Scientists ask if antimatter falls up instead of down

Scientists have embarked on one of the strangest experiments ever — to see whether atoms of exotic antimatter fall up instead of down.

Antimatter is weird stuff, being a kind of mirror image of ordinary matter with an opposite electric charge.

When an particle of normal matter meets its antimatter counterpart the two annihilate each other in a flash of light.

That much scientists already know. What is much less certain is whether antimatter has fundamental properties that are different from normal matter — especially the way it is affected by gravity.

A few experts have proposed the outlandish idea that antimatter might be repelled by the gravity — in other words, that it falls up.

Now scientists have taken the first steps towards answering this question. A paper reported in the journal Nature Communications describes the first direct measurement of gravity’s effect on antimatter.

Lead scientist Professor Joel Fajans, from the University of California at Berkeley, US, said: “Is there such a thing as anti-gravity? Based on free-fall tests so far, we can’t say yes or no.

“We certainly expect antimatter to fall down, but just maybe we will be surprised.”

The work was conducted at Cern, the European Centre for Nuclear Research in Geneva, Switzerland, home of the Alpha (Antihydrogen Laser Physics Apparatus) experiment.

At the Alpha laboratory, antimatter protons — antiprotons — are combined with antielectrons, or “positrons”, to make atoms of antihydrogen.

These can be stored for just a few seconds in a magnetic trap. The scientists set about studying how the antihydrogen falls out of the trap when the magnetic field is switched off.

What sounds simple is actually a very tricky operation. When the magnets are turned off, the anti-atoms quickly touch the ordinary matter of the trap’s walls and are immediately destroyed.

To discover the fate of the antimatter atoms it is necessary to pinpoint where and when they are annihilated and to measure their precise location and velocity the moment the trap is turned off.

Alpha is being upgraded and should provide more precise data once the experiment resumes next year.

“We need to do better and we hope to do so in the next few years,” said co-author Prof Jonathan Wurtele, also from the University of California at Berkeley.


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