In special relativity, it is impossible to travel faster than light.
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.
Even worse, it would be possible to travel back in time. This can be seen clearly on a Spacetime diagram such as: Figure 48. "Spacetime diagram illustrating how faster-than-light travel implies time travel.".
- https://www.physicsmatt.com/blog/2016/8/25/why-ftl-implies-time-travel shows the causailty violation on a spacetime diagram
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