Theories unifying gravity with other interactions suggest spatial and temporal variation of fundamental "constants" in the Universe. A change in the fine structure constant, α = 2π e2/hc, could be detected via shifts in the frequencies of atomic transitions in quasar absorption systems. Previous studies of three independent samples of data, containing 143 absorption systems spread from 2 to 10 billion years after big bang, hint that α was smaller 7 – 11 billion years ago.

To continue this study we urgently need accurate laboratory measurements of atomic transition frequencies. We have compiled a current list of transitions of importance to the search for α variation. They are E1 transitions to the ground state in several different atoms and ions, with wavelengths ranging from around 900 – 6000 Å, and require an accuracy of better than 10⁻⁴ Å.

Isotope shift measurements for transitions to the ground state in Fe II, Cr II, Ni II, and Si II are also needed because the isotope abundance in the gas clouds sampled in the quasar spectra may not match those on earth. Accurate measurements of the isotope shift are required to resolve systematic errors in the variation of α. They can also be used to determine the abundances in the early universe directly, to test models of nuclear processes in stars. Isotope shift measurements have a further use in determining changes to the nuclear structure between isotopes.

An up-to-date and complete list of lines is available as a PDF: QSOlines.pdf.
Researchers who are interested in doing these measurements should contact us directly:

Victor Flambaum: flambaum@phys.unsw.edu.au
Julian Berengut: jcb@phys.unsw.edu.au