title: Will a Decaying Atom Feel a Friction Force?
abstract: We show how a simple calculation leads to the surprising result that an excited two-level atom moving through a vacuum sees a tiny friction force of first order in v/c. At first sight this seems to be in obvious contradiction to other calculations showing that the interaction with the vacuum does not change the velocity of an atom. It is even more surprising that this change in the atom's momentum turns out to be a necessary result of energy and momentum conservation in special relativity.
authors.affiliation: School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, United Kingdom.
authors.forename: Matthias
authors.initials: M
authors.lastname: Sonnleitner
authors.affiliation: School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, United Kingdom.|Institut für Angewandte Physik, Technische Universität Darmstadt, D-64289 Darmstadt, Germany.
authors.forename: Nils
authors.initials: N
authors.lastname: Trautmann
authors.affiliation: School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, United Kingdom.
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Barnett