"Possible worlds are causally isolated from each other."We can't ever interact with another world, by definition. By definition, modal realism is immune to experiment. It is metaphysics. QED.
I suspect delusions of this type get privileged over the competition because they erode the citizen's confidence in their own perceptions and judgments. If a physicist says it is true, who are we to question? Makes it easier when it comes time to sell quantitative easing. In reality, if one can't understand it is normally the fault of the explanation, not the skeptic.
Many-Worlds suffers from exactly the same flaw, mitigated somewhat by offering an opportunity to make fun of Rationality Czar Yudkowsky.
"The debate should already be over. It should have been over fifty years ago. The state of evidence is too lopsided to justify further argument. There is no balance in this issue. There is no rational controversy to teach. The laws of probability theory are laws, not suggestions; there is no flexibility in the best guess given this evidence. Our children will look back at the fact that we were STILL ARGUING about this in the early 21st-century, and correctly deduce that we were nuts."
The laws of experimentation are laws, not suggestions. The evidence says that particles have spooky comm systems, that wave functions collapse, that the past is different from the future, and that only one thing happens. No experiment has ever shown otherwise. DEAL WITH THE EVIDENCE.
It turns out that seeing no argument and there existing no argument are two different things. It is much easier to correctly describe the experimental results than to correctly explain them. The many-worlds explanation appears to assume the description is wrong, and contradicts key properties of the description. If I'm trying to exploit quantum mechanics in a new kind of car engine, the key property for me is that wave functions collapse, not whether "the same laws govern at all levels". If I get it right, the car will go from point A to point B regardless of whether I have quantum clones.
Arrogance is an occupational hazard of all scholarly professions, especially philosophy. It is imperative I keep this hazard in mind; but either the worlds are causally isolated and nobody ever need consider them; or we're both wrong, they're not causally isolated, and someone could show me an experiment reflecting the interaction. Someone can build a quantum device that does require its clones to function properly. But even without considering evidence, I can know that the fancy explanation is far, far more likely to be wrong than the simple description.
Until then, those who forget philosophy (denigrate it, in this case) are doomed to repeat its mistakes.