This has been an interesting thread so far, but let me bring it back to topic for the Everything List. It has been assumed in most posts to this list over the years that our current state must be a "typical" state in some sense. For example, our world has followed consistent laws of physics for as long as anyone has been able to determine - the old "no white rabbit worlds" observation. In the face of ensemble type theories such as the MWI of QM, this is seen as presenting a problem: if "anything that can happen, does happen", why does our experience of the world include only a very limited, orderly subset of this "anything"?

There have been many attempts to answer the above question, eg. see Russell Standish' paper "Why Ockham's Razor?" But does our current orderly world imply that most possible worlds are orderly? It seems to me that there is an asymmetry between (a) what we can expect for the future, and (b) what we can deduce about the probability implicit in (a) from what actually does happen.

Suppose that according to X-Theory, in the next minute the world will split into one million different versions, of which one version will be the same sort of orderly world we are used to, while the rest will be worlds in which it will be immediately obvious to us that very strange things are happening, eg. dragons materialising out of thin air, furniture levitating, the planet Jupiter hurling itself into the sun, etc. I think it is reasonable to expect that if X-Theory is correct, we will very likely see these bizarre and frightening things happen in the next minute.

Now, here we are, a minute later, and nothing bizarre has happened after all. Does this mean that X-Theory is probably wrong? Perhaps not. After all, the theory did predict with 100% certainty that one version of the world will continue as before. The objection to this will no doubt be, "yes, but how likely is it that WE end up in that particular version?" And the answer to this objection is, "it is 100% certain that WE end up in that particular version; just as it is 100% certain that 999,999 copies of us end up in the bizarre versions". Those 999,999 copies are not continuing to type away as I am, because they are running around in a panic.

The above is simply a version of the Anthropic Principle as applied to intelligent life in the universe. A particular ensemble theory may predict that it is overwhelmingly unlikely that a particular universe will allow the development of intelligent life. Does the fact that we are here, appparently intelligent and alive, count as evidence against that theory? No, because the theory predicts that although unlikely, it is certain to happen in at least ONE universe, and obviously that universe will be the one we find ourselves in.

Stathis Papaioannou

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