Weight of the World

Summary

Aaron Mahnke's Cabinet of Curiosities

Episode: "Weight of the World"
Release Date: July 23, 2026
Host: Aaron Mahnke
Production: iHeartRadio and Grim & Mild

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Episode Overview

In this installment of "Cabinet of Curiosities," Aaron Mahnke explores two extraordinary stories where the weight of history—both metaphorically and literally—shaped the world. The first story reveals how Superman, the pop culture icon, helped curb the influence of the Ku Klux Klan. The second story descends into the vault beneath Paris to uncover the tale of La Grande K—the original kilogram—and how this tiny object defined mass for the entire world, before being retired in favor of a new scientific method.

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Story 1: Superman vs. the Ku Klux Klan

[01:10 – 07:36]

Key Discussion Points:

• Stetson Kennedy’s Fight:
  Stetson Kennedy, a Florida-born Southerner, spent years working to dismantle the Ku Klux Klan after witnessing their violence and exploitation growing up—an effort compounded by his personal shame over having an uncle in the Klan.

  • “He saw having a relative in the Klan as a stain on his family's reputation. So Stetson did everything that he could to stop them.” (01:59)

• Infiltration and Discovery:
  Kennedy and his friend, John Brown, infiltrated Klan meetings in Atlanta, learned about their rituals, corrupt practices (raking in money from members, union busting, selling useless insurance), and directly aided anti-Klan efforts:

  • “They learned that the KKK was no more than a racket where wealthy white men took advantage of poor white men and directed their anger at minorities.” (03:00)

• Resistance from Authorities:
  Despite sharing what he discovered with unions and state officials, Kennedy found institutional resistance—many in power privately supported or benefited from the Klan.

• A New Strategy:
  Sitting in an Atlanta park, Kennedy had a realization: if adults wouldn’t listen, maybe children would. Radio was then the family’s media hub, and "The Adventures of Superman" was a national sensation.

• The Superman Solution:
  Kennedy connected with the Anti-Defamation League, who got in touch with Superman’s radio show producers. They devised a new multi-part storyline, “The Clan of the Fiery Cross,” directly—if thinly disguised—targeting the Klan and exposing their inner workings:

  • “The storyline ended up being called the Clan of the Fiery Cross to avoid the potential legal consequences of actually depicting the KKK by name. But despite the name change, it was very clear that the group was the KKK.” (04:40)
  • Example from the plot: “During the scene, the Klan is depicted as using a strange two finger salute, something that Stetson potentially shared with the producers.” (05:30)

• Impact and Results:
  The show was a smash hit, receiving critical acclaim and helping to shift public perception. Membership in the Klan declined noticeably in the years following.

  • “Soon enough, the KKK was seen as the strange, pathetic, dishonest thugs they actually are. Politicians who were once privately supporting them began to publicly denounce them.” (06:25)

Notable Quote:

• “Curiously, though, the reason he was successful was because he realized that oftentimes fiction is more convincing than real.” (07:15)

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Story 2: The Kilogram’s Secret Vault

[08:22 – 13:58]

Key Discussion Points:

• The Parisian Vault:
  Deep beneath Paris, a heavily secured vault holds La Grande K—a platinum-iridium cylinder that, for more than a century, defined exactly what a kilogram was.

• Origins in Revolution:
  During the French Revolution, disparate and inaccurate units of measurement caused widespread confusion and resentment—fuel for revolution. France's solution: invent and standardize the meter, liter, and kilogram.

• The Problem with Water:
  Initially, a kilogram was meant to be equal to a liter of water, but water proved too unstable for reliable storage due to evaporation and contamination.

• La Grande K is Forged:
  In 1889, scientists forged the platinum-iridium cylinder—La Grande K—which became the master reference for mass. Prototypes were distributed worldwide to synchronize measurements.

• A Troubling Discovery:
  In 1989, after a century in its climate-controlled vault, scientists found that La Grande K was lighter than its replicas—by roughly 50 micrograms (the weight of a fly’s wing):

  • “Le Grand K is by definition the kilogram, which would mean that everything we thought was 1kg would actually be slightly heavier than a kilogram. All because the kilogram was shrinking.” (11:39)

• Searching for Answers:
  Possible causes, including cleaning protocols and outgassing, were debated, but ultimately—like all physical objects—“they lose atoms when touched.” Even minute environmental or handling effects, over generations, had changed its mass.

• A New Scientific Benchmark:
  In 2018, global representatives voted to retire the artifact. The kilogram is now defined by the Planck constant, measured through electromagnetic force and a device called a Kibble balance.

  • “Why should global science depend on a physical object that could be damaged or lost?” (12:53)
  • “Today, mass is defined by the Planck constant using a kibble balance, which measures weight via electromagnetic force. Which of course, everyone knows, right?” (13:22)

• Legacy of La Grande K:
  The artifact remains in its vault, outmoded but preserved “for future research on changes in mass.”

Notable Quote:

• “While its loss as the definitive kilogram weighs heavily on some of the scientific community, there is comfort in knowing that this new definition actually holds water.” (13:47)

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Memorable Moments & Quotes

• Fiction’s Power Over Fact:
  “Curiously, though, the reason he was successful was because he realized that oftentimes fiction is more convincing than real.” — Narrator (07:15)

• Science’s Shifting Standards:
  “Why should global science depend on a physical object that could be damaged or lost?” — Narrator (12:53)

• Historical Irony:
  “While its loss as the definitive kilogram weighs heavily on some of the scientific community, there is comfort in knowing that this new definition actually holds water.” — Narrator (13:47)

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Key Timestamps

• Superman vs. the KKK:

  • [01:10] Introduction to Stetson Kennedy’s anti-Klan mission
  • [03:00] Infiltration details and discovery of the Klan’s real agenda
  • [06:25] Public reaction and the Klan’s rapid decline

• La Grande K:

  • [08:22] Story begins—descent into the Parisian vault
  • [10:01] History of measurement during the French Revolution
  • [11:39] Discovery of the shrinking kilogram and worldwide implications
  • [13:22] Retirement of La Grande K and adoption of the Planck constant

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Episode Character & Tone

Aaron Mahnke’s storytelling combines sharp, meticulously researched historical insight with wry, understated humor and an appreciation for irony—always reminding listeners that the world's curiosities often reveal our greatest truths, and that sometimes, the smallest details carry the greatest weight.

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For more strange stories from history, check out the Cabinet of Curiosities book and website (grimandmild.com/curiosities). And as always: stay curious.

Transcript

[Podcast Announcer]

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[Erin Menke]

thoughts why did I search the Internet for answers to my cold sore problem? Now I'm stuck down a rabbit hole filled with images of alarmingly graphic sores in various stages of ooze. I can clear my search history, but I can never unsee that.

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[Erin Menke]

Welcome to Erin Menke's Cabinet of Curiosities, a production of iHeartRadio and Grim and Mild.

Our world is full of the unexplainable, and if history is an open book, all of these amazing tales are right there on display, just waiting for us to explore. Welcome to the Cabinet of Curiosities.

[Narrator]

I think it's fair to say that Superman is an American icon, so much so that his influence goes beyond fiction. In fact, there was one curious moment in history where Superman actually helped to defeat the Some real life villains it was 1946 and Florida born Southerner Stetson Kennedy had reached a dead end in his fight against the Ku Klux Klan. It would be an understatement to say that he hated them with a passion. He grew up in the south seeing the promise of the Reconstruction era destroyed by the KKK through their implementation of segregation. He saw his black neighbors harassed, robbed, assaulted and lynched by this white supremacist gangster. Stetson also had an uncle who was actually in the Klan, which made him deeply ashamed. His family tree included men who signed the Constitution. He saw having a relative in the Klan as a stain on his family's reputation. So Stetson did everything that he could to stop them. He and his friend John Brown infiltrated the Klan's headquarters in Atlanta posing as white supremacists. They attended meetings and learned as much as they could. They learned the silly greetings and the handshakes that they used. They learned that wealthy business owners were paying them to violently break up union rallies. They learned that they were targeting anti Klan journalists by jumping them in the streets and whipping them. And they learned how leadership charged new members $25 for their robes. They even sold them useless insurance policies. It became clear that the KKK was no more than a racket where wealthy white men took advantage of poor white men and directed their anger at minorities. Stetson passed information on to local unions warning them whenever the Klan planned to attack. He shared information on the Klan's violent activities with the Georgia Attorney General, hoping that they would be prosecuted and he also wrote to the Governor of Georgia, pointing out that the KKK was registered as a non profit to avoid taxation, when in fact it was profiting in several ways. However, none of these attacks seemed to stick. The problem was that many of the people in power in the south were secretly approved of the kkk. Either they were white supremacists themselves or they were profiting off of the KKK's union busting activities. Stetson sat in a park in Atlanta one day, dejected, trying to think of how he could bring the Klan to justice. He saw children playing and it occurred to him that maybe he would have to reach them if the adults wouldn't listen. And he knew just the way to do it. Throughout the previous few decades, radio had become the primary source of entertainment and news for most Americans and one of the most popular shows was the Adventures of Superman, a weekly 15 minute program that adapted adventures from the comic books. Stetson reached out to the Anti Defamation League who worked to fight against hate groups like the kkk. In turn, they reached out to the producers of the Adventures of Superman and began to collaborate on a storyline for the series where Superman exposed exposed and fought the kkk. The storyline ended up being called the Clan of the Fiery Cross to avoid the potential legal consequences of actually depicting the KKK by name. But despite the name change, it was very clear that the group was the kkk. They wore white pointy headed robes, they burned crosses, and they follow many of the same practices that Stetson uncovered. In the storyline, the young white boy named Chuck is playing baseball when a young Asian American boy named Tommy accidentally hits him with the ball. Chuck's Uncle Matt immediately accuses Tommy of trying to purposely harm Chuck and takes Chuck to a meeting of the Clan of the Fiery Cross where he pressures Chuck into misrepresenting the accident with Tommy. During the scene, the Klan is depicted as using a strange two finger salute, something that Stetson potentially shared with the producers. In the storyline, the Klan attacks Tommy and his family, which prompts none other than the Daily Planet reporters Jimmy Olsen and Clark Kent to investigate. Chuck's Uncle Matt is also shown climbing up the ranks of the Klan until he meets the leader who reveals that the white supremacist angle of the Klan is all a cynical ploy to get its members to buy robes. In the end, once Clark uncovers the truth, he changes into his Superman costume and beats up and arrests the members of the Klan. The storyline was a huge hit. The radio show received accolades in the press and from groups such as the National Conference of Christians and Jews. The adventures of Superman got the ball rolling on a sea change in the United States. Soon enough, the KKK was seen as the strange, pathetic, dishonest thugs they actually are. Politicians who were once privately supporting them began to publicly denounce them. Within just a few years, the Klan's membership had sharply declined. Stetson had been successful in his mission to hurt the kkk. Curiously, though, the reason he was successful was because he realized that oftentimes fiction is more convincing than real. This episode is sponsored by BetterHelp. We talk about mental health a lot more openly these days, which is definitely a good thing. But asking for help can still feel hard, and BetterHelp's latest research confirms it. 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On the outskirts of Paris, six floors beneath the cobblestone city streets, four people moved swiftly and silently through a long, narrow corridor. The precise, constant chill of this floor crept into their bones, making each movement a little stiff. Finally, though, the four arrived at their destination, a gleaming triple padlocked vault. One of the four stepped forward, the first of the Three keyholders, all present for this momentous occasion. With each key, another of the three silver pistons retracted from the lock until the door swung open to reveal the priceless treasure inside. Not a painting, not a diamond, not a stack of money or gold. It was a kilogram of technically, it was called La Grande Kilogram, or La Grand K. A small cylindrical weight made of 90% platinum and 10% iridium. And even inside this vault, it was also protected by three glass clutches shaped like nested bells. But La Grand K wasn't an ordinary kilogram. It was the kilogram, standardized, inarguable and exact. The object around which all other international units of mass are fixed. It might be hard to see why such a thing would be necessary, but the idea actually came as a solution to injustice. You see, during the French Revolution, units of measurement were locally decided on and very imprecise. As traveling and trading became more common, though, this created real problems. A pound of flour in Lyon might be equivalent to two pounds of flour in Saint Etienne. People understandably, were resenting paying more for less. Particularly at a time when economic injustice was enough to fan the flames of all out war. So in 1791, the French national assembly came up with a solution to all of this chaos. Three agreed upon units. The meter, the liter and the kilogram. For this last measurement, they would keep a definitive weight for posterity. Water, clean or dirty, weighed the same everywhere and was accessible to everyone. So the national assembly agreed that they would store one liter of water inside a vault. That one liter of water would equal one kilogram. But storing exactly one liter of water for all time proved to be challenging. Water evaporates when it's too hot, and it freezes when it's too cold. It leaks, it spills, it's messy. So in 1880, the plan changed. One liter of water would still be a kilogram. But instead of storing the water, they would store this platinum iridium sphere of equal weight inside. Problem solved, right? Well, not so fast. You see, when La Grand Cay was forged in 1889, France sent out national prototypes to several other countries. These were official copies that were meant to garner international cooperation through a single standardized weight. And every few decades, these copies were compared to the original. Le Grand Cay stayed in an artificial environment six floors down in the International Bureau of Weights and Measurements in Paris. Everything from humidity and temperature to air pressure and dust particles were controlled for in the vault. Exactly one century after La Grande Cay was forged, in 1989, four individuals made their way down through all those levels of security to measure Le Grand Cay. And they discovered something shocking. Le Grand Cay was shrinking lighter than the other copies by a whopping 50 micrograms, about the same weight as a fly's wing. Cue international panic. Legrand K is by definition the kilogram, which would mean that everything we thought was 1kg would actually be slightly heavier than a kilogram. All because the kilogram was shrinking. As you'd imagine, scientists scrambled for an explanation. Explanation after all, La Grand K was meticulously kept and maintained. Any change, even one as small as a fly's wing, was seen as unacceptable. So, for example, had the highly vetted cleaning process damaged the sample somehow? Alternatively, some physicists theorized the issue was something called outgassing, where solid objects release microscopic amounts of water vapor or cleaning solvents when exposed to a low pressure environment. Eventually, the best explanation they could come up with was that all physical objects absorb molecules from the air and they lose atoms when touched. And yes, atoms are small, but multiply that over the course of a century and that could explain the difference of 50 micrograms. After widespread attempts to find a solution which included a perfectly round silicon sphere, physicists had enough. Why should global science depend on a physical object that could be damaged or lost? Remember, the origins of Le Grand Cay came from a need for a weight that everyone had access to. And so on November 16th of 2018, representatives from 60 nations voted to retire Le Grand Cay. Today, mass is defined by the planc constant using a kibble balance, which measures weight via electromagnetic force. Which of course, everyone knows, right? La Grande Cay is still in its vault in Paris, preserved for future research on changes in mass. While its loss as the definitive kilogram weighs heavily on some of the scientific community, there is comfort in knowing that this new definition actually holds water. I hope you enjoyed today's guided tour

[Erin Menke]

through the Cabinet of Curiosities. This show was created by me, Erin Manke, in partnership with iHeart Podcasts, researched and written by the Grim and Mild team and produced by Jesse Funk. Learn more about the show and the people who make it [e-mail] curiosities. You'll also find a link to the official Cabinet of Curiosities hardcover book available in bookstores and online, as well as ebook and audiobook. And if you're looking for an ad free option, consider joining our Patreon it's all the same stories, but without the interruption, a small monthly fee. Learn more and sign up [e-mail] grimandmild and until next time, stay curious.

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