A smartphone app turns black hole physics into a real lab course

A smartphone app called Black Hole Vision lets students treat simulated black hole images as real experimental data — measuring the black hole's mass three independent ways, mapping coordinate distortions with a Jacobian, and even quantifying the chaotic instability of near-bound photon orbits via a Lyapunov exponent. All of this is designed for undergraduates, with extensions for graduate courses. It's a rare case where general relativity gets the hands-on lab treatment usually reserved for introductory physics.