Theories unifying gravity with other interactions (electromagnetism and the strong and weak nuclear forces) suggest that spatial and temporal variation of fundamental "constants" in the Universe is possible. A change in the fine structure constant, α, could be detected via shifts in frequencies of atomic transitions in quasar absorption systems.
(A simpler explanation of what that means is here.)

We studied three independent samples of data containing 143 absorption systems spread from 2 to 10 billion years after Big Bang. All three data samples hint that α was smaller 7 – 11 billion years ago. The latest results give Δα/α = (−0.543 ± 0.116) ×10−5.

To continue this work, we need measurements of transition frequencies. Some of the lines in the absorption spectra have not been measured on Earth to the precision necessary to detect a variation in α. More information is in the section on Atomic Spectroscopy.

There is a systematic effect which has the potential to account for the observed α variation. Our group has assumed that the isotope abundance in the gas clouds sampled in the quasar spectra is the same as that on earth. In fact, this may not be true. Accurate measurements of the isotope shift are required to resolve systematic errors in the variation of α study. Isotope shift measurements can also be used to determine the abundances in the early universe directly, to test nuclear models in stars.

Due to the lack of such measurements, we have attempted to calculate the isotope shifts, and this work has formed the bulk of my PhD.