I've been looking forward to this presentation, given today at CfA by Adam Riess, who won the Nobel Prize for the discovery that the universe's expansion is accelerating. In this talk he discusses the latest work in measuring the Hubble constant with improved data sets and reduced uncertainties, which yield a greater value than that from the Planck-CMB results. (I.e. the universe appears to be expanding a bit faster than we thought from Planck), and what the discrepancy between these results might mean for the Lambda-CDM model.
The Hubble constant remains one of the most important parameters in the cosmological model, setting the size and age scales of the Universe. Present uncertainties in the cosmological model including the nature of dark energy, the properties of neutrinos and the scale of departures from flat geometry can be constrained by measurements of the Hubble constant made to higher precision than was possible with the first generations of Hubble Telescope instruments. A streamlined distance ladder constructed from infrared observations of Cepheids and type Ia supernovae with ruthless attention paid to systematics now provide 2.4% precision and offer the means to do much better. By steadily improving the precision and accuracy of the Hubble constant, we now see evidence for significant deviations from the standard model, referred to as LambdaCDM, and thus the exciting chance, if true, of discovering new fundamental physics such as exotic dark energy, a new relativistic particle, or a small curvature to name a few possibilities. I will review recent and expected progress.