University of Chicago│ Chicago, Illinois
University of Chicago │ Chicago, Illinois
For scientific investigations that established precision measurements of the expansion rate of the universe, and for leading efforts to make the next generation of these measurements even more precise.
For the latter half of the 20th century, astronomers tried in vain to pin down a number that acts like a master scale bar, that little cartographical ruler icon, on our map of the Universe. Get it wrong, and everything that follows becomes shaky: how big the Universe is, how long it has been expanding, and how quickly it is changing today. The value of what we call the Hubble Constant had been the source of contentious debate since Edwin Hubble’s early unsuccessful attempts to measure it based on the state-of-the art, but ultimately inaccurate, data.
In the 1990s, Wendy Freedman became a central figure in changing that, harnessing the power of what was then arguably the most advanced technology to leave Earth. An observational cosmologist now at the University of Chicago, Freedman led the Hubble Space Telescope Key Project. The aim was to utilize the Hubble Space Telescope to derive precise distances to galaxies, and from those distances, to deliver a definitive measurement of the universe’s current expansion rate.
The timing was dramatic. The Hubble Space Telescope had launched in 1990, and almost immediately the mission faced a public crisis: its primary mirror had been ground to the wrong shape, producing blurred images that threatened many of the telescope’s most demanding science programs. NASA and its partners responded with an engineering rescue that has since become legend. In 1993, astronauts installed corrective optics during the first servicing mission, effectively giving Hubble “glasses” and restoring its intended sharp vision.
For astronomers chasing faint, faraway targets, that fix was not merely cosmetic. It was essential. Freedman’s Key Project depended on Hubble’s ability to do something exquisitely difficult: measure precise brightness changes of Cepheid variable stars in other galaxies. Cepheids are stars that rhythmically brighten and dim, and the timing of that rhythm is tied to their intrinsic luminosity. If you can measure the rhythm and compare intrinsic brightness to observed brightness, you can infer distance. The brilliance of the Key Project was not simply using Cepheids but using them as a foundational calibration for multiple other distance-measuring techniques that reach even farther into the universe.
That cross-checking became the project’s signature. Rather than betting everything on one rung of the cosmic distance ladder, Freedman and her team used Cepheid distances to anchor several “secondary indicators” that could be applied to galaxies too distant for Cepheids to be easily measured. In practice, this meant building an interlocking chain of measurements, each one tested against the others, so that systematic errors could be identified and squeezed down. The Key Project’s final results, published in the early 2000s, delivered a measurement with a clearly stated uncertainty and helped settle a long-running debate that had persisted for decades. What made Freedman’s role especially consequential was her insistence that the result had to be earned the hard way: through careful calibration, transparency about uncertainties, and independent paths to the same answer. The Key Project was designed around that philosophy from the start, with an explicit goal of measuring the expansion rate by building redundancy and checks into the method. In other words, it was not enough to produce a number. The project had to produce confidence.
Freedman’s story also includes a second act that speaks to how science actually progresses. Once the findings of Freedman’s team settled the bigger debate around the Hubble Constant, a more subtle challenge emerged: discrepancies between different modern measurement approaches began to suggest that there might be factors missing from the cosmological model. Freedman responded by helping lead an effort to re-measure the expansion rate using an independent distance route, reducing reliance on Cepheids and testing the ladder with different stellar signposts. Through the Chicago-Carnegie–Hubble Program, she and collaborators have used alternative calibrators, including methods based on older stellar populations, to provide an independent check on the distance scale.
Freedman has also helped shape the field’s next big ground-based observatory. From 2003 to 2015, she served as the founding chair of the board of directors of the Giant Magellan Telescope (GMT) project, an international effort to build an extremely large optical telescope at Las Campanas Observatory in Chile. With four times the resolving power as the space-based James Webb Telescope, Freedman hopes the GMT will help detect signatures of life among the stars.
Freedman’s legacy is about making the universe measurable. She helped turn the Hubble Space Telescope into a cornerstone for the modern cosmic distance scale. Then she kept going, stress-testing the result with independent approaches and helping design the next generation of observatories that will sharpen our view even further. In a science where the biggest truths can hinge on the tiniest calibration choices, that is a rare and enduring kind of impact.
A native of Toronto, Wendy Freedman earned her doctorate at the University of Toronto and then joined the Carnegie Observatories, where she became director in 2003. In 2014, she joined the University of Chicago as a University Professor, continuing her work using space- and ground-based observatories to refine cosmological distances and the expansion history of the universe.
Information as of March 2026