He doesn't pay TAs. The university does. They work for the university, not for individual professors. If you have no idea how teaching works in US universities, probably better not to comment on it.
Thanks for explaining to me how the academic system I work in functions. Just like most managers don't literally pay their employees, the company does. The university pays TAs through funds from their various revenue streams, including endowment, tuition, grants to the university, and through indirect costs collected from research grants to researchers, probably including Borcherds own grants. So really a lot of different things pay the TAs, the university is just the clearing house.
faculty research overhead pays for department TAs. that's why departments with rich professors maintain their TAs even through budget cuts.
> If you have no idea how teaching works in US universities, probably better not to comment on it.
define:irony
The majority comes from tuition budgets, which are assigned per credit-unit. This also pays for faculty salaries. Math is heavily dependent on tuition because they get little overhead. Life sciences is buying millions of dollars of equipment, chemicals, animals, lab staff that incur overhead, none in math.
>departments with rich professors maintain their TAs even through budget cuts
In fact the University of California does not get to keep any overhead. It goes right back into the State of California General Fund and the CA Legislature, as part of the budgeting process, decides where it goes (obviously considering where it came from). During a budget squeeze, overhead can be diverted elsewhere.
Because of this, for a number of years, it was unknown whether the research enterprise at the University of California was actually covering its overhead costs or operating at a loss.