The AIP news feed features a story about a paper suggesting that the universe is ellipsoidal. Or at least, that it was, back in the early days.
The work is based on the famous WMAP picture of the microwave background (and no, it’s not because the picture is oblong):
As you know, Bob, the picture shows the distribution of temperature fluctuations in the early universe. These temperature correlations correspond to slight variations in the density of matter at that time, density fluctuations that eventually evolved into galaxies and galaxy clusters.
(Explanation after the cut.)
We can’t directly compare this measured distribution to the current distribution of matter that we see, or to theoretical models, but it is possible to do a statistical sort of comparison. Mathematically, this is expressed in terms of functions called “spherical harmonics” (the term “moments” is also used), but the basic idea is just a measurement of how likely you are to find a structure of a particular angular size. Basically, you measure how frequently blobs of a certain size occur in the WMAP image, and compare that the frequency at which blobs of that size occur in theoretically generated plots of temperature fluctuations.
These comparisons work very nicely for a certain class of theoretical models, with one exception. The models all predict more structure at larger scales than is seen in the WMAP image– there’s a nice summary graph at the bottom of this page. The problem is that the theory curve turns up at the left-hand edge of the graph, while the experimental points drop down.
The new claim being touted by AIP is that this arises naturally from a model in which the early universe is not spherically symmetric, but is stretched very slightly (about one percent) in some direction. The authors claim that by introducing a slight bulge, they can exactly match the WMAP data. This could be caused by a magnetic field filling all of space, or the wonderfully Star Trek sounding “a defect in the fabric of spacetime.”
How solid is this result? Beats me. This isn’t my field at all, but maybe Steinn will have something to say. I mostly just wanted to use the Python quote in the post title…
I’m a little surprised that the article didn’t mention cosmic variance (the phenomenon, not the blog). We have only one sky, and we can’t expect it to look exactly ideal. This is particularly true at the larger scales. Given that we’re discussing essentially one datapoint here, I’m not convinced that any departure from the concordance model is required for this one. It’s always possible to construct a model that fits the data better than the correct one. Hence Occam.
The measurements of low multipoles are subject to cosmic variance (we only have one sky to measure), so I think most people don’t think it’s worth trying to find much meaning in the discrepancy. But some people persist. There is a weird alignment between the quadrupole and octopoles, which Land and Maguiejo dubbed “The axis of evil” (astro-ph/0502237), which led to one of the best paper titles ever, “Local Pancake Defeats Axis of Evil” by Chris Vale. I think some people like to think this is meaningful, but I’m skeptical. (On the other hand, this is a bit removed from my field….)
Just watch out that you don’t get the crackpot who calls himself “island” coming in here trying to tell you it means the existence of humans stabilizes the universe, or some such nonsense.
Maybe next week, if Sean doesn’t get to it first.
The “ellipsoidal universe” paper is astro-ph/0606266. In the paper, they write:
(i) “Note, however, that the probability of quadrupole being low is not statistically significant [1].” Reference [1] is the paper reporting the WMAP results: astro-ph/0603451.
(ii) “In conclusion…we have seen that such a small eccentricity could be generated by a uniform cosmic magnetic field whose actual strength, B~10^â9 Gauss, is of the correct order of magnitude to account for the observed magnetic fields in galaxies and galaxy clusters.”
My understanding is that effects from early universe magnetic fields are very speculative. I don’t know anything about them, though.