Influence of Cosmic Expansion on Solar System Dynamics
Recent experiments confirmed that the cosmos undergoes an accelerated expansion. Could this expansion have a measurable influence on the dynamics within the solar system?
Modern cosmology is described within the framework of General Relativity in which the geometry of space and time is subject to dynamical change. All current models of our Universe have in common that space is presently in a state of expansion. The question addressed in this project is whether, and to what extent, does this expansion influence the dynamics on small scales (as compared to cosmological scales), particularly in our Solar System. Here our reference order of magnitude for any effect is given by the apparent anomalous acceleration of the Pioneer 10 and 11 spacecrafts which is of the order of 10−9m/s2. It is distinguished between dynamical and kinematical effects. We reanalyze and essentially confirm a fully relativistic argument by Dicke & Peebles concerning the orbits of electromagnetically bound systems. It was found that in the Solar System dynamical effects can be safely modelled by suitably improved Newtonian equations, showing that effects do exist, but are smaller by many orders of magnitude compared to our Pioneer reference. On the other hand, the kinematical effects need a proper relativistic treatment and have been argued by others to give rise to an additional acceleration of the order Hc, where H is the Hubble parameter and c is the velocity of light. This simple and suggestive expression is intriguingly close to the anomalous Pioneer acceleration. We reanalyzed this argument and found a discrepancy by a factor of (v/c)3, which strongly suppresses the alleged Hc–effect for the Pioneer spacecrafts by 13 orders of magnitude. The project therefore concluded the fundamental importance to understand precisely, i.e. within the full dynamical theory (General Relativity), the back-reaction effects of local inhomogeneities for our interpretation of cosmological data, a task which is not yet fully accomplished.
LiteratureThis topic was investigated within an Ariadna study in collaboration with the university of Freiburg. For more information you can download the final report.