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In physics, there is the prevailing intuition that we are part of a unique external world, and that the goal of physics is to understand and describe this world. This assumption of the fundamentality of objective reality is often seen as a major prerequisite of any kind of scientific reasoning, delineating science from pseudoscience, and explaining why successful empirical science is possible in the first place. However, here I argue that we should consider relaxing this assumption in a specific way in some contexts. Namely, there is a collection of open questions in and around physics that can arguably be addressed in a substantially more consistent and rigorous way if we consider the possibility that the first-person perspective is ultimately more fundamental than our usual notion of external world. These are questions like: which probabilities should an observer assign to future experiences if she is told that she will be simulated on a computer? How should we think of cosmology’s Boltzmann brain problem or assign probabilities to properties of ‘possible worlds’? What can we learn from the fact that measurements in quantum theory seem to do more than just reveal preexisting properties? Why are there simple computable laws of physics in the first place? In the talk, I sketch a mathematically rigorous approach along these lines, suggesting a simple and unified framework (rooted in algorithmic information theory) to address questions like those above. It is not meant as a ‘theory of everything’ (in fact, it predicts its own limitations), but it shows how a notion of objective external world, looking very much like our own, can provably emerge from a starting point in which (only) the first-person perspective is primary. Based on arXiv:1712.01826 (full version) and arXiv:1712.01816 (short version).

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Markus Mueller
Seminar Room 0.03, ETP
Contact: D. Gross