Antimatter falls like matter, upholding Einstein’s theory of gravity

It’s official: Antimatter falls down, not up.

In a first-of-its-kind experiment, scientists dropped antihydrogen atoms and watched them fall, displaying that gravity attracts antimatter towards Earth, somewhat than repelling it.

The research confirms a pillar of Einstein’s common principle of relativity generally known as the weak equivalence precept. Based on that precept, gravity pulls on each object in the identical method, it doesn’t matter what it’s manufactured from. “This idea is on the coronary heart of our comprehension of gravitation,” says physicist Ruggero Caravita, who was not concerned with the brand new work.

Antimatter is the mirror picture of matter, carrying the other electrical cost however the identical mass. An electron’s antiparticle, for instance, is a positively charged particle referred to as a positron. A proton’s alter ego is a negatively charged antiproton, and so forth.

Most physicists didn’t significantly entertain the concept that antimatter may fall up as an alternative of down, says Jeffrey Hangst of Aarhus College in Denmark. However scientists had by no means been in a position to immediately take a look at it earlier than. “Antimatter is type of mysterious … so we need to really verify that habits,” says Hangst, who’s the spokesperson for the Antihydrogen Laser Physics Equipment, or ALPHA, collaboration, which reported the brand new consequence.

Not solely did the antimatter fall as anticipated, however it additionally dropped with roughly the identical acceleration as regular matter, the group discovered.

The outcomes, described within the Sept. 28 Nature, showcase scientists’ rising management over antimatter, and antihydrogen specifically. Antimatter is a wily substance that may be troublesome to work with. If it touches something manufactured from matter — the partitions of a storage container or molecules of air — it shortly annihilates. It has taken a long time of labor to measure any impact of gravity on antimatter in any respect, Hangst says.

Within the experiment, carried out on the European laboratory CERN close to Geneva, scientists trapped antihydrogen atoms with robust magnetic fields. These antihydrogen atoms had been made by mixing antiprotons, created at CERN, with positrons from a radioactive supply.

The researchers then launched the antihydrogen from its magnetic cage, counting what number of atoms went up versus down. If gravity treats antimatter and matter equally, most atoms ought to fall down, with just a few flying upward because of the preliminary jostling motions of the atoms. That’s simply what the researchers discovered.

“It’s a really good, very neat and quite simple idea,” says theoretical physicist Yunhua Ding of Ohio Wesleyan College in Delaware, Ohio, who was not concerned with the research.

To additional verify that the antihydrogen behaved as anticipated, the researchers altered the magnetic fields to push atoms upward, canceling out gravity’s impact. In that take a look at, roughly equal numbers of atoms went up and down. Additional various the magnetic fields likewise matched expectations.

Earlier experiments already hinted that gravity treats matter and antimatter the identical. In 2022, the BASE experiment, additionally at CERN, reported that oscillations of confined antiprotons not directly confirmed that matter and antimatter really feel the identical tug of gravity (SN: 1/5/22). However ALPHA’s experiment is the primary to immediately observe antimatter particles falling.

The concept various kinds of objects fall with the identical acceleration far predates Einstein. Legend states that within the sixteenth century, Galileo dropped completely different objects off the Leaning Tower of Pisa to reveal this impact. Scientists have since examined it in quite a lot of conditions, even with objects in orbit round Earth (SN: 9/14/22). However they’d by no means executed the take a look at with antimatter till now.

Though physicists didn’t anticipate the antimatter to fall up, some researchers have proposed that antimatter could fall with a barely completely different acceleration than regular matter. “If we discover even the tiniest distinction, this may be a sign that one thing new is occurring,” says Caravita, of the Nationwide Institute for Nuclear Physics in Trento, Italy, who’s the spokesperson of the AEgIS collaboration at CERN. AEgIS is one among a cadre of experiments there additionally working towards measuring gravity’s impact on antimatter.

The present experiment isn’t exact sufficient to suss out these refined variations. However new methods, similar to cooling antihydrogen atoms with lasers, may make future exams extra exact (SN: 4/5/21). That would assist scientists see, on the subject of matter and antimatter, whether or not gravity is really agnostic.