As one of the audience at your Big Questions debate the other week, I though that you put up a good argument for an essentially untenable position – trying to defend the modern day equivalent of epicycles. I am still not quite sure whether you were merely playing ‘devil’s advocate’ for the purposes of educating and entertaining the general public, or whether you do indeed believe in the Lambda-CDM ‘Concordance Model’. Presumably you are aware of the number of alternative theoretical cosmological models that are out there, which explain the apparent cosmic acceleration (and galactic rotation curves and the rest), in an elegant and economical manner without the need for recourse to the Voodoo physics of dark energy and dark matter? The Conformal Gravity model (Mannheim et al), is a case in point. You are in the fortunate position, as a member of one of the Planck consortia, of very soon being in possession of the data that could validate (or refute) some of these alternative models. This might be a more fruitful avenue of research than merely fine tuning the parameters of those epicycles!