Variation of fundamental constants of Physics: Observatinal constraints in the early Universe – VACOUL

Fundamental constants of Physics are expected to be neither strictly fundamental nor constant. In particular, variation of the traditional `constants', at some level, is a common prediction of most modern proposals for fundamental physics beyond the Standard Model. Testing the variation of constants is therefore a fundamental test of General Relativity.

The last several years have seen considerable activity in both theoretical and experimental explorations of variable constants. This has been motivated partially by reports of a systematic variation of the fine structure constant, alpha, in high redshift quasar absorption systems, as well as the emergence of the cosmological concordance model dominated by dark energy. Only astronomical observations can tell if the constants have maintained the same value through cosmological time or can change value from one place to the other in space.

Our group has been actively involved in this field. Already in the 1990's some of us have been among the first to constrain the variation of fundamental constants from observations of molecular absorption lines in the radio domain. More recently, we have used high quality data to derive
strong constraints on the variation of alpha and mu.

The field is at the moment very controversial however and a large effort has been engaged to solve the contoversies and derive the best limit that can be achieved with present-day instrumentation. The next four years will be very important as:
(i) A Large Programme of 37 nights of VLT-UVES observations has just been accepted to be conducted over the next three years to increase the sensitivity of the measurements for alpha and mu by about a factor of ten;
(ii) This period will see the advent of new radio and submm capabilities and in particular new instrumentation at IRAM and ALMA that will boost the field of constraining the variation of constants with radio observations.
Our group is strongly involved in both projects and will need manpower and financial support to maintain a leading place in the strong competition that prevails in this field.

Why upper limits are interesting ?
If the detection of a variation would revolutionize physics, astrophysical non-detections to smaller and smaller limits yield very important physical information: (i) first, this is one of the best way to test General Relativity and to extend its domain of validity; (ii) second, this can set strong constraints on certain classes of models of dark energy; (iii) third, the very high precision required for such measurements makes the field of high-precision spectroscopy progress at high speed which is very important to prepare future experiments with forthcoming high-resolution spectrographs on VLT (Expresso) and ELTs (CODEX); (iv) last but not least, the quest for finding variability in fundamental constants has important bearing on many different astrophysical domains such as, e.g. the chemical evolution of galaxies in a cosmological context, the high redshift molecular gas or the primordial yields.

This field of research is highly recommended in the Science Vision Document by the ESA-ESO Working Group (WG) on Fundamental Cosmology and is one of the science case considered by the ESO WG on E-ELT. The IAU has devoted a Joint Discussion on this subject during the last General Assembly in August 2009 (three of the proposers were in the scientific organizing committee and two were invited speakers).