In the far future(10^85 years) an “element” called positronium will develop with a diameter of the current observable universe of 93 billion light years. (Remember that light travels at 3 × 10^8 m/s). This element consists of an electron and a positron, both of which have a mass 9.11 × 10^−31 kg orbiting a common center of mass. The force between them is given by Coulombs law F = Ke^2/r^2 where K = 8.99 X 10^9Nmi^2/C^2, e = 1.602X10^-19C, and r is the distance between particles. How long does it take for these particles to orbit each other? I.e. what is their orbital period? Edit: For the sake of physics homework, we can suspend our knowledge of atomic structure and just treat this as a question about orbital period. Have I posted in the right section?