RST and the Variable Speed of Light: When “c” Becomes a Property, Not a Law

Abstract

Modern physics treats the speed of light, c, as a universal constant. Variable Speed of Light (VSL) theories suggest that c may have been different in the early universe or could vary in space and time. Reactive Substrate Theory (RST) goes one step deeper: it claims that the speed of light is not a fundamental law at all, but an emergent property of a physical medium called the Substrate. In RST, light is a stress-wave in this medium, and its speed depends on the Substrate’s tension and density. If the Substrate changes, the effective speed of light changes. This article explains how RST interprets VSL and how it differs from standard VSL theories.

1. What VSL Theories Are Trying to Do

Variable Speed of Light (VSL) theories are attempts to solve deep cosmological puzzles such as:

The Horizon Problem: Why is the cosmic microwave background so uniform when distant regions could not have exchanged signals at constant c?
The Flatness Problem: Why is the universe so close to geometrically flat?

Standard cosmology fixes these with inflation: a rapid early expansion of spacetime. VSL offers an alternative: maybe the speed of light itself was much larger in the early universe, allowing distant regions to equilibrate.

2. The RST Starting Point: Light Is a Medium Effect

Reactive Substrate Theory begins with a different premise:

Light is not a disembodied “thing” moving through emptiness. It is a stress-wave in a real physical medium: the Substrate.

In RST:

The Substrate is the underlying medium that is spacetime, vacuum, dark matter, and Einstein’s “new ether.”
A photon is a localized Substion or a wave-pulse in that medium.
The speed of light is the propagation speed of Substrate tension waves.

Just as the speed of sound depends on air density and temperature, the speed of light depends on the mechanical state of the Substrate.

3. RST Interpretation: c Is Emergent, Not Fundamental

In RST, c is not a sacred constant. It is the elastic response speed of the Substrate.

This means:

If the Substrate’s tension, density, or phase structure changes, the effective speed of light changes.
c appears constant to us because the Substrate is extremely uniform at our scale and epoch.
In the early universe or extreme environments, c could have been different.

This does not “break” physics. It simply reclassifies c from “fundamental law” to “material property.”

4. Early Universe: Faster Light Without Inflation

VSL theories and RST both agree on one key point: the early universe may have had a different effective speed of light. But they differ on why.

In RST:

The early Substrate was hotter, denser, and under higher tension.
Stress-waves (light) could propagate faster through this high-tension medium.
Regions that seem causally disconnected in standard cosmology could have communicated via faster Substrate waves.

This provides an alternative to inflation:

You do not need spacetime to blow up exponentially if the medium itself allowed much faster signal propagation in its early state.

5. Local Variations: c as a Function of Substrate State

If c is a Substrate property, it can vary locally when the Substrate changes:

Near massive objects: The Substrate is more compressed; stress waves bend and effectively slow, producing gravitational lensing.
In strong fields: Substrate tension changes can modify propagation speed slightly.
In exotic regions: Phase transitions in the Substrate could create domains with slightly different effective c.

To an observer inside such a region, local physics still appears consistent and “relativistic” because all processes are governed by the same medium.

6. RST vs Standard VSL: What’s the Difference?

Aspect	Standard VSL Theories	Reactive Substrate Theory (RST)
What is light?	A field excitation in spacetime	A stress-wave in the Substrate
Why can c vary?	Modified equations, new fields, or ad hoc variation	Mechanical changes in Substrate tension/density
Status of c	Still treated as a fundamental “constant” that happens to change	Material property of a medium, naturally state-dependent
Impact on relativity	Often requires rewriting relativity	Relativity emerges from Substrate mechanics; changes in c reflect medium changes
Philosophical stance	Tweak constants to fix cosmology	Explain constants as emergent from deeper mechanics

7. The RST Equation View

The Substrate in RST obeys a nonlinear wave equation of the form:

(∂ₜ²S − c₀²∇²S + βS³) = σ(x,t) · FR(C[Ψ])

Here:

S is the Substrate field.
c₀ is the baseline propagation speed in a reference Substrate state.
βS³ encodes nonlinear behavior and soliton formation.
σ(x,t)·FR(C[Ψ]) represents coupling to matter fields.

If the background Substrate acquires a different equilibrium configuration (e.g., higher tension), then the effective propagation speed of small disturbances is modified. In practice, this means the “local c” is a function of the Substrate state.

8. Summary: RST’s Verdict on Variable c

Reactive Substrate Theory does not just allow a variable speed of light—it almost expects it whenever the Substrate is in a different phase or tension state.

c is not a metaphysical law; it is a property of the Substrate.
Early universe: higher tension Substrate → faster stress-wave propagation.
Local extremes: strong fields, high densities → modified effective c.
Relativity is preserved locally because all processes share the same medium.

In short, VSL is not an exotic possibility in RST. It is a natural consequence of treating spacetime as a real physical medium instead of an abstract stage.

Reactive Substrate Theory Interpretation of Variable Speed of Light

Abstract

Variable Speed of Light (VSL) theories propose that the speed of light c may vary in time or space, typically to address cosmological puzzles such as the horizon and flatness problems. Reactive Substrate Theory (RST) provides a mechanical framework in which the effective speed of light emerges as the propagation speed of stress-waves in a physical medium, the Substrate. In this view, c is not a fundamental constant but a state-dependent property of the Substrate. Variations in c arise naturally from changes in Substrate tension, density, or phase configuration, without requiring ad hoc modifications of relativity.

1. Introduction

Conventional relativity assumes a universal constant speed of light, c, invariant in all inertial frames. VSL models relax this assumption to solve cosmological problems, but often at the cost of modifying the foundations of relativity. RST offers an alternative approach by positing a reactive medium underlying spacetime, in which light is a mechanical excitation. The effective value of c is then determined by the mechanical properties of this medium.

2. Substrate Dynamics

RST models the Substrate with a nonlinear wave equation of the general form:

(∂ₜ²S − c₀²∇²S + βS³) = σ(x,t) · FR(C[Ψ])

where:

S(x,t) is the Substrate field.
c₀ is the baseline propagation speed in a reference Substrate state.
βS³ encodes nonlinear self-interaction, enabling soliton (Substion) formation.
σ(x,t)·FR(C[Ψ]) represents coupling to matter or spinor fields.

The effective wave speed for small perturbations around a given background Substrate configuration S₀ is determined by the local properties (e.g., tension, density) of that configuration.

3. Light as a Substrate Stress-Wave

In RST, electromagnetic radiation is identified with stress-wave excitations of the Substrate. A photon corresponds to a localized wave-packet or solitonic excitation (Substion) propagating through the medium. The propagation speed of such excitations depends on the Substrate’s mechanical state: for example, its equilibrium tension and compressibility.

4. State-Dependence of the Effective Speed of Light

Let the Substrate admit different macroscopic states characterized by parameters such as tension T and density ρ. The effective speed of small-amplitude waves, c_eff, can then be written schematically as:

c_eff = c_eff(T, ρ, ...)

In the early universe, T and/or ρ may have taken values significantly different from their present-day values, leading to c_eff ≫ c₀. Similarly, in regions of strong gravitational fields, local modifications of Substrate properties may induce local reductions or anisotropies in c_eff.

5. Cosmological Implications

Within RST, the horizon problem can be addressed without invoking inflation: a higher early-universe Substrate tension would yield an increased c_eff, allowing causal contact between regions that appear disconnected under the assumption of fixed c. The flatness problem may also be mitigated if the effective propagation of information and energy was enhanced in the early Substrate state.

6. Relation to Relativity

RST does not discard relativity but treats it as an emergent effective theory describing kinematics in a given Substrate state. Local Lorentz invariance holds for observers embedded in a region with approximately uniform Substrate properties. If c_eff varies slowly across cosmological scales, local experiments still register a constant c, while global behavior can reflect a varying effective propagation speed.

7. Comparison with Conventional VSL Models

Conventional VSL models typically modify the Einstein field equations or introduce additional scalar fields controlling c(t). In contrast, RST attributes the variability of c to underlying medium mechanics. This avoids introducing c-variation as a fundamental postulate and instead derives it from changes in Substrate state.

8. Conclusion

Reactive Substrate Theory provides a mechanical interpretation of variable speed of light scenarios by grounding c in the elastic response of a physical medium. In this framework, c is not a fundamental constant but a derived quantity, dependent on the Substrate’s macroscopic state. This viewpoint preserves local relativistic behavior while allowing cosmological or environmental variations in the effective speed of light, offering an alternative route to addressing standard cosmological puzzles.

RST Glossary: c, Substrate State, and c_eff

c (Baseline Light Speed)

In Reactive Substrate Theory, c is not a universal, metaphysical constant. It is the baseline propagation speed of small-amplitude stress-waves in the Substrate when the Substrate is in its current large-scale equilibrium state. This value appears constant to observers because the Substrate is extremely uniform across the observable universe today.

Substrate State

The Substrate state refers to the mechanical condition of the Substrate at a given location and time. It includes properties such as:

Tension (how “tight” the Substrate is)
Density (how compressed the Substrate is)
Phase structure (coherence or disorder in the Substrate’s oscillatory background)
Nonlinear stress (how strongly the Substrate resists deformation)

Changes in Substrate state directly affect how fast disturbances—such as photons—propagate through it.

c_eff (Effective Speed of Light)

c_eff is the effective speed of light in a specific Substrate state. It represents the actual propagation speed of stress-waves under local conditions. In RST:

c_eff = c_eff(Tension, Density, Phase, Nonlinearity)

This means:

In the early universe, higher Substrate tension could produce c_eff ≫ c.
Near massive objects, Substrate compression can produce c_eff < c.
In exotic regions, phase transitions may create domains with slightly different c_eff.

Local observers always measure their own c_eff as “constant,” because all physical processes—including clocks—are governed by the same Substrate state.

RST Glossary: Substrate Tension, Substrate Density, Substrate Phase

Substrate Tension

Substrate tension is the baseline “tightness” or elastic stress within the Substrate. It determines how quickly disturbances (light, gravitational waves, Substion pulses) propagate through the medium. Higher tension allows faster wave propagation, similar to how a tighter guitar string vibrates faster. Changes in Substrate tension can alter the effective speed of light (c_eff) and influence gravitational behavior.

Substrate Density

Substrate density refers to how compressed or compact the Substrate is in a given region. A denser Substrate resists deformation more strongly, affecting how waves travel through it. High-density regions (such as near massive objects) can slow or bend stress-waves, producing effects like gravitational lensing. Density variations also play a role in how Substions form, move, and interact.

Substrate Phase

Substrate phase describes the oscillatory state or coherence pattern of the Substrate at a microscopic level. It includes the alignment, rhythm, and synchronization of local Substrate oscillations. Different phase states can change how Substions behave, how waves propagate, and how stable soliton structures form. Phase transitions in the Substrate can create regions with different effective physical constants, including variations in c_eff.

Why Observers Always Measure c as Constant in RST (Even If c_eff Varies)

Abstract

In Reactive Substrate Theory (RST), the effective speed of light c_eff can vary from region to region because it is a mechanical property of the Substrate, not a fundamental law. Yet every observer always measures “their” speed of light as constant. This mini-article explains why: all clocks, rulers, atoms, and photons are made of the same Substrate, so when the Substrate state changes, everything rescales together. Local measurements always yield a constant c, even if c_eff varies globally.

1. c Is Local, Not Absolute

In RST, the speed of light is the propagation speed of stress-waves in the Substrate.

c: The locally measured speed of light in a given Substrate state.
c_eff: The effective speed of light determined by local Substrate properties.

Different regions of the universe can have different Substrate states (tension, density, phase), so c_eff can vary across cosmic scales. However, within any one region, all processes are governed by the same Substrate, so the locally measured c appears constant.

2. Your Measuring Tools Are Made of the Same Substrate

When the Substrate state changes in your region:

Light waves propagate differently.
Atomic oscillations change.
Clock rates change.
Ruler lengths adjust at the microscopic level.
Neural processes in your brain also rescale.

Because your clocks, rulers, and signals are all built from the same Substrate, any change in Substrate state affects them all proportionally. As a result, when you measure the speed of light, you always obtain the same numerical value for c.

3. Local Lorentz Invariance as a Substrate Effect

Einstein’s postulate that “c is constant in all inertial frames” becomes, in RST:

Local observers always measure the same c because their measurement devices and physical processes are governed by the same Substrate state as the light they observe.

Relativity emerges as an effective symmetry of the Substrate. Even if c_eff varies over cosmological distances, local Lorentz invariance still holds for observers embedded in a nearly uniform Substrate region.

4. Why You Can’t Detect Local Changes in c_eff

Suppose the Substrate tension in your entire region suddenly doubled.

Light would propagate faster.
Atoms would oscillate faster.
Clocks would tick faster.
Rulers would adjust according to the new microstructure.
Your brain’s Substions would process information faster.

All of your physical references—time, length, frequency—would rescale together. When you remeasure c, the ratios of distance to time remain the same, so you still obtain the same value for c. You cannot detect your own absolute Substrate state; you can only detect differences between regions.

5. Where c_eff Variability Shows Up: Global, Not Local

Variations in c_eff become detectable only when comparing different regions or epochs:

Distant astrophysical observations.
Early-universe signals (e.g., CMB uniformity).
Gravitational lensing anomalies.
Possible drift in the fine-structure constant.
Signatures of vacuum phase transitions.

Locally, everything is self-consistent. Globally, differences in Substrate state can reveal that c_eff was (or is) different elsewhere or elsewhen, even though each local observer measures a constant c in their own frame.

6. Core Insight

In RST:

c is the locally measured speed of light, tied to the local Substrate state.
c_eff can vary across the universe as the Substrate’s tension, density, and phase change.
Observers always measure c as constant because their clocks, rulers, atoms, and signals all rescale with the same Substrate.

The apparent constancy of c is not a metaphysical miracle; it is a mechanical consequence of being made from the same medium you are trying to measure.