Theory Colloquium: A tale of many Hubble constants

Video

Abstract:

The Hubble constant should be a single number. Yet precision cosmology
seems to offer several, not all mutually compatible. The issue is often
framed as a disagreement between the local distance ladder and the
cosmic microwave background, but the landscape is much richer.
Geometric distances, standard candles, cosmic rulers, and stellar ages
provide different routes to the present-day expansion rate, each relying on
different physical processes and assumptions. Understanding what each
route actually constrains, how independent the determinations are, and
where systematic uncertainties enter is essential to interpreting their
apparent discrepancies.
I will use this tale of many Hubble constants to examine the remarkable
success, and increasing rigidity, of the standard cosmological model, and
reflect on what clues these complementary consistency tests, spanning
different physical regimes, might offer towards a more complete
description of the Universe.

Short Biography: 

Licia Verde is a leading Italian cosmologist and theoretical physicist. She studied physics at the University of Padua and obtained her PhD from the University of Edinburgh in 2000 under the supervision of Alan Heavens and Sabino Matarrese. After research positions at Princeton University and Rutgers University and a faculty appointment at the University of Pennsylvania (2003–2007), she became an ICREA Research Professor at the University of Barcelona, where she has built a leading research group in cosmology. She has also held visiting positions at the Institute for Advanced Study, CERN, Harvard's Radcliffe Institute, and the University of Oslo. In addition to her research, she serves as Scientific Director of the Journal of Cosmology and Astroparticle Physics (JCAP) and, since 2024, as Scientific Director of the Institute of Cosmos Sciences (ICCUB).

Verde's research focuses on observational and theoretical cosmology, particularly the large-scale structure of the Universe, the cosmic microwave background, dark matter, dark energy, inflation, and statistical methods for precision cosmology. She is internationally recognized for her contributions to the analysis of the WMAP mission data and to the development of rigorous statistical techniques for interpreting galaxy surveys. Her work has played a major role in determining cosmological parameters and in understanding the expansion history and composition of the Universe. She has also led major international research projects, including three European Research Council grants, and is a prominent member of collaborations such as SDSS and DESI.

Licia Verde has received numerous prestigious distinctions for her contributions to cosmology. Among her most notable honors are the

• Gruber Cosmology Prize (2012, with the WMAP team)
• the Breakthrough Prize in Fundamental Physics (2018, with the WMAP collaboration)
• the National Research Award of Catalonia (2018)
• the Rey Jaime I Prize for Basic Research (2021) and
• the Physics Medal of the Spanish Royal Physical Society (RSEF/BBVA) (2024).

She has also delivered the Lodewijk Woltjer Lecture of the European Astronomical Society (2019), has been recognized as a Highly Cited Researcher, and is among the very small number of scientists to have been awarded three European Research Council grants, including an ERC Synergy Grant in 2025.