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Comment by coldtea | Hacker News Reader

>The best explanations I have seen seem to amount to "we got lucky with our universe, the best way to explain that luck is that there are a lot of universes".

Perhaps you haven't looked that hard?

The idea of multiverse as the "best way to explaining our luck with our universe" was in the bottom of the list of concerns to theorize a multiverse - if it appeared at all:

https://en.wikipedia.org/wiki/Multiverse

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I been to the wiki page before. If anything my question is common enough it is discussed in the wiki page which contains this quote.

>Indeed, invoking an infinity of unseen universes to explain the unusual features of the one we do see is just as ad hoc as invoking an unseen Creator. The multiverse theory may be dressed up in scientific language, but in essence it requires the same leap of faith.

— Paul Davies, The New York Times, "A Brief History of the Multiverse"

So while it may be at the bottom of the list, it very much appears.

I think one crucial difference is that this actually has scientific precedence. For example, the Earth lies in an incredible number of "Goldilocks zones", which have just the right conditions for life to develop. For example, the Earth lies at just the right distance from the Sun for water to be in liquid form. To close and it would all evaporate, too far and it would all freeze. Why is this? Early astronomers (Kepler, I think) spent many years trying to discover some physical reason for why the Earth should be at this particular distance. From what physical principles could the distance be deduced? As we know now, this search was in vain, because there was no fundamental reason. Turns out, it was just a coincidence! With the discoveries of the (appropriately) named Kepler telescope, we have discovered thousands of exoplanets in thousands of star systems. With the billions upon billions of stars in the universe, there are likely trillions of planets out there. With odds like that, it is almost certain that a planet with our properties would show up somewhere, which it did. As it turns out, astronomers do invoke an "infinity" of unseen planets to explain the unusual features of this one, and I doubt Paul Davies thinks that's a leap of faith!

I think you raise a good parallel with Earth but I don't think it applies directly to the possibilities for a multiverse because we cannot see other universes but we can see other planets.

Imagine if our solar system was inside a nebula and the only star we could see was Sol. Until we figure a way to send a probe outside the nebula we have no idea if their are more stars or not. Do you see a way to "send a probe outside" and see if there are more universes or not?

Off the top of my head I don't really remember, though Brian Greene does devote a whole chapter to the question of detecting other universes in his book, so that might be a good place to look further. At the moment though, this doesn't really bother me. For example, Giordano Bruno suggested the existence of exoplanets in 1584, and certainly he could not have predicted the modern techniques the Kepler telescope uses to detect them! It may be centuries before we have the theory or technology to determine if other universes are detectable or if they exist. A long time to wait perhaps, but this should not be a reason for ruling them out (though of course, solid evidence would be required before a multiverse theory could be accepted).

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