The mystery of how antimatter — the less abundant, polar opposite of normal matter — interacts with groups of atoms has finally been solved 94 years after it was discovered.
In 1928, physicist Paul Dirac, proposed a theory for the existence of particles identical to the negatively charged electrons that were known to whizz around the outskirts of atoms, except in one respect: they had a positive charge.
Dirac came up with an equation that described new particles — which later came to be known as positrons — which also described all the other matter and antimatter in existence.
The brilliant Dirac was, however, unable to explain exactly how this antimatter interacted with regular groups of atoms held together by chemical bonds — molecules. In the near century since, no one has managed this feat — until now.
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“Scientists have struggled to properly explain how antimatter interacts with molecules,” says Dr Dermot Green of QUB School of Mathematics and Physics. The breakthrough was a consequence of working with Dr Charles Patterson of TCD School of Physics — their findings have been published in the current issue of Nature.
“Our breakthrough provides fundamental understanding of these interactions, unprecedented accuracy, and the ability to make predictions, which may help support fundamental physics and develop antimatter-based applications in materials science and medical imaging,” Dr Green adds.
Antimatter, like matter, is everywhere; in rocks, oceans and stars. It is also found everywhere in the subatomic world, where particles such as electrons and protons always have a twin, or anti-version of themselves.
Matter and antimatter are identical, except have opposite charges. When matter and antimatter twins meet, they annihilate one another, and disappear in a burst of light.
Antimatter is often described in science fiction novels, films and television series; perhaps most famously in the 1960s hit show Star Trek, where it was used as a fuel to power the Starship Enterprise up to reach “warp speed”.
It is considered exotic and rare yet is readily available in many research laboratories around the world, where it is used to advance physics and high technology industries.
“The ability of positrons to annihilate with electrons in atoms and molecules — producing characteristic bursts of light — makes them a unique probe of matter,” Dr Green notes.
Positron research can be used to develop more sensitive diagnostics for important materials, he says; to improve the PET scans used to confirm cancer and test how far its spread, and to better understand the Universe we live in.
Dr Green knew that a combination of powerful computers and advanced software would be needed to solve the problem of how matter interacts with molecules. The computing power he needed was in QUB, but he had to look south, to TCD, to find the software required — at Patterson’s lab.
Dr Patterson had developed the Exciton software code over many years to enable him study how materials absorbed and emitted light. The data such research produced could help develop new light emitting diodes (LEDs) and solar cells. He said he was pleasantly surprised when Dr Green knocked at his door.
“I am delighted that Dermot Green and his group were able to adapt the code to study how positrons interact with molecules,” Dr Patterson says. “There are there have been various approaches to doing these calculations. And these calculations are the first ones that have really got quantitative agreement with experiment for a wide range of molecules. That’s the importance of it, and that’s why it’s in nature.”
Despite this latest breakthrough, Dr Green says there remains many mysteries yet to be solved about antimatter. One of the most puzzling of these mysteries is why the Universe has so much more matter than antimatter.
“There should have been equal amounts of matter and antimatter created in the “Big Bang”. What we see, and experience is a universe dominated by normal matter, with only minuscule amounts of antimatter. Something has tipped the balance, and we don’t yet know what,” he adds.