The WEAX experiment

Einstein's weak equivalence principle (WEP) states that gravitational mass is identical to inertial mass. This hypothesis has withstood experimental t ests to an impressive accuracy of one part in 10(11). Various hypotheses ba sed on theory and observations with matter suggest violations of WEP for an timatter may exist anywhere from the one part in 10(6) to the 200% level. A n observed violation at any level would have a profound impact, e.g. it wou ld offer an explanation as to why matter and antimatter are so distinctly s eparated in the cosmos. We propose a precise test of WEP for antiprotons in microgravity. We expect to test WEP for antimatter to about one part in 10 6, and foresee that additional advancements of several orders of magnitude in precision could follow with further technical developments.