Whitehead's Relativity of Time

Two Different "Time" Projects

An earlier guide in this series touched on Whitehead's epochal theory of time — the mature, 1929 doctrine that "becoming" happens in indivisible drops, answering Zeno's paradoxes. This guide is about something related but distinct: Whitehead's engagement, roughly a decade earlier, with Einstein's theory of relativity — both his own philosophical account of why time and simultaneity are relative to an observer's motion, and his own full rival physical theory of gravitation, built to compete directly with Einstein's General Relativity. Where the epochal theory concerns the internal structure of becoming, the relativity of time concerns the external structure of measurement — what it means for two events, for two different observers, to count as happening "at the same time."

1919: The Eclipse and the Provocation

In May 1919, an expedition led by Arthur Eddington photographed a solar eclipse and measured the bending of starlight around the sun — a direct test of Einstein's General Relativity, published just three years earlier. The results were announced at a joint meeting of the Royal Society and the Royal Astronomical Society in London that November, an event Whitehead is recorded as having attended, and which he later described as a moment of genuine intellectual drama: Newtonian physics, unquestioned for over two centuries, visibly overturned in real time.

Whitehead took the occasion not as a call to accept General Relativity wholesale, but as a provocation to rethink the foundations of physical science from the ground up — a project that occupied him across three books in quick succession: An Enquiry Concerning the Principles of Natural Knowledge (1919), The Concept of Nature (1920), and finally The Principle of Relativity with Applications to Physical Science (1922), in which his own rival theory of gravitation appears in full.

Events, Not Points

Classical physics builds nature out of durationless instants and dimensionless points, treating both as primitive, self-evident starting materials. Whitehead reverses the order of explanation entirely. The fundamental deliverances of nature, given directly in perception, are events — always extended, always related to other events by relations of whole and part, overlap, and extension, never simple or point-like. A point, an instant, a particle: these are not the raw material of nature but sophisticated abstractions, logical constructions built out of the concrete extended events actually given to us.

This is a deliberate inversion of the usual order of explanation in physics, where events are treated as things that happen at pre-existing points and instants. For Whitehead, points and instants are late arrivals, derived from the prior, richer fabric of overlapping concrete events — a philosophical move with real technical teeth, since it is exactly this move that lets him later argue that the geometric structure of spacetime should not be treated as a free-floating, independently-variable backdrop.

Against the Bifurcation of Nature

Whitehead coins a memorable target in The Concept of Nature: the bifurcation of nature — the widespread assumption that there are really two natures, one "apparent" (the colored, sounding, warm world of ordinary perception) and one "causal" or "scientific" (colorless molecules and electromagnetic waves, the supposed real cause of the first). On this bifurcated picture, redness and warmth are merely subjective additions of the perceiving mind, layered on top of a genuinely existing but qualityless physical substrate.

Whitehead rejects the split outright: there is only one nature, disclosed in different ways to different modes of awareness, not two natures with one causing the other. This insistence on a single, unified nature — rather than a "real" physical layer plus a merely apparent perceptual layer added on top — is the deep motivation behind his later resistance to treating spacetime geometry as an abstract mathematical scaffold floating free of the concrete events that are nature's actual content.

Extensive Abstraction

If points and instants are not primitive, how does Whitehead recover them for use in physics and geometry? His method, extensive abstraction, constructs them as logical limits of infinite, converging series of ever-smaller concrete events — a "point" is definable as the class of all events that would be reached by indefinitely continuing to select smaller and smaller overlapping events converging toward it, without ever needing to posit a literally point-sized, durationless event as a starting ingredient. Whitehead thereby recovers all the geometric machinery mathematical physics needs, while keeping concrete, extended events as the only truly fundamental furniture of nature.

Durations and Cogredience

A duration, in Whitehead's technical vocabulary, is a finite temporal slab of nature: the whole class of events that are, in some definite sense, "all at once" — a genuine extended present, never a durationless instant. But "all at once" relative to whom? Whitehead's answer turns on a further technical relation he calls cogredience: a duration is cogredient with a given percipient event — roughly, the bodily standpoint of an observer — when that observer counts as being "at rest" throughout that whole duration.

Crucially, an observer moving differently — walking rather than standing still, or moving at a different velocity entirely — is at rest relative to a different family of events, and so picks out a different duration as "simultaneous, now." Whitehead arrives, by this purely philosophical route through events and cogredience, at essentially the same startling conclusion Einstein reached through light-signal thought experiments: there is no single, universal "now" shared by every observer regardless of motion. Simultaneity is relative.

Time-Systems

Each family of mutually cogredient durations defines what Whitehead calls a time-system — corresponding, in physical terms, to a particular state of motion, a particular inertial frame. Different time-systems slice the four-dimensional fabric of events into "moments" differently, exactly as different inertial observers in Einstein's Special Relativity disagree about which distant events are simultaneous with a given event here and now.

Whitehead insists this relativity of simultaneity is not merely a quirk of light-based measurement, as a narrowly operationalist reading of Einstein might suggest, but a structural feature of nature's own event-fabric, recoverable from the metaphysics of extension and cogredience alone.

A Uniform BackgroundThe Principle of Relativity, 1922

So far, Whitehead and Einstein travel together: both accept the relativity of simultaneity and the four-dimensional structure of Special Relativity. They part ways decisively over General Relativity. Einstein's theory identifies gravity with the curvature of spacetime itself — a variable geometry, different at every point, determined by the local distribution of mass and energy. Whitehead found this deeply objectionable on philosophical grounds: if the very geometric structure that makes measurement and comparison between distant events possible is itself contingent on the accidental distribution of matter, then the "uniformity of nature" that all scientific measurement quietly presupposes has no fixed foundation to stand on.

Whitehead's alternative, developed in The Principle of Relativity (1922): keep spacetime's underlying geometric structure fixed and uniform — flat, in the manner of Special Relativity, everywhere and always — and treat gravity instead as a distinct physical field, impressed on top of that fixed geometric background, in some ways analogous to the electromagnetic field, rather than being identical with geometry's own variation.

Predictions and the Verdict

A rival theory earns its keep only by making testable predictions, and Whitehead's did. Remarkably, for the handful of "classical tests" available in the 1920s — the anomalous precession of Mercury's perihelion, and the gravitational bending of starlight measured by Eddington's eclipse expedition — Whitehead's theory reproduced numerical predictions extremely close to Einstein's, since both theories agreed to the relevant order of approximation in these particular weak-field cases. For a time, the two theories were near-indistinguishable by the observational evidence then available — a genuine, instructive case of underdetermination of theory by evidence.

Continuity with the Epochal Theory

The event-based philosophy of nature developed here is not a detour from Whitehead's mature metaphysics but its direct ancestor. The concrete, extended events of 1920 mature into the actual occasions of 1929; durations — extended, cogredient slabs of simultaneous events — anticipate the way each actual occasion inherits a determinate temporal "epoch" from its predecessors. And the core conviction driving Whitehead's rival gravitational theory — that a fixed, uniform relational structure must underlie nature for measurement, comparison, and communication between events to be possible at all — persists into Process and Reality as the fixed extensive continuum, the necessary relational scheme within which actual occasions concresce, even as the theory of gravitation itself faded from live physics.

There is, arguably, a real tension worth naming: the fluid, organic, ceaselessly novel universe of Whitehead's mature process philosophy sits somewhat uneasily beside his insistence, as a physicist, on a perfectly uniform and unchanging geometric background. Whitehead himself seems to have felt no contradiction — the extensive continuum is a realm of pure, general possibility, uniform precisely because it is not yet actual, while all genuine novelty and process belongs to the actual occasions that arise within it.

Legacy and Philosophy of Science

Whitehead's theory of gravitation is now chiefly of interest to historians and philosophers of science rather than to working physicists — but it remains a genuinely instructive case study. For a period, two theories built on different foundational commitments, agreeing on the available evidence yet radically disagreeing about the deep structure of spacetime, were empirically on a par. This is close to a real-world instance of the Duhem–Quine thesis discussed in the earlier guide on the analytic turn: no theory is tested in isolation, and evidence alone does not always immediately force a unique choice between rival frameworks — sometimes it takes new tests, new instruments, and decades, as it did here, for the tribunal of experience to finally rule.

Philosophically, Whitehead's insistence on grounding physics in concrete events rather than abstract points, and his refusal to treat geometry as a free-floating mathematical stage detached from nature's actual content, remain live threads in the philosophy of physics and in process-oriented approaches to the philosophy of time, even where his specific gravitational theory has not survived.

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