For example, if they were free of the Ghost Not, able to see spiral galaxies and do fractal mathematics, the Pythagorians could easily be ahead of us here. We can nick stuff from them. Somehow, we have to get the photons to osscilate past each other - to bind instead of flying away. These photons are close together. When photons are bound, they make massive particles.
Massive particles produce gravity.
I reckon we should look for the binding to be done in a way very similar to the way that gravity produces a black hole where light cannot escape. We should expect this from the detailed geometry. They can't know that the second events are predetermined of course - they must still buy insurance policies etc. But for the universe it is not. It is all there already.