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“Fun”-damental physics: robophysical models for General Relativity and Quantum Mechanics

Presented by: 
Daniel Goldman Georgia Institute of Technology
Thursday 30th November 2017 - 10:10 to 10:50
INI Seminar Room 1
What happens when physicists build robots? In my group, we do not view these machines as labor-saving devices or demonstrations of control principles, but as scientific instruments, with which to have fun and study fascinating new dynamical systems. We call this approach “robophysics” (see Aguilar et al, Rep. Prog. Phys., 2016), and in this talk I will highlight two of our recent studies in which we observe aspects of “fundamental” (or “modern”) physics in simple self-propelling robots. 1) When transiting a regular array of rigid posts, a ~80 cm long slithering snake-like robot passively scatters into preferred directions, the extent of which is inversely related to the post spacing; these behaviors thus mimic aspects of matter waves complete with diffraction patterns, the diffraction-pattern destroying “measurement” phenomena, Poisson spots, an uncertainty principle, and the beautiful Talbot carpet (a near-field diffraction effect). Of course, there is nothing quantum mechanical about our system: a model based upon robot head-post collisional dynamics and interference of neighboring posts captures much of the observed dynamics. 2) Inspired by the standard (but inaccurate) science-museum type demonstration of General Relativity (e.g. marbles orbiting a central depression), we create an experiment in which the orbiting mass does not lose energy and thus displays persistent dynamics. When confined to a ~2 m diameter flexible spandex sheet with an imposed central depression, a ~10 cm diameter circular two-wheeled robot car executes trajectories that have aspects of orbits in the Schwarzschild solution to Einstein’s field equations in General Relativity (GR). Our system displays closed orbits (like in Newtonian gravity) as well as beautiful patterns of precessing orbits. The latter obey a precession formula derived from the Schwarzschild solution, but with negative precession, indicating that the GR-like correction term in our system acts to repel orbits. In addition to the fun one can have with these systems, we argue that robophysical devices have educational utility: students (and faculty) of all ages gain insight into a diversity of natural phenomena via hands-on construction and play using low-cost but sophisticated  devices.
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University of Cambridge Research Councils UK
    Clay Mathematics Institute London Mathematical Society NM Rothschild and Sons