But here’s one new record you might not have expected to see: A team of scientists has come up with a plan for the smallest possible refrigerator. If it is ever built, it would be much smaller than the kitchen kinds.

It would be so small, we couldn’t see it — even with ordinary microscopes. That means it would be useless for cooling things like chocolate milk and frozen pizzas, but its designers say it may have other uses — like, say, creating faster computers.

The scientists weren’t thinking about how the mini fridge would be used. They wanted to know if such tiny objects transfer heat the same way larger objects, such as refrigerators, do. The area of physics in which scientists study heat and other types of energy is called thermodynamics.

Sandu Popescu, Paul Skrzypczyk and Noah Linden are three scientists who worked on the project. “We believe this is the smallest possible thing you can call a fridge,” Linden told Science News. All three researchers work at the University of Bristol in the United Kingdom.

For objects we can see, like baseballs, physics follows rules. If you hit the ball, it moves away from you. If you have two baseballs, and hit one, the other one doesn’t move. If you hit the second one, the first one doesn’t move. And baseballs certainly don’t talk to each other.

For the extremely small particles studied in a field of research called quantum mechanics, nature gets strange. Sometimes, tiny particles behave as though they’re talking to each other — even if they’re not close together. If a scientist stops one of the particles and measures it, for example, the other particle may act like it’s also been stopped to get measured.

When particles “talk” like this, they’re said to be “correlated.”

The tiny refrigerator works by using three correlated particles. These particles are called “qubits.” To understand how it works, imagine you’re playing a game, called “Qubit Refrigerator,” with two friends. Let’s call them Alice and Sam. The object of the game is to make you cold.

At the beginning, each of you is wearing a few coats. The game has three rules: 1. If Alice gets hot, she gives a coat to Sam. 2. If Alice gives a coat to Sam, you have to give a coat to Sam at the same time. 3. If Sam gets hot, he throws his extra coats on the floor.

Here’s how it works. Someone (who is not playing the game) starts giving coats to Alice. Alice puts them on. She keeps getting coats and putting them on, until she’s hot — and then she starts giving her coats to Sam. When she gives a coat to Sam, you also have to give a coat to Sam. Sam gets hot and throws these extra coats on the floor.

Alice is given more coats to wear. The more extra coats Alice is given, the more she gives to Sam. This means you have to give more coats to Sam. And as you lose coats, you get colder. The more coats Alice is given, the more she gives to Sam, and the more you give to Sam — and the colder you get. The game acts like a machine that makes you colder!

This may be the strangest science game you’ve ever played, but it’s similar to the a property of thermodynamics that explains how your refrigerator at home works. Your refrigerator has to be cooler than the air around it. But usually, heat moves from a warmer place to a cooler place — so heat should be warming up your refrigerator all the time. But if you — or your refrigerator — does work on the air outside, it’s possible to keep the air inside cold. This idea — that you can keep something cold by doing work — also helps explain the scientists’ tiny refrigerator. In the case of the “Qubit Refrigerator,” work is done when someone gives coats to Alice.

Here’s how the game connects to the scientists’ work: Instead of you and two friends, the “players” in the tiny refrigerator are tiny particles called qubits. And instead of giving coats, two qubits (you and Alice) are actually giving heat to the third qubit (Sam). The hotter Alice gets, the colder you get.

The researchers found that as the hottest qubit (Alice) gets hotter, the refrigerator gets colder. And as long as the hot qubit stays hot, this quantum fridge continues to work.

“Once you set it up, it just sits there, gently cooling away,” Linden told Science News.

Right now, the tiny fridge is just an idea, and the scientists have only devised the device. They haven’t actually built one. “We don’t want to claim that we know of a place where this happens,” Linden told Science News.

POWER WORDS (adapted from the Yahoo! Kids Dictionary, NASA Science and Science News for Kids)

qubit A quantum bit; a unit of information in quantum mechanics.

refrigerator An appliance for storing substances at a low temperature.

physics The science of matter and energy and of interactions between the two, grouped in traditional fields such as acoustics, optics, mechanics, thermodynamics and electromagnetism, as well as in modern fields including atomic and nuclear physics, solid-state physics, particle physics and plasma physics.

particle A very small piece or part; a tiny portion or speck.

“It’s bothersome,” says Bruce Hamaker. He’s a food chemist at Purdue University in West Lafayette, Indiana. “It can chip teeth if people aren’t paying attention.”

Artville

Instead of just grumbling about the problem, Hamaker and his coworkers have used science to try to figure out a way to reduce the number of unpopped kernels at the bottom of a bag of microwave popcorn.

The results may do more than just do away with the annoyance of biting into rock-hard kernels in the middle of a movie. Popcorn is an important crop in Indiana, Nebraska, and other states. Growing types of popcorn that pop better than current varieties do could improve popcorn sales.

Pressure cooker

Not just any type of corn will pop. Popcorn kernels are rounded and hard on the outside. They contain moisture on the inside. For a kernel to pop properly, water must make up between 14.5 and 15 percent of a kernel’s weight

Each kernel of popcorn is like a pressure cooker waiting to blow. As a kernel heats up in a microwave, pot, or air popper, water naturally found inside heats up, turns to gas, and expands. The pressure builds up inside the heated kernel until its shell bursts.

These little explosions turn kernels inside out, leaving behind airy balls of fluff that somehow make movies more special.

Depending on the variety of popcorn, kernels pop to form one of two shapes. The “butterfly” type, which is most common, is big and fluffy and looks as if it has wings. The “mushroom” type is round and compact. It’s better at holding cheese, caramel, and other coatings without falling apart.

The “butterfly” type of popcorn is big and fluffy.

Fatty coatings

To tackle the unpoppable popcorn problem, Hamaker and his coworkers started with a hunch.

Previous research had suggested that certain kernels lose moisture too quickly, either when stored or when heated. Without the proper amount of steam inside, the kernels would then fail to pop.

So, the researchers began by looking for coatings that would prevent moisture loss. Pretty soon, they found that coating kernels with certain types of fat could practically eliminate unpopped kernels.

Coating kernels before popping them isn’t an ideal solution, however. Extra fat could make popcorn greasy. And adding coatings would create more work for popcorn processing companies.

“They’d rather not add something to the process,” Hamaker says.

Crystal hull

Instead, the scientists decided that it might help to understand why some kernels lose moisture faster than others do in the first place.

Food chemist Bruce Hamaker has studied a variety of foods. Here, he’s examining samples of sorghum.

Purdue University

So, they studied 14 varieties of popcorn that had different microwave popping qualities. When the worst varieties were heated, as many as 47 percent of the kernels didn’t pop. The best varieties had only a 4 percent failure rate.

The secret, it turns out, lies in the structure of a kernel’s outer hull, also called the pericarp.

One-third of a popcorn kernel’s hull is made up of a material called cellulose. Found in all plant cells, cellulose is a kind of carbohydrate—a compound made up of carbon, hydrogen, and oxygen.

When heated, the cellulose in a kernel’s pericarp rearranges itself into an orderly structure known as a crystal. “It’s interesting that cellulose would undergo this kind of transition,” Hamaker says.

The crystalline sheet is tighter than the original cellulose, which is only partially ordered. “It forms a better barrier,” he says, “and keeps moisture in the kernel better.”

Why some popcorn kernels are better poppers than others depends on how orderly these crystalline sheets are, the researchers found. The best poppers have cellulose that’s especially good at turning into crystals.

Better coatings

This popcorn research could prove useful to popcorn growers. One good strategy would be to breed corn that produces kernels with pericarps made of a type of cellulose that turns into nice crystals.

NASA

The chemical processes involved in popcorn popping could also end up being of interest in other fields of food science, Hamaker says. Perhaps scientists could come up with cellulose coatings that would keep moisture inside fruits or grains and keep them fresher longer.

Hamaker had never studied popcorn before. After endless batches of popcorn, popped and eaten in his lab, he was surprised at how much there is to learn about something as seemingly simple as popcorn.

“Everything’s more complicated than you think,” Hamaker says. “The interesting thing about science to me is when you learn something unexpected that gives you an answer to a problem you’re working on.”

Going Deeper:

Additional Information

Questions about the Article

Word Find: Popcorn

Science Project Brainstorms

Are you interested in investigating popcorn? Here are some questions that may be worth tackling.

• How does the type of coating (fat) affect the number of unpopped popcorn kernels?
• Do different brands of popcorn leave different amounts of unpopped kernels?

For other science project ideas, go to www.popweaver.com/popcorn101/science/
science_list.html (Weaver Popcorn Company) or www.exploringminds.ca/e/featuring_science_fair/
qp_pop_corn.html (Exploring Minds).