Sean Carroll's Mindscape: Science, Society, Philosophy, Culture, Arts, and Ideas

370 | Daniel Akerib on a Faint Hint of Dark Matter

October 3, 2026

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5 min read

In June of 2023, a single particle interaction deep inside a seven-ton tank of liquid xenon, a mile underground in a former South Dakota gold mine, produced a signal that the scientists running the LZ (Lux-Zeppelin) experiment cannot explain away. It is a faint, solitary blip on a plot that otherwise shows only well-understood background noise. The event is consistent with what a dark matter particle—a WIMP—would look like if it smacked into a xenon nucleus. But it is also consistent with a statistical fluke or a background the team has not yet thought of. The statistical significance is 2.8 sigma, well below the 5-sigma threshold for a discovery. The collaboration has three times more data already recorded but not yet analyzed. Whether this event becomes the first chapter in the story of dark matter or a footnote in the history of experimental caution, the process by which the scientists are handling it is a textbook case of how real science works.

The Case for Dark Matter

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What you'll learn

1 (02:03) **Why This Episode Now** - Sean explains the two reasons for discussing the LZ experiment: a potentially exciting but statistically weak signal, and a lesson in how real science handles ambiguous data.
2 (06:39) **What is Dark Matter and Why Look for It** - Dan defines the dark matter problem: gravitational forces in galaxies are too strong for the visible matter alone.
3 (11:31) **The Many Possible Forms of Dark Matter** - The theoretical landscape of dark matter candidates, from WIMPs to axions to the "dark sector."
4 (18:07) **The WIMP Search: Past and Present** - The history of direct detection experiments and the evolution of technology from germanium to liquid xenon.
5 (21:56) **How the LZ Detector Works** - A detailed description of the LZ experiment: a 7-ton target of liquid xenon, deep underground, looking for billiard-ball-like nuclear recoils.
6 (26:17) **The Xenon Supply and Underground History** - The practical challenges of procuring xenon, and the historical precedent for deep underground physics.
7 (33:01) **The New Event That Has Everyone's Attention** - The discovery of a single high-energy event that is consistent with a nuclear recoil and inconsistent with known backgrounds.

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Show Notes

One reason it's been so hard to directly detect the dark matter is that we're not sure what it is. But for a long time, a leading candidate has been "Weakly Interacting Massive Particles" (WIMPs), so an impressive amount of experimental effort has been put into trying to detect them. Recently, a single provocative event appeared in the LUX-ZEPLIN (LZ) dark matter experiment. Daniel Akerib, a physicist at LZ, joins us to talk about dark matter and the recent data, which has low statistical significance but is intriguing nevertheless.

Blog post with show notes and transcript: https://preposterousuniverse.com/podcast/2026/10/05/370-daniel-akerib-on-a-faint-hint-of-dark-matter/

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Daniel Akerib received a Ph.D. in physics from Princeton University. He is currently Professor of Particle Physics and Astrophysics at the SLAC National Accelerator Laboratory and Professor of Physics, by courtesy, in the physics department at Stanford University. He has been searching for dark matter since the early 1990s, first with the Cryogenic Dark Matter Search and more recently with the LUX and LUX-ZEPLIN projects.