Short Stuff: The Mpemba Effect

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• 0:00Speaker 00

  This is an iHeart Podcast. Guaranteed Human.

• 0:04Josh Clark?

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• 1:05Josh Clark?

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

• 1:09Speaker 03

  Yeah, we're going to tell you in part about a remarkable young teenager in Tanzania in the 1960s, and his name was Arasto Mpemba.

• 1:18Josh Clark?

  Is it Mpemba?

• 1:22Speaker 03

  It's Mpemba.

• 1:23Josh Clark?

  Okay. The reason why we're talking about Arasto Mpemba today is because he was a pretty remarkable kid. 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.

• 1:56Speaker 03

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

• 2:00Josh Clark?

  Very nice. I was thinking about that movie the other day. I was like, I used to be so into that. And now it's so juvenile.

• 2:07Speaker 03

  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.

• 2:20Josh Clark?

  Yeah, because it exists happily in the past. You know what I mean?

• 2:23Speaker 03

  Yeah, exactly.

• 2:24Josh Clark?

  I heard at the premiere, Brad Pitt leaned over to Edward Norton and said, I'll never be in a movie this cool again.

• 2:32Josh Clark?

  And he was right.

• 2:33Speaker 03

  I think he was.

• 2:34Josh Clark?

  So, yeah, we're talking about Erasto Mempa because he discovered what's called the Mempa effect after him. And I think I said earlier that he rediscovered it. It 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 Erasto Mempa 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. It makes no sense whatsoever.

• 3:16Speaker 03

  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, he, you know, 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 liked it, ice cream. Now that I think about it.

• 3:41Josh Clark?

  Sure.

• 3:42Speaker 03

  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.

• 4:00Josh Clark?

  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 got too much to deal with. So you run along, Erasto.

• 4:15Speaker 03

  Yeah, I'm not curious like you.

• 4:17Josh Clark?

  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 Erastho and Pemba saw his chance and said, Professor Osborne, I've got something that may knock your socks off. Check this out.

• 4:49Speaker 03

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

• 4:57Josh Clark?

  Yes, they're all drinking wine and rolling their ice.

• 5:00Speaker 03

  So annoying, so annoying, all the scientific curiosity out of this kid.

• 5:03Josh Clark?

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

• 5:09Speaker 03

  He likes this kid and they, he invited him in to, to, you know, to perform experiments to see if it worked. And then by 1969, I guess Empembba 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.

• 5:27Josh Clark?

  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?

• 5:33Speaker 03

  All right.

• 5:47Josh Clark?

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• 8:06Josh Clark?

  Okay Chuck, so the reason that the Mpemba effect is so strange is because according to the laws of thermodynamics,

• 8:15Josh Clark?

  molecules that are moving much faster than other molecules in, say, like a hot liquid in 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.

• 8:58Speaker 03

  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.

• 9:24Josh Clark?

  No.

• 9:25Speaker 03

  Yeah.

• 9:26Josh Clark?

  Are you serious?

• 9:27Speaker 03

  Yeah.

• 9:28Josh Clark?

  Are you pulling my leg?

• 9:29Speaker 03

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

• 9:33Josh Clark?

  That's really great.

• 9:34Speaker 03

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

• 9:37Josh Clark?

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

• 9:42Speaker 03

  Yeah, right.

• 9:43Josh Clark?

  So, I guess essentially, a good analogy that I came up with, that's why I think it's good, is that Arasso and Pemba basically found that there's a footrace between, like, hot water and cold water, and that, well, I screwed up my analogy already, Chuck. Do you want to take it?

• 10:01Speaker 03

  I believe that there's a footrace, 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?

• 10:21Josh Clark?

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

• 10:23Speaker 03

  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 was, it's on YouTube, it's very cool to watch, because you could tell that she knew what she was doing.

• 10:50Josh Clark?

  Nice.

• 10:51Speaker 03

  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.

• 11:02Josh Clark?

  Wow.

• 11:03Speaker 03

  And whipped him. It was great.

• 11:05Josh Clark?

  That's awesome. I remember they used to have giant hammers and rulers and stuff.

• 11:10Speaker 03

  Oh, they still do.

• 11:11Josh Clark?

  Sponsored by Home Depot Racing.

• 11:12Speaker 03

  Yeah.

• 11:13Josh Clark?

  They have multiple races at Braves games now?

• 11:15Speaker 03

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

• 11:22Josh Clark?

  So silly. I gotta go this year, man.

• 11:25Speaker 03

  Yeah, I've been to a few games.

• 11:27Josh Clark?

  Well, let's go.

• 11:28Speaker 03

  They stink.

• 11:30Josh Clark?

  Oh, really?

• 11:31Speaker 03

  Oh, yeah. The Braves are terrible this year.

• 11:33Josh Clark?

  I haven't been following them.

• 11:34Speaker 03

  Very big disappointment. But, you know, what are you gonna do?

• 11:37Josh Clark?

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

• 11:41Speaker 03

  Thanks.

• 11:42Josh Clark?

  So it turns out that answering this weird problem has been trickier than you'd think. Trickier than physicists thought.

• 11:49Speaker 03

  Yeah.

• 11:49Josh Clark?

  Because some physicists conducting experiments in the Ampemba 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 Mpemba effect.

• 12:12Speaker 03

  Yeah.

• 12:12Josh Clark?

  But 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 are 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 Mpemba effect. It's really just some mistaken variable in the experiments.

• 12:40Speaker 03

  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 gonna do something like this, you've got to agree what that, 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.

• 12:57Josh Clark?

  No.

• 12:57Speaker 03

  That's obvious. So you've got to 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, uh, actually, guys, and not at all helpful.

• 13:21Josh Clark?

  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.

• 13:37Speaker 03

  Yeah, that's not what we're talking about, MIT.

• 13:39Josh Clark?

  No.

• 13:39Speaker 03

  No one is talking about that.

• 13:41Josh Clark?

  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.

• 13:53Josh Clark?

  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 zero degrees Celsius first, the freezing point?

• 14:07Speaker 03

  Yeah.

• 14:08Josh Clark?

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

• 14:12Speaker 03

  Yeah.

• 14:13Josh Clark?

  And different experimenters have been using essentially what you call like different stopwatches, even though they're not actually standing there with a 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.

• 14:37Speaker 03

  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 we feel like we've accounted for all the variables and perhaps there might be some unknown variable that we haven't discovered yet.

• 14:57Josh Clark?

  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 quibbles, which are the quantum computing version of

• 15:38Josh Clark?

  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.

• 15:55Speaker 03

  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.

• 16:06Josh Clark?

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

• 16:17Speaker 03

  Yeah, for sure. As for M. Pimba 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 of years ago in 2023.

• 16:29Josh Clark?

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

• 16:34Speaker 03

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

• 16:38Josh Clark?

  Yes, and that means short stuff is happening.

• 16:44Speaker 04

  Stuff You Should Know is a production of iHeartRadio. For more podcasts, iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows.

• 16:59Josh Clark?

  Buy smart, drive for less, and trade for more. That's Toyota Ford Ability, and it starts with a great deal on an off-road ready-to-coma or half-ton Tundra, two of Toyota's longest-lasting trucks, combining power for work, tech for adventures, and style in between. And they're built on a reputation for quality and reliability, which is why Toyota trucks are known for holding their value, which could mean big savings when it's time for your next Toyota. So get a great deal today and a great value tomorrow. Shop toyota.com for more. Toyota, let's go places.

• 17:30Speaker 00

  This is an iHeart Podcast. Guaranteed Human.