10.6 — Why G Appears Constant Locally (and When It Might Not)

If gravity is a material response of a mechanical medium, a natural objection arises:

Why does the gravitational constant G appear universal?
Why don’t we see it vary from place to place?

If G is not fundamental, shouldn’t it change?

The short answer is: it can—just not where we usually look.

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What G Really Encodes

In the conventional picture, G is treated as a fundamental coupling constant.

In a mechanical framework, G plays a different role:

G encodes a constitutive ratio of the medium.

Specifically, it summarizes how:

• stiffness,
• density,
• and stress redistribution

combine to produce an observable surface acceleration.

It is not a property of space.
It is a property of the medium in its current regime.

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Why Local Measurements All Agree

Most measurements of G are made:

• near Earth,
• using laboratory-scale masses,
• in environments with nearly identical medium properties.

Under these conditions:

• density gradients are weak,
• stiffness variations are negligible,
• stress remains far below failure thresholds.

As a result, G appears constant to high precision.

This is not evidence of fundamentality.
It is evidence of local uniformity.

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Why G Cancels So Often

Recall from earlier posts:

• Surface gravity depends on $\rho R$
• Escape velocity depends on $\rho R^2$
• Orbital speed depends on $\rho R / r$

When expressed this way, G often disappears entirely—absorbed into ratios of material response.

This is a strong hint that G is not primary.

It behaves like:

• Young’s modulus in elasticity,
• bulk modulus in fluids,
• or sound speed in air.

Constant locally.
Variable globally.

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Where G Could Vary

If G is a constitutive parameter, then variation would require:

• significant changes in medium stiffness,
• extreme compression or rarefaction,
• or a change of mechanical regime.

Possible environments include:

• strong-field astrophysical objects,
• early-universe conditions,
• ultra-low-density intergalactic regions,
• or near phase transitions of the medium.

In ordinary planetary and laboratory settings, none of these apply.

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Why We Haven’t Seen Clear Variation (Yet)

Detecting variation in G would require:

• isolating stiffness effects from geometry,
• comparing environments with genuinely different constitutive states,
• or probing regimes beyond weak-field gravity.

Most experiments are not designed to do this.

They assume G is fundamental—and design around that assumption.

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Why This Is Not a Problem for the Model

A constant G locally is not a weakness.

It is a prediction.

The mechanical framework expects:

• local constancy,
• global variability only under extreme conditions,
• and smooth transitions between regimes.

This is exactly what we observe.

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What Would Count as Evidence

Within this framework, evidence for non-fundamentality would include:

• correlated deviations in gravity and clock rates,
• environment-dependent gravitational behavior,
• anomalies tied to density or stiffness gradients rather than mass alone.

These are not violations of physics.
They are constitutive fingerprints.

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A Final Compression

At the start of this series, we asked:

What can be derived from density and stiffness alone?

The answer, it turns out, is almost everything we normally attribute to gravity as a force.

Surface gravity.
Escape velocity.
Orbits.
Planetary shape.
Time dilation.
And even the apparent constancy of G.

All emerge from the same mechanical substrate.

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Key Takeaway

G is not a fundamental constant—it is a locally stable material parameter of the vacuum medium.

It appears universal because the medium is locally uniform.
It may vary only where the medium itself changes regime.

With that, Series X completes its task:

not to overthrow known physics,
but to show how much of it can be re-derived from first mechanics.

From here on, the question is no longer whether the mechanical picture works—but how far it can be pushed.