[hep-th/0407213] Scientific alternatives to the anthropic pr
Posted: May 17 2006
This is an interesting paper, and well worth reading. He attacks various rather silly definitions of the anthropic principle, and describes his black hole evolution model, which, at the very least, is a very nice logically possible example of a multiverse with interesting predictive properties.
However he also attacks some sensible versions of the anthropic principle. In fact he seems to be even using one in his 'scientific alternative'! This sensible version is basically the mediocrity principle, Copernican Principle, self-sampling assumption - whatever you want to call it: the idea that if there are many observers we should expect to be typical. A very simple and I'd have thought rather uncontroversial example is Bostrom's explanation of why cars go faster in the other lane:
http://plus.maths.org/issue17/features/ ... index.html
The author does not seem to have any valid complaints against this use of the principle. A feature about this argument is that you can only make statistical refutations - but then anyone dealing with data is used to living with that anyway.
In particular I find his argument against the Doomsday argument rather odd. His argument seems to go like this: there were observers 10 000 years ago; these observers could have made the Doomsday argument; these observers would have said the world was likely to end soon; these observers would have been wrong (we exist!); hence the Doomsday arguement is wrong. What seems to be wrong with this is that of course the 10 000-year old observers are untypical: if you make a statistical argument about typicality, of course a small number of atypical observers will be wrong! So I don't understand his criticism of this use of the anthropic principle (the Doomsday argument may well be wrong, but I don't think it is wrong for this reason).
Finally, the evolving black holes. The idea here is that if universes bud off from black holes, and parameters mutate between universes, the ensemble will come to be dominated by universes that are fine-tuned to produce maximal numbers of black holes. But to then make the (scientific) prediction that parameters we observe should be tuned to maximise the number of black holes, he needs to argue that most observers will be in the most abundant type of universe. i.e. precisely a sensible version of the anthropic principle - we should be a typical observer. If you don't make this argument there is no reason why we shouldn't be living in one of the universes which is very rare (atypically makes few black holes) but happens to contain life.
In conclusion, I think his title should be: "Scientific versions of the anthropic principle". Then I agree with almost everything he says (save above comments). Similar comments apply to e.g. astro-ph/0605173 where the authors are also using the mediocrity priciple to locate ourselves in the most long-lived vacuum, while at the same time appearing to be claiming a non-anthropic argument.
However he also attacks some sensible versions of the anthropic principle. In fact he seems to be even using one in his 'scientific alternative'! This sensible version is basically the mediocrity principle, Copernican Principle, self-sampling assumption - whatever you want to call it: the idea that if there are many observers we should expect to be typical. A very simple and I'd have thought rather uncontroversial example is Bostrom's explanation of why cars go faster in the other lane:
http://plus.maths.org/issue17/features/ ... index.html
The author does not seem to have any valid complaints against this use of the principle. A feature about this argument is that you can only make statistical refutations - but then anyone dealing with data is used to living with that anyway.
In particular I find his argument against the Doomsday argument rather odd. His argument seems to go like this: there were observers 10 000 years ago; these observers could have made the Doomsday argument; these observers would have said the world was likely to end soon; these observers would have been wrong (we exist!); hence the Doomsday arguement is wrong. What seems to be wrong with this is that of course the 10 000-year old observers are untypical: if you make a statistical argument about typicality, of course a small number of atypical observers will be wrong! So I don't understand his criticism of this use of the anthropic principle (the Doomsday argument may well be wrong, but I don't think it is wrong for this reason).
Finally, the evolving black holes. The idea here is that if universes bud off from black holes, and parameters mutate between universes, the ensemble will come to be dominated by universes that are fine-tuned to produce maximal numbers of black holes. But to then make the (scientific) prediction that parameters we observe should be tuned to maximise the number of black holes, he needs to argue that most observers will be in the most abundant type of universe. i.e. precisely a sensible version of the anthropic principle - we should be a typical observer. If you don't make this argument there is no reason why we shouldn't be living in one of the universes which is very rare (atypically makes few black holes) but happens to contain life.
In conclusion, I think his title should be: "Scientific versions of the anthropic principle". Then I agree with almost everything he says (save above comments). Similar comments apply to e.g. astro-ph/0605173 where the authors are also using the mediocrity priciple to locate ourselves in the most long-lived vacuum, while at the same time appearing to be claiming a non-anthropic argument.