J. Rogers, SE Ohio
On the Self-Referential Temporal Ambiguity of the Gravitational Constant
A Foundational Critique of Dimensional Analysis in Gravitational Physics
Abstract
Newton's gravitational constant G carries units of m³ kg⁻¹ s⁻². The s⁻² term introduces a specific time scale into the law of gravitation. However, general relativity establishes that gravity is not a force acting across a fixed time — it is a gradient of time rates. Every point in a gravitational field has its own proper time, running at a rate that depends on the local gravitational potential. This paper poses a question that has not been formally addressed in the literature: which second does G introduce? We demonstrate that this question has no well-defined answer, that G's temporal dimension is therefore physically ambiguous, and that this ambiguity is the root cause of G's notorious measurement inconsistency across experiments spanning 200 years. We further show that G/c² — which appears in the dimensionless gravitational parameter τ = (G/c²)(m/r) — is free of this ambiguity, is known to GPS precision (10 significant figures), and is the only combination of G that the universe actually uses.
1. The Unit Contamination Problem
Newton's law of gravitation is standardly written as:
F = G · mM / r²
where F is force in kg·m·s⁻², m and M are masses in kg, r is distance in meters, and G = 6.674 × 10⁻¹¹ m³ kg⁻¹ s⁻². The dimensional structure reveals an immediate problem: the quantities mM/r² have units of kg²/m². They contain no time. Gravity, as a geometric relationship between masses and distances, introduces no clock.
G injects s⁻² into this equation for one reason only: Newton's second law F = ma defines force to include acceleration, which is measured against a clock. The second was already in F via kinematics. G absorbs s⁻² as a compensating factor to preserve dimensional consistency across a unit system that was never designed for gravitational physics.
The alternative is immediate. Define force geometrically:
F ≡ mM / r² [units: kg²/m²]
Then gravity is exact, unit-free in the physical sense, and contains no clock. The constant migrates:
F = ma / G ⇒ G = ma / F
G becomes the constant of inertia — the conversion factor between geometric force and kinematic response. The temporal ambiguity now lives in kinematics, where it belongs, not in the description of gravitational geometry.
2. Gravity Is a Time Gradient
General relativity does not describe gravity as a force. It describes gravity as spacetime curvature, and in the weak-field limit, this curvature is predominantly temporal. The gravitational redshift formula is:
Δf/f = ΔΦ / c² = (G/c²) · (M/r)
A clock deeper in a gravitational well runs slower. The rate difference between two clocks at different gravitational potentials is continuous, position-dependent, and exact. This is not a perturbative correction to flat-space physics — it is the physics. Gravity IS the gradient of proper time rates across space.
GPS confirms this operationally. Satellite clocks must be corrected for gravitational time dilation to maintain nanosecond synchronization. These corrections are computed using τ = (G/c²)(M/r) and are accurate to 10 significant figures. GPS does not fail at the 5th significant figure despite G being known only to 5 significant figures.
This is the central empirical fact that demands explanation.
3. The Self-Referential Temporal Ambiguity
We now state the core problem precisely.
G has units m³ kg⁻¹ s⁻². The s⁻² encodes a specific time rate — a second. Every Cavendish-style measurement of G uses a clock to measure acceleration, force, or oscillation period. That clock runs at a rate determined by the local gravitational potential.
But G is supposed to describe the gravitational potential itself.
The second embedded in G is therefore evaluated inside the very field that G is meant to characterize. This is not a small systematic error. It is a logical circularity:
• To measure G you need a clock.
• Your clock rate depends on the local gravitational potential Φ.
• Φ depends on G.
• Therefore G measured anywhere depends on G at that location.
G is not a universal constant. It is a local quantity, contaminated by the gravitational potential of the measurement site, that has been treated as universal because the contamination is small enough at Earth's surface to hide within experimental uncertainty — until experiments became precise enough to disagree.
The 40-sigma disagreement between precision G measurements — experiments disagreeing by 40 times their stated error bars — is not experimental incompetence. It is the universe signaling that the quantity being measured is not well-defined.
4. Which Second? The Gradient Problem
Consider a gravitational field with potential Φ(r). The proper time rate at position r relative to a clock at infinity is:
dτ/dt = √(1 + 2Φ(r)/c²) ≈ 1 + Φ(r)/c² [weak field]
In a gradient, every point r has a distinct proper time rate. There is no canonical 'the second' in a gravitational field. The second at r₁ and the second at r₂ differ by:
Δ(dτ/dt) = Φ(r₁)/c² - Φ(r₂)/c² = (G/c²)(M/r₁ - M/r₂)
When a Cavendish experiment uses a torsion fiber with period T to extract G, T is measured in coordinate seconds at the lab's gravitational potential. When an atom interferometry experiment uses laser pulse timing to measure acceleration, those pulse intervals are proper time intervals at the apparatus's location. The two experiments embed different seconds into their extracted values of G, and neither second has been corrected to a common reference.
The question 'which second does G introduce?' therefore has the answer: whichever second existed at the location and gravitational potential of the measurement, uncorrected for the field being measured. This is not a universal second. It is a local, potential-dependent, self-referentially contaminated second.
5. G/c² Is the Clean Quantity
The combination G/c² is free of this ambiguity. To see why, note that c is also measured locally using local clocks. The local second that contaminates G also contaminates c² in the same measurement context. When you form G/c², the local temporal factor cancels:
G/c² = [m³ kg⁻¹ s⁻²] / [m² s⁻²] = m / kg
The seconds are gone. G/c² has units of meters per kilogram — a purely geometric ratio. It is the Schwarzschild radius per unit mass, the conversion factor between mass and the spatial curvature it produces.
The dimensionless gravitational parameter is then:
τ = (G/c²) · (m / r) = (l_P / m_P) · (m_SI / r_SI)
where l_P = √(hG/c³) and m_P = √(hc/G) are the Planck length and mass. Crucially, l_P/m_P = G/c² exactly. The Planck quantities are not fundamental here — they are a convenient factorization that makes explicit what is happening: the SI unit standards for length and mass (l_P, m_P) are introduced and then immediately cancelled by the actual physical ratio m_SI/r_SI. What remains is pure dimensionless physics.
τ is the same number regardless of where in a gravitational gradient you compute it, because G/c² carries no net temporal dependence. This is why GPS works to 10 significant figures using τ while G itself is uncertain at the 5th figure.
6. The Measurement Implication
If G/c² is the physically clean quantity, the experimental program should measure G/c² directly rather than G alone. Several consequences follow:
• Atom interferometry experiments that measure gravitational acceleration a = GM/r² and laser interferometry experiments that measure r with electromagnetic precision are already measuring G/c² implicitly. The c² enters through the electromagnetic calibration of the length standard.
• Experiments that attempt to measure G in isolation — by measuring a gravitational force against a mass standard defined by the kilogram — are attempting to separate G from c² in a context where the universe has no opinion about that separation.
• The disagreement between G measurements performed by different methods may reflect genuine physical differences in the local gravitational potential of each laboratory, uncorrected for the temporal self-reference described in Section 3.
A 2026 NIST proposal to measure G via laser spectroscopy of the axion Compton frequency — connecting G to h, e, and nucleon masses — is the correct structural approach. It measures G through electromagnetic invariants, which share the same local temporal frame as c, and therefore directly accesses G/c² in the physically meaningful sense.
7. The Hume Boundary in Physics
The deeper issue is epistemological. A measurement is not a property that an object possesses. It is a ratio between an object and an arbitrary unit standard. The table does not have a length; it has a ratio to the meter. The meter is a convention, adopted in Paris in 1793, with no physical necessity.
Newton's equation F = GmM/r² embeds three independent arbitrary conventions — the meter, the kilogram, and the second — inside G. These conventions were chosen for unrelated practical reasons by humans at a specific historical moment. There is no physical reason they should combine into a clean gravitational constant. They do not.
This is Hume's is-ought distinction applied to metrology. From descriptive physical facts you cannot derive normative unit definitions. No chain of measurements proves that a mile has 5280 feet. That is a social fact, true inside the convention, meaningless outside it.
G is partly a social fact. The 6.674 × 10⁻¹¹ carries the fingerprints of 18th century French surveying decisions. τ does not. τ is the universe's own dimensionless statement about relativistic compactness, independent of every convention ever adopted.
8. Conclusions
We have identified a fundamental ambiguity in the gravitational constant G: its s⁻² dimensional factor encodes a specific time rate, but gravity is a gradient of time rates with no single canonical value. The second embedded in every measurement of G is local, potential-dependent, and self-referentially contaminated by the field G is meant to describe.
This ambiguity predicts exactly what is observed: G measurements disagree across experiments by far more than their stated uncertainties, and no experimental improvement has resolved the disagreement in 200 years. The quantity being measured is not well-defined.
G/c² is well-defined. Its temporal factors cancel exactly, leaving a purely geometric m/kg ratio. GPS navigation confirms G/c² to 10 significant figures without requiring G to 10 significant figures. The universe computes τ = (G/c²)(m/r). It does not compute G and c² separately.
The experimental program for precision gravitational metrology should target G/c² directly through electromagnetic measurements, where the cancellation of temporal contamination is structurally guaranteed. Continuing to measure G in isolation is continuing to ask the universe a question it has no answer to.
The second in G was always the wrong second. There is no right one.
Note on Priority
The central argument of this paper — that G’s temporal dimension is self-referentially ambiguous because gravity is a time gradient — was developed in conversation and has not, to the authors’ knowledge, been stated in this form in the existing literature. The GPS precision argument for G/c² as the physically clean quantity is an empirical observation available in any precision navigation reference but whose metrological implication for G measurement has not been made explicit.