# Am I faster than my shadow?

I guess that everything that happens to me (or I do), happens before my shadow "records" the information. Is that right? Is it the same for any observer?

-
Imagine a much slower speed of light. If you accelerate, the speed of your head's shadow will be slower as the ground is recieving light (and information about the blockage of light) from yourself a few seconds ago. Note that I'm assuming detectors on the ground, not eyes, measure the speed of shadows. –  Alyosha Dec 13 '12 at 13:28

It depends on the situation and interpretation, but it certainly can be the case that your shadow is faster than you. If you imagine a single spotlight shining in front of you, you would cast a shadow behind. If the spotlight moves to behind you, even if you stand still, your shadow will move to the other side. Depending on the distance of the object onto which the shadow is cast, this "motion" of your shadow can be very fast indeed; it could even be faster than the speed of light!

By another interpretation, you are only very slightly faster than your shadow. Again, imagine the spotlight in front of you. This time the light stays still, but you hold your arm out and sweep it up. As light from the spotlight passes you, your arm reflects or absorbs some of it; the wall behind you reflects only the light that falls on it which corresponds to the light that did not fall on your arm, this is the shadow. As you sweep your arm upwards, the pattern on the wall follows the movement. However, because it takes some time for light to travel from the point where it passes you to the wall, the shadow will slightly lag your movement. For real life cases, this lag is miniscule, but if the wall were a sufficiently long distance away, it could be significant. When you consider the added distance from the wall to the observer, the apparant lag time increases.

-
Not sure that observer always sees greater lag. What if the observer is on the wall? Or behind it on the same line the light traveled? –  Paolo Dec 13 '12 at 15:37
Unless the "observer" is the wall, then there will always be a greater lag to account for the time of light travel from the wall to the observer. This does, I guess, assume that the person, the wall, and the observer share a reference frame. If you wanted to get into relativity, you could change things however you like. –  AdamRedwine Dec 13 '12 at 16:54

Your Shadow is the absence of light done by yourself . So it can be faster than you .

-
Surely it depends on what one means by "faster" no? –  AdamRedwine Dec 13 '12 at 12:56
Yes, I agree with Adam, the edge of the shadow is the union of the loci of intersection of the bounding light rays at the edge of the dark region. Being loci,they can move at any speed. Imagine a flashlight behind you casting your shadow on the moon (it's a powerful flashlight and we'll turn off diffraction!), if you move a bit your shadow will move awfully fast! –  twistor59 Dec 13 '12 at 13:37