
What’s the chance you have drunk the same water molecule twice? - rargulati
https://www.reddit.com/r/askscience/comments/4mndsq/whats_the_chance_of_having_drunk_the_same_water/
======
pjdorrell
In Quantum Field Theory, the concept of "the same water molecule" is not a
well-defined concept, because of wave-function symmetry. (The only water
molecules that are fully distinguishable are those where the isotopes of
hydrogen or oxygen are different.)

~~~
deciplex
You can still chart the history of a single molecule in theory, you just can't
tag two molecules and tell them apart later without context. I guess that's
another way of saying "the only true quantum configuration is the entire
universe" though.

