Interesting, if true

There was an interesting article in the ArXiv (better known as the repository of all astrophysical knowledge) earlier in the week. Rachel Bean wrote an interesting article in which she claims to have ruled out general relativity at the 3-sigma (99.9%) level. Disproving Einstein? You better believe it would be big news.

Normally, I’d be very skeptical, and I still am. However, Bean has done a lot of good work, and she’s super smart, so unlike the random crayon scribblings that I normally find in my inbox, I had to look at this claim a little more closely. What she does, in essence, is look at how much structure (in the form of clusters of galaxies) has grown in the real universe using the “Integrated Sachs-Wolfe Effect.” Essentially this is a measure of the net energy gain by a photon as it falls into a cluster compared to the energy loss when it escapes. Since the cluster grows in the interim, the ISW effect allows us to figure out how fast the cluster is growing. Different models predict different amounts of growth.

The problem, as I see it is that the growth of structure in the linear regime (when the bumps and wiggles in the universe are very small) are very easy to model. As structure becomes bigger (think clusters), these calculations become tougher. They’re impossible, actually, without simulations, and the nonlinear corrections are only going to be approximate.

So as I said, this is a very interesting result, if true.


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