| I don't see a problem there. The definition of causality is circular anyway. There's no formal mathematical self-consistent proof of causality. It's just sort-of assumed, and then there are back-arguments from relativity that say "Well, that violates something we sort of assume." The problem is that in science, if you assume things in a naive way ("What goes up must come down." "Planets travel in circles") you're almost certainly wrong - because the details of physical reality are usually counter-intuitive and unexpected. So what we really know is: 1. Spacetime is a thing. It has bulk properties described by GR.
2. Er - that's it. We don't know what spacetime is made of, or what you can do with the things it's made of, or what their properties are. So I'd classify this as "definitely not known due to lack of knowledge" rather than "definitely not proven." Proposals like Quantum Dynamical Triangulation, Causal Sets, and Loop Quantum Gravity are beginning to ask what spacetime is made of, but they're barely in their infancy. The one thing they have in common is the idea that there's a network of - something... - and the reality we recognise propagates across the network. If the elements are discrete - and they almost certainly are, because of the Planck limit - there will be some moment where an element changes state. How fast does that happen? What's the mechanism? What limits the state changes? (Adjacency? Some other property?) It's completely mysterious, and I think it's unwise to make definitive statements about it until it stops being a mystery. |