In Conways game of life, there is a the concept of an [orhpan pattern.][1]

Basically, an orphan is a finite pattern such that each configuration containing that pattern is a Garden of Eden (a pattern that cannot have a predecessor).

The smallest such pattern has not been found yet. A computer search 2011, restricted to *symmetric* orphans gave a pattern that fits in a 10x11 rectangle. 

Thus, the smallest orphan will fit in a 10x11 rectangle, but it is probably smaller. 
Note that there are roughly $2^{10 \times 11}$ possible configurations that fit within these bounds.

[1]: https://en.wikipedia.org/wiki/Garden_of_Eden_%28cellular_automaton%29