Laboratory for Particle Physics (LTP)

LTP Colloquium

Unravelling the Gravity of Antimatter: First Results from the ALPHA-g Experiment

Thursday, March 14, 2024, 16:00
WHGA Auditorium

April Cridland, CERN

The general theory of relativity [1] is an extremely successful and well-tested description of gravitation but it defies unification with quantum theory. It is therefore important to test its underlying principles in a variety of systems, including that of antimatter. Until now there was no direct observation of antimatter atoms experiencing the Earth's gravitational field, leaving the door open to theories which rely on repulsive antigravity to explain dark matter and dark energy [2, 3]. The ALPHA-g experiment has now confirmed that antihydrogen falls in a way that is consistent with gravitational attraction towards the Earth, ruling out repulsive antigravity [4]. This initial confirmation of the sign of antimatter's gravitational acceleration paves the way for precision studies to investigate the magnitude of this acceleration and rigorously test the Weak Equivalence Principle.

[1] Einstein, A. Fundamental Ideas of the General Theory of Relativity and the Application of this Theory in Astronomy. In Proc. Prussian Academy of Sciences (1915).

[2] Villata, M. CPT symmetry and antimatter gravity in general relativity. Eur. Phys. Lett. 94, 20001 (2011).

[3] Dimopoulos, C., Stamokostas, G. L., Gkouvelis, L. & Trigger, S. Hubble law and acceleration curve energies in a repulsive matter-antimatter galaxies simulation. Astropart. Phys. 147, 102806 (2023).

[4] Anderson, E.K., Baker, C.J., Bertsche, W. et al. Observation of the effect of gravity on the motion of antimatter. Nature 621, 716-722 (2023).