Scientists at CERN have used lasers to cool down antimatter for the first time. The milestone could help unlock some of the secrets of this weird substance, including why it didn’t annihilate the universe soon after the Big Bang.
Unlike the elusive dark matter, antimatter is a bit more tangible to us, having been isolated, produced and examined in recent years. Essentially, it’s just normal matter with the opposite electric charge, which means that if antimatter and matter so much as touch, they annihilate each other in a burst of energy.
That of course makes it tricky to store and transport, let alone study. Over the last decade or so, CERN scientists have developed better and better containers that use electromagnetism to keep antimatter suspended in a vacuum for longer periods of time, from fractions of a second, to several minutes, to well over a year.
That’s allowed scientists to study the stuff in a variety of ways, such as its spectrum and how it reacts to gravity. The main goal of all this is to investigate whether electric charge is the only difference between matter and antimatter.
But these studies are bumping up against another problem, besides its tendency to annihilate everything: the temperature of the antiatoms makes for a noisy environment to take precise measurements. So for the new study, researchers at CERN’s ALPHA project cooled atoms of antihydrogen using lasers.
This cooling technique is often used on regular matter, but had never been achieved with antimatter before. The atoms (or antiatoms) absorb photons from the laser light, pushing them briefly into a higher-energy state. Soon, they emit the photons again and decay back into their lower-energy state, and if this cycle is repeated the atoms will gradually slow down further and further, because the photons impart momentum.
In this experiment, the ALPHA researchers used a pulsing laser light specially designed for antihydrogen atoms, with a frequency just below that required for the transition between its lowest- and higher-energy states. After a few hours of zapping the atoms, the team found that their median kinetic energy dropped to just a tenth of its initial energy. That cooled them down to 0.012 K, a fraction above absolute zero.
Having achieved this, the team went on to find that the spectral line for the laser-cooled antihydrogen was around four times narrower than usual. That indicates that this technique can help scientists make more precise measurements of antimatter, which would be instrumental in figuring out how different it is from regular matter.
That, in turn, could unravel some of the most profound mysteries of cosmology, such as why we’re even still here. It’s thought that the Big Bang should have created equal amounts of matter and antimatter, but they would have canceled each other out, annihilating everything. The fact that matter dominates the universe we see today indicates some difference between the two that upset the scales.
The research was published in the journal Nature. The team describes the work in the video below.
Source: CERN