Obvious Leo wrote:As Dubious suggests some hypotheses are more credible than others and at least the eternal and cyclical universe is soundly grounded metaphysically and has a few millennia of philosophy behind it. It is also a perfectly valid mathematical solution to Einstein's field equations in GR and accords perfectly with the empirical data on black hole entropy, which the "one-off" universe can not.
The multiverse is a popular concept because it's theoretically possible. At one stage humanity believed there were no other lands but their own. Explorers found otherwise. We believed that stars were lights in a dark canopy but researchers - mental explorers - found otherwise. We that there were no other other galaxies until a faint smudge in a night sky was found to be Andromeda, not a nebula. Still, we believed there were no other planets until fairly recently. Every time humanity has set a limit on reality we find that the limits were only our own. So I remain open. It would seem that string theory remains the key to the existence of the multiverse or not.
My understanding is that so far the LHC has so far not been encouraging for string theory. However, Peter Higgs's ideas were disregarded for a long time until future developments raised the boson question again and subsequent testing verified his mathematical models. The trouble with string theory is, as with theism, it may prove impossible to entirely falsify, at least for a long time.
It makes metaphysical sense that events at the Planck scale will affect other scales but I don't know of another theory that as deeply considers reality at the smallest possible scale. Are there any other theories in the area?
As usual, consideration of the largest of scales relies heavily on knowledge gained from considering the nature of the smallest.
One of the stronger arguments for the existence of the multiverse is:
why fundamental constants of nature, such as the fine-structure constant that characterizes the strength of electromagnetic interactions between particles and the cosmological constant associated with the acceleration of the expansion of the Universe, have values that lie in the small range that allows life to exist. Multiverse theory claims that there are billions of unobservable sister universes out there in which all possible values of these constants can occur. So somewhere there will be a bio-friendly universe like ours, however improbable that is.
Some physicists consider that the multiverse has no challenger as an explanation of many otherwise bizarre coincidences. The low value of the cosmological constant — known to be 120 factors of 10 smaller than the value predicted by quantum field theory — is difficult to explain, for instance.
[size=85]http://www.nature.com/news/sci ... 0:0[/size]
There are two possibilities. String theory could be thought of as a randomised, mathematical approach. All configurations can be explored by reality but very few are viable, where universes would be akin to a shower of many thousands of jellyfish eggs, of which perhaps one or two will survive.
The other approach is more biologically based, or more correctly, breaking down the distinctions we normally make between geology and biology. That way the universe would seem like a multilayered, constantly metamorphosing entity, effectively containing ever "evolving" geology prior to a continuation of that evolution as "biology".
I had an idea recently I'd like to run past you. As far as I can tell, the evolution (using the word loosely) of both geology and biology involves the same process - constantly turning inside out. That's what interaction with environment is, a gradual process of turning inside out. Inflation. A full iteration of turning inside out is a lifespan, be it for a human, rock or universe. New iterations of cycled reality are augmented by the information of their predecessors, hence the arrow of evolution, despite outmoded Gouldian random models.
Locally, it would seem that every aspect of reality is in the process of turning inside out, all at different tempos. A "living" universe would be simply going through its processes like its inhabitants, more or less as any ecosystems do (although it remains to be seen whether the universe has an environment from which it draws energy). If you consider the notion of "geological life" (a roughly equivalent but different kind of "life"), the fact that the universe supports life seems less mysterious, to be expected, perhaps a predictable phase in universes just as any life will have predictable phases. If the universe is already quasi alive, then abiogenesis would seem inevitable.
I've used many inverted commas because I do know the formal criteria for life but, since we have no semantically satisfying language to describe dynamic systems that grow, develop through stages and die, if they lack cells, metabolisms, and don't reproduce with heritable characteristics.
What other possibilities are there to explain the fine tuning of cosmological constants? Either reality works differently at the largest of scales, allowing for exceptionally randomised universe possibilities in a multiverse, or the largest scales of reality are essentially of similar nature to its components, with each scale going through its own "living" and living cycles.