How Many Leaves Are on a Tree? | Kirk Johnson

Are Black Holes Dark Matter?

David Kaiser thinks tiny black holes from the dawn of time could be the solution to the dark matter puzzle. David joins Hakeem to discuss primordial black holes, tiny objects that may have formed in the first fraction of a second after the Big Bang. First proposed by Stephen Hawking more than 50 years ago, this hypothesis requires no new physics and no new particles, making it one of the most grounded ideas currently on the table… and one that may solve more than one cosmic mystery. David explains what these primordial black holes are, why many in the physics community are returning to this decades-old idea, and how it could potentially solve the dark matter mystery.  Make sure to subscribe now so you never miss an episode. Learn more about NOVA [https://www.pbs.org/wgbh/nova/] and visit YouTube [https://www.youtube.com/channel/UCjHz5SVHeMT0AViCYZvsGDA]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.

Why Dark Matter Matters

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 [https://www.pbs.org/wgbh/nova/] and visit YouTube [https://www.youtube.com/channel/UCjHz5SVHeMT0AViCYZvsGDA]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.

How Many Leaves Are on a Tree? | Kirk Johnson

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 [https://www.wgbh.org/podcasts/particles-of-thought/extended-interview-fossil-hunting-sinkholes-and-paleobotany-with-kirk-johnson] with Kirk Johnson. Learn more about NOVA [https://www.pbs.org/wgbh/nova/] and subscribe to our YouTube [https://www.youtube.com/channel/UCjHz5SVHeMT0AViCYZvsGDA]channel.

The Air You Breathe Is Bacteria Poop | Peter Girguis

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 [https://www.wgbh.org/podcasts/particles-of-thought/extended-interview-extremophiles-the-deep-sea-and-alien-life-with-peter-girguis] with Peter Girguis. Learn more about NOVA [https://www.pbs.org/wgbh/nova/] and subscribe to our YouTube [https://www.youtube.com/channel/UCjHz5SVHeMT0AViCYZvsGDA]channel.

The Fish That Could Walk | Sean B. Carrol

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 [https://www.wgbh.org/podcasts/particles-of-thought/evolution-of-new-species-venom-wings-and-more-extended-interview-with-sean-b-carroll]with Sean B. Carroll. Learn more about NOVA [https://www.pbs.org/wgbh/nova/] and subscribe to our YouTube [https://www.youtube.com/channel/UCjHz5SVHeMT0AViCYZvsGDA]channel.