"... astronomy is not the place to look. The big numbers of astronomy are additive. They arise because we are counting stars, planets, atoms and photons in a huge volume. If you want really huge numbers you need to find a place where the possibilities multiply rather than add. For this you need complexity. And for complexity you need biology.
10^70,000,000,000,000
This is the modern estimate of the number of different electrical patterns that the brain could hold. In some sense it is the number of different possible thoughts or ideas that a human brain could [think]."
-John D. Barrow