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Atom test could solve antimatter puzzle

An artist's impression of an antihydrogen atom

An artist's impression of an antihydrogen atom - a negatively charged antiproton orbited by a positively charge anti-electron, or positron - trapped by magnetic fields(Source: Katie Bertsche)

Up or down? Physicists are closer to answering one of science's great questions: do the same laws of gravity apply to antimatter -- the obscure counterpart of matter as we know it?



For more than 50 years, scientists have debated whether gravity would attract or repel antimatter particles -- whether they would fall down like conventional matter or "up" due to a kind of antigravity.

While the question remains unsolved for now, a team of scientists have developed the beginnings of a test that should lead to a conclusive answer.

Their research is reported today in the journal Nature Communications .

"This is the first word, not the last," says Joel Fajans, a member of the research team at the European Organisation for Nuclear Research's (CERN) Alpha experiment.





Up or down?

Scientists are also unsure whether antimatter would respond in the same way as matter to gravity, or whether it would move in an different direction at a different speed.

Some believe the fact the Universe is comprised almost entirely of matter could be explained if antimatter did indeed "fall" up.


"We certainly expect antimatter to fall down, but just maybe we will be surprised," says Fajans, a University of California physics professor.

"In the unlikely event that antimatter falls upwards, we'd have to fundamentally revise our view of physics and rethink how the universe works."

The Alpha team reported the first direct measurements, though experimental and within a very wide range, of gravity's effect on antimatter in free fall.

The experiment works on manufacturing and trapping antihydrogen atoms -- the antimatter counterparts of the simplest atom, hydrogen.

The atoms are placed in a magnetic trap which is then switched off, allowing them to "fall out" and hit the trap walls in flashes of energy.


If antimatter acted the same as matter, the rate of its gravitational mass to inertial mass would be the same: 1 -- less than this and the antimatter would be falling upwards.

Gravitational mass is determined by a body's response to gravity, while inertial mass measures to its resistance to acceleration.

From its early measurements, the team was able to place outer limits on the ratio of plus 110 on the one side and minus 65 on the other -- a margin that will be refined with more accurate tools and methods.


Tags: physics