- TL;DR Summary
- A request for notational clarification in an old paper
I'm reading Tipler's 1976 paper, "Causality Violation in Asymptotically Flat Spacetimes" and he keeps using a symbol which seems to resemble the symbol for Future Null Infinity in a strange font, but it's usage doesn't make sense with what I would expect if that's what the symbol meant. He doesn't define it anywhere in the paper, so I assume it must be standard notation that I'm missing. The symbol in question is the one that in the first photo we're interested in the causal past of, and in the second photo, we're evaluating at the point q.