Concerning the clarification of the paragraph:
But now we can make a potential identification with standard quantum
formalism: we suppose that the Lagrangian density ℒ corresponds to the
total flux in all directions (or, in other words, the divergence) of
causal edges at each point in multiway space.
Complemented by:
By the way, it’s worth mentioning what a “flux of causal edges.”
corresponds to. Each causal edge represents a causal connection
between events that are, in a sense “carried” by some element in the
underlying hypergraph (the “spatial hypergraph”). So a “flux of causal
edges” is in effect the communication of activity (i.e. events),
either in time (i.e. through spacelike hypersurfaces) or in space.
(i.e. through timelike hypersurfaces). And at least in some
approximation we can then say that energy is associated with activity
in the hypergraph that propagates information through time, while
momentum is associated with the activity that propagates information in
space.
Reference: Finally We May Have a Path to the Fundamental Theory of Physics
Notice that S. Wolfram is proposing a more fundamental framework than the usual framework of energy and momentum. The idea is not to compute energy, momentum and the Lagrangians from the Wolfram Model and then go back to the mainstream physics, but to use the Wolfram Model to explain physical phenomena without using the notions from the previous paradigm: energy, momentum, Lagrangian, etc. The association between energy and activity in the hypergraph that propagates information through time is a hint for substituting energy in the explanations by the role of the activity in the hypergraph that propagates information through time.
For example, imagine an explanation of some property of a black hole in terms of energy. This explanation should be easy to translate to an explanation in the Wolfram Model using the activity in the hypergraph that propagates information through time without any need to compute the energy for the explanation to be consistent. Of course, at some point, the activity in the hypergraph that propagates information through time should explain the results of the measurements of energy.
The obvious question is: What is the problem with energy, momentum, etc? Well, these are real numbers and maybe real numbers are not the best way to describe nature at its most fundamental level. Maybe a real number is too reductive. To use discrete relations rather than real numbers is one of the starting points of the Wolfram Model.
Here is a reflection about the role of explanations in physics due to David Deutsch.