Some setup is necessary before I can get to asking my question.
In Ken MacLeod's Newton's Wake, FTL is possible. There is a form of chronology protection:
Say ye try tae send a signal intae the past, or your ship’s course mucks about too much wi the light-cone consistency conditions. Ye’ll find the transmitter disnae work, or your course takes longer or goes a different way than you plotted it, or – as the saying goes – she was never your grandmother in the first place.
Chronology protection is leveraged in a combat scene to win a battle:
The other two friendly ships, having diverged, were again converging. Another of the enemy ships fittled [went FTL]. The Stanley Blade’s and the Small Arrangement’s trajectories instantly halted. The enemy appeared, as it seemed on this scale, right beside them, and as rapidly was destroyed.
‘Ya beauty!’ yelled Lucinda.
‘What happened there?’ Armand asked.
‘Chronology Protection trap. It came out of the jump just too far away to hit them, and it couldnae fittle the remaining distance without going outside its own light-cone or back in time. They had a moment while it waited tae catch up wi itself, fired off a nuke, and—’ She clapped her hands.
So on to my questions: when she says "couldnae fittle ... without going outside its own light-cone or back in time," I'm confused because any time you go FTL, you leave your light cone, and there exists some frame in which you appear to travel backward in time. But this character is talking like sometimes that isn't true. So what am I missing here?
My other question is, if the author's treatment of FTL travel makes sense here, what does it mean for the ship to "catch up wi itself"? It has something to do with waiting until causality constraints pass, but how exactly does it work? I can't quite wrap my head around it.