Relativity is one of the great triumphs of modern physics. It is mathematically elegant, empirically robust, and astonishingly unifying. Few theories have reshaped scientific practice so profoundly.
And yet, when physicists speak about relativity rather than within it, a familiar pattern reappears — one we have already encountered in discussions of quantum mechanics.
It is the move from theory to ontology, performed so smoothly that it often goes unnoticed.
From Theory to Reality
Relativity is, at its core, a theory of spacetime structure. It specifies how measurements of space and time relate to one another under well-defined constraints. Within those constraints, it delivers precise, testable predictions — and it delivers them spectacularly well.
Problems begin not with the mathematics, but with a particular style of commentary that accompanies it. We are often told that relativity has revealed something decisive about reality itself:
that time is “just another dimension”
that past, present, and future all equally exist
that becoming is an illusion
that the universe is, fundamentally, a four‑dimensional block
These claims are typically presented as unavoidable consequences of the physics. To resist them is portrayed as sentimental attachment to everyday experience or metaphysical naïveté.
But here a quiet shift has occurred.
A theory describing relations among measurements has been promoted to a verdict about what there is.
“Just Doing Physics” — Again
When challenged, physicists often respond in a familiar way:
This isn’t philosophy. It’s just what the theory says.
The phrase “just spacetime” functions rhetorically much like “just doing physics” did in debates about quantum mechanics. It signals a refusal to acknowledge that an interpretive cut has been made at all.
Yet the move from mathematical structure to ontological claim is not forced by the equations. It is an act of interpretation — one that carries philosophical commitments whether they are recognised or not.
To point this out is not to criticise relativity. It is to insist on intellectual honesty about what kind of work is being done.
Geometry as Explanation
Relativity replaces forces with geometry. Gravitation is no longer something that acts on matter from outside; it is the manifestation of spacetime curvature itself.
This is a profound reconceptualisation — but it is also a potential source of confusion.
Geometry, in this context, explains constraint. It tells us which trajectories are possible, which intervals are invariant, which relations must hold given the structure assumed.
What it does not do is explain why spacetime exists at all, or why it has the structure it does.
When geometry is mistaken for ontology, constraint is mistaken for metaphysical necessity.
The Seduction of Elegance
Part of the persuasive power of these ontological readings lies in the elegance of the theory itself. Relativity is clean, spare, and conceptually unified. It feels like the kind of thing that ought to reveal reality’s deepest structure.
But aesthetic satisfaction is not ontological warrant.
The history of physics is littered with elegant frameworks later understood as limited, approximate, or context-bound. Relativity’s success does not exempt it from this lesson.
To say this is not to predict its downfall. It is simply to resist the slide from works extraordinarily well to tells us what reality fundamentally is.
Owning the Cut
The central issue, then, is not whether spacetime is “really real” or whether the block universe is “true.” These questions already assume that a particular interpretive frame has been silently adopted.
The real issue is responsibility.
At some point, an explanatory cut is made:
from relations to relata
from structure to substance
from model to metaphysics
Relativity does not make this cut for us. We make it.
Owning that fact does not weaken the theory. It clarifies its reach.
Looking Ahead
In the next post, we will examine the most famous — and most forceful — of relativity’s ontological extrapolations: the block universe, and the claim that becoming is an illusion.
This will allow us to ask a sharper question:
What, exactly, does relativity require us to give up — and what has been surrendered too quickly?
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