(Davies, 2014)
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Quantum Indeterminism and the Block Universe: Why Relativity and Quantum Mechanics Are Ontologically Incompatible
1. Introduction
The long-standing claim that quantum mechanics and relativity are merely technically incompatible has obscured a deeper and more troubling conclusion: the two theories embody mutually exclusive ontologies. Drawing on Nicholas Maxwell’s underappreciated arguments concerning the incompatibility of quantum indeterminism with relativistic block spacetime (Maxwell, 1985, 1988, 1993; Rietdijk, 1966, 1967; Stein, 1991), this paper argues that no mathematical unification—whether via quantum gravity, many-worlds interpretations, or covariant reformulations—can resolve the conflict. The problem is not one of formalism but of ontology: a genuinely indeterministic universe cannot be a four-dimensional block, period. Attempts at reconciliation succeed only by covertly abandoning indeterminism or by emptying it of ontological significance.
2. The Myth of a Merely Technical Conflict
It is commonly asserted that the conflict between quantum mechanics (QM) and relativity—special (STR) or general (GRT)—is a technical one: a mismatch of formalisms awaiting a deeper theory. On this view, the incompatibility is analogous to the pre-relativistic conflict between Newtonian mechanics and electromagnetism, ultimately resolved through conceptual refinement and mathematical innovation.
In this essay, we reject that analogy. The conflict between QM and relativity is not a temporary failure of formal unification, but a fundamental ontological contradiction. Nicholas Maxwell was among the first to articulate this clearly: quantum mechanics, if taken realistically, is indeterministic in a way that is incompatible with the block universe ontology presupposed by relativity.
What follows develops Maxwell’s insight and pushes it further. The conclusion will be that no mathematical manoeuvre can reconcile a genuinely indeterministic ontology with a four-dimensional spacetime in which all events—past, present, and future—equally exist.
3. The Relativistic Commitment: Block Spacetime
Both STR and GRT are most naturally interpreted as committing us to a block universe ontology:
- Spacetime is a four-dimensional manifold.
- All events are equally real.
- Temporal passage or “becoming” is not an objective feature of the world.
- Physical laws describe relations within the entire spacetime structure, not processes unfolding in time.
This is not a controversial claim among philosophers of physics. It is defended explicitly or implicitly by figures such as Minkowski, Earman, Norton, Pooley, and many others. Even where presentism or becoming is discussed, it is widely acknowledged that such views sit uneasily—if not incoherently—within relativistic physics.
Crucially, solutions to Einstein’s equations are entire spacetimes, not evolving histories. Once a solution is specified, nothing is left ontologically open.
4. Quantum Mechanics and Ontological Indeterminism
Quantum mechanics, by contrast, appears to involve genuine indeterminism:
- Measurement outcomes are not fixed by prior states.
- Probabilities are not merely epistemic.
- The future is, in a strong sense, not yet settled.
This is true not only of collapse interpretations but also, arguably, of any interpretation that treats quantum probabilities as physically meaningful rather than as bookkeeping devices.
Nicholas Maxwell repeatedly emphasized that this indeterminism is ontological, not merely epistemic. It concerns what exists, not merely what is known.
As Maxwell argues (notably in his papers in Philosophy of Science), if quantum theory is true in this realist sense, then the future cannot already exist.
5. Maxwell’s Incompatibility Argument
Maxwell’s core argument can be stated simply:
Relativity implies a block universe in which all events—past, present, and future—are equally real.
Quantum mechanics implies genuine indeterminism, such that future events are not fixed in advance.
A future that already exists cannot be indeterminate.
Therefore, quantum mechanics and relativity are ontologically incompatible.
This is not a claim about mathematical inconsistency. It is a claim about mutually exclusive pictures of reality.
What is striking is how rarely this argument is addressed directly. Instead, it is typically bypassed by interpretive or mathematical strategies that leave the block universe intact.
6. Why Mathematical Reconciliation Cannot Work
Contemporary attempts to reconcile QM and relativity—whether through quantum gravity, string theory, loop quantum gravity, or many-worlds interpretations—share a common feature: they preserve global determinism at the ontological level.
Examples include:
- Many-worlds interpretations, in which all outcomes occur within a fixed branching spacetime or multiverse.
- Covariant quantum field theories, which define dynamics over an already-given spacetime.
- Path integral formulations, which sum over entire histories.
- Time-symmetric or retrocausal approaches, which treat past and future boundary conditions symmetrically.
In every case, indeterminism is displaced rather than resolved. The universe—or multiverse—remains a completed structure. Probability becomes perspectival, indexical, or epistemic.
Thus, these approaches do not reconcile QM with relativity. They reconcile relativity with a deterministic reinterpretation of QM. Maxwell’s challenge remains untouched.
7. General Relativity Theory Does Not Help
It might be thought that General Relativity Theory (GRT), with its dynamical spacetime geometry, offers resources unavailable in Special Relativity Theory (SRT). This hope is misplaced.
While spacetime geometry is dynamical in GRT, the ontology remains block-like:
- A solution to the Einstein field equations is still a complete four-dimensional spacetime.
- Matter and geometry jointly form a fixed structure.
- Indeterministic matter fields do not restore an open future.
- Indeed, GRT arguably deepens the problem by undermining any objective notion of temporal becoming.
Thus, the incompatibility identified by Maxwell applies a fortiori to GRT.
8. The Deeper Moral: Ontology Trumps Mathematical Formalism
The persistence of reconciliation programs reflects a deeper methodological commitment: the belief that sufficiently sophisticated mathematics can resolve any conceptual conflict.
Maxwell’s argument exposes the limits of this belief. No amount of mathematical ingenuity can reconcile two theories that describe incompatible kinds of worlds.
A universe in which the future genuinely does not yet exist is not the same kind of universe as one in which the future is already part of spacetime. One of these pictures must give way.
9. Conclusion: A No-Go Result for Unification
The incompatibility between quantum mechanics and relativity is not a technical problem awaiting deeper mathematics. It is a clash between two ontologies:
- a deterministic block universe, or
- a genuinely indeterministic, open future.
Nicholas Maxwell was right to insist that this conflict cannot be wished away. What must now be acknowledged is the stronger conclusion: any purported unification that preserves block spacetime necessarily abandons real indeterminism. If quantum indeterminism is real, relativity—at least in its standard ontological interpretation—cannot be.
But a deeper difficulty now emerges. The block-universe interpretation of relativity is not merely metaphysically contentious, but in fact epistemologically self-undermining. Special relativity theory was established through operational thought experiments involving clocks, light signals, simultaneity judgments, and observers in relative motion. These procedures presuppose real temporal succession, dynamical processes, and the intelligibility of measurement as something that occurs. Yet if spacetime is a timeless four-dimensional block in which all events equally exist, then motion, signal transmission, and observation are not genuine processes, but instead merely static worldline segments within a frozen manifold. In that case, no clock literally ticks, no signal is transmitted, and no measurement is performed — there are only tenseless geometric relations between events. But a theory whose dominant ontology renders the very notion of experimental confirmation unintelligible thereby undermines its own epistemic foundations. The block universe thus does not merely conflict with indeterminism, as Maxwell showed; it threatens the coherence of relativity theory itself by dissolving the temporal preconditions of its own empirical justification.
REFERENCES
(Davies, 2014). Davies, P. “Time’s Passage is Probably an Illusion.” Scientific American. 24 October. Available online at URL = <https://www.scientificamerican.com/article/time-s-passage-is-probably-an-illusion/>.
(Maxwell, 1985). Maxwell, N. “Are Probabilism and Special Relativity Incompatible?” Philosophy of Science 52, 1: 23–43.
(Maxwell, 1988). Maxwell, N. “Are Probabilism and Special Relativity Compatible?” Philosophy of Science 55, 4: 640–645.
(Maxwell, 1993). Maxwell, N. “On Relativity Theory and Openness of the Future.” Philosophy of Science 60, 2: 341–348.
(Rietdijk, 1966). Rietdijk, C.W. “A Rigorous Proof of Determinism Derived from the Special Theory of Relativity.” Philosophy of Science 33, 4: 341-344.
(Rietdijk, 1976). Rietdijk, C.W. “Special Relativity and Determinism.” Philosophy of Science 43, 4: 598-609.
(Stein, 1991). Stein, H. “On Relativity Theory and Openness of the Future.” Philosophy of Science 58, 2: 147-167.
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