[nessus42]

I guess I am unclear on one of your points: Let's say we toss a fair quantum coin many, many times. In the Everett Interpretation, yes, there is a "world" in which that coin has always come up heads. But our chance of finding ourselves in that world is vanishingly small.

In the Bohm Interpretation, that coin could always come up heads too, but again with a vanishingly small probability.

So they seem equivalent experimentally to me. (And to the experts who have written entire books on the subject.)

Max Tegmark came up with a way to experimentally determine if the Everett Interpretation is correct. (I believe it was Tegmark who came up with this.) It has a high cost for the experimenter, though!

What you do, is rig a gun to a fair quantum coin, so when you pull the trigger, the gun fires 50% of the time. Now shoot yourself in the head with it many, many times. If you end up surviving many rounds of this, you can be pretty darn certain that the Everett Interpretation is correct.

Never mind the billions of other versions of yourself that you murdered to discover the truth!

[tlb]

For this to work, the gun has to terminate your consciousness before the state of the coin can become entangled with the world. Objects as large as guns cannot (currently) be kept in an unentangled state for the milliseconds required for a bullet to do its work. If it were possible, the entire gun-bullet-head system would need to be cooled to microkelvin temperatures, at which guns or consciousness don't work.

[nessus42]

I don't understand your comment. In the Everett Interpretation, the wave function never collapses. Everything is always entangled. "Decoherence", however, causes the perception that the wave function collapses, and consequently this interpretation is often called the "Many World Interpretation", because the theory results in a different "world" (for all intents and purposes) for every possible outcome.

Hence, in the Everett Interpretation, if you shoot yourself using such a quantum gun, every time you pull the trigger, there will end up being one "world" in which the gun didn't go off and one world in which you put a bullet in your head.