Ciro Santilli
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In special relativity, it is impossible to travel faster than light.
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One argument of why, is that if you could travel faster than light, then you could send a message to a point in Spacetime that is spacelike-separated from the present. But then since the target is spacelike separated, there exists a inertial frame of reference in which that event happens before the present, which would be hard to make sense of.
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Even worse, it would be possible to travel back in time. This can be seen clearly on a Spacetime diagram such as: Figure 44. "Spacetime diagram illustrating how faster-than-light travel implies time travel.".
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Figure 44. Spacetime diagram illustrating how faster-than-light travel implies time travel. Legend an explanation are shown in this answer.
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