I study “exotic atoms”. In ordinary atoms, electrons orbit around the atomic nucleus. If instead a negatively-charged particle such as an antiproton (the antiparticle of the proton, having a negative charge but the same mass as the proton) is bound to the nucleus, we call such a system an “exotic atom”. Exotic atoms do not exist in nature. They must be artificially synthesized using accelerators. You might ask why it is of any use to study such things, if they are not the building blocks of the universe. Good point. It turns out that “atomic spectroscopy” techniques, the methods to study the discrete atomic energy levels by observing the “atomic transitions” (emission and absorption of light quanta by the atom), which is the established method to study ordinary atoms, can be applied to study exotic atoms (sounds simple, but in reality, it took us many years to develop such techniques). Our data can then be used to test fundamental symmetries of nature, such as the matter-antimatter symmetry. One of the central questions is, “is the proton mass exactly the same as the antiproton mass?” This is one of my main activities, which is being done at CERN (European laboratory for high energy physics), Switzerland.