Skip to Content
MIT News magazine

WD-40 for Micromachines

Calculating the effects of Casimir forces

In the age of tiny devices, Casimir forces have emerged as troublemakers. Discovered in 1948, these complicated quantum forces affect only objects that are very, very close together. And in micromachines like the accelerometers in the iPhone or the micromirrors in digital projectors, Casimir forces can cause tiny moving parts to stick together.

the force is with them: With this arrangement of tiny objects, the ordinarily attractive Casimir forces become repulsive.

MIT researchers have developed a powerful new tool for calculating the effects of these forces. With it, they’ve found a way to arrange tiny objects so that the ordinarily attractive forces become repulsive. If engineers can design micro­electromechanical systems (MEMS) so that the Casimir forces actually prevent their moving parts from sticking together, it could lower the failure rate of existing MEMS and new ones, such as tiny micro­fluidic devices that can perform hundreds of chemical experiments in parallel.

Casimir forces are caused by the way, in the quantum-mechanical view of the universe, subatomic particles constantly flash in and out of existence. There are so many of these particles, which might last only a few sextillionths of a second, that the forces they exert generally balance each other out. But when objects are very close together–as they must be in micro­machines–there’s little room for particles to flash into existence between them. Consequently, there are fewer transient particles between them to offset the forces exerted by the transient particles around them. The difference in pressure ends up pushing the objects toward each other.

In the 1960s, physicists developed mathematical equations that, in principle, describe the effects of Casimir forces on any number of tiny objects of any shape. But in most cases, those equations remained prohibitively hard to solve.

Associate professor of applied mathematics Steven Johnson, physics PhD students Alexander McCauley and Alejandro Rodriguez ‘07, and physics professor John Joannopoulos have mathematically demonstrated that the effects of Casimir forces on objects 100 nanometers apart can be precisely modeled using objects 100,000 times as big and 100,000 times as far apart, immersed in a fluid that conducts electricity. Instead of calculating the forces exerted by tiny particles flashing into existence around tiny objects, the researchers calculate the strength of an electromagnetic field at various points around centimeter-scale objects.

For objects with odd shapes, calculating electromagnetic-field strength in a conducting fluid is still fairly complicated. But it’s eminently feasible using off-the-shelf engineering software. “Almost any geometry you can think of has not been calculated,” says Rodriguez. With the MIT researchers’ new approach, that’s about to change.

Keep Reading

Most Popular

This startup wants to copy you into an embryo for organ harvesting

With plans to create realistic synthetic embryos, grown in jars, Renewal Bio is on a journey to the horizon of science and ethics.

VR is as good as psychedelics at helping people reach transcendence

On key metrics, a VR experience elicited a response indistinguishable from subjects who took medium doses of LSD or magic mushrooms.

This nanoparticle could be the key to a universal covid vaccine

Ending the covid pandemic might well require a vaccine that protects against any new strains. Researchers may have found a strategy that will work.

Stay connected

Illustration by Rose Wong

Get the latest updates from
MIT Technology Review

Discover special offers, top stories, upcoming events, and more.

Thank you for submitting your email!

Explore more newsletters

It looks like something went wrong.

We’re having trouble saving your preferences. Try refreshing this page and updating them one more time. If you continue to get this message, reach out to us at with a list of newsletters you’d like to receive.