Some memories from meeting Albert Einstein in 1951-52
cqgplus.com
cqgplus.com
There's beginner, and then there's 'beginner'.
I don't know about the "quasis" but it sounds like a linear algebra problem. Hyperbolic might be the form of the solutions to each of the differential equations, or of their combined solution. "Lorentzian metric" presumably means the usual Minkowski space of relativity.
If you want to explore this topic from another point of view, get to know the work of Jeremy Bernstein, a theoretical physicist and long-time writer for The New Yorker. Bernstein also spent some time at the IAS when he was a young scientist, and has written a great deal about Einstein.