How? If I understand the question - just like everything else. (Bends light, for example.)

yess, but then the numbers that power quantum physics stop working. something about the renormalization group?

My incorrect understanding is something like: quantum models imply a uniform layer of “virtual” particle/anti-particle pairs popping in and out of existence. but if the space they’re in is curved like general relativity describes, then the pairs don’t find each and annihilate each other reliably and all your math trends towards infinity instead of towards zero. or something vaguely like that.