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If you build a arbitrarily large Dyson sphere, the shadows cast by planets orbiting the sun inside the Dyson sphere onto the inner surface of the Dyson sphere w
by roywiggins 3y ago
If you build a arbitrarily large Dyson sphere, the shadows cast by planets orbiting the sun inside the Dyson sphere onto the inner surface of the Dyson sphere will appear to "move" arbitrarily fast.
If a planet orbits in, say, a day, its shadow will make a full circuit of the Dyson sphere in a day. Make the circumference of the Dyson sphere larger than a light-day, and now the shadow is "moving" faster than light.
- samatman 3y agoYes, but if the Dyson sphere is 2 light hours away from the planet, the planet will cross the actual geometric line between the Sun and a given point on the Dyson sphere two hours before the shadow is visible. What you're saying is like saying that vision is faster than light, because I can look at Sirius, and then look at Aldebaran a second later.
- roywiggins 3y agoWell yeah, that's why I said it appears to move. Shadows aren't objects at all so they don't really move, but colloquially we think of them as moving as much as we think of a laser dot moving (which also can "move" faster than light).