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Comment by mr_mitm | Hacker News Reader

Plus, any FTL signal will violate causality.

The speed of light being a speed limit is a consequence of the geometry of spacetime. I'm convinced FTL is as impossible as it is to have an angle greater than 180 degree between two lines in Euclidean geometry.

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> Plus, any FTL signal will violate causality.

I have to say I'm uncomfortable with the idea that we've discovered everything there is to know about the physical rules of the universe.

Me too, and that is indeed not what I said.

"I'm convinced FTL is as impossible", with causality as the apparent reason, would seem to imply a belief that we understand that particular concept fully.

It is as firm as our understanding of gravity. There is still plenty left to learn about gravity, but if I throw a ball into the air I'm pretty damned certain it will fall back to the ground. The fundamentality of c as a limit of information propagation is one of those properties that has shown itself to be true so often that anything showing it false is considered a mistake until we can prove otherwise. Conservation laws are similar.

Sure, any reasonable scientist would tell you that there is a non-zero chance that we're wrong about these things and both perpetual motion and FTL are actually possible, it's just that we have an extremely high confidence they're not.

We've definitely discovered that the speed of light is a constant in all reference frames. That's sufficient (IIRC anyway) for FTL to violate causality, regardless of whatever we may discover in the future.

Well we have only ever measured the round trip speed of light. Our current understanding of physics seems definitely imply the one way speed should be the same, but we have not been able measure it. If it some reason does turn out to be different then rate at which causality moves then depends on direction. https://en.wikipedia.org/wiki/One-way_speed_of_light

Maybe it suffices to say that as long as all experiments continue to be consistent with light being the same speed in all directions, all experiments will also continue to be consistent with FTL breaking causality, so bringing up a barely, hypothetically possible conspiracy of reality against experiment is a distraction at best.

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