>>14267070It's possible, but it does require a lot of time and experience. It's actually fairly common for non-academic routes for scientists to flip fields and become experts in something tangentially related. You could argue that the field of NLP required expertise in both linguistics and math, although the subjective term here is "expert".
I got my PhD in cell bio, switched fields after PhD and am now an "expert" in ML; I went from publishing cell-bio exclusive papers to cheminformatics papers to now a couple of ML-exclusive papers
I have a friend who got a masters in language something or another, and I've been helping him on a pet project for a year and half now, where I'm not necessarily an expert but we could publish some NLP papers if we really wanted, we've made a few discoveries we think might warrant an arxiv upload.
If by "expert" you mean "could I win a nobel prize in two fields simultaneously", that's like asking "can I win the lottery twice", because nobel-prize winning work is usually right-place, right-time, and the impact on the field is only know after it's been published and used
