Study with frozen antimatter could revolutionize physics – 02/28/2024 – Science

Positronium is an extremely rare substance that usually exists for just 142 billionths of a second and is capable of generating large amounts of energy. Studying it could bring more understanding about the antimatter that existed at the origin of the Universe and, with that, revolutionize physics, cancer treatment and perhaps even space travel.

Until now, however, it has been almost impossible to analyze the substance because its atoms move so much.

Now scientists have an alternative solution: freezing it with lasers.

“Physicists are in love with positronium,” said Ruggero Caravita, who led the research at the European Organization for Nuclear Research (Cern), which is located near Geneva. “It’s the perfect atom to do antimatter experiments.”

“Now the entire field of study is unlocked.”

But what exactly is positronium?

It is a so-called exotic atom formed by matter and antimatter — something quite unusual, in fact.

Matter is what the world around us is made of, including the stars, planets, and us.

Antimatter is the opposite. It was created in equal quantities when the Universe came into being, but it exists only momentarily in nature today, with very little occurring naturally in the cosmos.

Figuring out why there is now more matter in the Universe than antimatter — and therefore why we exist — will take us a long way toward a new, more complete theory of how the Universe evolved, and positronium could be the key , according to Lisa Goggler, a doctoral student working on the project.

“Positronium is such a simple system. It consists of 50% matter and 50% antimatter,” he said. “We hope that if there is a difference between the two, we will be able to see it more easily than in more complex systems.”

One of the first experiments in which frozen positronium could be used is to see if its antimatter portion follows Einstein’s theory of general relativity in the same way as the matter portion.

Matter, which forms the world around us, consists of atoms, the simplest of which is hydrogen, which is the most abundant element in the Universe. Hydrogen atoms are made of a positively charged proton and a negatively charged electron.

Positronium consists of an electron and its antimatter equivalent, a positron.

It was first detected by scientists in 1951, in the United States, but it has been difficult to study because the atoms move a lot — they are the lightest atoms known.

But cooling reduces the speed of atoms, making it easier for scientists to study.

Until now, the coldest temperatures for positronium in a vacuum have been around 100°C. The CERN team has now reduced it to more than -100ºC, using a technique called laser cooling. This is a difficult and complicated process in which laser light is shined on atoms to stop them from moving so much. The research was published in the scientific journal Physical Review Letters.

In order for it to be used in research, the positronium has to be frozen even further, down to around -260 ºC. The laser approach gave researchers a way forward, according to Professor Michael Charlton, a positronium expert at Swansea University who was not involved in the latest breakthrough.

“This is a very encouraging first step,” he told BBC News. “It’s opening the door so you can see the light on the other side, beckoning us to a new era of positronium physics.”

And the Cern group is not alone in the search for frozen positronium. A group at the KEK Slow Positron Facility in Tokyo is about to publish similar results.

It’s becoming a scientific race, involving other groups around the world as well, because this esoteric substance could have enormous practical benefits.

When an electron and a positron combine, they release enormous amounts of energy. This could be harnessed to create so-called powerful gamma-ray lasers.

Interstellar travel

Some of the applications are imaging tests, cancer treatments and there is even talk of propelling spacecraft at speeds close to that of light, which could enable interstellar travel in the distant future.

The work was carried out at Cern’s antimatter factory, which recently created and stored the largest quantity of antimatter hydrogen atoms in the known Universe.

Last year, another team of researchers tested whether antihydrogen responded differently to gravity, seeing whether it fell up or down when released.

It was found to fall downwards, but whether at the same rate as normal hydrogen is not yet known.