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Can a shadow move faster than the speed of light?

Image a plane flying over a cityscape near the equator with the sun directly above the plane so it casts a sharp shadow on the landscape below. When the plane passes over a tall vertical sided building, does the shadow move up the side of the building faster than the speed of light?
Christopher Barrow from Leicester (Age 45-54)

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3 Responses

  1. Yes the shadow can move faster than the speed of light, but since no physical object or information can be passed between the top and bottom of the building by doing this then the principle of relativity (that nothing can move faster than light) hasn’t been violated.

    Imagine you have a very powerful torch and you point it at a star, now you move your torch and point it at another star in a different part of the sky. These stars are at least a few light years apart, so the ‘end’ of the beam of light moves faster than the speed of light, but the situation is the same: you cannot pass any information this way so relativity survives.

  2. “Imagine you have a very powerful torch and you point it at a star, now you move your torch and point it at another star in a different part of the sky. These stars are at least a few light years apart, so the ‘end’ of the beam of light moves faster than the speed of light, but the situation is the same: you cannot pass any information this way so relativity survives”

    this entire statement is based on a false concept of a “BEAM” of light. The beam is composed of photons. These photons are discrete individual items, and moving the beam simply causes the NEXT photon to come out of the projector to have a different vector from the last. NOTHING is moving faster than light here. It is an optical illusion based on the fact that the beam of light approaches visually infinite distance, and so appears to be “touching” the distant object. In reality, the beam of light is nowhere NEAR the star when you see it… it will not be for hundreds, or even thousands of years. When you sweep the beam across the sky, what you are really doing is scattering photons across the sky.

  3. I would say no, since a shadow is the absence of light and therefore nothing is moving.

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