Question

How big is the universe in AU?

Answer 1

According to one model by Einstein , he put it at `10^8` light-years back in 1932.

Explanation:

What is know as "Einstein's Forgotten Model of the Universe" is worth looking up.
In a 1931 paper he described a universe that expands after the Big Bang and then contracts-- called the Big Crunch.

Maybe an oscillating universe? Much like the Hindu cosmological cycle?

For details check out this paper:

https://arxiv.org/abs/1312.2192