It’s always amusing to think about time travel and the grandfather paradox but invoking a flawed interpretation of the dual-slit experiment (the Copenhagen doctrine) seems just as ad hoc as any other explanation. When one truly considers the implication of the many-worlds notion it becomes absurd: imagine 10 to the 15th power of new universes popping into existence every nanosecond if, and only if, the Earth is the only place where observer effect occurs. If, on the other hand, it occurs also in a small number of places elsewhere in the universe, add a few dozen more zeros to that power function… It seems blindingly unlikely that any “explanation” that implies such astonishing profligacy is likely to be correct.
Which means, just because there’s currently no sensible interpretation of the dual-slit experiment (at least, not quite) we’re not entitled to let rip with ideas that have nonsensical consequences. When we do, we arrive inevitably at silly ideas like Boltzmann brains simply because we used the wrong logical predicates to begin with.