How can the universe be endless?
According to one model by Einstein , he put it at 10^8 light-years back in 1932.
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: