Short Wave

Fluoridating the public water supply has been common practice for nearly 80 years in the U.S. It's an acclaimed public health intervention that helps prevent cavities. For just as long, some have raised concerns about the practice that can veer from evidence-based to unsubstantiated conspiracy. An analysis by government researchers, published Monday in JAMA Pediatrics, is adding to the debate. The research found that exposing babies and kids to high levels of fluoride might be associated with neurodevelopmental harm. Frankly, it's a lot to digest — so we invited health correspondent Pien Huang onto the show to wade through the debate.

Questions, story ideas or want us to dig into another public health debate? Email us at [email protected] — we'd love to hear from you!

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Some weapons used by the U.S. military are so powerful they can pose a threat to the people who fire them. Today, we meet two Marines, William Wilcox and Michael Lozano, who spent years firing missiles and rockets, then developed the same rare brain condition: arteriovenous malformation, or AVM. The condition sends high pressure blood from a tangle of abnormal blood vessels directly into fragile veins, which can leak or burst. Most AVMs are caused by genetic changes that affect the growth of blood vessels, so the connection between weapon blasts and AVM isn't always immediately clear. But NPR's brain correspondent Jon Hamilton reports that recent research suggests that blast waves can alter genes in the brain — and that the evidence is even stronger for less extreme blood vessel changes.

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There are hundreds of atomic clocks in orbit right now, perched on satellites all over Earth. We depend on them for GPS location, Internet timing, stock trading ... and space navigation?

Today on the show, hosts Emily Kwong and Regina G. Barber learn how to build a better clock. In order to do that, they ask: How do atomic clocks really work, anyway? What makes a clock precise? And how could that process be improved for even greater accuracy?

For more about Holly's Optical Atomic Strontium Ion Clock, check out the OASIC project on NASA's website.
For more about the Longitude Problem, check out Dava Sobel's book, Longitude.

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Funeral services begin today for former President Jimmy Carter. He died Sunday, at 100-years-old. Carter brought attention to global health challenges, particularly "neglected" tropical diseases like Guinea worm. With reporter Jason Beaubien, we look at that decades-long effort and how science was central to Carter's drive for a better world.

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(encore) Snowflakes. These intricate, whimsical crystals are a staple of magical wintry scenes, but how big can they really get? Well, according to the Guinness World Record keepers, the "largest snowflake" ever recorded was a whopping 15 inches in diameter. It was spotted near Missoula, Montana in 1887. But Kenneth Libbrecht, a physicist at Caltech, has long been skeptical of that record. So he set out to find what makes a snowflake a snowflake and whether that 1887 record is scientifically possible. You can read more about what he discovered here.

Want to share the snowflakes you've spotted this winter? Email us a photo at [email protected].

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Happy New Year, Short Wavers! What better time to contemplate the conundrum that is zero than this, the reset of the year? Zero is a fairly new concept in human history and even more recent as a number. It wasn't until around the 7th century that zero was being used as a number. That's when it showed up in the records of Indian mathematicians. Since then, zero has, at times, been met with some fear — at one point, the city of Florence, Italy banned the number.

Today, scientists seek to understand how much humans truly comprehend zero — and why it seems to be different from other numbers. That's how we ended up talking to science writer Yasemin Saplakoglu about the neuroscience of this number that means nothing.

Read more of Yasemin's reporting on zero for Quanta Magazine. Plus, check out our episode on why big numbers break our brains.

Thirst for more math episodes? Let us know what kind of stories you want to hear from us in 2025 by emailing [email protected]!

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2024 was full of science news. There was a total solar eclipse, the Paris Olympics, elections in the United States and elsewhere, technological breakthroughs and many space launches. But perhaps above all, it was a huge year in health. So, today, we're talking through some of 2024's biggest health stories — from what's in our drinking water supply, to bird flu, obesity drugs and this year's record heat. They're also the stories we think will continue to be big in 2025. See you in the new year, Short Wavers! <3

Questions or suggestions for what else we should cover? Email us at [email protected]!

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The thick-billed parrot is the only surviving parrot species native to the United States. These brightly colored birds once roamed across the American Southwest and as far south as Venezuela — but today, the only wild population remaining lives high in the forests of Mexico's Sierra Madre mountains.

For years, conservation organizations like OVIS (Organización Vida Silvestre) and the San Diego Zoo Wildlife Alliance have been working on a multi-faceted conservation project to save these birds. Host Regina G. Barber and producer Rachel Carlson dive into the details of that project — and how tiny "bird backpacks" are helping to make it all happen.

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In pop culture, squirrels are often seen as jerky, excited critters on the hunt for nuts to stuff themselves with and tuck away for later. But squirrels are on the hunt for something a bit meatier in the California Bay Area. Their target: local voles. The entire process — from hunt to kill — was captured on video.

Want to hear more biology stories? Let us know by emailing [email protected]!

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In the early 20th century, a blight fungus wiped out most of the 4 billion American chestnut trees on the eastern seaboard. The loss was ecologically devastating. Short Wave host Emily Kwong dives deep into how scientists are trying to resurrect the American chestnut tree — and recent controversy over a plan to plant genetically modified chestnuts in the wild.

Want to hear about more efforts to recover endangered or lost species? Let us know by emailing [email protected]!

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