This theory makes appealingly simple predictions. Variations in α of a few parts per million should have a completely negligible effect on the expansion of the universe. That is because electromagnetism is much weaker than gravity on cosmic scales. But although changes in the fine-structure constant do not affect the expansion of the universe significantly, the expansion affects α. Changes to α are driven by imbalances between the electric field energy and magnetic field energy. During the first tens of thousands of years of cosmic history, radiation dominated over charged particles and kept the electric and magnetic fields in balance. As the universe expanded, radiation thinned out, and matter became the dominant constituent of the cosmos. The electric and magnetic energies became unequal, and α started to increase very slowly, growing as the logarithm of time. About six billion years ago dark energy took over and accelerated the expansion, making it difficult for all physical influences to propagate through space. So α became nearly constant again.
This predicted pattern was consistent with our earlier data from the Keck telescopes, which seemed to indicate that a redshift dependence of α might be linked to a time variation. But the new VLT data throw a large wrench in the works. If the Keck data are right and if the VLT data are also right, even if time variation does take place, it must be small compared with the spatial variation we may now be seeing.
Alpha Is Just the Beginning
Any theory worthy of consideration does not merely reproduce observations; it must make novel predictions. The above theory suggests that varying the fine-structure constant makes objects fall differently. Galileo predicted that bodies in a vacuum fall at the same rate no matter what they are made of—an idea known as the weak equivalence principle, which was famously demonstrated when Apollo 15 astronaut David Scott dropped a feather and a hammer and saw them hit the lunar dirt at the same time. But if α varies, that principle no longer holds exactly. The variations generate a force on all charged particles. The more protons an atom has in its nucleus, the more strongly it will feel this force. If our quasar observations are correct, then the accelerations of different materials differ by about one part in 1014—too small to see in the laboratory by a factor of about 100 but large enough to show up in planned missions such as STEP (space-based test of the equivalence principle).
So where does this flurry of activity leave science as far as α is concerned? We await new data and new analyses to confirm or disprove that α varies at the level claimed. Researchers focus on α, over the other constants of nature, simply because its effects are more readily seen. If α is susceptible to change, however, other constants should vary as well, making the inner workings of nature more fickle than scientists ever suspected.