Antimatter is weird stuff. It was created during the Big Bang along with traditional matter, but it has the exact opposite properties of the kinds of matter we know: anti-electrons (or positrons) have a positive charge rather than negative, for example, while antiprotons, the antimatter versions of positively charged protons, are negatively charged. Scientists can create antimatter through high-energy collisions in a lab — at a cost of about $100 billion per milligram. But antimatter is incredibly rare in the real world, because when matter and antimatter come into contact, they annihilate each other.
Confused? That's okay. Even physicists have a hard time wrapping their minds around antimatter. But now, for the first time, they are able to measure it.
Writing in the journal Nature on Monday, researchers at the European Organization for Nuclear Physics (CERN) announced that they found a way to study the properties of an anti-atom by zapping it with a laser beam. The particles within the anti-atom are excited by the laser, causing them to absorb some light wavelengths and emit others. By comparing that spectrum to the one that comes from regular atoms, the scientists hope to figure out what makes antimatter so weird. The advance could open the door to testing some of the fundamental principles of physics.
“It's a stunning result,” Alan Kostelecky, a theoretical physicist at Indiana University, Bloomington, who was not involved in the CERN research, told Science.
For nearly a century, since antimatter's existence was first theorized in 1928, physicists have dreamed of using a spectrometer to understand the elusive particles. But it took several decades to find a way to create antimatter atoms; then researchers had to find a way to trap them.
At CERN's ALPHA-2 lab, scientists can do both. They create antihydrogen — an atom made up of one positron and one antiproton, just as a hydrogen atom is made of one electron and one proton — by smashing large numbers of positrons and antiprotons together in a cylindrical trap. Using magnets, they are able to snag just a few of the newly created anti-atoms into a vacuum before they get obliterated by matter.
In this latest experiment, the CERN researchers then shined a laser through the trap; they found that antihydrogen responded to light in the same way as regular hydrogen.
This supports scientist's models for how antimatter should behave. Some of the basic rules of physics predict that antihydrogen and hydrogen would emit the same light spectra — including Einstein's theory of special relativity, which states that light is the fastest moving thing in the universe; the Standard Model, which explains how elementary particles interact; and something called Charge, Parity, and Time Reversal symmetry, or the CPT theorem, which says that energy levels in matter and antimatter should be the same.
For now, the ALPHA-2 experiment seems to have affirmed that theory.
“We're kind of really overjoyed to finally be able to say we have done this,” Jeffrey Hangst, a member of the ALPHA-2 group and a physicist at Aarhus University in Denmark, told NPR. “For us, it's a really big deal.”
But the measurement of antihydrogen's light spectrum was about 100,000 times less precise than the best measurements of the spectrum for regular hydrogen. The researchers want to probe antimatter with a broader range of laser energies, and measure the results to a much higher degree of accuracy, before drawing any absolute conclusions.
The end game of all this particle zapping is to understand one of the fundamental mysteries of existence. If the Big Bang created matter and antimatter in equal amounts, the two types of particles should have canceled each other out. The universe should have become void before it even got started, precluding the possibility of stars, solar systems, Earth and all of us. Yet here we are.
“Something happened, some small asymmetry that led some of the matter to survive,” Hangst told NPR. “And we simply have no good idea that explains that right now.”
Spectroscopic analysis is one way to try to understand that asymmetry, but the technique used at CERN has a lot of room for improvement. Hangst says his adventures in antimatter are just getting started.