Researchers Work To Find Out How Gravity Affects Antimatter

John P. Millis, Ph.D. for — Your Universe Online

All fundamental matter in the Universe — protons, electrons, etc. — has counterparts known as antimatter. In most ways, antimatter simply mirrors regular matter. For instance, the antimatter counterpart to the electron is the positron, a particle of the same mass of the electron, but possessing the opposite charge and opposite spin.

When normal matter encounters its antimatter counterpart, the pair will annihilate and convert its mass into energy. This is not as common an occurrence as one might first expect, however. The reason is the Universe is dominated by, what we perceive to be anyway, normal matter. Antimatter, conversely, is relatively scarce, arising only during very specific processing, such as interactions of very high-energy photons in our atmosphere.

The small number of samples, as well as the difficulty in containing the antimatter because it can´t be allowed to touch normal matter for risk of annihilation — means there are still some things we don´t know about these particles. But a new study out of Lawrence Berkeley National Laboratory, in concert with their colleagues at CERN´s ALPHA experiment, has revealed new insights into one of the long standing questions about antimatter.

It is well known that normal matter falls in a gravitational field, such as that created by Earth. But some researchers had speculated antimatter could possibly interact differently with gravitational fields and, as a consequence, fall up instead of down. After all, since antimatter is characterized by having opposite quantum properties as their normal matter counterparts, why not opposite gravitational interactions as well?

This is an important issue as Joel Fajans of Lawrence Berkeley National Laboratory explains, “in the unlikely event that antimatter falls upwards, we´d have to fundamentally revise our view of physics and rethink how the universe works.”

Using data from CERN´s ALPHA experiment, which studied 434 antihydrogen atoms, the team realized they would be able to detect anomalies in the gravitational interactions if they were strong enough.

Antihydrogen atoms are created in a chamber at CERN and are held in a strong magnetic trap. The magnetics are then turned off and the antiatom will move toward a wall of normal matter and annihilate. The team could then, knowing the original position and speed, calculate the influence of gravity on its motion.

The experiment proved such measurements are possible, and future work on this experiment could reveal the nature of gravitational interactions with antimatter. However, the results presented in this first round of tests were inconclusive as the team could not pinpoint with enough accuracy the initial parameters of the atoms to see effect. So if any antigravity effect is present, it is relatively small.

“Is there such a thing as antigravity? Based on free-fall tests so far, we can´t say yes or no, “ reports Fajans. “This is the first word, however, not the last.”

The ALPHA experiment is currently being prepared for an upgrade, dubbed ALPHA-2, that would allow a significant improvement in sensitivity over the current system. Team members, therefore, hope within the next five years they can bring closer an answer to this question that has long been on the minds of theoretical physicists.

The researchers have published their findings in the April 30, 2013 edition of Nature Communications.