Tripping the light fantastic...
Tripping between universes can happen as a single individual or a handful. Most Natural* trippers will be single individual when they trip for the first time, though pairs or even triples have been known to occur.
What does happen is that people from different verses initiate all at once and arrive together. These trippers become linked by the shared experience, a bond only death can break.
Quite often a first trip is literally that, a trip flash stars and you are somewhere else. After only a few trips however the signs of an impending trip and proximity to a trip point starts to become apparent. Its as if the fact that you are tripping increases your sensitivity to it.