The many-worlds interpretation is cool and jazzy and all. But as an explanation for why we observe what we do, and why we are what we are, it's just a whacky idea rooted in the hallucinatory world of a Beatnik generation. It's like the kid on acid who says, "Wow, now I get it". Get what? "It's connected". What's connected? "Everything". It purports to explain what it doesn't explain. It's hardly different from the following explanation of why my cat is black:
My black cat is black because blackness is what we see when we look at my black cat.
Or phrased in more a Schröringeresque context, with a 1950's avantgarde flavor:
The cat is dead because the dead cat is what you see when you open the black box. Oh, and by the way there is a guy who saw a live cat because a live cat was what he saw when he opened the white box. And did you know that that other guy is really you? Well, not really you but sort of you because you did have the same mother after all. Or did you? Weird, eh. Mind-boggling awesomeness. Do you have Buddha-nature? Don't bogart that joint my friend!
I'm not saying that it is not in some ways a useful mental construct. In some sense, I relied on the same idea for Anything Goes. My point is along the lines of my previous critique directed at Max Tegmark's Scientific American article. Even if there is a reality to the idea of quantum doppelgängers, it does nothing to explain the very reality that we experience what we experience and not what our supposed doppelgängers experience.
Supposedly, decoherence explains everything. Editors at Wikipedia have written.
Before an understanding of decoherence was developed the Copenhagen interpretation of quantum mechanics treated wavefunction collapse as a fundamental, a priori process. Decoherence provides an explanatory mechanism for the appearance of wavefunction collapse and was first developed by David Bohm in 1952 who applied it to Louis DeBroglie's pilot wave theory, producing Bohmian mechanics, the first successful hidden variables interpretation of quantum mechanics. Decoherence was then used by Hugh Everett in 1957 to form the core of his many-worlds interpretation.
And then after a few sentences, presumably after the various editors all had a few too many bowls of hashish or got a little too caught up in the Rigveda, add:
Decoherence does not provide a mechanism for the actual wave function collapse; rather it provides a mechanism for the appearance of wavefunction collapse. The quantum nature of the system is simply "leaked" into the environment so that a total superposition of the wavefunction still exists, but exists — at least for all practical purposes — beyond the realm of measurement.
So what is it? Does it explain it or does it not explain it? Is this just an indication that the wiki process is incapable of resolving differences of opinion rationally? Or is it an indication that no one knows what the heck they are talking about? I don't doubt that Mr. Everett provided us with a potentially deep insight as Max Tegmark wants us to note.
Perhaps we will one day be able to superimpose ourselves with our doppelgängers over a cup of tea. And what might we talk about? Well, as our tea party keeps being inundated by newly calculated superpositions, I suppose we will talk about why I happen to be me and my doppelgängers happen to be my doppelgängers. I mean why they happen to be themselves and I happen to be their doppelgänger. Scoot over my friend, make space for the new guy who just arrived. No, no, I'm not the new arrival, you are!
How about this beauty from Wikipedia:
One thing to realize is that the environment contains a huge number of degrees of freedom, a good number of them interacting with each other all the time.
Okidoki. I know what I get when I put a lot of little black arrows on multidimensional piece of paper: a very dark mess.
Ah,yes. It's that bottom of the barrel epistemic truth: my black cat is black because blackness is what we see when we look at my black cat. I think I'll stick with the Copenhagen interpretation for now. But I look forward to maybe meeting all my doppelgängers some day. Bring out the hookah-pipe Mr. Caterpillar!