An open invitation
Is space a medium? Let's find out together.
A growing number of physicists are asking whether the vacuum behaves like a substance: a fluid, even a superfluid. Graviton Pressure Theory comes to the same question from another direction, by asking what physically touches a falling body. This is an invitation to everyone working on the question to share what we've found, test it hard, and help find the answer.
You're not alone in asking
The idea that space is a physical medium is being taken seriously in several fields of mainstream research.
Analogue gravitySince William Unruh's 1981 paper, physicists have shown that sound in a flowing fluid obeys the same equations as light near a black hole. In 2016 Jeff Steinhauer reported the quantum analogue of Hawking radiation in a flowing Bose–Einstein condensate.
Barceló, Liberati and Visser, Analogue Gravity, Living Reviews in Relativity 14, 3 (2011)
The universe in a helium dropletGrigory Volovik has shown how features of particle physics and gravity emerge in superfluid helium-3, treating the vacuum itself as a kind of quantum liquid.
G. E. Volovik, The Universe in a Helium Droplet (Oxford University Press, 2003)
Is spacetime a superfluid?Stefano Liberati and Luca Maccione tested whether spacetime could behave as a fluid by checking whether high-energy light from the Crab Nebula loses energy on its way to us. Their answer: if it is a fluid, it must be an almost frictionless superfluid.
Scientific American: If spacetime were a superfluid…
Superfluid dark matterLasha Berezhiani and Justin Khoury propose that dark matter forms a superfluid inside galaxies, whose sound waves produce the extra pull usually attributed to unseen mass.
Berezhiani and Khoury, Theory of Dark Matter Superfluidity, Physical Review D 92, 103510 (2015)
The river modelAndrew Hamilton and Jason Lisle showed that the geometry around a black hole can be pictured exactly as space flowing inward like a river, at the escape speed at every radius.
Hamilton and Lisle, The river model of black holes, American Journal of Physics 76, 519 (2008)
These researchers work within their own frameworks. They are listed to show the breadth of the question, not to suggest they support Graviton Pressure Theory.
Where Graviton Pressure Theory fits
Common ground first, then what this framework adds to the conversation.
What we share
- Space is physicalThe vacuum has properties: pressure, a speed limit for waves, the ability to flow. It is not nothing.
- Geometry as a fluid descriptionGeneral Relativity's equations can be read as describing how a medium flows, the way the equations of fluid dynamics describe water without naming its molecules.
- The inflow is already in the mathematicsThe Gullstrand–Painlevé form of the Schwarzschild solution, the river model, is an inward flow at the escape speed. Graviton Pressure Theory derives the same flow from one requirement and treats it as real.
What it adds
- What touches whatEvery explanation is asked to name its physical interface: what is in contact, and what is exchanged. That question is applied to mainstream physics and to Graviton Pressure Theory alike.
- A mechanism at the atomMatter takes in gravitons, sorts them and ejects them in a neutralized state. That cycle is proposed as the interface for weight and for inertia: one coupling, counted twice, which is why the two masses are equal.
- Weight as a pushThe inflow presses matter toward the mass, and the ground pushes back. The Equivalence Principle becomes a consequence: in a rocket and on a planet, the same relative acceleration between matter and medium is at work.
What's already worked out
From one requirement, that the medium carries a stationary observer into the floor at g, the inflow reproduces these results.
- DerivedInflow at the escape speed. v = √(2GM/r) follows from requiring the medium to carry a stationary observer into the floor at g.
- DerivedFree fall and Kepler's laws. Universality of free fall follows from one coupling for weight and inertia; circular orbits and T² ∝ r³ follow from the inflow.
- DerivedClock rates. A clock's speed through the medium gives General Relativity's gravitational time dilation exactly, and the GPS satellites' net gain of about 38 microseconds a day.
- DerivedLight. Given a refractive index n = 1 + v²/c², the bending of starlight (1.75″ at the Sun) and the Shapiro delay follow, the same for radio and visible light.
The problems we'd like help with
These are the places where the work goes next. Each one is stated in the papers, with what has been tried.
- The medium's equation of stateWorking hypothesis: the count of gravitons rises toward a mass while the active pressure falls, because the inflow mixes with neutralized gravitons that exert no pressure. Needed: an equation of state that produces this, and the background pressure it requires. Where it stands →
- The coupling at the atomThe momentum exchanged per second, per unit of impedance, in the intake–sorting–ejection cycle. This is where the mechanism names its interface, and where it can be tested most directly. Where it stands →
- The refractive indexDerive n = 1 + v²/c² from the medium's properties, rather than adopt it because it matches observation. Where it stands →
- Lorentz invarianceShow that the exchange between matter and medium produces exactly the relativistic contraction and time dilation that hide steady motion through it, in the tradition of Lorentz's own account. Where it stands →
- ShieldingIf matter absorbs part of the flux, it should cast a gravitational shadow. Lunar laser ranging limits any such absorption to about 10⁻²² m²/kg. Show the mechanism stays below that, or produces no shadow. Where it stands →
- Field equations for a moving mediumRotation, frame dragging and gravitational waves, written as the dynamics of the medium. Where it stands →
- An experiment that tells the theories apartEvery reinterpretation of a known result fits both pictures. The search is for a measurement where they predict different numbers. Where it stands →
How we work
Open accessEvery paper is free to read in full, with plain-text copies for people and AI tools. LaTeX sources are available on request.
Credit where it's dueContributions are credited by name, and joint work is co-authored.
Errors corrected in publicWhen a mistake is found, the correction is published with the paper, in an editor's note, so the record stays honest.
Physics kept separateThe physics papers make physical claims only. People of the World's philosophical and spiritual writing lives in its own place.
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