Darkness travels at the speed of light. More accurately, darkness does not exist by itself as a unique physical entity, but is simply the absence of light. Any time you block out most of the light – for instance, by cupping your hands together – you get darkness. In the context of talking about speeds, darkness is what you get after the light stops coming, and therefore travels at the speed of light. For instance, consider that you are in distant space, far from all light sources such as the sun, and you have a light bulb on the nose of your space ship. The light from the light bulb is spreading out in all directions through space at the speed of light. If you briefly turn off your light bulb and then turn it back on, there is light traveling out in all directions from before you dimmed the bulb, and behind it there is light traveling in all directions from after you dimmed the bulb. But between the two spheres of light there is no light, because no light was created when the blub was briefly off. And no light means darkness. So there is a band of darkness in between the two spheres of light. Since both spheres of light are expanding outwards in all directions at the speed of light,