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c4c313.jpg
Prince Emerald Fluff
c4c313
Sorry for the thread derail for a moment there. I do so enjoy non-Euclidean physics, regardless of how poorly I can calculate the exact equations. There are many reasons it's "impossible" to go faster than the speed of light, and one of them is the fascinating time travel implications.
My favorite example is travelling between a supernova and a nearby star. (Thought this quest was inspired by that thought experiment initially.) Suppose you went 2x the speed of light away from a star going supernova, to another star one light year away. If you looked out the window upon arrival, you'd be seeing light from the supernova a year ago, when it was still an ordinary star. It would effectively seem like you were a year in your own past, and if you waited a year, the light would catch up and you'd see the supernova.
If instead of waiting, suppose you cause this second star to supernova, and flee from it back to your original location at again 2x the speed of light. Once you reached your original location you would be seeing light a year in the second star's past, and you'd have to wait a year to see that second star to supernova.
I don't know exactly how the geometry works out, but once you account for relativity things get impossibly weird in this situation. From the perspective of the second star, it goes supernova immediately, and then your original star goes supernova one year later. So if you were seeing light one year before the second star's supernova, your original star couldn't supernova for 2 years, otherwise the light of its supernova would reach the second star too early! When you left your original star was going supernova immediately, but when you returned it wasn't going to do so for another 2 years. So faster-than-light round trip space travel is effectively the same as travelling backwards in time, to a universe in a state of lower entropy than before. That violates thermodynamics (since entropy can never decrease ever) and causality, since you would return to your original star 2 years before you even left!
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