Why I’m Skeptical About the Changing Fine-Structure Constant

Not long ago, a new preprint on the fine structure constant got a bunch of press, nicely summed up by the Knight Science Journalism Tracker last week. I meant to say something about this last week, but what with it being the first week of classes and all, I didn’t find the time.

I still think it’s worth writing about, though, so after a reproduction of the key figure, we’ll have the usual Q&A-format explanation of why I don’t quite trust this result:


So what’s this all about? The preprint in question is the latest in a series of attempts to measure possible changes in the fine structure constant by looking at the spectra of distant galaxies. Not only do they seem to see a change in the constant, the change seems to be different in different parts of the sky.

Back up a minute. A constant is changing? Well, a dimensionless ratio of fundamental constants, though some people would say that those are the only constants that matter. We’ve talked about this sort of thing before, but the short version is that some theories predict that the ratio of the electron charge squared divided by Planck’s constant and the speed of light could change over the history of the universe. This paper claims that they have not only measured the change by looking at light from distant quasars, whose spectra should depend on the value of the constant billions of years ago, but see it changing differently in the northern sky than the southern.

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