ABSTRACT

Over the past few decades, cosmologists have for the first time identified the major constituents of the universe. Surprisingly, the universe hardly resembles what we thought only a few decades ago. The universe is filled with dark matter that is not visible and energy that permeates all of space, causing its expansion to speed up with time. Accurate distances remain central to a number of fundamental problems in astrophysics and cosmology. They are critical for measurements of the acceleration of the universe using supernovae. A more accurate measurement of the Hubble constant is critical for providing independent constraints on dark energy, the geometry, and matter density of the universe. The increased precision of cosmic microwave background fluctuations (most recently with the Planck satellite) make these direct comparisons even more critical, given the physical degeneracies amongst different cosmological parameters, and the apparent tension with the direct measurements of the Hubble constant. There has been fundamental progress over the last couple of decades in measuring extragalactic distances. The upcoming decade promises robust distances and a measurement of the Hubble constant to a few percent accuracy. New space and Earth-based telescopes planned for the next decade will address many of the current outstanding questions.

About the Speaker:

Wendy Laurel Freedman is a Canadian-American astronomer, best known for her measurement of the Hubble Constant, and as director of the Carnegie Observatories in Pasadena, California, and Las Campanas, Chile. She is now the John & Marion Sullivan University Professor of Astronomy and Astrophysics at The University of Chicago. Her principal research interests are in observational cosmology, focusing on measuring both the current and past expansion rates of the universe, and on characterizing the nature of dark energy.

Freedman is an elected member of the National Academy of Sciences and of the American Philosophical Society, and an elected Fellow of the American Academy of Arts and Sciences and of the American Physical Society. During her career, she has received numerous awards and honors for her contributions to observational cosmology, including a Centennial Lectureship of the American Physical Society (1999), the John P. McGovern Award in Science (2000), the Magellanic Premium Award of the American Philosophical Society (2002) and the Marc Aaronson Lectureship and prize (1994) "in recognition of a decade of fundamental contributions to the areas of the extra galactic distance scale and the stellar populations of galaxies". In 2009 Freedman was one of three co-recipients of the Gruber Cosmology Prize, widely considered to be astronomy’s equivalent of the Nobel Prize. Professor Freedman received the 2016 Dannie Heineman Prize for Astrophysics, awarded jointly by the American Institute of Physics and the American Astronomical Society, “for her outstanding contributions and leadership role in using optical and infrared space- and ground-based observations of Cepheid stars, together with innovative analysis techniques, to greatly improve the accuracy of the cosmic distance scale and thereby constrain fundamental cosmological parameters.”