Astronomers Discover a Group of Quasars 4 Billion Light Years Across

It's a good question. I think you've gotten things a little backwards, though, with regars to the problem of propagation - inflation is a proposed explanation for propagation in the sense that it allows otherwise separate regions of the sky to have been in causal contact in the past. But this certainly does have impact upon the current inflationary paradigm in the following sense:

If there were large structures or large inhomogeneities in the early universe (before inflation) then it would be hard to get inflation going. The basic models of inflation contain a field whose energy can be decomposed (and I'm playing very fast and loose here) into three parts: Potential, Kinetic and fluctuations. From these parts, we say that if the potential is large enough, the inflaton undergoes a "slow roll" down the potential during which our regular inflation happens. Fluctuations are treated as perturbations on this background, and it's from these that we expect to see the everyday structure in the universe. A warning though: We don't know the physics that causes these fluctuations to stop being quantum fluctuations and become classical perturbations in matter on this background.

Now, if the fluctuations are too big, this model breaks down - the inflaton can't be high enough up its potential, and so slow roll can't happen. Hence before inflation we have to assume that the universe is largely homogeneous and isotropic, and fluctuations begin very small (technically in the "Bunch-Davies vacuum state).

A big inhomogeneity AFTER inflation isn't too bad - it could well be that this is just the result of one of the longer wavelength fluctuations. Of course, one would then have to explain/why/ this wave in particular had such a large amplitude, but this really doesn't contravene inflationary models, it merely adds a new question about the initial conditions.

Now, if we had been dealing with a serious overdensity (tons of quasars in the same spot) rather than a large strung-out structure, we would certainly have a problem with inflation, but so far as I know this isn't too big of an issue.

Disclaimer: I work on the mathematical structure end of things, not the computation or observation, so there are certainly people more qualified than I, to whom I would happily defer if they want to post!

Source: http://rss.slashdot.org/~r/Slashdot/slashdotScience/~3/u4julZFK7bM/story01.htm

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