There are a lot of unanswered questions in both QM and GR. The major thing about both of them is that they work. They are really strange and trying to figure them out is impossible for most of us. But I'm not going to give up, after all, they do describe the world as we see it. It is just that we don't really 'see' it the way they describe it.

And of course Einstein really didn't like a lot of things about QM, even though he did a lot of the work that led up to it.

Bill Gill

C is not the speed of light in a vacuum.
C is the universal speed limit.