Measuring the Expansion History of the Universe, Tensely

I will give a talk on behalf of the Pantheon+SH0ES teams, which has made some of the leading measurements of the expansion history of the universe. On one hand, constraints from Pantheon+ show a universe consistent with the ΛCDM model, where dark energy can be described by a cosmological constant. On the other hand, constraints combining Pantheon+SHOES data find a high value of the Hubble constant, now 5σ away from the value inferred using ΛCDM from measurements of the Cosmic Microwave Background. How can both these statements be true? In this talk, I will go over these separate but overlapping measurements, and discuss how we can have tensions with some parts of the cosmological model but not others. I will also present new measurements of the Hubble constant using the Tip-of-the-Red-Giant Branch method from the CATS team, which appear to agree with with the SH0ES value. I will discuss possible explanations to the Hubble tension, and go over how other tensions have arisen in cosmology. I will also talk about how new telescopes, like JWST, can help resolve these controversies.

I hope to give a sense throughout the talk about the back-and-forth nature of research in cosmology these days, and how so many different parts of the cosmology and astrophysics community are engaging in this ‘conversation’ these days. While we don’t know how this story will end, this is a unique time in which scientists studying each different epoch of the universe can weigh in on a model that connects all of them.