A question about the speed of light puzzles me

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Discussion Overview

The discussion revolves around the concept of the speed of light in relation to the movement of shadows created by a rotating light source, particularly in the context of whether the speed of a shadow can exceed the speed of light. The scope includes theoretical considerations and conceptual clarifications.

Discussion Character

  • Exploratory, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant proposes that if a light source rotates with the Earth, the speed of the shadow could exceed the speed of light due to the large radius involved.
  • Another participant clarifies that a shadow is essentially the absence of light and questions the definition of a shadow as an object with mass.
  • Some participants argue that shadows can move faster than the speed of light without violating physical laws, as they cannot be used to communicate information faster than light.
  • A later reply emphasizes that any change at the light source would still need to propagate at light speed, reinforcing that no physical object is moving faster than light.
  • It is noted that the shadow itself is not a physical entity moving in the same way as light does.

Areas of Agreement / Disagreement

Participants express differing views on the nature of shadows and their relationship to the speed of light, indicating that multiple competing perspectives remain without a consensus.

Contextual Notes

Participants discuss the definitions and implications of shadows, the nature of light, and the conditions under which speed comparisons are made, but do not resolve these nuances.

yeti1112007
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if there is a light source rotate with the Earth (w), so there must be somewhere in the

universe(r) the speed of the shadow of the light (v=r*w) would exceed the speed of light

because the r could be very large. Is it right?
 

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If I'm understanding you correctly, you are saying that the shadow that is produced from the pole blocking the light source, would travel greater than c.

First of all, the shadow is just the absence of light surrounded by light, or it could just be defined as empty space. Further more, if you defined the shadow as an object, it would have 0 mass.
 
Shadows can certainly move faster than the speed of light. This does not break any laws of physics, because it cannot be used to communicate any information faster than the speed of light.

- Warren
 
Right, any change at the source would still need to travel at light speed before it could be seen by the viewer of the "shadow."

Keep in mind that no physical object in your scenario is actually moving faster than light. The photons are still mvoing from the source to the distant viewers at light speed. The "shadow" is the absence of light, which is itself not a physical thing that's moving any more so than a dot on your computer monitor is physically moving across the screen.
 
ok, I see.
 

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