having light, but it doesn’t refer to any actual physical phenomenon, it’s just simpler to say “it’s very dark outside” than it is to say “it’s very not light outside.”
That being said, if you turn off a light there is a very small delay between when the light goes out and when your eyes see the change. It’s basically imperceptible, but it can be measured.
As to the second part of the question: the speed is the same as the speed of light.
Here is an example…
What is the speed of an open road? We can measure the speed of cars, but what is the speed of the space between the cars? Well technically that space isn’t anything, the road isn’t moving and the space between the cars is just filled with air that isn’t traveling along with them for the most part. But there is a space, it’s just not a physical thing, it’s a concept. And as the cars move, the concept of that space moves as well. And what speed does it move at? The same speed as the cars.
Think of it another way, if darkness is just “not light” then what we are really measuring isn’t the darkness, we are measuring the speed of the *last light* that was emitted. As soon as that light passes, it leaves darkness in its wake. So the darkness “spreads” at the same speed that the light recedes and vice versa.
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