Precision tests of Einstein's Weak Equivalence Principle for antimatter

Einstein's Weak Equivalence Principle (WEP) states that gravitational mass is identical to inertial mass. This hypothesis has withstood experimental tests to an impressive accuracy of one part in one hundred billion. Various hypotheses based on theory and observations with matter suggest violations of WEP for antimatter may exist anywhere from the one part per million to the 200% level. An observed violation at any level would have a profound impact, e.g. it would offer an explanation of why matter and antimatter are so distinctly separated 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 per million, and foresee that additional advancements of several orders of magnitude in precision could follow with further technical developments. (C) 2000 COSPAR. Published by Elsevier Science Ltd.