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Antimatter gravity experiment answers big scientific questions

A TRIUMF physicist makes an adjustment to the Radial Time Projection Chamber, a position-sensitive particle detector that surrounds the antihydrogen trap. [Credit: TRIUMF]

 

 

Does antimatter fall up or down? Is it affected by gravity, or does it respond to antigravity? It's been a big mystery, but physicists say they now know the answers.

Looking as far back as The Big Bang, physics has predicted that when we create matter, we also create antimatter. The world around us is made of matter, but physicists have yet to find an explanation for the absence of antimatter.

Now, physicists at the University of Calgary, Simon Fraser University, TRIUMF, the University of British Columbia, York University, and the British Columbia Institute of Technology and research institutions from around the world have just answered a long-standing question that will lead to a deeper understanding of this mystery: Does antimatter fall up or down?

The Antihydrogen Laser Physics Apparatus (ALPHA) collaboration at CERN, the European Organization for Nuclear Research, completed the first direct measurement of gravity's effect on the motion of antimatter using its new ALPHA-g apparatus. As expected by much of the scientific community, antimatter falls downward. This is a tremendous scientific and technical achievement that marks a leap forward in the world of antimatter research. The collaboration's findings were published in Nature Sept. 27.

UCalgary's involvement with ALPHA is led by Dr. Robert Thompson and Dr. Timothy Friesen from the department of physics and astronomy. Physicists used antihydrogen, the simplest atom in antimatter, to perform the experiment.

"Right now, we don't have an explanation about where all the antimatter in the universe is. To find a solution for this conundrum, what we do is test the elements of physics of antimatter to see if we can find an inconsistency. In this case, we tested to see if the gravitational characteristics of antihydrogen mirror those of hydrogen, which is significant because it's never been done before," said Dr. Robert Thompson, PhD, professor of physics and associate vice president (Research) at UCalgary, and principal investigator of the ALPHA-g Canada Foundation for Innovation Project.

The antimatter gravity measurement was carried out in the new ALPHA-g apparatus, now in operation at CERN in Switzerland. After creating antimatter, trapping the neutral antihydrogen atoms in a magnetic bottle, and making the environment as cold as possible, physicists then released the antihydrogen within the vertical apparatus to witness and measure its gravitational behavior.

ALPHA has previously carried out precision measurements of the charge and color spectrum of antihydrogen, which to date remain all consistent with current physical models. The ALPHA collaboration recognizes this milestone as the first step in taking more precise measurements of the gravitational properties of antimatter to determine whether antimatter falls in the exact same way as matter. This could help physicists understand the lack of antimatter observed in the universe.

"We know there's a problem somewhere in quantum mechanics and gravity. We just don't know what it is. There has been a lot of speculation on what happens if you drop antimatter, though it's never been tested before now because it's so hard to produce and gravity is very weak," said Dr. Timothy Friesen, PhD, assistant professor, Physics and Astronomy, UCalgary, and major contributor to the Nature paper.

ALPHA-g was designed, constructed, and commissioned through an international partnership of research institutions including, on the Canadian side, the University of Calgary, Simon Fraser University, TRIUMF, the University of British Columbia, and York University, as well as post-secondary institutions and research institutes in Europe, the United Kingdom, and the United States.

Building the ALPHA-g apparatus was only the first step. Observing the free-fall of antimatter involved the entire ALPHA collaboration, including researchers from the above institutions and countries, as well as from the British Columbia Institute of Technology and researchers from Israel and Brazil.

"This milestone is a culmination of nearly 20 years of dedication and teamwork. The contributions of the members of ALPHA-Canada were critical to our success," said Dr. Makoto C. Fujiwara, senior scientist, TRIUMF, and ALPHA-Canada spokesperson. "ALPHA-Canada is a pan-Canadian collaboration made up of a diverse group of students, postdoctoral scholars, academics, and staff members, each who played a vital role in this project."

Source: University of Calgary

Published October 2023

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