The One-Way Speed of Light, Measurement Conventions, and Emergent Time

Why claims of a “fundamental flaw” in relativity misunderstand what is being measured — and how Reactive Substrate Theory reframes the issue

Abstract

Recent popular commentary has renewed claims that modern physics rests on a flawed assumption: that the one-way speed of light is unknowable, or potentially different from the measured two-way speed. These arguments often frame this as a hidden weakness in relativity or evidence of suppressed physics. In this article, we show that such claims rest on a category error between physical observables and measurement conventions. We then demonstrate how Reactive Substrate Theory (RST), in which time is emergent and locally defined, naturally resolves the issue by removing the assumption of global clock synchronization altogether. Rather than exposing a paradox, the one-way speed of light problem highlights the limits of treating time as a fundamental background coordinate.

1. What Is Actually Measured in Experiments

All direct measurements of the speed of light are round-trip measurements. A signal is emitted, reflected, and received at the same clock, allowing a time interval to be recorded without synchronizing distant clocks. These experiments establish, with extraordinary precision, an invariant two-way speed.

The so-called one-way speed of light would require comparing the emission time at one location with the reception time at another. This comparison implicitly demands a prior synchronization convention for spatially separated clocks. Without such a convention, there is no operational procedure that uniquely determines the one-way speed.

Crucially, this is not a failure of experimental ingenuity. It is a statement about what constitutes a physically well-defined observable.

2. Synchronization Is a Convention, Not a Hidden Variable

In special relativity, Einstein synchronization is adopted because it is simple, symmetric, and consistent with all observations. Alternative synchronizations are mathematically possible, but they do not lead to distinct empirical predictions so long as observable quantities remain invariant.

Claims that the one-way speed of light might be “different” typically conflate:

a choice of synchronization convention, with
a measurable physical asymmetry.

No experiment has demonstrated such an asymmetry. Nor could one, unless additional physical structure is introduced beyond standard relativistic observables.

3. The Clickbait Error: Treating Conventions as Physics

Popular treatments often present the synchronization problem as if it were an unresolved physical mystery rather than a known epistemic limitation. This rhetorical move transforms a statement like “the one-way speed is convention-dependent” into “physics is hiding something.”

This is not how foundational physics evaluates claims. If a quantity cannot be operationally isolated from a convention, it is not elevated to the status of a fundamental observable. It is demoted to a coordinate artifact.

The fact that no experiment requires knowledge of the one-way speed of light is not suspicious — it is decisive.

4. Reactive Substrate Theory: Removing the Hidden Assumption

Reactive Substrate Theory approaches the issue from a different starting point. Time is not treated as a universal background parameter to which all clocks refer. Instead, time is an emergent, local rate associated with physical processes and determined by the state of an underlying substrate field.

In RST:

Clocks measure proper time generated by local dynamics.
There is no requirement that distant clocks agree a priori.
Clock synchronization is itself a physical interaction mediated by signals.

As a result, the notion of a globally defined one-way speed of light is not merely unmeasurable — it is conceptually unnecessary.

5. Signal Propagation Without Global Time

In RST, signal propagation is described as the evolution of field excitations through the substrate. What observers measure are frequency ratios, arrival intervals, and correlations between local processes.

An observable frequency shift takes the form:

observed frequency ratio = (time-rate at emission) / (time-rate at reception)

This expression reproduces gravitational redshift, Doppler effects, and cosmological redshift without invoking an underlying global clock or a physically meaningful one-way speed.

The role played by “speed” is secondary to the role played by local time-rate variation.

6. Why the One-Way Speed of Light Is Not Fundamental

From the RST perspective, the one-way speed of light is not hidden — it is ill-posed. It presumes:

a global time parameter,
independent clock synchronization, and
an absolute simultaneity structure.

None of these are required to describe physical reality as we observe it. All measurable predictions depend on round-trip propagation and local process comparisons, which remain invariant.

7. What Would Count as New Physics

A genuine challenge to relativity — or support for alternatives — would require observations such as:

direction-dependent round-trip signal speeds,
violations of frequency-shift relations unexplained by local time-rate variation,
or clock comparison anomalies not attributable to known relativistic or environmental effects.

Speculation about unverifiable one-way quantities does not meet this standard.

8. Conclusion

The one-way speed of light problem is not evidence of a flaw in modern physics. It is a reminder that physical observables must be defined operationally, not metaphysically. Claims that portray this issue as a scandal rely on reifying measurement conventions into physical degrees of freedom.

Reactive Substrate Theory resolves the issue not by proposing a different one-way speed, but by removing the assumption that such a quantity must exist at all. In an emergent-time framework, only local dynamics and their correlations carry physical meaning.

What appears as a paradox dissolves once time itself is no longer treated as an absolute backdrop — but as a physical process.

Note on Scope

This article addresses conceptual interpretation, not experimental denial. All experimentally verified predictions of relativity are preserved. The critique is directed at misframing, not at established physics.

Appendix: Connection to Thermodynamics and Emergent Time in RST

The discussion above regarding signal propagation, clock synchronization, and the ill-posed nature of a global one-way speed of light connects directly to the thermodynamic framework developed in Thermodynamics in Reactive Substrate Theory (RST–Thermodynamics v1.0).

In that work, temperature is defined operationally as the rate at which a physical system explores its accessible microstates per unit proper time, with proper time determined by the local state of the substrate. This definition removes the assumption of a universal time parameter shared by all observers and systems.

The same conceptual move resolves the apparent paradoxes surrounding clock synchronization and one-way signal speeds. If time is emergent and locally generated by physical processes, then distant clocks do not possess an intrinsic synchronization until information is exchanged between them. Any attempt to define a one-way speed prior to such interaction necessarily smuggles in a synchronization convention rather than identifying a new observable.

From the thermodynamic perspective, what matters is not how fast a signal propagates with respect to a hypothetical global clock, but how energy exchange, state transitions, and correlations unfold relative to local proper time. Observable quantities—such as frequency shifts, thermal spectra, relaxation rates, and equilibrium conditions—are all determined by ratios of proper times along different worldlines.

This mirrors the treatment of temperature gradients in RST. Just as equilibrium temperature distributions reflect spatial variations in local time rates rather than violations of energy conservation, observed signal delays and redshifts reflect differences in accumulated proper time rather than a breakdown of relativistic invariance.

In both cases, apparent paradoxes arise only when one insists on interpreting fundamentally relational phenomena through the lens of an assumed global temporal backdrop. Once that backdrop is removed, both thermodynamics and signal propagation become internally consistent consequences of the same substrate-dependent time structure.

Thus, the one-way speed of light problem and the reinterpretation of temperature in RST are not separate conceptual issues. They are two manifestations of the same underlying principle: physical observables depend on how systems evolve with respect to local proper time, not on unobservable global conventions.

Cross-reference

Readers interested in the detailed formulation of temperature, entropy, equilibrium conditions, and cosmological thermal phenomena within Reactive Substrate Theory are referred to:

Thermodynamics in Reactive Substrate Theory (RST–Thermodynamics v1.0)
Available at: https://conspir-anon.blogspot.com/2026/01/thermodynamics-in-reactive-substrate.html

“The analysis above critiques how modern physics is often packaged for attention rather than accuracy. What follows is the theoretical framework I use to address the same questions without relying on misleading shortcuts.”

Reactive Substrate Theory v1.0 — A Unified Program

Reactive Substrate Theory (RST) v1.0 is not a single paper or isolated proposal. It is a coordinated theoretical program built around a shared minimal ontology: that spacetime, time, matter, and physical laws emerge from the dynamics of a single underlying substrate field. Each RST v1.0 paper addresses a specific domain of physics, but all are constructed to interlock through a common set of assumptions, definitions, and correspondence principles.

Rather than attempting to replace established theories such as general relativity or quantum mechanics, RST adopts a reinterpretive strategy. Existing theories are treated as experimentally validated effective descriptions that emerge from substrate dynamics in appropriate limits. The goal of RST v1.0 is therefore conceptual closure rather than expansion: to identify a minimal substrate-based framework capable of reproducing known results while resolving long-standing conceptual tensions.

Core Structural Assumptions

All RST v1.0 papers share the following foundational commitments:

Time is not a fundamental coordinate, but an emergent rate determined by local physical processes.
Proper time is operationally defined through physical clocks and oscillators coupled to the substrate.
Spacetime geometry in general relativity is an effective description of spatial variations in substrate state.
Quantum behavior arises from coherent excitations and resonant modes of the substrate, not from intrinsic indeterminism.
All observables are defined relationally, through ratios of locally accumulated proper times and energies.

RST v1.0 Papers and Their Roles

Each paper in the RST v1.0 series addresses a historically problematic interface between theories:

RST Core (Minimal Closure): Introduces the substrate field, its minimal dynamical equation, and the emergence of local time rates and effective metrics. Establishes the correspondence with weak-field general relativity.
Thermodynamics in Reactive Substrate Theory: Reinterprets temperature as the rate at which a system explores its accessible microstates per unit proper time. Demonstrates recovery of classical thermodynamics, relativistic temperature gradients, and cosmological blackbody behavior without invoking a global time parameter.
Signal Propagation and Clock Synchronization in RST: Analyzes the operational meaning of signal speeds and synchronization procedures in an emergent-time framework. Shows why quantities such as the one-way speed of light are not independently observable and how invariant two-way measurements naturally arise.
Cosmological Implications: Applies the substrate framework to large-scale structure, redshift, and the cosmic microwave background, reinterpreting expansion and horizon phenomena as cumulative effects of evolving proper-time rates.

These works are intentionally modular. Each can be read independently, but full conceptual clarity emerges when they are read as a unified set.

Why This Structure Matters

Many speculative frameworks fail not because they contradict data, but because they introduce unnecessary complexity or lack internal coherence. RST v1.0 takes the opposite approach: it minimizes assumptions, enforces correspondence with existing empirical results, and treats unresolved concepts—such as the nature of time, temperature in gravity, and signal synchronization—not as mysteries to be bypassed, but as guides for reconstruction.

By addressing thermodynamics, relativity, and measurement theory within a single substrate-based framework, RST v1.0 aims to clarify where current theories end as descriptions and where deeper structure may begin.

Status of the Framework

RST v1.0 is a closed, internally consistent proposal intended to be evaluated on conceptual clarity, mathematical coherence, and empirical compatibility. It makes no claim to finality. Subsequent versions (v1.1 and beyond) are explicitly reserved for justified extensions, simulations, and test-driven refinements.

Readers are encouraged to treat RST v1.0 not as a replacement for existing physics, but as a lens through which its foundations can be re-examined with fewer hidden assumptions.

Conspiranon