A New Experiment Directly Measures Effect of Gravity On Antimatter
25 Oct 2023
- Hywel Owen

Observation of the effect of gravity on the motion of antimatter






A new paper​ has been published in Nature that shows for the first time that antimatter definitely falls under the action of the Earth's gravity in the same way as normal matter.

Whilst Einstein's Weak Equivalence Principle would lead us to expect that antimatter behaves the same way as ordinary matter, an earlier proof-of-principle experiment at CERN by the ALPHA collaboration was not conclusive; a better direct measurement was needed.

Mark Johnson, now a staff member in ASTeC's accelerator physics group and a co-author of this new paper, helped develop the ALPHA-g beamline used to conduct the measurement as part of his PhD. This beamline was delivered using a number of collaborating researchers across the Cockcroft Institute and using the ELENA accelerator to provide antiprotons from the CERN accelerator complex - the ELENA project also benefitting from Cockcroft Institute research contributions.

In the ALPHA-g experiment, antiprotons and positrons are combined within the trap to give antihydrogen. The antihydrogen atoms are released from the trap, and the number going up and down are counted; the numbers obtained are consistent with what happens with ordinary hydrogen atoms. This is an important milestone in basic physics; more detail is given in an article on the Cockcroft Institute website.

A CERN/ALPHA video ​explains the trapping process in more detail.


Mark Johnson, co-developer of the ALPHA-g beamline and current member of the ASTEC Accelerator Physics group.

Contact: Baker, Emily (STFC,DL,AST)