I agree, I should have written a conditional:
This is because, if we could measure them with full precision, the current position, direction, and speed of an atom (and all other measurements if we could do them physically) are only possible with one and only one specific history of everything else in the universe.
I will edit above.
Other than our ability to measure these dimensions I think that their current state is only possible with only one history of the universe since the beginning.
That is not at all true; for example, see the inverse problem (http://en.wikipedia.org/wiki/Inverse_problem). Although the atom's position is uniquely determined by the rest of the universe, the inverse is not true: Multiple different states of the universe could correspond to the same position of the atom. And as long as the atom's position does not uniquely identify the rest of the outside universe, there is no way to infer the state of the universe from the state of the atom, no matter how much precision you can measure it with. The reason is that there...
One of the themes of current scientific progress is getting more and more information out of tiny amounts of data. Who'd have thought that we could learn so much of distant and recent biological history from DNA, and so much about distant planets, stars, galaxies, and the cosmos from tiny differences in very small amounts of light?
Pratchett's death puts an extra edge on the question-- to what extent can people be re-created from what they've left behind them, especially if they've written novels which include a lot of their personality?
Any thoughts about theoretical limits of how much can be figured out from small amounts of data?