Recently J.Webb submitted paper which has extraordinary claim - that Fine Structure Constant is different in different directions in space! He (with others) measured $\alpha$ using quasar spectrum absorption method in different directions and found small variation. There is huge debate about this finding, but lets suppose it is true.

Do you think spacial variation of Fine Structure Constant could have some influence to the Cosmic microwave background radiation? Because $\alpha$ influences the Electromagnetic interactions which is responsable for atom formation. And neutral atoms were the key for transparent universe in its early development sages.

Could this be observed?

  • $\begingroup$ Without have read anything more than the abstract or being qualified to comment on the observations or analysis, I'll note that I have seen 4 sigma effects evaporate before. That's a decent level of significance, but not iron clad. $\endgroup$ Jan 22, 2011 at 18:01
  • $\begingroup$ This question is almost identical to this one. $\endgroup$
    – user346
    Jan 22, 2011 at 19:24

1 Answer 1


if the fine-structure constant had different values at different places of space (which I don't believe for many reasons), then the size of the atoms e.g. in Planck units would depend on the location, too. Correspondingly, electrons and protons would "sit" into Hydrogen atoms at slightly different moments and different places would perform recombination - the birth of atoms when the Universe became nearly transparent and when the CMB was born - at slightly different moments. At different moments, the temperature was a bit different.

So a part of the observed anisotropy of the temperature of the CMB radiation could be blamed on the non-uniformity of the fine-structure constant in the times when the CMB was created. However, physicists would always think that the non-uniformity of alpha didn't arise "just for fun" but it was probably driven by something else. So they would ultimately reparameterize the influence of a variable $\alpha$ to the influence of something else, anyway.

You can't see any alpha-effects in the detailed structure of the microwave background itself - except for the overall temperature discussed above. It's because the CMB radiation is a black body radiation which doesn't depend on the character of objects at the time when CMB emerged. Photons are massless and their properties - except for interactions with charged objects - don't depend on any alpha, either. In fact, the CMB radiation is the most accurate natural black body radiation we have ever observed.

Best wishes Luboš


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