Take the image below for example:

For the shadow to travel from point A to B would be extremly fast on the surface on the moon but probably not breaking the speed of light. But if the moon were 20 times larger then it would appear that the shadow would be travelling 20 times faster appearing to break the speed of light on the surface of the moon.

So in essence the bigger an object is the quicker that shadow would appear to move on the surface of that object.

So what does this mean in terms of breaking the speed of light?

Also for interesting purposes, what is the speed of dark (if it even has a speed?)

enter image description here

  • $\begingroup$ Remember that a shadow is just a collection of points in a pattern where there is no light. If you turn on/off the light at different points, then these points are lit at the speed of light, but doing it in the right sequence where you keep the shape of the shadow can make the "illusion" of the shadow as an object moving. $\endgroup$
    – Steeven
    Aug 14, 2015 at 7:58
  • 1
    $\begingroup$ This is a duplicate question. See physics.stackexchange.com/q/63434 and physics.stackexchange.com/q/48328 In short, shadows can break the speed of light, but they not contradict relativity, since no information can travel with the moving shadow. There is no limit to the speed of darkness. $\endgroup$
    – sintetico
    Aug 14, 2015 at 8:14


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