anthropic principle

Okay, I admit that discussion of the anthropic principle does not count as research (see rules at right). But really, the people who use the anthropic principle are confused! I agree that you can't observe a universe that cannot contain observers. No duh! But a universe that contains observers arbitrarily different from us is observable. Recall: The anthropic principle is invoked to reduce the range of possible predictions for the properties of the Universe from the vast range allowed by, eg, string theory. You can't use observations of our Universe (such as that it contains galaxies and carbon-based life) to trim down the possible fundamental predictions, because then they aren't predictions. You must only use the fact that the Universe is observed, which requires only observers, not carbon-based observers, not observers in galaxies, not observers around stars, etc. Interestingly, many people who have worked on this problem for many years, including Susskind and Vilenkin (who spoke today at NYU) have got this wrong, and they call the requirement that there be galaxies the anthropic principle.

The fact that the Universe contains galaxies is an observation; the requirement that it is in principle observable is properly the anthropic principle. Of course we don't know how to compute observability, given a stated theory (indeed, we cannot even predict the proton from the standard model, let alone observers!). Until observers are predictable, the anthropic principle is not useable for science, in practice.