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Antimatter might fall up, say physicists

A paper published this week suggests that antimatter could exhibit antigravity, potentially resolving some of physics' biggest mysteries.

This 2010 image shows untrapped antihydrogen atoms annihilating on the inner surface of the ALPHA trap.


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Does antimatter fall up?

That's what particle physicists are asking after they reported their first direct measurements, published in the current issue of Nature Communications, of gravity's effects on the antimatter equivalent of hydrogen. 

The measurements were taken at CERN, the huge particle physics laboratory on the French-Swiss border. CERN's  Antihydrogen Laser Physics Apparatus, or ALPHA, captures positrons and antiprotons, which are just like regular electrons and protons except that they have opposite charges and quantum "spins," in a vacuum chamber where they combine to form antihydrogen. 

When antimatter comes into contact with ordinary matter, the two obliterate each other in a flash of radiation and other subatomic smithereens (which is why we should all be grateful that Isaac Newton was never struck on the head by an antiapple). So, to get a good look at the antihydrogen before it vanishes, the ALPHA scientists trap it in a magnetic "bottle" that takes advantage of the antiatoms' magnetic properties to hold them in place.

The ALPHA team has actually gotten pretty good at confining antihydrogen: In 2011, they set a record by trapping the atoms for more than 16 minutes, an eternity for particle physics.

Now they're asking what happens after the magnets are turned off and the antihydrogen is released. Does it fall down or up?

Sadly, the measurements were inconclusive. The antihydrogen atoms have proven too squirrely and the ALPHA equipment too imprecise to give a definitive answer.

This is the first word, not the last,” said Joel Fajans, a University of California at Berkeley physicist and ALPHA team member, in a UC Berkeley press release. “We’ve taken the first steps toward a direct experimental test of questions physicists and nonphysicists have been wondering about for more than 50 years. We certainly expect antimatter to fall down, but just maybe we will be surprised.”


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