10 April 2011

Non political: Problems with Inflationary Theory (Cosmology, not dollars and sense)

As part of an occasional foray into other than politics, this is from an e-mail I sent to a friend who shares my interest in such things:

There's an article in the current Scientific American about the rather serious ... maybe fatal... theoretical problems that have cropped up in the Inflationary Cosmological Theory, (first proposed by Alan Guth and presented by him in a general public pop sci book in 1998 The Inflationary Universe, perhaps you read it).

The gist as I get it is that the whole attraction of inflation (which I confess I never really grasped) was basically twofold: 1. It explains the current state of the universe in ways that most people trying to make numbers work with an unadorned Big Bang couldn't seem to get to work; and 2. it provides a mechanism for "smoothing out," and vastly increasing the volume of, the universe in the first few zillionths of a second, which makes the relatively but not quite perfectly flat and uniform universe we now see conceivable.

The gist of the new problems, if I understand them, is that it turns out that Quantum theory mandates that inflation is eternal; but that in regions of space time it might come to an end (like a ball rolling down a hill and coming to rest in the valley of the energy curve). Our universe is such a region. Fine, but quantum physics requires that what we see... such a spontaneous end of inflation very soon after the BB, is actually extremely unlikely. Later such regions would be equally if not more habitable, and far more likely. So they must predominate in  the meta universe. But then, why are we a special case? There isn't even an anthropic principle answer. It seems like Inflation requires a lot of special pleading, which is the death knell of a scientific theory. The main problem is that in its current form it necessitates a prediction that everything that's possible happens, and this particular universe is rather odd and unlikely, so the theory predicts nothing useful: lots of other possibilities would and presumably do also exist in other regions. Over a broad swath of possible universes, ours would be spectacularly rare and unlikely. Of course that doesn't mean it can't exist, but it's unsatisfying to pursue a theory that makes reality as we know it a highly unlikely special case, without even the anthropic principle to explain it.

The article's author, Paul Steinhardt, favors a new kind of cyclic theory, wherein Big Bangs are part of oscillations in the Meta Universe, and that's where the smoothing out occurs. Unfortunately, at the nonmathematical conceptual level of pop sci writing it's very difficult to assess what makes sense and what doesn't; we pretty much have to wait for people much smarter than we are to figure out all the logical problems and observational confirmations, and to tell us what's what.

Anyway, I ordered a couple of relatively recent books that at least touch on these topics, and hopefully they'll give some sense of current cosmological thinking:  Caroll; From Eternity to Here; the Quest for the Ultimate Theory of Time; and, Steinhardt and Turok; Endless Universe: Beyond the Big Bang -- Rewriting Cosmic History.

Just intuitively, and partly from a Buddhist bias in favor of what's referred to as "beginningless time" this seems right to me. Regions, like the "universe", may have beginnings, may expand "forever" and evaporate into entropy, but there's always other beginnings, other expansions, other life, other time.

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