Podcast Summary: Stuff You Should Know — "Short Stuff: The Mpemba Effect"

Host: Josh and Chuck
Date: September 3, 2025
Podcast: iHeartPodcasts | Stuff You Should Know

Overview

In this episode, Josh and Chuck delve into the fascinating and perplexing Mpemba Effect—the scientific observation that, under certain conditions, hot liquids can freeze faster than cold ones. With their trademark curiosity and humor, they recount the story of how a Tanzanian teenager, Erasto Mpemba, brought renewed attention to this centuries-old phenomenon and why it continues to puzzle scientists today.

Key Discussion Points & Insights

1. The Discovery and History of the Mpemba Effect

• Erasto Mpemba’s Story

  • As a young teenager in Tanzania during the 1960s, Mpemba noticed that hot milk froze faster than cool milk while making ice cream at school.
  • Repeatedly dismissed by his teachers, he persisted until he met visiting British physicist Dennis Osborne, who took his claim seriously.
  • Together with Osborne, Mpemba published a paper on the effect in 1969, which was subsequently named after him.
  • Notable Quote
    • “He was a persistent little cuss… just kept going until he finally got the ear of somebody who could help him.” – Josh [01:27]

• Historical Precedents

  • The effect wasn’t entirely new: philosophers and scientists as far back as Aristotle, Roger Bacon, and René Descartes had noted similar observations.
  • Notable Quote
    • “So what they all noticed… is that hot liquids placed in a freezer can freeze faster than cool liquids placed in the same freezer at the same time. That makes no sense whatsoever.” – Josh [02:43]

2. The Physics (and Puzzlement) Behind the Phenomenon

• Why It’s Baffling

  • According to thermodynamics, it makes no sense that a hotter liquid (with faster-moving molecules) would transition to a frozen state before a cooler one.
  • The “molecular motion” argument: slowing down from a high-energy state should logically take longer.

• Everyday Example

  • The hosts reference the viral “boiling water in cold air” demonstration: Throwing hot water into super-cold air (like in Minneapolis in January) makes it freeze into an icy mist instantly, a behavior not replicated by cold water.
  • Notable Quote
    • “If you go outside with a cup of warm water and throw it into the air, that will go into an icy mist instantaneously… If you do that same thing with a glass of cold water, that won’t happen.” – Chuck [08:48]

3. Experimental Challenges and Controversy

• Experimental Inconsistencies

  • Some scientists reproduce the Mpemba effect, while others cannot, fueling debate over whether the phenomenon is real or simply the result of overlooked variables (e.g., mineral content, freezer air flow).
  • Notable Quote
    • “The fact that it happens under some cases and not others is not only even weirder, it also suggests to dissenters… that there’s some variable that some experimenters aren’t taking into effect.” – Josh [11:32]

• Defining “Freezing First”

  • There’s no universal agreement on what it means for something to “freeze first”: Is it reaching 0°C/32°F, the appearance of ice crystals, or some other milestone?
  • MIT’s engineering school offered an unhelpful answer: “All liquids freeze at the same rate once they reach the freezing temperature… so no liquid can technically freeze faster than another.” [13:11]

• Recent Advances

  • In 2025, Kyoto researchers introduced a standardized measurement protocol, allowing labs to compare results meaningfully and potentially resolve debate over the effect’s validity.

4. Scientific and Practical Importance

• Why It Matters
  • Beyond satisfying scientific curiosity, understanding this effect has practical implications.
    • Quantum Computing: The phenomenon might reveal novel ways to cool quantum bits (qubits) quickly, addressing a significant challenge in quantum computing.
    • New Materials/Sensors: Improved knowledge could lead to technological advancements.
    • Better Appliances: It could inform the design of more efficient freezers and refrigerators.
  • Notable Quote
    • “…just knowing how fluid dynamics or systems under fluid dynamics relax or cool… would actually open up or overcome a huge hurdle that quantum computing is facing right now.” – Josh [15:14]

5. Erasto Mpemba’s Legacy

• Despite early obstacles and skepticism, Mpemba enjoyed a long career as a game warden. He passed away in 2023 at the age of 73.
• Notable Quote
  • “But our scientific curiosity hat is off to you, sir.” – Chuck [16:24]

Notable Quotes & Memorable Moments

• “The first law of thermodynamics is you don’t talk about thermodynamics.” – Chuck, jokingly referencing Fight Club [02:00]
• “He was like, hey, the freezer space is getting low and I want to make my special ice cream… And an hour and a half later, he was like, hey everybody, my ice cream is ready before yours. In your face.” – Chuck [03:20]
• “Luckily, Dennis Osborne was like, ooh, I like that. Let’s talk a little more about it.” – Josh [05:08]
• “MIT… that’s not what we’re talking about. No one is talking about that.” – Josh & Chuck on academic nitpicking [13:27–13:31]
• The playful Braves "Mr. Freeze" analogy, comparing the foot race in the effect to a baseball stadium stunt [09:52–10:54]

Timestamps for Key Segments

• [01:14] — Introduction to Erasto Mpemba and outline of his discovery
• [03:20] — Mpemba’s school experiment and early skepticism
• [04:21] — Dennis Osborne takes Mpemba seriously; joint research begins
• [07:57] — Explanation of why the effect is so puzzling according to physics
• [08:48] — Real-world example: boiling water in sub-freezing air
• [11:32] — Discussion of the controversy and variable factors in replication
• [13:11] — MIT’s unhelpful “freezing is freezing” stance
• [14:02] — The need for a standardized measurement, Kyoto’s 2025 breakthrough
• [15:14] — Potential applications: quantum computing and beyond
• [16:07] — Erasto Mpemba’s career and legacy
• [16:24] — Tribute to Mpemba

Tone and Style

Josh and Chuck bring their signature mix of light-hearted banter (“He was a persistent little cuss…”) and scientifically grounded curiosity. The episode moves briskly, packed with real-life anecdotes, analogies (like Mr. Freeze and Braves games), and a touch of skepticism toward overly academic responses.

Conclusion

The Mpemba Effect, first stubbornly observed by a Tanzanian teenager, continues to baffle the scientific world more than half a century after it captured his imagination. As Chuck and Josh highlight, the story serves as a testament to scientific curiosity, persistence, and the importance of questioning things that “don’t make sense”—because sometimes, the coldest mystery springs from the hottest ideas.