Two GPC seminars today: General Physics Colloquium (CSS) Wed. 18 May at 14.15 in 1532-214 Speaker: Richard Dawid Stockholm University Title: String theory and the scientific method Abstract: For the last thirty years, string theory has played a highly influential role in fundamental physics without having found empirical confirmation. The presentation will analyse reasons for the high degree of trust many physicists have developed in a theory that, according to classical standards of theory assessment, would have to be called an unconfirmed speculation. It will be argued that the case of string theory suggests an extension of the concept of theory confirmation that allows for confirmation by observations that are not predicted by the theory in question (to be called "non-empirical confirmation"). The relevance of non-empirical confirmation reaches far beyond the context of fundamental physics and may throw new light on a number of core debates in the philosophy of science. Coffee and cake will be available from 14.05 General Physics Colloquium Wed. 18 May at 15.15 in Fys. Aud. Speaker: James M. Lisy University of Illinois at Urbana-Champaign Title: Non-covalent interactions: Balancing enthalpy and entropy, enabling size-selectivity, and controlling dynamics Abstract: While the focus of chemistry in the 20th Century was on understanding the nature of the chemical bond, it has been argued that the challenge for the 21st Century will be understanding the nature of non-covalent interactions. With a range of strengths from very weak (van der Waals) through hydrogen bonds to strong ion-neutral electrostatic interactions, they pose a significant challenge to both experimentalists and theoreticians. In particular, the balance between these interactions, their ability to both compete and cooperate, governs the structure, stability and function of complex systems, such as proteins and DNA. However examples of all of these effects can easily be found in smaller systems, such as clusters of molecules, atoms and ions. This presentation will be an overview of experimental and supporting computational studies of gas-phase molecular clusters containing a single ion, where the size and composition of the cluster can be controlled at the molecular level, using mass spectrometric methods. Structural and dynamical information on these species are obtained from their infrared spectra. Coffee and cake will be available from 15:05