One of the greatest unsolved mysteries of our universe is why normal matter—the stuff that makes up stars, planets, and our bodies—is so much more abundant than antimatter, an exotic material made of antiparticles that hold the opposite charge of regular particles.
Now, scientists have announced that they have manipulated antimatter for the very first time using a specialized laser, a major breakthrough that could shed light on this open question, among many others.
The novel technique successfully slowed antihydrogen particles down by cooling them to temperatures near absolute zero, an innovation that “has far-reaching implications for antimatter studies,” according to a paper published on Wednesday in Nature. The ability to analyze and manipulate antimatter will allow scientists to test fundamental hypotheses about the makeup of reality, for example if antimatter particles are really identical to matter except for their charge.
The milestone was achieved by the Antihydrogen Laser Physics Apparatus (ALPHA) project, an international collaboration based at European Organization for Nuclear Research (CERN) in Geneva. For team members like Makoto Fujiwara, a researcher at the University of British Columbia’s TRIUMF laboratory and the spokesperson for ALPHA-Canada, the new study is the culmination of decades of imagination and grit.
“I have been working in this field of antimatter physics for over 20 years and laser-cooling antimatter has been really one of my dreams for a long time,” Fujiwara said in a call. “When I started, we didn't even know how to make antimatter atoms in large quantities—this was in the late 1990s—so this was completely wishful dreaming at that time.”
“It's really, really exciting—it’s beyond words,” he added, referring to the new study. “It’s exciting in two ways: One is that, of course, we have achieved a dream that we set out to do many years ago. But I'm even more excited about the opportunities that this opens up” which he said were “unthinkable before.”
Laser cooling and manipulation of various materials is a decades-old technique that has led to many groundbreaking results, but this is the first instance of its success with antimatter atoms.
But before diving into the mechanism and implications of the new experiment, it’s worth taking a step back to understand why antimatter has remained such a giant question mark in models of the universe.
Antimatter particles are thought to be identical to particles that make up regular matter, except they carry the exact opposite charge. The counterpart of an electron in a normal particle is a positron in an antimatter particle; a proton is an antiproton, and so on. Because they are equal but opposite forms of matter, particles and antiparticles spectacularly annihilate each other when they collide, a reaction that creates byproducts that can be detected in laboratories and that prove antimatter does exist.
According to modern physical theories, the Big Bang should have endowed the universe with equal amounts of particles and antiparticles. The result of such a configuration would cause all these matter-antimatter pairs to destroy each other in an epic cosmic showdown, leaving nothing behind but remnant energy for all time.
You may have noticed that in reality, the universe is not just some vibing husk of vestigial energy. It is a physical entity in which matter somehow ended up being far more plentiful than antimatter, raising a problem now known as the “matter asymmetry problem.”
To probe this mystery, scientists need to study antimatter in laboratory conditions. But as Fujiwara noted, that’s easier said than done. Because of its combustible relationship with regular matter, it’s tricky to make large amounts of this material in our antimatter-hostile world. When the first antimatter atoms were generated at CERN during the 1990s, they only existed for a tiny fraction of a second, far too short a period to examine them in detail.
By 2011, however, CERN had pioneered a technique that trapped antihydrogen atoms for a record 1,000 seconds. Fujiwara, who was a co-author of that study, saw this as the breakthrough that could one day make laser-cooling of antimatter particles a reality. This advance could dramatically slow down experimental antimatter atoms from speeds of around 300 kilometers per hour (186 miles per hour), which would allow for more precise observations—and even manipulation—of this bizarre entity.
“Of course, at that time, people kind of laughed at it,” Fujiwara said. “Because it's such a difficult thing to do, everybody knew. In particular, the laser that was required for antihydrogen-cooling is known to be tremendously difficult. So at that time, it was kind of a pipe dream.”
Despite the intimidating obstacles, Fujiwara was encouraged by a conversation about the topic with Takamasa Momose, another UBC physicist with expertise in laser-cooling, whom he just happened to bump into at a UBC cafeteria. Momose was optimistic that this specialized instrument could be built, and joined the ALPHA collaboration to lead the development of the laser.
Now, a decade later, the team’s hard work has paid off. During that time, Momose and his colleagues fine-tuned the ALPHA laser to shoot light at just the right frequency to cool antihydrogen atoms to temperatures approaching absolute zero, which in turn decelerated them to speeds of under 50 kilometres per hour (31 miles per hour).
In this cold and slowed-down form, the laser light can actually manipulate the antihydrogen, meaning that the antimatter can be controlled and moved with unprecedented precision, allowing researchers to make new observations of its odd properties and behavior.
To that point, the ALPHA team plans to continue improving the technique so that they can test out fundamental predictions that antimatter is identical to matter, except for its charge. If they find any other deviations in the antihydrogen particles, it could hint at the existence of new and mind-boggling physics beyond the well-corroborated Standard Model.
The team also hopes to examine other open mysteries, such as the matter asymmetry problem or antimatter’s unknown interactions with gravity: that latter line of research that could provide a novel test of the equivalence principle in Albert Einstein’s theory of general relativity. These are just a few high-profile examples of possible applications of this technique, but given antimatter’s essential and puzzling role in our cosmos, any new information about its weird characteristics will be valuable for understanding the very underpinnings of our reality.
To that end, Fujiwara and Momose have also founded a new project called Hydrogen Antihydrogen Infrastructure at Canadian Universities for Quantum Innovations in Antimatter Science (HAICU) to push the boundaries of their research further.
“The long-term goal in our field is really to try to make as precise-as-possible comparisons of the properties of matter and antimatter,” Fujiwara concluded. “The properties and the equivalence of matter and antimatter is deeply connected to the foundations of our physical understanding of nature.”