Mathematics
In JL Heilbron’s The Sun in the Church he states in his introduction, and in his 66th citation, “Among the old meanings of “Matematizzare”, to mathematise, was ’to cast a spell.”
Apparently, Einstein developed some equations but didn't like the result so he changed them to prove the point he had in mind.
Towards the end of his life he became increasingly uneasy with his Theory of General Relativity. It breaks down completely at the centre of a black hole, or singularity.
I'm no physicist but I bet there's lots of mathematics involved.
