Lecture 1 

Speaker : Prof. Adam Riess (Johns Hopkins University and Space Telescope Science Institute)

Title : “New Determination of the Hubble Constant with Gaia EDR3, Further Evidence of Excess Expansion”

Abstract : 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% 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 ΛCDM, 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, most recently based on measurements from Gaia EDR3 released in December, 2020.

 Lecture 2 

Speaker : Prof. Lloyd Knox (UC Davis)

Title : “Cosmic Discord: Implications for and of Cosmological Theory”

Abstract : The most precise of the direct measurements of the current rate of cosmic expansion (the Hubble constant) is inconsistent with the even more precise, but indirect, model-dependent inferences. In particular the Riess et al. (2019) measurement is more than four standard deviations higher than the inference based on the standard cosmological model with its free parameters constrained by Planck satellite observations of the cosmic microwave background. In this talk I will explain the beautifully simple physics that allows for a prediction of the Hubble constant from observations of temperature and polarization patterns in the sky at millimeter wavelengths and I will entertain the exciting possibility that the origin of this discrepancy is a deficiency of the standard cosmological model. Finally I will address the prospects for future observations of the cosmic microwave background to point us from discord to concord.