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The thought experiment is to glue a "bat" figure on a light source (e.g., lamp). The shadow created by the bat figure is projected into the void, as in Batman. The trick is to rotate the lamp. As the lamp rotates, so does the bat shadow, projected into the space. The trajectory of the shadow is a great circle with the lamp at its center. (Actually, the "circle" itself will be expanding at the speed of light, but the author ignores this aspect, as far as I can tell.)
At a sufficiently large distance from the lamp, the circumference of the circle will have expanded to such a great length that the shadow will be rotating at a speed exceeding the speed of light. At least, that's what I understand the article to be saying. The author does not explain (nor do I remember) the formula tying the speed of the shadow to that of the lamp, but the principle must be similar to the concept of "gear ratio."
The author then goes on to explain how that does not violate relativity.
Comments?
At a sufficiently large distance from the lamp, the circumference of the circle will have expanded to such a great length that the shadow will be rotating at a speed exceeding the speed of light. At least, that's what I understand the article to be saying. The author does not explain (nor do I remember) the formula tying the speed of the shadow to that of the lamp, but the principle must be similar to the concept of "gear ratio."
The author then goes on to explain how that does not violate relativity.
Comments?