Particles of Thought

David Kaiser knows the universe is hiding something enormous – and no one can see it. Dark matter appears to be all over our universe, but what is it? As a physicist and science historian, David joins Hakeem to discuss one of astrophysics most impossible puzzles. Nearly a century of observations - from the motion of galaxy clusters to the rotation of individual galaxies to the subtle patterns in the cosmic microwave background - has built a remarkably consistent case that most of the matter in the universe is invisible to us. Kaiser and Hakeem work through how that evidence accumulated, why the leading candidate explanations have become increasingly constrained, and one tantalizing idea that is getting physicists excited. Make sure to subscribe now so you never miss an episode. Learn more about NOVA and visit YouTube channel. --------------------------Guest Bio:David Kaiser is a professor of physics and the history of science at MIT. His research spans the history of modern physics, cosmology, and the foundations of quantum theory. He is the author of several books, including How the Hippies Saved Physics, and is a frequent contributor to public conversations about science and its history.

Need to know how many leaves are on that tree? Paleobotanist Dr. Kirk Johnson shares the surprisingly nerdy method—because you never know when leaf math will come in handy.For more, check out the extended interview with Kirk Johnson.Learn more about NOVA and subscribe to our YouTube channel.

Long before trees and grass, microbes were shaping our atmosphere. Evolutionary biologist Peter Girguis explains how ancient bacteria learned to split water for energy, and why their waste product changed Earth forever.For more, check out the extended interview with Peter Girguis.Learn more about NOVA and subscribe to our YouTube channel.

How did animals first make the giant step from water to land? Evolutionary biologist Sean B. Carroll explains how the discovery of Tiktaalik—a fossil with both fish and limb-like features—revealed a key moment in evolution.For more, check out the extended interview with Sean B. Carroll.Learn more about NOVA and subscribe to our YouTube channel.

Black holes aren’t the cosmic monsters Hollywood makes them out to be. Astrophysicist Janna Levin explains why they’re so hard to detect, why they’re not as destructive as you might assume, and how you could safely orbit much closer than you think.For more, check out the extended interview with Janna Levin.Learn more about NOVA and subscribe to our YouTube channel.

Could the universe be governed by a law we haven’t discovered yet? Mineralogist Robert Hazen and astrobiologist Michael Wong propose a new rule—the law of increasing functional information—to explain why complex systems evolve and why complexity keeps emerging over time.For more, check out the extended interview with Robert Hazen and Michael Wong.Learn more about NOVA and subscribe to our YouTube channel.

AI isn’t just coming for office jobs—it’s coming for some hands-on blue collar professions, too. AI expert Hany Farid explains which jobs are safe, and which are at risk. For more, check out the extended interview with Hany Farid. Learn more about NOVA and subscribe to our YouTube channel.

Scientists claimed in 2024 that they "de-extincted" the dire wolf… so what’s next, and what determines whether a species can be brought back? Evolutionary biologist Beth Shapiro explains some of the factors that go into deciding what to try and bring back. For more, check out the extended interview with Beth Shapiro. Learn more about NOVA and subscribe to our YouTube channel.

Dinosaurs might not have been the roaring beasts many imagine. Neuroscientist Erich Jarvis explains why modern birds—living dinosaurs—offer clues about vocal learning and why dinosaurs could have been singers.For more, check out the extended interview with Erich Jarvis. Learn more about NOVA and subscribe to our YouTube channel.

If the universe is expanding, why aren’t galaxies stretching apart? Cosmologist Adam Riess breaks down the physics behind cosmic expansion, the forces that resist it, and why dark energy dominates the vast spaces between.For more, check out the extended interview with Adam Riess.Learn more about NOVA and subscribe to our YouTube channel.