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Zenith Grant Awardee

Lidia del Rio

University of Bristol


Renato Renner, ETH Zurich; ,

Project Title

Many worlds, many times: Emergent observers in non-probabilisitic theories

Project Summary

Do you remember the childhood books where you could choose how the story ended? The book asks you to make decisions or roll dice; based on the result you jump to a certain page, where the story takes a different turn. So works quantum theory: upon performing a measurement, several outcomes are possible, but we only experience one. According to many-worlds interpretations, all possibilities are real, in the same way that all stories are contained in the book. If you had to reconstruct the book from its loose pages, how would you distinguish past and future of a storyline from different alternatives? You could search the pages for traces of each other: the future may remember the past, but alternative stories do not refer to each other. We apply the same principle to time and observations within quantum theory. This allows us to find notions of local time, and ask questions such as \"when can two agents agree on a time?\" or \"why do we have memory of the past but not of alternatives?\"

Technical Abstract

Here we use a non-probabilistic framework to explore the concepts of time and many worlds within quantum theory. We bring together three building blocks: the Page-Wootters formalism of time as correlations, the notion of local knowledge via coarse-grainings of a global picture, and a mapping between wave functions and the sets of possible outcomes of measurements. Together, these building blocks put time on an equal footing with alternative \'worlds\' resulting from quantum measurements. In order to distinguish past and present from different alternatives, we search for compatibility conditions and causal relations between agents\' observations. In addition, we will relax the Page-Wootters formalism to explore minimal clocks and notions of common time between different agents. inally, we study how properties of physical systems affect the kind of knowledge they may hold – the agents they may represent.

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