**Quantum Theory Cannot be Extended** - Roger Colbeck

According to quantum theory, measurements generate random outcomes, in stark contrast with classical mechanics. This raises the important question of whether there could exist an extension of the theory which removes this indeterminism, as famously suspected by Einstein, Podolsky and Rosen. Although Bell showed this to be impossible, existing results do not imply that the current theory is maximally informative. Could it be that hidden variables allow us to make more accurate predictions of the outcomes? In this talk, I will focus on this question and present a new result that, under the assumption that measurements can be chosen freely, the answer is negative: no extension of quantum theory can give more information about the outcomes of future measurements than quantum theory itself.