I wonder if it is even meaningful to ask what the 'plain text' might look like.
Suppose we somehow managed to decrypt the universe and obtain its Theory of Everything. Then we notice that there's a pattern in the Theory which can be easily compressed (maybe a repeated constant bitstring). Wouldn't we then appeal to Kolmogorov and say the 'real' Theory of Everything is the shorter program which generates our larger Theory with its repeating constants?
And so on, for all the patterns we find, until we wind up with a Theory which looks like a substring of Chaitin's Omega - all completely random bits? At which point, why do we think we actually decrypted the random observations into this random Theory-string?
But maybe I'm just saying something someone else has said here or is implied by the general line of thought?
Short version: Why can't cryptanalysis methods be carried over to science, which looks like a trivial problem by comparison, since nature doesn't intelligently remove patterns from our observations? Or are these methods already carried over?
Long version: Okay, I was going to spell this all out with a lot of text, but it started ballooning, so I'm just going to put it in chart form.
Here is what I see as the mapping from cryptography to science (or epistemology in general). I want to know what goes in the "???" spot, and why it hasn't been used for any natural phenomenon less complex than the most complex broken cipher. (Sorry, couldn't figure out how to center it.)
EDIT: Removed "(cipher known)" requirement on 2nd- and 3rd-to-last rows because the scientific analog can be searching for either natural laws or constants.