Professor Wendy Freedman was awarded the National Medal of Science last month for her work in cosmology and astronomy and her research on the Hubble constant. According to the U.S. National Science Foundation (NSF), this presidential medal is awarded for “outstanding contributions to knowledge… in service to the Nation.” The award recipients are chosen by a committee of distinguished scientists and engineers assembled by the NSF’s president. Only 14 nominations received by the committee were awarded this honor, including Freedman.
Freedman, UChicago’s John and Marion Sullivan University Professor in Astronomy and Astrophysics, spoke with the Maroon about her research and its long-lasting impact on the scientific community.
Freedman was recognized for her groundbreaking research on the Hubble constant, a value that has allowed scientists to determine how old the universe is and the rate at which it is expanding. In 2014, Freedman brought her work to UChicago to further research how to increase the accuracy of Hubble constant measurements to determine whether something fundamental is missing from the modern understanding of physics.
“We were working on ways to improve the accuracy that we could [use to] measure these quantities,” Freedman said. “There arose this potential problem that the measurement that we were making of how fast the universe is expanding, we’re making this locally in our sort of astronomical backyard. We can now compare with measurements that people are making of tiny fluctuations in the temperature of the microwave background.”
The question is, Freedman continued, ‘Is there a real discrepancy, or are there still unknown systematic errors that might be affecting the measurements?’”
Freedman, who grew up in Canada, explained that she has always been interested in astronomy, but was only able to start pursuing it when she attended the University of Toronto for her S.B. in astronomy and Ph.D. in astronomy and astrophysics.
Following a postdoctoral fellowship at Carnegie Observatories in Pasadena, California, Freedman was hired to Carnegie’s full-time staff in 1987. At Carnegie, Freedman used the Canada-France-Hawaii Telescope to measure the distances to different galaxies.
Freedman later co-led a team of 30 astronomers on the Hubble Key Project at Carnegie, an extension of the research being done on the Hubble constant using the Hubble Space Telescope (HST). The HST Key Project team measured the distances to 24 different galaxies using Cepheid variable stars—stars that brighten and dim periodically and are 500–30,000 times brighter than the sun.
“When the Hubble Space Telescope was launched, I became the scientific lead for the project that was aimed at trying to solve this issue of how fast the universe is expanding,” Freedman said. “We resolved that debate people had been arguing about whether the universe was 10 or 20 billion years old.”
Freedman’s team estimated the universe’s age by her Hubble constant measurement of 72 km/s/Mpc, which indicates the universe is between 13.7 and 13.8 billion years old.
Freedman was the first woman ever to hold a full-time position with the observatory. According to Freedman, women were still getting turned away from fellowships with Carnegie until the mid-1970s, with Freedman describing their excuse as that they “had no restroom facilities for women on the mountain.”
“I really do feel grateful that I entered at a time when it was possible to become a leader of a major program on a new facility like the Hubble Space Telescope and to become director of a major observatory. Those just were things that were not open to women,” Freedman said. “It’s very pleasing to see how that has changed over the course of my career, and how many more women there are now entering the field.”
At UChicago, Freedman’s team has measured the expansion rate of the Hubble constant with a new technique that studies the tips of red-giant-branch stars to obtain a reliable measurement for distance calculations. In 2019, Freedman published her team’s research with the conclusion that there was no real discrepancy in the Hubble constant measurements many scientists were analyzing.
However, according to Freedman, her team’s conclusion is a scientific controversy that has yet to be fully resolved, as some scientists still believe the discrepancy corresponds to a real error in measurement.
In her recent work, Freedman is excited by the possibility that something is missing from the modern understanding of the standard model of cosmology because it could lead to determining, as Freedman describes it, “the ultimate evolution of the universe.”
“If both types of measurements are correct, the measurements of the microwave background and the local measurements, it would suggest that there’s something really fundamental that’s missing… and that would be really interesting,” Freedman said. “That would be how we could discover new physics.”
UChicago Astronomy and Astrophysics Chair Joshua Frieman, who worked with Freedman’s team many years ago to combine supernova data to constrain dark energy, says that he frequently relies on Freedman’s advice and “wise counsel.”
“Wendy is a fantastic colleague and devoted mentor to students and early career scientists, who shows us all by example what scientific excellence and leadership look like,” Frieman said.
Frieman noted that the projects Freedman has led throughout her career, at Carnegie and at UChicago, have been critical to the scientific understanding of the fields of astrophysics and astronomy.
“Wendy’s measurements using the Hubble Space Telescope 25 years ago resolved what had been a long-standing controversy in the field of cosmology in the second half of the 20th century,” Frieman said. “Her team’s more recent measurements using the James Webb Space Telescope appear to be on the brink of resolving a similar controversy that has dominated the field for the past 10 years. Resolving this issue is central to whether our current model of cosmology will stand or fall, so the stakes are very high.”
Freedman said her current work with data from the James Webb Space Telescope has been exciting because she was part of the committee that first recommended the telescope be built over 25 years ago. She added that going from watching the telescope and its data measurement capacity develop over the years to now being able to use the telescope’s data has been “very rewarding.” She also underscored the importance of overcoming the obstacles in one’s path when it comes to pursuing a passion, explaining that she has been “guided” by the fact that she “just really love[s]” what she does.
“Don’t get discouraged by the hurdles. Find ways to get around them, get over them. Everybody will go through times when things will seem difficult, but don’t give up,” Freedman said. “If you are enjoying what you’re doing, you will find a path.”
Correction, February 25, 2025, 6:02 p.m.: This article previously stated that women were barred from fellowships at Carnegie Observatories until the mid-1980s. Carnegie’s earliest women fellows were admitted in the mid-1970s. Additionally, the article has been updated to better contextualize some quotes.
