We have now made a fairly radical move.
We began by questioning whether spacetime is fundamental.
We then asked how geometry could emerge from physical relations.
Our provisional answer was that actualised relations can become sufficiently stable and regular that they acquire a geometric description.
If that is so, however, another familiar feature of physics immediately comes under scrutiny.
What is gravity?
The conventional answer seems straightforward.
Gravity is associated with spacetime curvature.
Matter and energy determine the geometry of spacetime, and physical bodies move through that geometry.
But our investigation has already removed the ontological status of the thing that is supposed to be curved.
There is no fundamental physical substance called spacetime waiting to be bent.
So we need to ask a more basic question:
What would gravity be if there were no gravitational thing?
Perhaps the answer is surprisingly simple.
Perhaps gravity is not something that exists.
Perhaps it is something that happens.
The gravitational thing
The language of physics encourages us to reify gravity.
We say:
- gravity pulls;
- gravity acts;
- gravity bends;
- gravity attracts;
- gravity gets stronger;
- gravity propagates.
The grammar makes gravity sound like an agent.
But this is not necessarily what the physics says.
We know that general relativity does not describe gravity as an ordinary force acting through space.
A freely falling object follows a geodesic.
Locally, it is not being pushed away from inertial motion.
The familiar Newtonian picture of a force pulling an object toward a mass has been replaced by a geometric description.
That was a profound conceptual achievement.
But perhaps we stopped halfway.
We abandoned the idea of a gravitational force as a thing while retaining the idea of gravitational geometry as a thing-like entity.
Our relational ontology asks us to take the next step.
What do we actually observe?
Suppose an apple falls.
What is physically observed?
The apple changes its position.
A clock carried by the apple records a particular elapsed proper time.
A clock higher above the Earth records a different elapsed time.
Light travelling between different gravitational potentials exhibits predictable frequency shifts.
Two freely falling bodies initially separated from one another may move closer together.
Or, in another configuration, they may move apart.
These are physical observations.
None of them requires us to observe a thing called gravity.
We observe patterns in the behaviour of physical processes.
Gravity is the name we give to the systematic organisation of those behaviours.
That is a very different ontology.
Gravity as a pattern
Consider the falling apple again.
In Newtonian language:
Earth exerts a gravitational force on the apple.
In Einsteinian language:
The apple follows a geodesic in curved spacetime.
In the relational ontology we have been developing, we can go one step further:
The apple participates in a systematic pattern of spatial and temporal relations associated with the presence of mass-energy.
The difference may sound linguistic.
It is not.
The first formulation makes gravity a force.
The second makes geometry fundamental.
The third makes the relational pattern fundamental.
The geometry is the mathematical expression of that pattern.
Gravity is the physical regularity expressed by it.
There is no need for an additional gravitational entity.
Shorter space, longer time
This returns us to the interpretation of gravity with which we began.
Rather than imagining space as a substance that is somehow bent, we can describe the gravitational effect in terms of changing intervals.
Spatial intervals behave differently in the direction of a mass.
Temporal intervals behave differently as well.
Clocks at different gravitational potentials do not accumulate proper time at the same rate.
Free trajectories respond accordingly.
The important physical fact is therefore not that an invisible thing called gravity pulls an object downward.
It is that the relations among physical intervals change systematically in the presence of mass-energy.
This gives us a remarkably economical description.
Gravity is not something added to geometry.
Gravity is the name for the organised behaviour of physical relations that geometry describes.
The geodesic does not need to be pushed
This also changes the way we think about free fall.
Imagine throwing a ball.
The Newtonian picture says that gravity continuously accelerates the ball downward.
General relativity gives us a different picture.
In free fall, the ball is following its natural trajectory.
The trajectory is a geodesic.
There is no gravitational force pushing it off that trajectory.
Our interpretation sharpens the point.
The geodesic is not a path carved through a physical substance called spacetime.
It is a regularity in the relations among physical processes.
The ball follows that regularity.
The clock carried by the ball follows another.
Light follows another.
The different behaviours fit together into one relational structure.
The geometry summarises this structure.
Then what falls?
This apparently innocent question is revealing.
If gravity is not a force, what exactly is falling?
An object.
But the object does not need to be thought of as a thing possessing a hidden gravitational response.
It is itself a stable relational pattern.
Its constituents maintain particular relations.
The object as a whole participates in the surrounding relational structure.
What we call its “falling” is a change in those relations.
Thus the ontology becomes entirely relational:
object
→ stable relational pattern
gravity
→ stable relational pattern involving the object and its environment
trajectory
→ temporal development of those relations
geodesic
→ geometric description of the resulting regularity
Nothing additional needs to be inserted.
Gravity is relational all the way down
This is where the ontology begins to become particularly economical.
A gravitational effect is not an interaction between two things mediated by a third thing called gravity.
It is a relation between physical processes within a larger relational structure.
The Earth is not first a thing with gravitational properties and then a source of a gravitational field.
Rather, the Earth is an enormously complex stable relational structure.
Its presence changes the possible and actual relations among nearby physical processes.
Those altered relations manifest themselves in:
- trajectories;
- clock rates;
- light propagation;
- spatial intervals;
- tidal effects.
We call the coherent pattern gravity.
Gravity is therefore not an entity hidden behind these phenomena.
It is their relational organisation.
Why does mass matter?
This immediately raises another question.
Why does the presence of mass-energy produce this pattern?
Here we should be careful.
General relativity gives us an extraordinarily precise mathematical relationship between the stress-energy content of a system and its geometry.
But from our present ontological perspective, the question becomes:
Why does this particular form of physical organisation generate this particular relational structure?
We should not pretend that our ontology has already answered this.
It has changed the question.
Instead of asking why matter “creates a gravitational field” as though the field were an independently existing thing, we ask why particular configurations of physical actuality produce particular patterns of relational intervals.
That is a deeper question.
And it is precisely the kind of question that an underlying theory would have to answer.
Einstein's equation as a relation
The familiar schematic form of Einstein's field equation is:
We should not read this as:
matter is sitting inside spacetime and pushes on it.
The equation establishes a relation between two descriptions of physical organisation.
On one side is the geometric structure.
On the other is the distribution of energy and momentum.
The equation tells us that these are not independent.
Our relational interpretation pushes the point further.
Perhaps neither side should be regarded as fundamental.
The stress-energy description captures one aspect of physical organisation.
The geometric description captures another.
The equation expresses a stable relationship between them at the macroscopic level.
This is entirely compatible with the possibility that both arise from deeper relational processes.
Curvature without a curved substance
There is a useful distinction here.
A surface can have curvature without curvature being a material substance.
The curvature is a property of the relationships that define the surface.
Similarly, we can describe a physical system as geometrically curved without imagining that some material called spacetime has physically bent.
Our previous essay went further still.
The geometry itself may be emergent.
Then curvature is doubly non-substantial.
It is:
a property of an emergent relational structure describing stable physical regularities.
There is no “curvature stuff”.
There is no “gravity stuff”.
There is no fundamental spacetime stuff.
There are physical processes and their relations.
The mathematical concepts capture the regularities.
Why do bodies accelerate?
Here the relational interpretation gives us a useful conceptual distinction.
A freely falling body does not accelerate because a gravitational thing pushes it.
Nor, strictly speaking, does it accelerate in its own local inertial frame.
Its worldline is geodesic.
What an observer who remains at a fixed position relative to the Earth calls acceleration arises from comparing different physical trajectories.
This comparison is itself relational.
An object sitting on the ground is not following a free geodesic.
The ground continuously constrains its motion.
The falling object is following the geodesic.
Thus the apparent gravitational acceleration of the falling body is partly a consequence of the observer's choice of trajectory.
This is not merely a philosophical curiosity.
It shows how thoroughly the meaning of gravitational motion depends upon relations among physical processes.
Weight is relational
The distinction becomes especially clear if we ask what it means to have weight.
An astronaut in orbit around Earth is in free fall.
The astronaut feels weightless.
A person standing on Earth feels weight.
But the Earth's gravitational environment has not disappeared when the astronaut becomes weightless.
What has changed is the relation between the astronaut's trajectory and the surrounding physical structure.
The ground prevents the person standing on Earth from following a free-fall geodesic.
The floor exerts a physical force.
The astronaut does not experience that force because the astronaut is freely falling.
Thus:
gravity and weight are not the same thing.
Weight is the physical consequence of being prevented from following a free trajectory.
Gravity is the larger relational structure within which those trajectories are defined.
This distinction becomes clearer once gravity is not treated as a thing.
Tidal effects are particularly revealing
There is, however, one phenomenon that deserves special attention.
Tidal effects.
If gravity were simply an acceleration field, we might imagine that the gravitational effect could be eliminated locally by entering free fall.
And indeed, locally, a freely falling observer can eliminate the effects of gravity.
But tidal effects remain.
Two nearby freely falling objects can move relative to one another.
Their geodesics can converge or diverge.
This is where curvature enters general relativity.
But again, what is physically observed?
Not a piece of curved spacetime.
We observe relative acceleration between neighbouring freely falling systems.
That is a relational fact.
The geometric curvature tensor is a compact mathematical description of the systematic structure of those relative behaviours.
This makes tidal gravity especially important for our ontology.
It is perhaps the clearest example of gravity as relation rather than thing.
The geodesic deviation picture
Imagine releasing two small objects side by side.
Initially, they are at rest relative to one another.
As they fall, their separation may change.
The reason is not that some gravitational force is pulling each object independently in exactly the same way.
Their trajectories respond to the relational structure of the gravitational environment.
The difference between those trajectories is what matters.
General relativity describes this through geodesic deviation.
The mathematics of curvature therefore captures something fundamentally relational:
how neighbouring possible trajectories differ.
That is a very different conception of curvature from the mental picture of a rubber sheet bending.
The rubber-sheet metaphor makes curvature look like deformation of a thing.
Geodesic deviation reveals what curvature actually does.
It organises the relations among possible paths.
Gravity as an affordance structure
We can now make a connection with the idea of affordance introduced earlier.
A gravitational environment does not merely tell an object where it is.
It constrains what trajectories are available.
A freely falling body follows one family of possible paths.
A massive body can alter those paths.
Light follows null trajectories.
Clocks accumulate proper time according to their paths.
Thus gravity establishes a structured field of physical affordances.
It changes what can happen.
This is strikingly compatible with our quantum ontology.
Quantum potential describes structured possibilities.
Gravitational geometry describes structured possibilities for physical trajectories.
Perhaps these are not two unrelated kinds of possibility.
Perhaps they are different descriptions of the same underlying relational process at different levels.
The quantum and gravitational pictures begin to meet
This gives us a new way of viewing the problem of quantum gravity.
Quantum theory tells us that physical systems possess structured potential.
General relativity tells us that large-scale physical processes exhibit a structured geometry of possible trajectories.
The conventional question is:
How do we quantise that geometry?
But our ontology suggests another:
How does quantum potential organise itself into the relational structure that appears macroscopically as gravitational geometry?
This is a much more radical question.
And it does not require us to imagine that gravity itself is a quantum substance.
Perhaps there is nothing to quantise
We can now state the provocative possibility explicitly.
If gravity is not a fundamental thing, then perhaps the phrase:
“quantum gravity”
contains a hidden ontological assumption.
It assumes that gravity is something with a fundamental physical state that can be quantised.
But perhaps gravity is analogous to temperature.
Temperature is real.
It is measurable.
It has laws.
It can fluctuate.
It can even exhibit quantum effects indirectly.
But we do not normally regard temperature as a fundamental field requiring its own fundamental quantum ontology.
It is an emergent property of microscopic physical relations.
Perhaps gravity is similar.
Not because gravity and temperature are physically identical.
They are not.
But because both might be higher-level relational properties rather than fundamental substances.
If so, the correct task is not to quantise gravity.
It is to explain why gravitational behaviour emerges.
But general relativity is not merely thermodynamics
We should immediately qualify the analogy.
General relativity is extraordinarily different from ordinary thermodynamics.
Its equations describe a dynamical geometry with profound causal consequences.
The gravitational field is not merely an average over particles in any simple sense.
So we should not conclude:
“Gravity is just statistical mechanics.”
That would be premature.
The point is ontological.
A theory can describe something fundamentally real without the entities appearing in its equations being fundamental things.
General relativity may therefore be completely correct within its domain while still describing an emergent level of reality.
The equivalence principle becomes ontologically interesting
The equivalence principle is particularly suggestive in this context.
Locally, gravitational effects can be transformed away by entering free fall.
This tells us something profound.
Gravity is not locally distinguishable from inertial structure in the way an ordinary force is.
What remains physically invariant are the relational effects that cannot be removed globally—especially tidal structure.
This fits our ontology beautifully.
The fundamental fact is not:
“There exists a gravitational force.”
The fundamental fact is:
Physical trajectories exhibit a particular relational organisation.
The force-like appearance is observer-dependent.
The relational structure is not.
Gravity without agency
We should therefore be careful with our verbs.
Gravity does not “make” the apple fall.
Gravity does not “tell” the photon where to go.
Gravity does not “pull” the planet.
These are useful metaphors.
But ontologically, what happens is simpler.
The physical system has a particular relational structure.
Given that structure, certain trajectories and clock behaviours occur.
The word gravity names the systematic pattern.
There is no need for a gravitational agent.
This may sound like a small linguistic adjustment.
It is actually a major ontological simplification.
What produces the pattern?
But now we arrive at the question that cannot be avoided.
If gravity is a pattern, what produces the pattern?
Our previous essay gives us a possible answer.
Physical actuality produces relations.
Relations organise into stable patterns.
At large scales, those patterns acquire geometric form.
The gravitational structure would therefore be a consequence of the organisation of actual physical relations.
This gives us:
potential
↓
actualisation
↓
physical events
↓
relations
↓
stable relational organisation
↓
geometry
↓
gravitational behaviour
The arrows should not yet be read as a complete physical theory.
They are an ontological hypothesis.
But they tell us where the real explanatory work must now occur.
Gravity as emergent constraint
Perhaps the most useful way to describe gravity is therefore this:
Gravity is an emergent constraint on physical becoming.
It constrains the trajectories available to physical systems.
It constrains the accumulation of proper time.
It constrains causal relations.
It governs the large-scale organisation of matter and energy.
But it does not need to be a thing imposing those constraints.
The constraints arise from the relational structure itself.
A chessboard does not contain a “queen-moving force”.
The rules arise from the relational structure of the game.
Likewise, a gravitational geometry does not contain a “falling force”.
The possible trajectories arise from the relational structure.
The analogy is imperfect, but the distinction between thing and constraint is important.
The gravitational field reinterpreted
What, then, should we make of the gravitational field?
Again, we should not throw away the mathematics.
The metric field is extraordinarily useful.
But its ontological status can be reconsidered.
Rather than treating the field as a substance spread throughout spacetime, we can regard it as a compact representation of the relational constraints governing physical processes.
The field tells us:
- how intervals behave;
- which trajectories are geodesic;
- how clocks accumulate proper time;
- how light propagates;
- how neighbouring trajectories diverge or converge.
It is therefore a powerful summary of relational structure.
The field is real.
But its reality may be the reality of an emergent organisation.
Why this matters for quantum gravity
We can now see why the phrase “quantum gravity” may be misleading.
If one starts with the assumption that the gravitational field is fundamental, then the obvious task is to find its quantum description.
One quantises the metric.
One quantises gravitons.
One searches for a quantum theory of spacetime.
But if the metric itself is emergent, then these approaches may be trying to quantise a higher-level variable.
They may be mathematically fruitful.
They may even reveal something profound.
But they need not constitute the fundamental theory.
The deeper problem would be:
What quantum relational process produces the effective gravitational geometry?
That is a different target.
The wild goose chase
This is where our suspicion about the search for quantum gravity becomes sharper.
Perhaps the difficulty is not that physicists have failed to find the right mathematical machinery.
Perhaps they have been searching for something that does not exist at the ontological level they assume.
If gravity is emergent, then the demand for a fundamental quantum gravitational entity is misplaced.
It would be like searching for the microscopic constituents of the weather while insisting that “weather” itself must be a fundamental substance.
The weather is real.
But it is a pattern.
Likewise, gravity may be real.
But it may be a pattern.
The question is then not:
What is the quantum of gravity?
but:
What relational organisation produces gravitational behaviour?
That is a much more interesting question.
What would count as an explanation?
This also changes our standard of success.
A successful deeper theory would not necessarily contain an elementary particle called the graviton.
It would instead need to show how the appropriate large-scale relational structure arises.
Ideally, it would recover:
- the equivalence principle;
- geodesic motion;
- causal structure;
- gravitational time dilation;
- gravitational redshift;
- tidal effects;
- the effective metric;
- and, in the appropriate limit, Einstein's equations.
If it could do this from a fundamentally relational quantum ontology, we would have something much more interesting than a quantised version of general relativity.
We would have an explanation of why general relativity works.
The remarkable possibility
There is a striking possibility here.
Perhaps quantum theory and general relativity are not fundamentally incompatible theories.
Perhaps they are theories of different ontological levels.
Quantum theory describes:
structured potential and its actualisation.
General relativity describes:
the emergent geometry of stable actualised relations.
If so, the apparent conflict between them arises because we have tried to make the second description fundamental in the same way as the first.
The solution would not be to reconcile two incompatible fundamental ontologies.
It would be to understand how one level emerges from the other.
And what of the gravitational wave?
There is an obvious objection.
Gravitational waves propagate.
They carry energy.
They have observable effects.
Surely this means gravity must be something physical?
Not necessarily.
A wave is not automatically a substance.
A wave is a propagating pattern.
A wave on water is a pattern in the relations among water molecules.
A sound wave is a pattern in the pressure and motion of a medium.
A gravitational wave can similarly be understood as a propagating pattern in the relational structure governing physical processes.
Its physical reality is unquestionable.
But physical reality does not entail substance ontology.
A propagating relation is still a relation.
This is exactly the distinction we need.
The absence of the thing
We can now see what has happened.
At the beginning, we imagined:
a thing called gravity.
General relativity replaced this with:
a curved spacetime geometry.
Our relational ontology replaces even that with:
a stable, dynamical pattern in physical relations.
The progression is:
force
↓
geometry
↓
relation
This is not a rejection of Einstein.
It is arguably the completion of one of Einstein's deepest insights.
Gravity ceased to be a force in the Newtonian sense.
Perhaps the next step is for it to cease being a thing in the geometric sense.
The next question
We can now return to the original problem.
Why is quantum gravity so difficult?
Perhaps because we have been trying to quantise gravity.
But gravity may not be fundamental.
Perhaps we have been trying to quantise spacetime.
But spacetime may not be fundamental.
Perhaps we have been trying to quantise geometry.
But geometry may itself be emergent.
If so, there may be nothing wrong with quantum theory.
There may be nothing wrong with general relativity.
And there may be no contradiction waiting to be resolved between them at the level at which they actually operate.
The deeper task is to explain the emergence.
We have now arrived at the question:
If quantum potential gives rise to actual events, and actual events give rise to relational structure, how does that relational structure become the classical world described by general relativity?
In other words:
How does the quantum become the gravitational?
Perhaps the answer lies not in quantising gravity, but in understanding how stable macroscopic reality emerges from a world of potential and actualisation.
And that takes us to the next question:
What becomes of the classical world when we stop treating it as fundamental?
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