In plain words
If this model is right, empty space is a material: a very cold, very stiff, disordered solid that remembers how the things inside it were born. Around the Sun it is fully engaged and gravity is Newton's; in a galaxy it still has give, and that give is what we have been calling dark matter. This page says what that would mean, what part of it is old (many physicists have proposed that gravity is the mechanics of a substrate), what part is new (the memory), and what still rests on an unproven step. Unfamiliar words are in the glossary.
The core claim
The vacuum is a mechanical medium.
What we call gravity at low acceleration would be the deformation of a medium, not a property of empty geometry.
It would have an elastic modulus, yield thresholds, a response to stress. That places the picture in a known lineage — gravity as the thermodynamics or elasticity of a substrate (Sakharov, Jacobson, Verlinde) — but only for the anomalous part of gravity. Spacetime itself is not claimed to emerge: light, matter and gravitational waves resolve scales no lattice can reach, so the medium sits in spacetime rather than being it (see Black holes). The model’s own contribution is to say what kind of medium it is.
One temperature, cosmological
The horizon is its thermostat.
The medium sits at the de Sitter temperature, 2.8×10−30 K, set by the cosmological horizon. In this reading the cosmological constant is not just a term in Einstein’s equation; it is what holds the vacuum cold. The gravitational anomaly appears at a cosmological acceleration, a₀ ≈ cH₀/2π, because the medium’s temperature is cosmological. The smallest galactic acceleration and the largest radius in the Universe stop being a coincidence.
The strange, new part
The vacuum remembers.
Space is aged.
A glass carries frozen disorder, can jam, and keeps the trace of its formation. If the model holds, space remembers the density at which structures collapsed within it.
Engaged here, slack there.
The vacuum around the Sun is fully engaged and Newtonian; the vacuum of a galaxy keeps its slack and responds. Both are solids. Empty space would be neither uniform nor without history.
This is the one genuinely novel claim, and the most unsettling. The vacuum would be a fossil of structure formation, a record written into space itself — and that record is, in principle, readable, through the pockets around stars and the memory that sorts star clusters from dwarf galaxies.
Marginal where it responds, deep in the solid where it remembers
Because a₀ tracks the de Sitter temperature, the responding medium sits at a fixed, marginal distance from its glass point at every epoch. The engaged pockets cannot be marginal: the Sun's pocket bathes in a galactic field of 1.7 a₀, above the mean threshold, and a marginally rigid solid would yield to it. Where the vacuum remembers, it is deep in the solid phase.
The load-bearing assumption
Acceleration heats it.
The deepest step, and the least proven: an accelerated element sees a warmer vacuum (the Unruh effect), and the vacuum responds. Inertia and gravity would be a response — almost a friction — of the vacuum to acceleration, and the Unruh effect would be the mechanism behind the MOND scale rather than a curiosity. Everything else leans on this, and it is not yet derived. One thing is now bounded: it is the element's own acceleration that counts, never an ambient horizon. If the medium thermalised with a black hole's Hawking temperature, every star around Sgr A* would orbit at c/√2; the orbit of S2 caps that coupling at 10−10 of the cosmological one.
A reframing
Dark matter, reread.
In this picture the missing mass of galaxies is the stress field of the vacuum around ordinary matter, not a new substance. The “dark-matter density” measured near the Sun would be the vacuum’s polarization — a state of the medium, not a new particle. The medium itself may weigh 1.7% of the critical density, as a smooth solid that cannot collapse. And because one medium runs from the star to the horizon and is thermostatted by the horizon, the motion of a single orbit would depend on the whole Universe: a Machian flavour, and a holographic one.
Sober footing
How much is new, how much is true.
Most of it is a tradition.
Vacuum as thermodynamic substrate (Sakharov, Jacobson, Verlinde), for the anomalous part; Einstein–aether and solid dark matter for the medium in spacetime; a₀ as Unruh = de Sitter (Milgrom). None of that is claimed here as new.
The vacuum as a glass.
Disorder, a jamming transition, and memory. That the vacuum is aged and history-dependent is the specific, testable, strange claim.
It rests on one step.
That acceleration couples thermally to the vacuum. Remove it and the picture has no foundation.
It still fails.
The ultra-faint dwarfs, the clusters, the cosmic microwave background. A vacuum this simple does not yet explain them.
So this is not what the vacuum is. It is what the vacuum would be if the model said true — and whether it does begins to be decided, on the ground, by the wide binaries of Gaia DR4 in December 2026. What a black hole is to such a vacuum, and what the vacuum then says about general relativity, is on the Black holes page.