Eicher says there are other reasons that mice don’t like to have their boxes changed. “Pretend I’m a mouse, living in my house,” she says. “I’ve just gotten the house set up. I’ve got my bedroom and my bed all made. I’ve got my bathroom all set up.” Mice urinate in the same place. They defecate anywhere, so the analogy’s not perfect, but you get the idea. In any case, the clean new cage might be aesthetically pleasing to humans, but to mice it means that every few days they have to rebuild their world. How much fun is that?
Then there’s how the move to a new abode occurs. “All of a sudden, some giant thing grabs you,” says Eicher. “And they grab you by the tail so your butt’s up in the air and your head is down.” What’s more, it tends to happen during the day, and mice are nocturnal. They sleep during the day.
Moving can also mean social disruption. “Maybe I’m with five or six males,” says Eicher. “And one of the males is a bully. He has made everybody else kowtow to him. But when we get moved into a new house, the bully has to reestablish himself, so he runs around biting everybody.” The rebuilding, the sleep disruption, the social anxiety—none of it is life threatening, it is simply disruptive and not at all how the mouse expected things to go.
In Italian, in response to a question like Come va? (How’s it going?), you might say, Tutto a posto, if things are going well. It means everything’s good, but more precisely, the expression means everything is in place. In a country like Italy, where drinking a cappuccino after eleven a.m. upsets the apple cart (perhaps you weren’t aware that milk interferes with afternoon digestion), it makes sense that the good life would be the ordered life.
This isn’t only an Italian thing (or a mouse thing). People generally like it when things are in place. Our natural tendency is to organize—from the cans in our cabinets to the files on our desktops to our careers and families. It’s frustrating when things are out of order.
This trait isn’t confined only to living things. Materials like to have things in place, too—particularly when it comes to the atoms that compose them. Yet sometimes a material is faced with competing forces that make it difficult to know how to arrange things. Frustration (in physics, too!) is a deep internal conflict with no clear resolution.
Physicist Leon Balents is a frustration expert, although he doesn’t know exactly where the term came from. “I’m not sure whether it’s that the theoretician is frustrated in not being able to figure out how the system should resolve these competing forces. Or whether the material is frustrated in not knowing how to resolve the competing forces.” It seems to work on two levels.
Glass and plastics are often frustrated, but “the classic thing to talk about in the case of frustration is a magnet,” says Balents, who works at the University of California, Santa Barbara. A frustrated magnet isn’t really what people think of as a magnet at all. Frustrated magnets won’t even stick to anything.
Take that sombrero magnet that your friend brought back from Mexico that you’ve hidden under a menu on the fridge door. The sombrero, technically a “ferromagnet,” sticks to the fridge because of its electrons and the way they spin inside the atoms that make up the magnet. In ferromagnets, all of the electron spins want to orient in the same direction, just as the magnet in a compass wants to point north. “In ferromagnets, each spin wants to line up with its neighbor,” says Balents. “You can think of it as a force, where each one tries to force the other one to line up.” The cumulative alignment of these electron spins gives the magnet its ability to attract things.
In these magnets, figuring out how to put things in place is straightforward—at least, at certain temperatures. “There’s always a simple way to minimize the energy of all pairs of spins,” Balents says. “Just point them all along the same axis.” Every electron spin goes in the same direction as the one next to it. Tutto a posto. The sombrero is not frustrated.
Ferromagnets are much less common than antiferromagnets, Balents says. And antiferromagnets want a different arrangement. Their tendency is to order their electron spins in opposite directions. (This is why antiferromagnets don’t repel or attract anything—there’s not a cumulative force in one direction.) And this is where things can get frustrating.
If the atoms are aligned in a row—think of a battleship pegboard—it’s easy to alternate the spins: one up, one down, one up, one down. If the atoms are arranged in a triangle, however, there’s not a clear solution. If the spin on top of the triangle goes up, and the spin on the right corner goes down, what does the left side do? “The first spin wants the second one to be anti-parallel to it,” Balents says, “but the third spin is in trouble because it can try to be anti-parallel to the first spin, but then it will be parallel to the second one. This is the simplest example of what a physicist calls frustration.”
The competing forces make it so that there is no clear resolution. No way to satisfy every need. No right answer. “So it will make a compromise,” Balents says. “Usually, there isn’t only one compromise that is the best one; there can be many, meaning many different ways to orient these little magnetic spins that are almost equally good in terms of energy. This is maybe not totally unfamiliar; if you try to negotiate something complicated between many parties, it is not obvious how to figure out what the best compromise is. It’s that way for a frustrated magnet as well.”
Some materials are more frustrated than others. To determine the severity of the case, Balents says that you can see how the material behaves at different temperatures. At higher temperatures, frustrated materials are less decisive: they go from compromise to compromise, never settling on one. If you start to cool a material down and it still cycles through different compromises, it’s considered highly frustrated. The lower the temperature is before the material settles down is the measure of the material’s frustration.
Some mice are also more frustrated than others. It’s easy to tell when a mouse is getting irritated. “You can see it in its ears and body language,” says Belinda Harris. She’s a mouse wrangler or, more formally, a biomedical technologist in the mutant mouse resource facility. Harris says that when a mouse is content with its environment, you can tell. “They generally put their ears up and look around and point their nose to where they want to be.” On the other hand, when irritated, “they put their ears back and they flinch or act like they are not comfortable in whatever situation,” she says.
If you’ve ever wondered whether mice poop when they are annoyed, Danneman and Harris have the same answer: “Yes.” The other obvious question to put to a mouse expert is, Do cats annoy mice? Again, the obvious answer is yes. Perhaps more surprising is that rats annoy mice. “People just think of mice as rat wannabes,” says Danneman. “But a rat is a threat to a mouse. It’s a predator-prey relationship. You will see that mice, if they’re housed in an area where they smell rats, they will be agitated.”
Michelle Curtain agrees with Eva Eicher about mice not liking to be handled. Curtain is one of the technicians at the mouse facility and a de facto expert in mouse behavior. She’s standing behind a table set up near the outside edge of the tent. The mice she’s brought with her are from a strain formally known as SOSTdc1, but Curtain says that everyone at the lab refers to them as Sharkey, because of their interesting phenotype.