The Null-Cone Structure Of Spacetime Viewed Through Systemic Functional Linguistics

Penrose (2004: 407):

In my discussion above, I have chosen to emphasise the null-cone structure of spacetime, even more than its metric. In certain respects, the null cones are indeed more fundamental than the metric. In particular, they determine the causality properties of the spacetime. As we have just seen, material particles are to have their world lines constrained to lie within the cones, and light rays have world lines along the cones. No physical particle is permitted to have a spacelike world line, i.e. one outside its associated light cones. If we think of actual signals as being transmitted by material particles or photons, then we find that no such signal can pass outside the constraints imposed by the null cones. If we consider some point p in 𝕄, then we find that the region that lies on or within its future light cone consists of all the events that can, in principle, receive a signal from p. Likewise, the points of 𝕄 lying on or within p’s past light cone are precisely those events that can, in principle send a signal to the point p; … The null cones indeed define the causality structure of 𝕄: no material body or signal is permitted to travel faster than light; it is necessarily constrained to be within (or on) the light cones.

Blogger Comments:

From the perspective of Systemic Functional Linguistic Theory, null cones are not causality structures of spacetime. Instead, null cones represent all the possible trajectories (world lines) to or from a location in spacetime. That is, null cones are structures of processes (motions), not spacetime, and it is a matter of modalisation (possibility), not cause (causality).

Again, this confusion of process with circumstance lies at the heart of the misconstrual of the curvature of trajectories (geodesics) as the curvature of space-time, in the General Theory of Relativity.