LLMs are aggressively trained to reproduce facts and consequently struggle to reject orthodoxy. There isn't any reason they can't, in principal, make big new discoveries just by getting lucky, which is sort of also how humans do it, but its ok to acknowledge that current AIs aren't so good at certain things.
So if the speed of propogation of EM waves is the same no matter your frame of reference (along with all the rest of physics) then the speed of light can't be relative (a conclusion that was aided by the Michaelson-Morley experiment) and what are the logical consequences of that.
If I'm incorrect in my understanding I'd appreciate any correction.