Logically, there can be no darkness without the existence of light. Think of a bright day accompanied by the shadows that the sun casts when blocked by something like a streetlamp.
Darkness is simply the absence of light, so it follows that it travels at the speed of light. The absence of light, or darkness, is determined by when the light stops travelling. Imagine the sun was shining its rays to Earth and there was a sudden blockage of the light.
If, somehow, something blocked the sun and the light that reached us at a speed of 299,792,458 m/s, the darkness that follows would be right after the light, and therefore be travelling at the same speed.
On a smaller scale, imagine a camping light hanging in a tent. The light emitted from the bulb is covering the whole inside of the tent in all directions. There is a blip in the light that it emits. So, the light that the bulb has already emitted is still travelling at the speed of light and reaches your face at that speed.
Then there will be a band of darkness to follow, this will also reach you at the speed of light. After the blip, the light returns and the band of darkness that travelled to you and the rest of the tent is replaced by another band of light. If this were to happen repeatedly throughout the night, imagine the waves of light and darkness that would be travelling at the same speed as one another in the tent.
The shadow that is formed by the streetlamp when it obstructs the sun is formed at the exact time that the sunlight hits the lamp itself. Therefore, darkness travels at the same speed as light, meaning it will take around 8 minutes and 19 seconds to reach Earth if the sun was ever blocked like in our previous analogy.
It can be hard to picture something like darkness having a speed. this is because we are so used to learning that light, something more visibly tangible to us, has a set speed. But light and darkness come as a set duo.
They are almost always found together, wherever there is a source of light in a room, you are definitely going to find darkness in the form of a shadow or the absence of light.
Think of darkness and light as a double act, with darkness always following light around the stage in quick succession. It may always come after the band of light, but it is just as quick as light itself.
To put it simply: darkness both follows and accompanies light. When we take the sun as an example of light, it is clear that the sun can cast shadows when its light is met with an obstacle.
The fact that makes it clear that darkness is just as fast as light, is that if the sun were to ‘go out’, it would take 8 minutes and 19 seconds for the last light to reach us on Earth, but it would also take that same 8 minutes and 19 seconds for the following darkness to reach Earth in the light’s absence.
So, the speed of dark is just the same as the speed of light, at 299,792,458 m/s. And will typically be found wherever you can see any source of light, I the form of a shadow or even just a dark room.
