Does antimatter fall up? The science-fictional idea of antigravity is now being taken seriously by a number of researchers around the world. We will develop novel experimental apparatus to measure the gravitational acceleration of antimatter.
Einstein’s General Relativity, the accepted theory of gravity, predicts no difference whatsoever between the gravitational behaviors of matter and antimatter. While well-established experimentally, General Relativity has never been tested with antimatter. If antimatter is found to fall up in the gravitational field of the Earth — or even if it falls down, but at a different rate from matter — it will fundamentally change our view not only of gravity but of the nature and evolution of the Universe.
The IPRO team will develop novel experimental apparatus to measure the gravitational acceleration of antimatter. Such a measurement will require a source of neutral antimatter atoms and a precision device to measure their motion under gravity. The approach for the project is to use muonium — a hydrogen-like atom composed of an antimuon bound to an electron. (Although the electron is matter, since the antimuon is 200 times heavier than the electron, muonium should act gravitationally like antimatter.) Muonium sources exist at a number of particle accelerator laboratories around the world. Since muonium decays on average in 2.2 microseconds, the measurement is difficult and requires extreme mechanical precision.
Working toward the above goal means that the IPRO team will continue developing a precision interferometer employing thin silicon-nitride gratings made at Argonne National Laboratory using nanotechnology fabrication techniques. This IPRO project started in the fall 2014 semester and has continued since then, with significant progress being made. The fall 2017 IPRO team will build on that progress by building gratings, characterizing their precision (and, if necessary, figuring out how to improve it). The team will carry out further design and simulation studies, including finite-element analysis (FEA) of the gratings, the optical bench, and their mechanical systems, in order to understand and optimize the performance of the experiment as a whole. The team will also continue experimental studies of our infrared-laser picometer-alignment system.