Off the top of my head: From the invention of the plus sign to the integral sign, Greek letters up the wazoo (and graphically futzing with them), logical notation, bra-key, Feynman, Penrose graphical notation.
This is what im thinking about: One could get by for a while without a multiply sign; but at a discrete point in time somebody worked out that adding repeatedly could be subsumed by a new symbol.
Ok, that’s a question 1) regarding symbols:
what/when/how/which symbols are created when a tipping point is reached, in whatever field (pure math, all the sciences).
Engineering, computer science, resource management–and hundreds of fields of investigation which i have no conception of–are invited. Engineering and CS may become unmanageable for fascinating reasons I can’t put my finger on, perhaps because they relate so strongly to question 2).
Question 2) some symbols are ad-hoc–like writing a long phrase and then "hereafter [abbrev.].
In math, “that thing we’re looking for” became x. I believe this is considered, like the numeral zero, a big deal for two reasons: conceptual novelty and it’s critical naturein the project of algebra and arithmetic, respectively.
I have Feynman diagrams in mind for a different application. If this wrong in itself it would be good to hear, and could elucidate the questions.
I believe my questions, hazily explored here, are in the main understandable.