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Spacetime Symmetries and the Origin of Antimatter (Bryan Roberts)

Delighted to have been joined by Bryan Roberts for our first in person seminar since covid. The symmetries of space, at least locally, appear to us to be given by the group of rigid Euclidean rotations. The symmetries of spacetime, again locally, appear to be the symmetries of Minkowski spacetime, called the Poincaré group. I will argue that both of these appearances are incorrect. Instead, I propose that the correct symmetries are given by a 'universal covering' for these groups. I then show how this non-intuitive assumption is required to explain an unusual fact about the nature of material bodies in our universe: that all ordinary matter has a twin counterpart called 'antimatter'. On this account of spacetime symmetries, antimatter is not just a postulate about material bodies, but a consequence of the structure of spacetime.