Observation of the effect of gravity on the motion of antimatter

September 27, 2023

Einstein’s general theory of relativity (GR), from 1915, remains the most successful  description of gravitation. From the 1919 solar eclipse to the observation of gravitational  waves, the theory has passed many crucial experimental tests. However, the evolving concepts of dark matter and dark energy illustrate that there is much to be learned about the gravitating  content of the universe. Singularities in the GR theory and the lack of a quantum theory of  gravity suggest that our picture is incomplete. It is thus prudent to explore gravity in exotic  physical systems. Antimatter was unknown to Einstein in 1915. Dirac’s theory  appeared in  1928; the positron was observed in 1932. There has since been much speculation about gravity  and antimatter. The theoretical consensus is that any laboratory mass must be attracted  by the  Earth, although some authors have considered the cosmological consequences if antimatter  should be repelled by matter. In GR, the Weak Equivalence Principle (WEP) requires that   all masses react identically to gravity, independent of their internal structure. Here we show   that antihydrogen atoms, released from magnetic confinement in the ALPHA-g apparatus,   behave in a way consistent with gravitational attraction to the Earth. Repulsive ‘antigravity’ is   ruled out in this case. This experiment paves the way for precision studies of the magnitude of   the gravitational acceleration between anti-atoms and the Earth to test the WEP.

Work support by the DOE Office of Fusion Energy Sciences and the NSF Program in Plasma Physics

National Science Foundation Department of Energy