Sara Imari Walker

Walker says she grew up in a rural town in Connecticut; her mother was an antique dealer and interior designer and her father a hairstylist, and both parents were interested in science.⁠[1]

She recalls that, unsure what to do after high school, she enrolled at a local community college, where a lecture on magnetic monopoles in her first-semester physics class convinced her to become a theoretical physicist.⁠[1]

She received an associate degree in math, science and pre-engineering from Cape Cod Community College in 2003 and a B.S. in physics from the Florida Institute of Technology in 2005.⁠[2]

In February 2008 she, Marcelo Gleiser and Joel Thorarinson posted the paper Punctuated Chirality, arguing that life’s homochirality may have resulted from sequential chiral symmetry breaking triggered by environmental events.⁠[3]

In 2010 she completed her Dartmouth CollegeDartmouth CollegeDartmouth College is a private institution of higher education in Hanover, New Hampshire, and a member of the Ivy League. Founded by Eleazar Wheelock, it received a royal charter on December 13, 1769. The 1819 Supreme Court ruling in Dartmouth College v. Woodward preserved its private status. Alongside undergraduate liberal arts education, Dartmouth includes the Geisel, Thayer, Tuck and Guarini schools. It enrolled 7,273 students in fall 2025 and held a $9 billion endowment at June 30, 2025. Sian Leah Beilock, in office since June 2023, remained president as of October 2026.Open the full entry dissertation, Theoretical models for the emergence of biomolecular homochirality.⁠[4]

She was a postdoctoral fellow at Georgia Tech’s Center for Chemical Evolution in 2010–2011 and a NASANASAThe National Aeronautics and Space Administration (NASA) is the U.S. federal agency responsible for the civilian space program, aeronautics research and space science. Established by law in 1958 and headquartered in Washington, D.C., it has run programs including Mercury, the Apollo Moon landings, the Space Shuttle, the International Space Station and Artemis.Open the full entry Postdoctoral Program fellow at the NASA Astrobiology Institute in 2011–2013.⁠[5]

She joined Arizona State University in 2013 and built a highly interdisciplinary origin-of-life research program, leading one of the largest theory groups in origins of life and astrobiology internationally.⁠[2]

She was assistant professor in ASU’s School of Earth and Space Exploration from 2013 to 2019, deputy director of the Beyond Center from 2016 and associate director of the ASU-SFI Center for Biosocial Complex Systems from 2018, becoming associate professor in 2019.⁠[5]

In 2015, at an origin-of-life conference in Washington, D.C., she heard the University of Glasgow chemist Lee Cronin describe comparing molecules by the number of steps needed to assemble them, and she joined him in developing the theory.⁠[6]

In 2017 Cambridge University Press published From Matter to Life: Information and Causality, edited by her, Paul C. W. Davies and George F. R. Ellis, which examines the role of information in the nature and origin of life from philosophy, biology, chemistry, physics and the cognitive and social sciences.⁠[7]

In May 2021 she, Cronin and colleagues published a paper in Nature Communications proposing a molecular assembly index that can be measured by mass spectrometry to identify molecular biosignatures in samples from Earth, outer space and the laboratory, as a basis for life-detection experiments beyond Earth.⁠[8]

On July 9, 2021, she appeared on episode 198 of the Lex FridmanLex FridmanLex Fridman is a Soviet-born, US-raised computer scientist and podcast host who works as an MIT research scientist on human-AI interaction and autonomous driving. His Lex Fridman Podcast is known for hours-long conversations with guests including heads of state and technology leaders.Open the full entry Podcast, discussing the origin of life, what life is, cellular automata, whether the laws of physics change with time, how to detect alien life and the shadow biosphere.⁠[9]

In November 2021, as an ASU associate professor, she was selected for the Stanley L. Miller Early Career Award of the International Society of the Study of the Origin of Life; she said she never expected it to go to theoretical research on what life is.⁠[10]

At the time she was also a principal investigator on a NASA Interdisciplinary Consortia for Astrobiology Research (ICAR) grant.⁠[11]

On April 24, 2022, she and Cronin appeared together on episode 279 of the Lex Fridman Podcast to debate alien life.⁠[12]

She was a 2023–2024 Berggruen Fellow, focusing during her fellowship on bringing concepts of life to the planetary scale and placing today’s evolutionary transitions in technology within the deep evolutionary history of life.⁠[13]

On October 4, 2023, Nature published the paper Assembly theory explains and quantifies selection and evolution by her, Cronin and colleagues, introducing a quantity called “Assembly” to capture how much selection is needed to produce a set of complex objects; she called the theory a major step toward a fundamental theory unifying inert and living matter.⁠[14]

The paper drew controversy: the theoretical biologist Johannes Jaeger argued in the Journal of Molecular Evolution that assembly theory has merit but is not nearly as novel as claimed and provides no new explanation of biological evolution or natural selection.⁠[15]

The microbiologist Rosemary Redfield publicly questioned how the paper passed peer review; a team led by the mineralogist Robert Hazen measured assembly indices as high as 30 for some minerals, a study Walker considers flawed because it copied methods designed for molecules.⁠[6]

On June 13, 2024, she appeared on episode 433 of the Lex Fridman Podcast as author of the new book Life as No One Knows It, discussing the definition of life, time and space, the technosphere, the origin of life, assembly theory, consciousness and artificial life.⁠[16]

On August 6, 2024, Riverhead Books, part of Penguin, published her book Life as No One Knows It: The Physics of Life’s Emergence.⁠[17]

The 272-page book argues that rather than debating definitions of life it is more productive to devise a test for it, and uses assembly theory to propose that things requiring 15 or more assembly steps should be considered living.⁠[18]

In the book she also proposes that time can be treated as a physical attribute, which for living things is the information accumulated over billions of years.⁠[19]

On October 21, 2024, she appeared on episode 388 of Sam Harris’s Making Sense podcast, discussing physics’ contributions to understanding life, Erwin Schrödinger, constructor theory, assembly theory, the Fermi paradox and the Great Filter.⁠[20]

On April 1, 2025, she gave a talk titled “An Informational Theory of Life” at the Long Now Foundation.⁠[21]

As of October 2026 she is a full professor at ASU with a joint appointment in the School of Earth and Space Exploration and the School of Complex Adaptive Systems, deputy director of the Beyond Center, an external professor at the Santa Fe Institute and a fellow of the Berggruen Institute, and serves on the advisory boards of the Sloan Foundation’s Matter-to-Life Initiative and the digital chemistry company Chemify.⁠[22]

She is active in public engagement, appearing at events such as the World Science Festival and on programs including Through the Wormhole and NPR’s Science Friday.⁠[23]

Personal website: Public link: https://emergence.asu.edu/ (opens in a new window)⁠[9]

X: Public account: https://x.com/Sara_Imari (opens in a new window)⁠[16]

Arizona State University: Official website: https://www.asu.edu/ (opens in a new window)⁠[2]

Santa Fe Institute: Official website: https://www.santafe.edu/ (opens in a new window)⁠[14]