Is the electromagnetic constant a constant?
Star study suggests life-friendly conditions could be regional
Could yet another universal constant, the value assigned to the electromagnetic force, be less constant than we thought? And could variability of the constant help explain life in the universe?
That’s the tantalizing hypothesis offered by Australian astronomers, who believe that the value alpha, referring to the strength of the electromagnetic force (and measured at 1/137.03599976), may not be constant everywhere.
According to a paper published on arxiv.org and by Physical Review Letters, the fine structure constant alpha increases at high redshifts and, to quote from the abstract, “fits a spatial dipole, significant at the 4.2σ level” – in other words, the constant’s value increases a little in one direction and falls in the other.
Actually, Dr John Webb of the University of NSW School of Physics has formed a stronger opinion about alpha: unless there’s an error in the data, he told The Register, he is positive that its value is different in different parts of the universe.
“I don’t see any other possibility, other than systematic effects in the data,” he said.
His observations raise interesting implications about our observation of life in the universe: it can only exist where alpha’s value allows complex molecules to form.
“At some point, the change is big enough that the chemical processing inside stars ceases to take place … and the heavy chemicals do not come into existence.”
That, Dr Webb suggests, gets rid of the need for physicists to argue about what’s called the “anthropic principle”, the essentially-circular argument that we can only make observations of the physical universe because it has the right conditions for us to exist.
Alpha, life and the anthropic principle
Stellar chemical processing ultimately gives rise to life, since the most complex matter comes into being in supernovae. If the value is too low, the density of matter would also be lower; too high, and heavier atoms would not form.
If alpha is variable, he argues, then life arises not because the whole universe managed by chance to have the right set of physics to create it. Rather, he told The Register, life has arisen in that region of the universe with the right value of the electromagnetic force. Where alpha lacks that value, the universe would either be interesting or boring, depending on your point of view.
So how has Dr Webb reached this somewhat remarkable conclusion?
The key datum comes from observations of the spectra emitted by distant objects.
The expansion of the universe means that we observe a red-shift: light emitted at one wavelength reaches an Earth-bound observer at a lower wavelength, and for the most distant objects, that effect is so pronounced that what we see isn’t light, but the microwave background radiation.
However, what Dr Webb observed is that for some more complex elements, the spectral shift isn’t what he expected. Instead of a uniform spectral shift for all elements – since all the “stuff” of the universe should be receding from us at the same rate – he found more complex elements showing a subtly different red-shift.
Some of the elements showing the anomalous results were iron, manganese, magnesium, silicon, nickel, chromium and zinc. (Hydrogen, he said, isn’t in the list because within the scope of his observations, the change in alpha isn’t great enough to change the behaviour of such a simple atom.)
The value of alpha can explain the observation. “If you change alpha, you change the strength with which electrons are bound to their nuclei”, he told The Register.
“You also change the amount of energy needed to move electrons from one energy state to another, and that means you change the spectral lines of that element,” he said.
This is because photons are emitted from the elements as the release of energy by which the electron “falls” to a lower energy state.
And the point is that because the velocity redshift is uniform, its effect is easily separated from the shift that’s characteristic of individual complex elements.
The Register asked Dr Webb why this effect hasn’t been noted before. “The present data are far, far more extensive than anything that’s been done before”, he explained.
“The nearest independent study was a sample of 23 measurements, while we have 300 measurements.
“And we have an analysis with more extensive sky coverage than has been accomplished before.”
Webb isn’t confident that his hypothesis will be accepted quickly. Writing at Australian academic journalism site The Conversation, he said the observations might need years to gain acceptance (if, in fact, they are correct).
John Barrow, a Fellow of the Royal Society and professor at the University of Cambridge, has collaborated with Dr Webb on this work since 1996. ®
Bootnote: I have chosen to use alpha rather than the α symbol so as not to distract readers unfamiliar with scientific symbology. I hope I haven’t offended real boffins among The Register’s readership. ®