Now and then in books, movies, or comic books, a mysterious “antimatter” pops up. Usually, what it is and what it does is so vague that it ends up being the sciency version of magic.

A creature of “antimatter” appears in an old Doctor Who episode. credit: doctorwhofromthestart.wordpress.com

Antimatter is very real: we know it so well we even use it in medicine. Discovering it was one of the greatest successes of theoretical physics. At the same time, though, it put us in quite a predicament.

In the 1920s and 30s, physicists were trying to connect Special Relativity and Quantum Mechanics. The only way to make it work was to introduce a new, strange matter, just like normal matter, but opposite. Like someone’s mirror image. They look the same and move the same, if one raises its left hand, the other raises its right. In particle words, if one has positive charge, or spin up, or anything, the other has negative charge, or spin down, or anything at the opposite. It was indeed more than matter’s mirror image, it was almost its evil twin: they called it antimatter.

credit: a113animation.com

The name came from exactly where you think it did— from being the opposite of matter.

As all opposites, when matter and antimatter meet, they cancel out. They disappear in a snap, turning into pure energy—a process called annihilation.

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Antimatter wasn’t just sleight of maths: soon scientists sighted the first antiparticles. Finding them was an unprecedented success: theory had traced the path to a then-unseen universe.

But why had it been unseen? Why does our universe consist of matter? Why is it at all? Shouldn’t it have annihilated with an equal and opposite anti-universe? Are the laws of physics different for antimatter?

The Alpha experiment at CERN tries to answer at least the last question. After managing to create and isolate atoms of anti-hydrogen—with anti-electrons, anti-protons and whatnot—scientists stimulated them with lasers. The reaction they saw from anti-hydrogen is exactly the same as the one we know from hydrogen. Antimatter seems equal in front of the law (of physics).

Probably, we’re all made of matter because there was a teeny bit more of it in the early universe. The origin of the microscopic imbalance that gave the universe to matter, however, remains one of the biggest mysteries in science.

A representation of the matter-antimatter imbalance at the Deutsches Museum in Munich (Germany). The tank of black sand represents antimatter in the early universe, the white one represents matter. They are 1 meter tall, the white one has a single grain more. credit: scilogs.spektrum.de

 

Cover photo: CC0 Julia Schwab/pixabay

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