Scientists Will Soon Drop Antimatter To See How It Behaves In Gravity

The ALPHA experiment at CERN (Photo: CERN)

Antimatter continues to behave just like regular matter, no matter what tests scientists throw at it. And in the face of yet another new challenge, antimatter has again refused to crack.

In a new study, physicists attempted to find differences between matter and antimatter — confusingly, also a kind of matter, but with the opposite charge and other differences. It’s like an evil twin. Also confusingly, the universe has way more matter than antimatter, for no clear reason.

Physicists haven’t found the specific differences they were looking for when studying the antimatter version of hydrogen, called antihydrogen, but they have demonstrated a way to study antimatter better than ever before.

Physicists group the universe’s matter in several ways, but the one that has inspired perhaps the most interest from us non-physicists is ordinary matter versus antimatter. Every particle has an antiparticle with the same mass but opposite charge (and other properties), like its mirror image.

Immediately after the Big Bang, there should have been an equal amount of matter and antimatter particles. When the two meet, they annihilate into energy, leading people to say things such as “the universe shouldn’t exist”.

But for some reason, the particles that make up you, me, the Earth, the Sun, and virtually everything we see are mostly ordinary matter. Only one in every billion particles in the universe is antimatter, according to CERN. 

“The antimatter physics community is trying to find the matter-antimatter difference at different frontiers,” Gunn Khatri, a physicist at CERN who was not involved in the new study, told Gizmodo. “Every step made is getting us closer to answer one question: ‘Why is antimatter so much less common than regular matter?’”

Scientists hoping to understand antimatter have a tool at their disposal called the Antiproton Decelerator at CERN. This machine produces, and slows, the proton’s antimatter counterpart. ALPHA (the Antihydrogen Laser Physics Apparatus) combines these antiprotons with positrons, the antimatter counterpart of electrons, to form an antihydrogen atom.

Once the researchers trap the antihydrogen atoms, they probe them the same way they might study a regular atom. For each round of the experiment, ALPHA scientists shot 500 antihydrogen atoms with laser pulses, causing the atoms’ electrons to jump into a higher energy state. The electrons then drop back down, and the antihydrogen atoms release photons with a characteristic wavelength.

This is the well-known Lyman-alpha transition, used frequently in astronomy to study very distant objects.

The researchers measured the photons that came out, and they were essentially the same as the wavelengths you’d expect from a regular hydrogen atom, according to the study published in Nature. At this point, researchers continue to see that properties they hoped might differ between matter and antimatter appear to be the same.

But this experiment has an important second use: “We want to use it to do laser cooling of antihydrogen,” Jeffrey Hangst, the spokesperson of ALPHA at CERN in Switzerland, told Gizmodo. “This is the first demonstration” that their new laser-cooling method is doable in experiments.

Physicists use lasers to trap and cool atoms to temperatures extremely close to absolute zero. Observing the electron jumping up an energy level and releasing photons in response to a laser pulse in antihydrogen is a “decisive technological step,” according to the paper. It demonstrates that scientists may soon be able to laser-cool antimatter atoms as well. That will allow them to perform more precise measurements.

ALPHA, for example, will soon be upgraded with equipment that will allow it to drop antihydrogen atoms to see whether they interact with gravity differently than hydrogen atoms do. This will be another important test. 

This has nothing to do with CERN’s transport-antimatter-with-a-truck folks, but it’s still important research. Any difference between antimatter and regular matter will ultimately help us determine why all of the universe’s matter didn’t just annihilate to nothing after the Big Bang.

Folks such as Hangst don’t know what they’ll find in their experiments, but every new result drives them to keep searching.

Said Hangst: “We’re just after the truth.”


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