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11 months ago in Philosophy of Science , Physics By Reno

Just before sunset, does your shadow move with infinite velocity?

This came up during a discussion about perception in physics. As the sun touches the horizon, the shadow elongation seems instantaneous. I'm curious whether this is an optical illusion or if it points toward a genuine relativistic or mathematical singularity in everyday observation.

     

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By Rohini Singh Answered 7 months ago

This is a fascinating intersection of perception and physics. In my experience teaching optics, the shadow doesn't move with infinite velocity. What you're observing is an angular effect; as the sun sets, its light rays become nearly parallel to the ground, causing your shadow's endpoint to project extremely far away. The rate at which this endpoint moves does increase dramatically, approaching a mathematical divergence, but true infinite speed would require an impossible instantaneous transfer of information. I’d recommend framing this as a classic example of how a mathematical model (like using similar triangles) can suggest a singularity, while the physical reality constrained by the finite speed of light and the sun's angular size remains finite and continuous. It's a perfect gateway into discussions about limits, models, and perception.

   

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