Two papers published this week lay out the puzzling origins and potential uses of antimatter, a substance that upends the rules of ordinary matter.
A paper published today in JCAP finds that cosmic ray antinuclei may be indicators of a specific kind of dark matter. In another paper published earlier this week in AIP Advances, researchers describe a method to use antineutrinos produced by nuclear reactions at a facility to detect the location and activity of nuclear reactors.
Antimatter is important because it may help explain fundamental cosmic mysteries, such as why the universe is made of matter rather than an equal mix of matter and antimatter. These studies fit into a larger effort to decipher some of physics’ biggest mysteries, including the nature of dark matter, physics at the smallest scales, and possibly even the origin of the universe itself.
Despite its name, antimatter is actually matter. It has quality. Antimatter refers to a group of particles that have the opposite charge to ordinary particles. You’ve heard of electrons (negatively charged) and protons (positively charged); their antimatter counterparts are positrons (positively charged) and antiprotons (negatively charged).
Despite the difference in the particles’ electric charges, antimatter is not completely alien to fundamental forces. Last year, a group of physicists discovered that antimatter responds to gravity in the same way as ordinary matter, a discovery that confirmed Einstein and the Standard Model of particle physics.
More similar to the idea of ”antimatter” in your mind is dark matter – which also has mass – but cannot be seen by the various detectors humans have designed so far. Scientists know that dark matter exists because its gravitational effects are visible, although the particle (or particles!) responsible cannot be directly observed.
For some reason, antimatter remains a puzzling issue (sorry, terrible pun). As Gizmodo explained in 2022:
The universe had a Big Bang 14 billion years ago, which theoretically should have created equal amounts of matter and antimatter. But look around you, or look at the latest Webb telescope images: We live in a universe dominated by matter. A prominent question in physics is what happened to all the antimatter.
Antimatter and dark matter fit perfectly in a recent JCAP paper, which argued that experiments are detecting more antimatter than there should be, and they suggested that dark matter is the culprit.
A number of different particles (as well as other more exotic objects) are thought to be the creators of dark matter. Among them: axions, a particle named after laundry detergent; Large Compact Halo Objects, or MACHOs; dark photons, which despite their name are more like axions than some insidious light; Primordial black holes are tiny black holes created at the beginning of the universe and floating in space.
Recent research has focused on another type – weakly interacting massive particles (WIMPs) – as the culprit. The theory is essentially that when weakly interacting particles collide, they sometimes annihilate – destroy each other – emitting energy as well as particles of matter and antimatter.
In the 2022 study mentioned above, a group of physicists using the ALICE experiment at CERN found that antimatter can easily pass through our galaxy rather than being annihilated by matter in the interstellar medium, which is true for AMS-02 It is a salvageable conclusion to wait for anti-nuclear probes to conduct experiments on the International Space Station.
Pedro De la Torre Luque, a physicist at the Institute for Theoretical Predictions, said: “Theoretical predictions show that although cosmic rays can produce reflections by interacting with gas in the interstellar medium, particles, but the number of antinucleons, especially antihelium, should be very low.
“We expected to detect an antihelium event every few decades, but the approximately 10 antihelium events observed by AMS-02 were many orders of magnitude higher than predicted based on standard cosmic ray interactions,” De la Torre Luque added road. “That’s why these counternuclears are reasonable clues to WIMP’s annihilation.”
However, De la Torre Luque added, WIMP can only explain the amount of antihelium-3, an antimatter isotope detected by AMS-02, but not the rarer, heavier antihelium-4. In other words, even if weakly interacting particles are responsible for dark matter, they don’t tell the whole story.
WIMP may be responsible for the antimatter detections being collected by space-based detectors. But regardless of the dark matter question—a question that will take a long time to answer—the design of antimatter-sniffing detectors for monitoring nuclear reactors on Earth shows practical applications right here and now. Taken together, these discoveries about antimatter could provide new ways to exploit the strange properties of the universe for practical applications, while also helping us understand more about the universe and our own planet.
