Dear PF Forum, I've tried to googled how causality can happen by FTL communcation (I use communication, because if it "travels", I'm having trouble calculating ##\gamma## imaginer). But from all examples that I've found it can violate causality if one of the party is moving relative to the other? I can 'understand' that picture above about violated causality if one of the party is moving. Is there an example about violating causality if one of the party is NOT moving? Thank you very much.