fold space

In Frank Herbert's Dune series, this is faster-than-light travel. Or rather, non-travel. The gargantuan space freighters, known as Heighliners, open their doors, and smaller ships fly into their bellies. Then the Guild Navigator (a human, whose life has been extended by the spice melange, body deformed into a icky fish-like bloated thing, and mind expanded to see deep into probability space and map out a safe way to travel) causes (what I understand to be) a fold in the fabric of space, and the heighliner suddenly appears anywhere else in the universe. Paul Muad'Dib makes a big deal about folding space; he calls it "travelling without moving".

Since only Guild Navigators have the capability to fold space, they have a bit of a monopoly. But doing it takes massive amounts of the spice melange, so the Guild (an thus, all interstellar travel) is in fact dependent on Arrakis, the Dune planet.

Alternatively, the abstract space of protein folds. That is, given all possible sequences of amino acids (theoretically infinite), the space of structures that they can fold into.

Of course, there is a practical upper limit on the length of sequence - most proteins are 100-1000 residues. Also, there are only so many sequences (out of the many, many possible ones) that have been 'attempted' - or synthesised. However, it is an interesting thought : Is fold space infinite? (that is, as sequences grow beyond physical limits, could they be folded in silico into new and different structures?)

Luckily, fold space is degenerate - several sequences can correspond to a single 'fold'. The concept of a fold is somewhat fuzzy, of course, but the definition could be made definate using RMSDs. This is what allows organisms to search through the space of folds using an evolutionary approach. If point mutations caused large changes in fold, it would make it more difficult to evolve folds.