Measuring the effect of gravity on antimatter


The study found antihydrogen and hydrogen had the same gravity

Scientists at the University of Liverpool have measured for the first time the effect of gravity on antihydrogen – the antimatter counterpart of hydrogen – marking an important step in understanding how antimatter behaves.

Whilst scientific evidence led scientists to assume that antihydrogen had exactly the same properties as hydrogen, it had not been proven.

Freefall gravity

Researchers from the University of Liverpool were part of CERN’s international ALPHA experiment which performed measurements on antihydrogen.  They trapped and then released antihydrogen atoms in order to measure its freefall gravity which enabled them to determine the ratio of antihydrogen’s gravitational mass to its inertial mass.

If it was exactly one to one then antimatter and matter responded to gravity in the same way and therefore had the same properties.

”We studied antihydrogen and made detailed comparisons with ordinary hydrogen and found that they had the same gravity”

However, due to the uncertainty in making this measurement, the team were able to put an upper limit on this ratio of lower than one to 75, in the absence of systematic errors.  They also obtained a similar limit for the behaviour under antigravity but this still meant they responded in the same way.

Professor Paul Nolan, from the Department of Physics who led the Liverpool team, said: “We studied antihydrogen and made detailed comparisons with ordinary hydrogen and found that they had the same gravity.

“Although the data does not allow a more accurate limit to be determined yet, future developments to the apparatus and methodology will allow the researchers to improve these measurements and test more accurately for possible deviations.”

Semiconductor Centre

The University’s Semiconductor Centre group was responsible for building, maintaining and operating the silicon vertex detector which detects the presence of the antimatter particle of antihydrogen and allows gravity measurements to be made on antimatter particles.

The work is published in Nature Communications and supported by the Engineering and Physical Sciences Research Council (EPSRC).


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