For many years, scientists have endeavoured to find out whether the fundamental constants of physics are really constant, or whether they have changed over the course of time. The search has mainly focused on the fine structure constant, known by the Greek letter alpha (a), which involves the speed of light, as well as the charge of the electron and another parameter from quantum mechanics known as Planck’s constant. Back in 1998, Vladimir Dzuba, Victor Flambaum, and John Webb of UNSW suggested a method of searching quasar spectra for varying a that would improve sensitivity by a factor of about one hundred over previous methods. Subsequent measurements provided the first hint that a was different in the distant past.

This unexpected result has inspired much of the work that we do. For example, we are trying to find systematic effects that could invalidate the conclusion that a is varying. The leading contender is that the isotopic abundances in the early universe were different to those on Earth today, which could make it look like a was different even though it was not.

At the same time we are looking for other ways to determine whether a is varying using atomic clocks. Atomic clocks can measure time using different lines in atomic spectra. If we compare two kinds of atomic clocks and see that one is losing time with respect to the other over the course of a few years, we may be able to conclude that a is still changing today. We are calculating how big this drift will be in atoms that are currently of interest to experimentalists. They will use our calculations to choose the most promising atomic clocks, namely those that will stray from each other most strongly. Our group has shown that we can also use atomic clocks to test for variation in the proton magnetic moment, which is another fundamental constant.

Our group has led the way in finding methods that test for changes in other constants of nature, such as quark masses and the constants that control the strong interaction. There are several methods for doing this, all of which involve probing processes that occurred in the early universe. The results that suggest a has varied were obtained by examining the spectra of very distant quasars, and this method can also be used to test whether the proton magnetic moment was different. Then there is the Oklo reactor, which was a natural nuclear reactor in Africa that was working around two billion years ago. Stringent limits can be placed on variation of constants because the reactions taking place back then were the same ones that can happen today. Had the constants been even slightly different, some of the Oklo reactions could not have occurred.

A different method of testing differences in physical constants at the earliest times comes from a theory called Big Bang Nucleosynthesis (BBN), which deals with how the first hydrogen nuclei fused together to create larger nuclei in the first minutes of the universe’s existence. Our group realised that the progress of the reactions depends strongly on the constants that control the strong nuclear interaction, as well as on quark masses. By looking at the resulting universe, we can infer their values at the beginning of time.

Julian Berengut