harmonic oscillator in 2D, Kepler problem in 3D and free particle on sphere in 4D. These are the same thing in different guises. Posted on 2020/12/18 by Carl Robitaille Wanna hear something crazy?1) harmonic oscillator in 2D2) Kepler problem in 3D3) free particle on sphere in 4DThese are the same thing in different guises.— Tamás Görbe (@TamasGorbe) December 17, 2020 Mysteries of the gravitational 2-body problem The Ellipse and the Atom