The question with which the last chapter ended went like this: does the object itself carry a record of its own past, and can this record be read by an instrument?
The answer came from Glasgow, and what came of it was at once an elegant measurement and one of the dirtiest scientific brawls of the last decade.
Let us start with an idea that is good if only because it can be explained on your fingers.
Take some word, say abracadabra, and build it from scratch, with the right to two actions: add one letter, or add in one piece any chunk you have already assembled before. You assembled “ab”, now you have “ab” in stock, and the second time it can be put in with one move instead of two.