Stanford University
APPLIED PHYSICS/PHYSICS COLLOQUIUM
Tuesday, April 16, 2024
Joel Fajans
Physics, UC Berkeley
“Measuring the Effect of Gravity on Antimatter”
Recent experiments have measured the effect of gravity on antimatter with the first “direct”, i.e., freefall-style or Galilean Leaning Tower of Pisa-style measurements. In agreement with theory and indirect experiments, these experiments, performed by CERN’s ALPHA collaboration, show that antimatter, specifically antihydrogen atoms, fall downward with an acceleration within about 25% of g=9.8ms2. Strongly ruled out is the possibility of antimatter falling upwards. Thus, the results are compatible with the weak equivalence principle. This talk will review why this topic remained a perhaps open question, document some of the current other experiments attempting to make a direct measurement, discuss some of the history of early, failed, attempts to do a direct measurement, and conclude with a description of how the measurement was actually made using a magnetic balance.