See also https://arxiv.org/pdf/1211.6468.pdf https://arxiv.org/pdf/1211.6468.pdf, which accompanies a theory recently published in the Archive of Formal Proofs:

See also https://arxiv.org/pdf/1211.6468.pdf https://arxiv.org/pdf/1211.6468.pdf, which accompanies a theory recently published in the Archive of Formal Proofs: http://www.isa-afp.org/entries/No_FTL_observers.shtml http://www.isa-afp.org/entries/No_FTL_observers.shtml It states rigorously what it means to be an object ("observer"), and what it means to travel faster than light, and proves that observers cannot travel FTL. In special relativity, though, not GR yet.