  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. 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.
