Abstract
Macro-realism is the position that certain macroscopic observables must always possess definite values: e.g. the table is in some definite position, even if we do not know what that is precisely. The traditional understanding is that by assuming macro-realism one can derive the Leggett-Garg inequalities, which constrain the possible statistics from certain experiments. Since quantum experiments can violate the Leggett-Garg inequalities, this is taken to rule out the possibility of macro-realism in a quantum universe. However, recent analyses have exposed loopholes in the Leggett-Garg argument, which allow many types of macro-realism to be compatible with quantum theory and hence violation of the Leggett-Garg inequalities. This paper takes a different approach to ruling out macro-realism and the result is a no-go theorem for macro-realism in quantum theory that is stronger than the Leggett-Garg argument. This approach uses the framework of ontological models: an elegant way to reason about foundational issues in quantum theory which has successfully produced many other recent results, such as the PBR theorem.
Highlights
The concept of macro-realism was introduced to the study of quantum theory by Leggett & Garg alongside their eponymous inequalities [1]
The theorem in this paper proves that quantum theory is incompatible with eigenstate support macro-realism (ESMR) and eigenstate mixture macro-realism (EMMR) macro-realist ontologies where the macroscopically observable property has n > 3 distinguishable values
This is stronger than the argument from the Leggett-Garg inequalities, which is only able to rule out EMMR ontologies
Summary
Macro-realism is the position that certain “macroscopic” observables must always possess definite values: e.g. the table is in some definite position, even if we don’t know what that is precisely. Since quantum experiments can violate the Leggett-Garg inequalities, this is taken to rule out the possibility of macro-realism in a quantum universe. Recent analyses have exposed loopholes in the Leggett-Garg argument, which allow many types of macro-realism to be compatible with quantum theory and violation of the LeggettGarg inequalities. This paper takes a different approach to ruling out macro-realism and the result is a no-go theorem for macro-realism in quantum theory that is stronger than the Leggett-Garg argument. This approach uses the framework of ontological models: an elegant way to reason about foundational issues in quantum theory which has successfully produced many other recent results, such as the PBR theorem
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