I wonder why negative probabilities should be avoided. Except the obvious “it just not possible!”. What happens if we assume that it is possible and just try to go ahead with it? I suggest looking at it on the MWI platform (even if you don’t like MWI). Why? Because MWI is deterministic, so there are no probabilities at all. We don’t know how probability is defined in MWI. So may be it is bad, but for the discussion of the subject it is good. So we have a number. We don’t call it a probability. It is >1 or <0? That’s fine! We know that in MWI the feeling or ‘being real’ does not depend on the value of what we call a ‘probability’. So my question is, except for the fact that it is ‘weird’, are any observable inconsistencies on the microscopic level for the ‘frogs’ in the ‘weird’ branches with ‘probabilities’ outside of 0..1 range?