# ELI5, does DARK have a speed at which it travels, in the same way that LIGHT does?

441 views
0

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

“dark” is the absence of light. so it moves at lightspeed if you want to give it a speed, but in general it doesnt make much sense to define the speed of “nothing”.

Light is a wave (enough of the time for this to work). So imagine you have a long piece of rope attached to the wall near the floor and pulled out perpendicular. You can give that rope a snap and send a pulse down it. If The speed of the pulse represents the the speed of light, then what you asking is what speed does the rope return to flat. So yeah, I think as far as we can talk about the speed of the returning absence of something, in this case light, the speed of dark is the speed of light.

Adding to the other comments, there is a nice video on youtube about this exact question by vsauce. As far as I remember shadow’s can move across a surface faster than light, but not in a way that it would be able to transfer information.

I think the ‘speed of dark’ is probably the amount of time it takes to go from light to dark after moving light across a surface. So wouldn’t it kind of be the same?

From the incomparably hilarious Terry Pratchett: “Light thinks it travels faster than anything but it is wrong – no matter how fast light travels it finds darkness has always got there first and is waiting for it”.