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Black holes could unlock the mysteries of creation and live at the heart of nearly every galaxy. But these invisible balls of extremely dense matter have never been fully understood, especially when they were only a theory. We travel through a cosmic wormhole back to the 1930s to learn how the first astrophysicist to successfully theorize a black hole, Subrahmanyan Chandrasekhar, was ridiculed and rejected by his scientific community.

The principles of thermodynamics are cornerstones of our understanding of physics. But they were discovered in the era of steam-driven technology, long before anyone dreamed of quantum mechanics. 

In this episode, theoretical physicist Nicole Yunger Halpern talks to host Steven Strogatz about how physicists today are reinterpreting concepts such as work, energy and information for a quantum world.

Observations of the cosmos suggest that unseen sources of gravity — dark matter — tug at the stars in galaxies, while another mysterious force — dark energy — drives the universe to expand at an ever-increasing rate. The evidence for both of them, however, hinges on assumptions that gravity works the same way at all scales. What if that’s not true? 

In this episode, theoretical physicist Claudia de Rham explains her work on an alternative explanation called “massive gravity” to host Janna Levin.

Within just a few years, artificial intelligence systems that sometimes seem to display almost human characteristics have gone from science fiction to apps on your phone. But there’s another AI-influenced frontier that is developing rapidly and remains untamed: robotics. Can the technologies that have helped computers get smarter now bring similar improvements to the robots that will work alongside us? 

In this episode, Daniela Rus, a pioneering roboticist at the Massachusetts Institute of Technology, talks to host Steven Strogatz about the surprising inspirations from biology that may help robots rise to new levels.

Can you keep a secret? Modern techniques for maintaining the confidentiality of information are based on mathematical problems that are inherently too difficult for anyone to solve without the right hints. Yet what does that mean when quantum computers capable of solving many problems astronomically faster are on the horizon? In this episode, host Janna Levin talks with computer scientist Boaz Barak about the cryptographic techniques that keep information confidential, and why “security through mathematics” beats “security through obscurity.”

Common sense rules our world. This fundamental, sometimes trivial knowledge is inherent to how humans interpret language. Yet, some of these simple human truths are so obvious that they're rarely put into words. And without the data of common sense to train on, large language models such as ChatGPT have bizarre, often humorous blind spots.

Yejin Choi, professor and the chair of computer science at the University of Washington, calls common sense the “dark matter” of intelligence. In this week’s episode of “The Joy of Why,” Choi talks with co-host Steven Strogatz about decoding the interstitial glue of language and comprehension. Together, they explore the question: Should we program more humanity into the next generation of artificial intelligence?

In the tiling of wallpaper and bathroom floors, collective repeated patterns often emerge. Mathematicians have long tried to find a tiling shape that never repeats in this way. In 2023, they lauded an unexpected amateur victor. That discovery of the elusive aperiodic monotile propelled the field into new dimensions. 
The study of tessellation is much more than a fun thought exercise: Peculiar, rare tiling formations can sometimes seem to tell us something about the natural world, from the structure of minerals to the organization of the cosmos. In this episode, co-host Janna Levin speaks with mathematician Natalie Priebe Frank on the subject of these complex geometric combinations, and where they may pop up unexpectedly. Specifically, they explore her research into quasicrystals — crystals that, like aperiodic tiles, enigmatically resist structural uniformity.

The universe seems like it should be unfathomably complex. How then is science able to crack fundamental questions about nature and life? Scientists and philosophers alike have often commented on the “unreasonable” success of mathematics at describing the universe. That success has helped science probe some profound mysteries — but as the physicist Nigel Goldenfeld points out, it also helps that the “hard” physical sciences, where this progress is most evident, are in major ways simpler than the “soft” biological sciences.

In this episode, Goldenfeld speaks with co-host Steven Strogatz about the scientific importance of asking the right questions at the right time. They also discuss the mysterious effects of “emergence,” the phenomenon that allows new properties to arise in systems at different scales, imposing unexpected order on cosmic complexity.

During traumatic periods and their aftermath, our brains can fall into habitual ways of thinking that may be helpful in the short run but become maladaptive years later. For the brain to readjust to new situations later in life, it needs to be restored to the malleable state it was in when the habits first formed. That is exactly what Gül Dölen, a neuroscientist and psychiatric researcher at the University of California, Berkeley, is working toward in her lab. What is her surprising tool? Psychedelics.  

In this episode, Dölen shares with co-host Janna Levin the surprising potential of psychedelics to change the lives of those grappling with addiction, depression and post-traumatic stress.

For decades, the best drug therapies for treating depression, like SSRIs, have been based on the idea that depressed brains don’t have enough of the neurotransmitter serotonin. Yet for almost as long, it’s been clear that simplistic theory is wrong. Recent research into the true causes of depression is finding clues in other neurotransmitters and the realization that the brain is much more adaptable than scientists once imagined. Treatments for depression are being reinvented by drugs like ketamine that can help regrow synapses, which can in turn restore the right brain chemistry and improve whole body health.

In this episode, John Krystal, a neuropharmacologist at the Yale School of Medicine, tells Steve Strogatz about the new findings in mental health research that are revolutionizing psychiatric medication.