[gore3000]

According to the so-called anthropic principle, there are perhaps an infinite number of universes, each with its own set of physical laws. And one of them happens to be ours. That's much easier to believe, say the anthropic advocates, than a single universe "fine-tuned" for our existence.

Of course it is easier to believe in multiple (really infinite universes) only if one is a thoroughgoing atheist. The idea of an infinite number of universes is really a refusal to believe in reality. In a sense, materialist/atheists who claim that nothing which they cannot feel, see, or touch can exist are contradicting themselves when they have to propose not just a few, but an infinite number of universes when no one has ever been able to see any evidence of a single one other than our own.

[Alamo-Girl]

Thank you so much for your post!

In a sense, materialist/atheists who claim that nothing which they cannot feel, see, or touch can exist are contradicting themselves when they have to propose not just a few, but an infinite number of universes when no one has ever been able to see any evidence of a single one other than our own.

Indeed, it is more irony, like the one mentioned at post 140.

There is little agreement on the multiple universe theory as we can see from this conference: PhysicsWeb - Life, the cosmos and everything

Andrei Linde and Alex Vilenkin invoked "eternal" inflation, in which the universe is eternally self-reproducing. This version of inflation predicts that there may be an infinite number of exponentially large domains - all with different laws of low-energy physics and different coupling constants...

On the other hand, Stephen Hawking objected to the eternal-inflation model on the grounds that it extends to the infinite past and thus violates his "no boundary" proposal for the origin of the universe... Hawking uses the path-integral approach to calculate the probability of a particular history but only sums over those histories that lead to observers.

Neil Turok elaborated on this theme, showing that there are so-called instantons that represent classical solutions of the Euclidean equations that possess a continuation to real Lorentzian space-time. Although the path integral favours inflationary periods shorter than required, anthropic selection can salvage this since one only considers histories containing observers. This permits either open or closed universes but he argued that Hawking's favoured (closed) solution is unstable.

Personally, I think "multiple universe from multiple quantum fluctuations" looks as kluged as Einstein's famous cosmological constant. Also, it seems presumptuous to me that the physical laws of this universe would be the same in any other universe.

There's more discussion in this article by Roger White: Fine-Tuning and Multiple Universes (pdf)

The Design hypothesis does not add to the probability that any particular universe will be fine-tuned. So the Multiple Universe hypothesis screens off the probabilistic link between the Design hypothesis and the fine-tuning data...

However, postulate as many other universes as you wish, they do not make it any more likely that ours should be life-permitting or that we should be here. So our good fortune to exist in a life-permitting universe gives us no reason to suppose that there are many universes.