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A bstract We study causality in gravitational systems beyond the classical limit. Using on-shell methods, we consider the 1-loop corrections from charged particles to the photon energy-momentum tensor — the self-stress — that controls the quantum interaction between two on-shell photons and one off-shell graviton. The self-stress determines in turn the phase shift and time delay in the scattering of photons against a spectator particle of any spin in the eikonal regime. We show that the sign of the β -function associated to the running gauge coupling is related to the sign of time delay at small impact parameter. Our results show that, at first post-Minkowskian order, asymptotic causality, where the time delay experienced by any particle must be positive, is respected quantum mechanically. Contrasted with asymptotic causality, we explore a local notion of causality, where the time delay is longer than the one of gravitons, which is seemingly violated by quantum effects. 

With our partners at Manylabs, we are developing Dataflow, a browser-based application that (unlike other IoT platforms) not only lets students collect and view sensor data, but also allows them to write programs that transform that data to control physical actuators. Dataflow uses Raspberry Pis as WiFi-enabled devices that can execute these control programs because they are inexpensive but powerful computers. The Pis run a client program that reads data from all USB-connected sensors, runs student programs, and sets the states of USB-connected actuators.