Wednesday, October 11, 2006

Asymmetry of the cosmic microwave background

One of these days I need to do a series of posts on the cosmic microwave background (CMB). It's seriously interesting stuff. If you're not into astrophysics that much, you've still heard of it recently, because it helped a couple of guys win this year's Nobel Prize in Physics. (More good reporting on this here, here, here, here, here.)

And that's not the first Nobel Prize it's responsible for. Back in 1978, two other guys got a Nobel Prize for "discovering" the CMB. (I used the scare quotes, because the discovery was rather serendipitous, and at first the discoverers thought they had found nothing more interesting than a little guano.)

But even the current Nobel was based on work done more than 10 years ago. Quite a lot has happened in the meantime. (See this good article for a quick summary.) And now, some very recent research has found that the universe isn't quite as isotropic (the same in all directions) on the large scale, as cosmologists have always assumed. The CMB is an ellipsoid rather than a perfect sphere:

Ellipsoidal Universe
One remaining oddity about the WMAP results, however, concerns the way in which portions of the sky contribute to the overall map of cosmic microwaves; samples of the sky smaller than one degree across, or at the degree level, or tens of degrees seem to be contributing radiation at expected levels. Only the largest possible scale, that on the order of the whole sky itself (the technical term is quadrupole moment), seems to be under-represented.

Now Leonardo Campanelli of the University of Ferrara and his colleagues Paolo Cea and Luigi Tedesco at the University of Bari (all in Italy) have studied what happens to the quadrupole anomaly if one supposes that the shell from which the cosmic microwaves come toward earth is an ellipsoid and not a sphere.

This is probably not going to invalidate all of what we think we know about the early universe, but it does certainly call for an explanation. The authors of the research article suggest that "a uniform magnetic field pervading the cosmos, or a defect in the fabric of spacetime, could bring about a non-zero eccentricity."

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