In this task you will be given a text passage from a trivia quiz. You should choose the category this question belongs to from these categories: History, Science, Social Science, Fine Arts, Literature. You can only choose one category, so if in doubt, please choose the closest match.
Q: It is the basis of a form of cryptography for which the BB84 and E91 key distribution schemes were developed; these methods use this rule to detect eavesdropping. Einstein considered a box filled with light, whose loss of energy would be associated with a loss of (*) weight, as means of refuting it. Its proof often employs the Cauchy-Schwarz inequality, and it commonly states that h-bar over 2 must be less than or equal to the product of the standard deviations of position and momentum. For 10 points, name this principle that states that certain pairs of observables cannot exactly be determined to arbitrary precision.
A:
Science