Way back in 1931, Albert Einstein visited the US for three months. Inspired by meetings with Edwin Hubble, he began thinking about the universe differently, writing a paper in four days to get down his thoughts—and now, those scribblings have been translated into English for the first time.
"On the cosmological problem of the general theory of relativity" explains a model universe that first expands and then contracts, with a singularity at the beginning and the end. In other words, a Big Bang followed by a Big Crunch.
A precursor to a proper piece of work published by Einstein and mathematician Willem de Sitter in 1932, this paper was a vital stepping-stone in his thinking. The arXiv blog explains that it gives an interesting insight into the work of a physicists in a rush:
[I]t assumes a universe in which the fabric of space-time has a positive curvature. That was necessary in Einstein's steady-state model of the universe. But he later discovered that it was unnecessary in an expanding model which could have positive or negative curvature or be flat. Indeed, the possibility that universe could be flat was one of the features of the Einstein/de Sitter model a year later.
One of the most interesting aspects of the paper is that Einstein uses this model to calculate the size of the universe, which he puts at 10^8 light-years or 9.5×10^25 centimetres in radius (several orders of magnitude smaller than today's estimates).
To make this calculation, he estimates the age of the universe at about 10 billion years old. (The current consensus is that the universe is about 14 billion years old).