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Research group | Quantum-Gravity Phenomenology, General and Special Relativity

An observer on Earth (represented by a solid vertical line in the given space-time diagram) sends a light signal (dashed straight lines) at space-time p0 to a satellite (solid curved line), where it is reflected at event p1, and finally received back on Earth at event p2. On its round trip it suffers three changes: one each on its way to and from the satellite due to variable space-time geometry, and one due to reflection. Accordingly, the quotient of the received (ω2) to the emitted (ω0) frequency receives three contributions, corresponding respectively to the three factors on the right-hand side of the displayed equation. We calculated them for some relevant curved models of space-time. Image: D. Giulini

According to General Relativity, the phenomenon of gravitation is an emergent one, a result of the particular geometric structure of space-time, the formation and evolution of which is ruled by Einstein’s equations. According to these laws, the geometry of space-time is directly influenced by the distributions of energy and momentum of matter. On the other hand, until now all non-gravitational interactions have been described by structures which are based on a fixed space-time geometry and which do not allow any dynamic interactions with the space-time geometry. Hence we face the inescapable problem of how to reconcile these two pictures. In particular, since all interactions but gravity are already described within the framework of Quantum Theory, we need to understand how to reconcile General Relativity with Quantum Theory.

The focus of this research group is to gain physical understanding and guidance in possible routes for this reconciliation. Concrete problems are studied, like the influence of varying space-time geometry on signal propagation, the relevance of which ranges from satellite tracking to possible signatures of Quantum Gravity proper due to characteristic changes in dispersion relations for ultra-high energy photons. In addition, the effects of curvature and cosmic expansion on the motion and stability of quasi-localised extended objects, like stars or galaxies are studied by this research group. On a much smaller scale, investigations are carried out on the possible effects of gravity on the spread and propagation of matter waves packets in Quantum Mechanics, which, according to some models, may well be within the reach of atomic interferometry.