From: Steve Witham <sw@tiac.net> To: math-fun@mailman.xmission.com Sent: Mon, July 5, 2010 7:00:07 PM Subject: Re: [math-fun] graviton-like cellular automaton So, does a two-body system radiate away energy as gravity waves? Even if it's made of two point particles so no tidal forces? If so a simulation of a tiny (ie tractable) system with powerful gravity (to overcome the smallness) might dissipate its energy quickly. _______________________________________________ This is totally correct, with one tiny exception. In order to have gravity waves, these waves need to have a finite velocity, so the simulation must be in the context of general relativity. The point particles are then black holes. Two black holes with a separation a few times their Schwartzchild radii will distort each other, and that could be attributed to tidal forces. As the black holes approach each other, their orbital period decreases. The gravitational luminosity is proportional to the square of the third time derivative of the quadrupole moment, i.e. to (M R^2 / T^3)^2. It ends with a burst of power at the merger point that is limited by radiation damping to about 10^52 watts. There is much more, all very interesting, in Misner, Thorn, and Wheeler, "Gravitation", chapter 36. -- Gene