Berkeley professors explore gravity’s effects on antimatter

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Antimatter opposes matter in many ways — but could that include gravity as well?

Researchers at UC Berkeley are conducting experiments to see whether antimatter, which is made of antiparticles that have the same masses but opposite charges as particles of ordinary matter, can defy gravity.

Joel Fajans, a professor in the department of physics, is part of a team of researchers at CERN, the European Organization for Nuclear Research, which used an apparatus known as ALPHA — Antihydrogen Laser Physics Apparatus — to conduct a gravity experiment with molecules of hydrogen and its equal-but-opposite counterpart, antihydrogen.

Fajans said the experiment mimicked Galileo’s legendary theoretical Leaning Tower of Pisa, experiment in which two balls of different masses were dropped from the tower to demonstrate that their rates of descent were independent of their masses.

The ALPHA collaboration used the apparatus to catch antihydrogen atoms, hold them without letting them into contact and then dropped them to see which direction they fell.

According to Fajans, the experiment produced inconclusive results about the effects of gravity on antimatter. The team published its results in a paper on April 30.

He and Jonathan Wurtele, a professor in the department of physics and a member of the ALPHA collaboration, said that it would be very unlikely that antimatter defies gravity.

“If we somehow discovered that antimatter fell upwards, almost everything about our understanding of the universe would change,” Fajans said. “All of the laws of physics would be completely destroyed.”

Fajans and Wurtele said they originally intended for the ALPHA apparatus to learn more about the spectral lines and glow of atoms. However, they found the apparatus could also give them a way to test gravity’s effects on antimatter.

Physicists believe that matter and antimatter were created in equal amounts during the Big Bang, but they have been unable to find significant quantities of antimatter in nature. Fajans and Wurtele said that physicists have been speculating for decades that this could be explained by a theory that antimatter falls upward, and ALPHA gave them a way to finally test that theory.

But because of how unlikely it is that antimatter defies gravity, Fajans and Wurtele said that the experiment was more about ruling out the possibility than proving it was true.

“Even though antimatter and matter may seem like opposites, they both give off light in the same way and they both behave according to the laws of physics,” Wurtele said. “They just seem opposite in the way we understand them.”

Fajans and Wurtele said that next year, the ALPHA collaboration will repeat the gravity experiments with CERN’s new and improved ALPHA-2 apparatus, which uses lasers to measure antimatter.

CERN is an international organization made up of physicists and engineers whose goal is to discover and understand the “fundamental structure of the universe,” according to the organization’s website. The CERN laboratory, housed in Geneva, is the world’s largest particle physics laboratory, and it houses the world’s largest and most complex scientific instruments to study particles.

Pooja Mhatre is the lead research and ideas reporter. Contact her at [email protected].

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