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10th October 2023

Cosmological questions: Why antimatter matters

Scientists have shown that antimatter also falls under gravity, holding up Einstein’s general theory of relativity against evolving scientific ideas
Cosmological questions: Why antimatter matters
Credit: NASA’s Chandra X-ray Observatory @ Flickr

A recent paper has confirmed that all things fall in the same way. This might not seem like big news, but it is actually a pretty huge experimental confirmation of Albert Einstein’s 1915 general theory of relativity. Antimatter, which was unknown to Einstein at the time of his theory, has long been speculated to be a potential outlier as an object under gravity, and as such, cosmological questions have been raised about our knowledge of the universe.

Until now, antimatter and its actions under gravity have been questioned, and the idea of ‘antigravity’ was not completely unconvincing. However, scientists in Geneva at the European Organization for Nuclear Research, known as CERN, have put antimatter to the test to see, and the evidence is pretty clear. Repulsive ‘antigravity’ (antiparticles falling up) has been ruled out by scientists – further confirmation of Einstein’s genius theory. 

What is antimatter?

Antimatter is a material composed of antiparticles. This is the idea that for every particle there is another which is oppositely charged but identical in mass. Meaning, all the properties of a particle we’re well-versed in (negative electrons, positive protons) are reversed. This concept wasn’t general physics knowledge when Einstein developed his general theory of relativity, and so experimental tests to find out whether this theory holds up under evolving scientific knowledge are crucial.

Primordial antimatter
Credit: NASA’s Chandra X-ray Observatory @ Flickr

The experiment

The concept of antimatter and ‘antigravity’ questions the weak equivalence principle of Einstein’s theory. According to that principle, gravity pulls on every object in the same way, no matter what it’s made of. 

The experiment aimed to test whether antimatter particles, in this case anti-hydrogen, behaved consistently with gravitational attraction to the Earth. An experiment which seems simple on the face of things is not quite as easy as it might sound. In reality, with over 70 authors on the published paper and reams of scientific departments across the world from the University of Manchester to Toronto’s York University involved with the research, this was far from amateur.

Being able to control antimatter is a feat that scientists have been attempting for nearly as long as the concept has been around. Antimatter is a somewhat difficult beast to tame. Once created – a process which requires a considerable amount of energy, speed and complicated science, antiparticles need to be confined in a magnetic cage and released on demand. This involves yet more intricate physics and the powerfully named ALPHA-g apparatus.

But the scientists involved have done it, and in doing so have proven through direct observation an answer that had only been hinted at in previous experiments. Antimatter is not so alien as it sounds – it surrenders to gravity just like the rest of us.


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