Short Stuff: The Mpemba Effect

Summary

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

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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.

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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]

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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]

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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

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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.

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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.

Transcript

[Josh]

This is an iHeart podcast.

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[Josh]

Hey, and welcome to the short stuff. Josh here, Chuck here. Giddy up. Yeah.

[Chuck]

We're going to tell you in part about a remarkable young teenager in Tanzania in the 1960s. And his name was Erasto Mpemba.

[Josh]

Is it Mpemba?

[Chuck]

It's Mpemba.

[Josh]

Okay. The reason why we're talking about Erasto Mpemba today is because he was a pretty remarkable kid. He. He stumbled upon, I guess you could say rediscovered a concept that just baffles physicists today because it doesn't make any sense. It may violate the second law of thermodynamics. And it ended up being named after him because he was a persistent little cuss who made this observation and just kept going until he finally got the ear of somebody who could help him try to figure it out.

[Chuck]

You know, the first law of thermodynamics is you don't talk about thermodynamics.

[Josh]

I was thinking about that movie the other day. I was like, I used to be so into that and now I'm so juvenile.

[Chuck]

I know. I almost put it on the other day as a laundry folding movie, which I like to do just to see parts of. And I had the same thought. I was like, I don't know if I just even want to go down that road again.

[Josh]

Yeah, because it exists happily in the past. You know what I mean? Yeah, exactly. I heard at the premiere, Brad Pitt leaned over to Edward Norton and said, I'll never be in a movie this cool again. And he was right. I think he was so, yeah, we're talking about Erasto Mpema because he discovered what's called the Mpemba effect after him. And I think I said earlier that he rediscovered was first noticed by Aristotle, or at least it was first written about all the way back to Aristotle. Medieval scientist Roger Bacon mentioned it as well. So did the Enlightenment philosopher Rene Descartes. And what they all noticed, and what Erastom and Pemba got his name attached to, 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.

[Chuck]

Yeah, he discovered this as a 13 year old. He was in class in Tanzania and they were making in school and they were making ice cream as a class. I don't know if that was for fun or if it was part of science. I like to think it was part of science. But regardless, they added sugar to the boiling fresh milk. You let it cool, you put it in a container, you put it in the freezer. They were doing this again another day. I bet they just like it. Ice cream, now that I think about it, sure. He was like, hey, the freezer space is getting low and I want to make my special ice cream. So he's like, I'm not going to let this stuff cool down. I'm just going to go grab that spot while it's available. And an hour and a half later, he was like, hey, everybody, my ice cream is ready before yours. In your face.

[Josh]

Yeah. And he said, but that doesn't make any sense because I put that hot milk in, so why would mine have frozen at all? And he went to his teacher and his teacher said, I've got too much to deal with. So you run along, Erasto.

[Chuck]

Yeah, I'm not curious like you.

[Josh]

No. And Erasto was undeterred. Over the years, teacher after teacher, as he made his way through middle school and then high school, he would talk to them about this discovery. And he was dismissed by all of them. And then finally one day at his high school, a physicist who was a visiting physicist to the University of Dar es Salaam, he was a British guy named Dennis Osborne. He came to give a lecture. And Erasto and Pemba saw his chance and said, professor Osborne, I've got something that may knock your socks off. Check this out.

[Chuck]

Do you think in the teacher's lounge over the years, everyone was like, hey, has Mpimba hit you up about this ice cream business?

[Josh]

Yes, they're all drinking wine and rolling around. So annoying.

[Chuck]

So annoying. All the scientific curiosity out of this kid.

[Josh]

I know. Luckily, Dennis Osborne was like, ooh, I like that. Let's talk a little more about it.

[Chuck]

He likes this kid, and he invited him in to, you know, to perform experiments to see if it worked. And then by 1969, I guess, Mpimba is 19 years old by this point. They had written a paper on this phenomenon, and he was like, hey, buddy, we got a name after you.

[Josh]

Yeah. Which I'm sure he was like, heck, yeah. Well, let's take a break and we'll talk a little more about the mpemba effect itself. How about that? All right.

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[Devin]

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[Josh]

Attention passengers. The pilot is having an emergency and we need someone, anyone, to land this plane.

[Devin]

Think you could do it? It turns out that nearly 50% of men think that they could land the plane with the help of air traffic control. And they're saying like, okay, pull this until this, pull that, turn this. It's just I can do my eyes closed. I'm Manny.

[Josh]

I'm Noah. This is Devin.

[Devin]

And on our new show, no such thing, we we get to the bottom of questions like these. Join us as we talk to the leading expert on overconfidence.

[Josh]

Those who lack expertise lack the expertise they need to recognize that they lack expertise.

[Devin]

And then as we try the whole thing out for real. Wait, what? Oh, that's the run, right? I'm looking at this thing. See? Listen to no such thing on the iHeartRadio app, Apple Podcasts, or wherever you get your podcasts.

[Josh]

Okay, Chuck, so the reason that the mpemba effect is so strange is because according to the laws of thermodynamics, molecules that are moving much faster than other molecules in, say, like, a hot liquid and a cold liquid, they take longer to slow down. And part of the very process of slowing down temperature, by the way, is a measurement of the excitement or movement of molecules in a substance. Right. Part of the process of slowing down is that it takes time. So it makes no sense intuitively, but also according to the laws of physics, that a hot liquid with faster moving molecules could get to the point of freezing faster than a cooler liquid with slower moving molecules because they're both trying to get to the point where they stop moving and are solid blocks of ice.

[Chuck]

Yeah. It would just make intuitive sense that something colder and closer to that temperature would do it faster. You can also observe this. If you go out in, let's say you live in Minneapolis and it's January, and you go outside with a cup of warm water and throw it into the air, that will go into an icy mist instantaneously if it's cold enough. If you do that same thing with a glass of cold water, that won't happen.

[Josh]

No. Are you serious?

[Chuck]

Yeah.

[Josh]

Are you pulling my leg?

[Chuck]

No. I mean, that's. I saw a video of it, and that's what they say is another example.

[Josh]

That's really great.

[Chuck]

I don't have firsthand experience because it doesn't get that cold here.

[Josh]

Very cool, though. No. Instead, you can fry an egg on a sidewalk. Am I right?

[Chuck]

Yeah.

[Josh]

Right. So I guess, essentially a good analogy that I came up with, that's why I think it's good, is that Erasso and Pemba basically found that there's a foot race between hot water and cold water, and that. Well, I screwed up my analogy already. Chuck, do you want to take it?

[Chuck]

I believe that there's a foot race, but one racer has started sooner, yet the one behind gets there quicker, even though they should supposedly be running at the same rate of speed. This happens at Braves games. Oh, and you know what? It's Mr. Freeze who they're racing. Isn't that funny?

[Josh]

Oh, wow. So they're clearly fans of the Mpemba effect.

[Chuck]

There's a track, clearly a track guy dressed up as Mr. Freeze, and they let a person from the stands, they bring him down in the outfield, and they give them a pretty long, like, a quarter of the distance head start. And then Mr. Freeze starts, and you almost always lose. But a young woman the other day beat Mr. Freeze, and it's on YouTube. It's very cool to watch. Because you could tell that she knew what she was doing because she was not running that hard until Mr. Freeze went. She was running at a decent clip. And then as soon as they hit the timer for Mr. Freeze to start, she kicked it into the next gear.

[Josh]

Wow.

[Chuck]

And whipped him. It was great.

[Josh]

That's awesome. I remember they used to have giant hammers and rulers and stuff by Home Depot racing. They have multiple races at home Braves games now.

[Chuck]

Yeah, they got Mr. Freeze and they have the Home Depot hammer drill. I can't remember what the third one was.

[Josh]

So silly. I gotta go this year, man.

[Chuck]

Yeah, I've been to a few games.

[Josh]

Well, let's go.

[Chuck]

They stink.

[Josh]

Oh, really?

[Chuck]

Oh, yeah. The Braves are terrible this year. They're a big disappointment. But, you know, what are you going to do?

[Josh]

Poor Braves. So, yeah, that was a great analogy, Chuck. Way to go.

[Chuck]

Thanks.

[Josh]

So it turns out that answering this weird problem has been trickier than you'd think. Trickier than physicists thought. Because some physicists conducting experiments in the mpemba effect have shown, Yep, this is definitely a thing. Other experimenters have not turned up any results. And they're like, no, I don't know what you're talking about. And so the fact that it happens under some cases and not others is not only even weirder, it also suggests to dissenters. People are like, there's no such thing as the impemba effect. That there's some variable that some experimenters aren't taking into effect. It could be different mineral contents in the water. It could be convection cells in the warmer water or causing it to freeze faster. It could be that our freezers work harder on warmer air than cooler air. So it'll freeze faster in a freezer. They don't know, but they're like, there's no such thing as the impemba effect. It's really just some mistaken variable in the experiments.

[Chuck]

Yeah, for sure. And there's also a long argument about this, about what freezing first actually means. Like, you have to. If you're going to do something like this, you got to agree when you're technically freezing and who got there first. It's not like Mr. Freeze running across that finish line and hitting his chest to that tape. No, that's obvious. So you gotta agree on freeze first. Is that like, hey, is it the first one to reach 32 degrees Fahrenheit, zero degrees Celsius, if it starts to form ice crystals? If it's good enough to put in a cocktail without getting too watered down? And I'm Gonna let you take MIT's engineering school response because it was very. Actually, guys. And not at all helpful.

[Josh]

It totally was. There was a blog post by them that basically said all liquids freeze at the same rate once they reach the freezing temperature, so no liquid can technically freeze faster than another. And you got the impression they really thought that they had solved the Mpemba effect.

[Chuck]

Yeah. That's not what we're talking about. Mit.

[Josh]

No.

[Chuck]

The rest of the world.

[Josh]

No.

[Chuck]

No one is talking about that.

[Josh]

No. The rest of the world is like, nope. We're talking about if you put a warm cup of water and a cool cup of water in a freezer at the same time, not what happens once they reach freezing. So if you. Even if you say, okay, we're going to talk about, like, we're going to use as the milestone or the finish line, which of these things gets to 32 degrees Fahrenheit or 0 degrees Celsius first? The freezing point.

[Chuck]

Yeah.

[Josh]

There's still a big discrepancy in how you track this kind of stuff.

[Chuck]

Yeah.

[Josh]

And different experimenters have been using essentially, what you call, like, different stopwatches, even though they're not actually standing there with the stopwatch. And it wasn't until some researchers from Kyoto in 2025 basically figured out a measurement standard that any lab could use to test the Mpemba effect. So now all of these experiments are going to be comparing apples to apples for results, and hopefully we'll get to the bottom of it.

[Chuck]

Yeah, for sure. This is the part that I think is the coolest, is that some researchers out there are like, hey, I guess in principle, I agree that we're not noticing some variable, but. But we feel like we've accounted for all the variables and perhaps there might be some unknown variable that we haven't discovered yet.

[Josh]

Yeah. Like some force or effect in nature that's just undiscovered that we're seeing in the Mpemba effect. Yeah, I'd love that, too. So you might say, like, okay, aside from just science being curious and wanting to know the answers to everything, like, what's the point in studying the Mpemba effect? And I was very surprised to find that there's a lot of reasons to understand this, that just knowing how fluid dynamics or systems under fluid dynamics relax or cool, it would actually open up or overcome a huge hurdle that quantum computing is facing right now. They have to figure out how to get qubits, which are the quantum computing version of ones and zeros, in traditional computers, back to their ground state as fast as possible. So if you can figure out how something like molecules stop moving faster than cool molecules, hot molecules, you might be able to apply that to quantum computing. And that would be a huge leap forward for it.

[Chuck]

Totally. Yeah. Because cooling those things down takes a lot of energy. And I want to do an episode about the AI's environmental cost at some point soon.

[Josh]

Okay, sure. You could also develop new sensors, new materials, and at the base, you could also make better freezers and refrigerators, too.

[Chuck]

Yeah, for sure. As for Mpemba himself, he overcame a lot of obstacles to eventually have a nice long career as a game warden and very sadly just passed away a couple years ago in 2023.

[Josh]

But he was older, right? Yes, 73. That's not bad, I guess.

[Chuck]

Yeah, not a bad life. But our scientific curiosity hat is off to you, sir.

[Josh]

Yes, and that means short stuff Is Happening.

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