Scientists have succesfully measured the direct influence of gravity on antimatter for the first time in history by dropping antihydrogen atoms from a magnetic trap, and observing as they annihalated themselves upon coming into contact with ordinary matter.
Physicists believe that for each positively charged regular particle in the universe, there exists a negatively charged antiparticle, whose mass and rate of spin are identical to their counterparts'. Equal amounts of matter and antimatter were thought to have been created in the Big Bang event that birthed the cosmos. Yet, despite this, antimatter is incredibly rare relative to the ordinary subatomic particles that make up our universe's ordinary matter. Understanding these exotic particles is a phenomenally challenging endeavour, partially owing to the fact that matter and antimatter immediately annihilate one another whenever they come into contact.
However, scientists from the CERN particle physics lab in Geneva were recently successful in shedding light on the characteristics of antimatter by observing how gravity — one of the four fundamental forces of nature that govern the behaviour of all subatomic particles in the universe — exerts its influence over antiparticles. As described in a new paper published in the journal Nature, scientists would expect antimatter to behave in the same way as regular matter when under the influence of gravity, and be accelerated towards its source, Earth.
What happens if you drop an anti-apple?
— CERN (@CERN) September 27, 2023
In a paper published today in @Nature, the ALPHA collaboration at CERN’s Antimatter Factory shows that, within the precision of their experiment, atoms of antihydrogen – a positron orbiting an antiproton – fall to Earth in the same way as… pic.twitter.com/oo83GbZT2Z
A discovery to the contrary would have massive implications for the field, as it could indicate that antimatter does not play nicely with Albert Einstein’s theory of general relativity, and that some kind of ‘antigravity’ effect was at play. On the positive side, the idea that antimatter is somehow repelled by mass would help explain why we see so little of it today.
To perform the experiment, a team of scientists at CERN known as the ALPHA collaboration created a population of antihydrogen atoms, the simplest antimatter particles known to exist, by binding antiprotons with positrons. The antihydrogen was then suspended in a magnetic trap, which prevented the particles from annihilating against the surrounding matter.
Groups of 100 antihydrogen particles were then placed in an instrument designed to measure the vertical location where the antimatter particles annihilate. The scientists then reduced the current flowing into the magnetic traps, allowing the antimatter to escape and destroy itself.
After averaging out the results from seven such experiments, the team discovered that around 80% of antihydrogen atoms escaped from the bottom of the magnetic traps due to the gravitational influence of Earth, while a mere 20% exited from the top.
The results lined up nicely with computer simulations of the experiment that modelled the behaviour of ordinary hydrogen atoms, which in turn suggests that gravity exerts a unified influence over both matter and antimatter alike.
“In physics, you don't really know something until you observe it,” explained Jeffrey Hangst, a spokesman for the ALPHA team. “This is the first direct experiment to actually observe a gravitational effect on the motion of antimatter. It’s a milestone in the study of antimatter, which still mystifies us due to its apparent absence in the Universe.”
Next up, the ALPHA scientists hope to increase the accuracy of the experiment by cooling the antihydrogen atoms using a special laser experiment located at the CERN lab.
“It has taken us 30 years to learn how to make this anti-atom, to hold on to it, and to control it well enough that we could actually drop it in a way that it would be sensitive to the force of gravity,” said Hangst. “The next step is to measure the acceleration as precisely as we can. We want to test whether matter and antimatter do indeed fall in the same way. Laser-cooling of antihydrogen atoms, which we first demonstrated in ALPHA-2 and will implement in ALPHA-g when we return to it in 2024, is expected to have a significant impact on the precision.”
Anthony is a freelance contributor covering science and video gaming news for IGN. He has over eight years experience of covering breaking developments in multiple scientific fields and absolutely no time for your shenanigans. Follow him on Twitter @BeardConGamer
Image Credit: U.S. National Science Foundation
