first expansion phase of the universe you can do this because you could do this in principle because you know you have the density of matter and dark matter ordinary matter dark matter photons whatever at every location and you can solve a partial differential equation which basically is just you know physics at every location and I'm gonna compute the evolution of the universe this way the problem of with this is that she only do this at the scale of the universe given the size of the the grid the grid that you have to