Particle physicists prove that antimatter doesn’t “fall up”

For a very long time, science fiction fans have dreamed that a material known as antimatter may have gravity that is opposite to that of regular matter. It is not.

The proverb "What goes up must come down" is generally accurate and holds true for all known substances. But what if that wasn't accurate? What if there was something that fell upward as opposed to downward? Science fiction authors and lovers of unidentified flying objects have long harboured suspicions that a material known as antimatter could experience gravity differently than regular matter. If this is the case, levitation may be feasible.

But an announcement published in the journal Nature by European physicists at the CERN laboratory will put an end to such wishful thinking: Antimatter falls, without question.

The matter with antimatter

Although antimatter seems more like a concept from science fiction, it exists in reality. It was initially proposed in 1928 and found in 1932. In essence, antimatter is what conventional matter is not. For instance, the positron, the electron's antimatter counterpart, is massless and identical in size to the electron, but it carries the opposite electrical charge.

Matter and antimatter are incompatible compounds. An enormous quantity of energy is released when you combine the two. The energy released by the simultaneous atomic bombs of Hiroshima and Nagasaki, for instance, would be the same if a gramme of matter and antimatter came into contact and destroyed one another.

There are antimatter counterparts for every known subatomic matter particle. For example, there are antineutrons and antiprotons. Even more intriguingly, an antimatter proton and an antimatter electron can combine to form an anti-hydrogen atom, just as a proton and electron can combine to form a hydrogen atom. And the new finding depends on the existence of such antimatter atoms.

Anti-hydrogen atoms

Use of anti-hydrogen: why? since it has no electrical charge. On the other hand, since each antimatter protons and electrons has an electrical charge, they are subject to electrical forces. The interactions between antimatter protons or antimatter electrons with any stray electrical fields would dwarf any gravitational effects because electric forces are much stronger than gravity.

ALPHA collaboration, which made this recent measurement, is one of the experimental groups that receives anti-hydrogen atoms created by the CERN Antimatter Factory. The researchers used a magnetic container to contain about 100 anti-hydrogen atoms in order to conduct their experiment. The magnets were then gradually turned off over the course of 20 seconds, and the number of magnets that escaped upward versus downward was counted. Gravity caused more atoms to fall to the ground.

According to this measurement, the anti-hydrogen atoms felt a downward gravitational force that was roughly 75% of normal gravity, which is similar to what hydrogen atoms feel. This information was obtained by the ALPHA collaboration. Since the measurement's uncertainty was only 20%, it is likely that matter and antimatter are subject to the same gravitational force. The possibility that their measurement was still consistent with antimatter experiencing an upward force equivalent to the opposite of gravity was quantified by the researchers using their data, and they excluded this possibility at one part in a quadrillion. Antimatter doesn't ascend vertically.

Debbie Downer

The outcome aligns with forecasts derived from general relativity, the primary scientific theory of gravity proposed by Albert Einstein. According to general relativity, matter and antimatter both have positive masses and are what undergo gravitational pull. Thus, within the experimental uncertainty, this measurement validates Einstein's prediction.

Nonetheless, tests of general relativity cannot be made precisely with a 20% uncertainty. Future measurements should be able to provide more conclusive evidence for the equivalency of matter and antimatter, so the ALPHA scientists are already working to improve their apparatus. Although it is still most likely that matter and antimatter are affected by gravity in exactly the same ways, there is still a chance that there are minute variations between the two based on current measurements.

Although this measurement is impressive and confirms our understanding of the laws of nature, many people will undoubtedly be disappointed. A surprising outcome would have necessitated a significant reorganisation of our comprehension of physics. Spokesman for the ALPHA collaboration Dr Jeffrey Hangst stated, "It would have been so much cooler if antimatter fell up." But sadly, it doesn't.

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