Why We Already Know that Antihydrogen is Almost Certainly NOT Going to Fall "Up"

Abstract

The ALPHA collaboration (of which I am a member) has made great strides recently in trapping antihydrogen and starting down the path of making spectroscopic measurements. The primary goal of the experiment is to test CPT invariance but there is also interest in testing another fundamental issue -- the gravitational interaction between matter and antimatter (the so-called question of "antigravity"). As well as the other antihydrogen trapping experiments -- ASACUSA and ATRAP -- there is also a new experiment in the Antiproton Decelerator hall at CERN called AEGIS which is dedicated to testing the gravitional interaction between antihydrogen and the Earth. It has been claimed in the literature that there "is no compelling evidence or theoretical reason to rule out such a difference (i.e., between $g$ and $\bar{g}$) at the 1% level." I argue in this short paper that bending of light by the sun provides a more stringent limit than this.