Proposition: Light as a Substrate Ripple, Not a Fundamental Entity
“If spacetime is the fabric, the substrate is the weave.”
In Reactive Substrate Theory (RST), there is no fundamental distinction between “spacetime” and “light.” Both are emergent behaviors of a single underlying nonlinear scalar field S(x,t), the substrate. The substrate is not something that exists in spacetime; rather, what we call spacetime is the large-scale, effective description of the substrate’s dynamics.
Note to the Reader: To be clear, the Substrate doesn't occupy space. It is the space. When the Substrate "bunches up" or "thins out," our clocks slow down and our rulers shrink. We aren't watching waves on a pond; we are the pond, and the ripples are our reality.
At the most basic level, the substrate obeys a nonlinear wave equation of the form:
d²S/dt² − c² ∇²S + β S³ = σ(x,t)
Here, c is the characteristic propagation speed of ripples in the substrate, β encodes nonlinear self-interaction, and σ(x,t) represents effective sources associated with emergent matter and energy. This equation is not written on top of spacetime; it is the substrate whose behavior gives rise to spacetime geometry and causal structure.
To study small excitations, we decompose the field into a background and a perturbation:
S(x,t) = S̄(t) + δS(x,t)
Linearizing in δS yields:
d²(δS)/dt² − c² ∇²(δS) + 3β S̄² δS = 0
Assuming wave-like solutions δS ∝ exp[i(k·x − ωt)] leads to the dispersion relation:
ω² = c² k² + 3β S̄²
In regimes where the nonlinear term is small, this reduces to the familiar form:
ω ≈ c k
In this limit, the perturbations behave exactly like conventional light: linear waves propagating at speed c. But in RST, this is not because photons are fundamental; it is because they are the simplest ripple mode of the substrate field. The constant c is therefore not “the speed of light” in a particle sense, but the maximum speed at which any disturbance can propagate through the substrate.
This reframes the usual relativistic speed limit: nothing outruns c because nothing can outrun the substrate’s own ripple speed. Light, gravity, and any other signal are all constrained by the same underlying medium.
A useful analogy is a guitar string. The string itself is the substrate. A vibration traveling along the string is like light: it moves at the speed determined by the string’s tension and density. That speed is not set by the vibration; it is set by the string. Likewise, in RST, light is just one kind of vibration of the substrate, moving at the speed allowed by the field’s internal dynamics.
This analogy also clarifies so-called “spooky action at a distance.” When you pull on one end of a guitar string, the fact that the string is a single connected object means its state is globally constrained, even though actual waves still propagate at a finite speed. In RST terms, entangled correlations reflect the global, connected nature of the substrate configuration, while the transmission of usable information remains limited by c. The substrate is everywhere, but its ripples are still bound by a finite propagation speed.
Thus, in RST, photons are not fundamental carriers of a pre-existing spacetime structure. They are emergent, linearized ripples of the substrate itself, and the universal speed limit arises from the substrate’s intrinsic properties rather than from any particular particle species.
