"Does the moon exist when no one is looking at it?"

—Albert Einstein, asked of Niels Bohr

Suppose you were just starting to work out a theory of quantum mechanics.

You begin to encounter experiments that deliver different results depending on how closely you observe them. You dig underneath the reality you know, and find an extremely precise mathematical description that only gives you the relative frequency of outcomes; worse, it’s made of complex numbers. Things behave like particles on Monday and waves on Tuesday.

The correct answer is not available to you as a hypothesis, because it will not be invented for another thirty years.

In a mess like that, what’s the best you could do?

The best you can do is the strict “shut up and calculate” interpretation of quantum mechanics. You’ll go on trying to develop new theories, because doing your best doesn’t mean giving up. But we’ve specified that the correct answer won’t be available for thirty years, and that means none of the new theories will really be any good. Doing the best you could theoretically do would mean that you recognized that, even as you looked for ways to test the hypotheses.

The best you could theoretically do would not include saying anything like, “The wavefunction only gives us probabilities, not certainties.” That, in retrospect, was jumping to a conclusion; the wavefunction gives us a certainty of many worlds existing. So that part about the wavefunction being only a probability was not-quite-right. You calculated, but failed to shut up.

If you do the best that you can do without the correct answer being available, then, when you hear about decoherence, it will turn out that you have not said anythingincompatible with decoherence. Decoherence is not ruled out by the data and the calculations. So if you refuse to affirm, as positive knowledge, any proposition which was not forced by the data and the calculations, the calculations will not force you to say anything incompatible with decoherence. So too with whatever the correct theory may be, if it is not decoherence. If you go astray, it must be from your own impulses.

But it is hard for human beings to shut up and calculate—really shut up and calculate. There is an overwhelming tendency to treat our ignorance as if it were positive knowledge.

I don’t know if any conversations like this ever really took place, but this is how ignorance becomes knowle...

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