“…The ALPHA (former ATHENA) [222,223], ASACUSA [224][225][226], and ATRAP [227][228][229] collaborations started at the antiproton decelerator (AD) at CERN a program to test CPT invariance by comparing the hyperfine splitting in the ground state (ASACUSA) or the 1s-2s transition frequency (ALPHA and ATRAP) of hydrogen with those of antihydrogen. Very recently, a forth collaboration, AEGIS, is preparing a new experiment for comparing the fall of hydrogen with that of antihydrogen in the gravitational field of the earth [230].…”