“Discrepancies in the Measured Expansion Rate of the Universe”

“Discrepancies in the Measured Expansion Rate of the Universe”

Abstract:
The most basic parameter in our description of the expanding Universe is the current expansion rate, given by the Hubble Constant.
A mere two decades ago, the value of that constant was uncertain to a factor of two. Since then, the face of cosmology has changed, and we are now in an era of precision cosmology. We are able to measure the value of the Hubble Constant to within a few percent. The problem is, we now have two measurements– one from nearby objects such as variable stars and low-redshift supernovae, and the other from statistics of fluctuations in the early Universe. The two measurements are different at about the six-percent level, which is greater than the uncertainties on the individual measurements. While astronomers of two decades ago would dream to be in this situation, we find ourselves questioning whether there is something going on in the expanding universe that we haven’t figured out, or whether it is a matter of systematic uncertainties that we haven’t yet identified.
In this talk, I will discuss the history of both the Universe and of our dominant model of the Universe. I will describe how the Hubble Constant went from being extremely uncertain to relatively well known… well enough that we can see a discrepancy in two different measurements. I will describe the two ways we measure the Hubble Constant, and talk about possibilities for resolving the discrepancy in their results.

— Rob Knop 

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