Two clocks separate, follow different journeys, and meet again with different readings. A detector registers light from a distant galaxy. A quantum experiment produces a pattern of outcomes. Each case connects physical activity with a mathematical description and a procedure for comparing records.
Changism asks how those connections should be understood. It treats change and productive interaction as fundamental while retaining the established equations and predictions of relativity. Its quantum discussions explore possible interpretations. Relational Tempo Cosmology, or RTC, takes a further step by proposing a programme of cosmological modelling whose physical claims must face observation.
These contributions have different responsibilities. An interpretation should explain what it adds to our understanding. A physical proposal must calculate what we should observe and identify results that would count against it.
What a clock measures
A clock operates through physical processes. An oscillator cycles, an atomic transition supplies a frequency reference, and a device accumulates a count. Its displayed reading makes that accumulated activity available for comparison.
In relativity, an ideal clock measures proper time along its worldline: its path through spacetime. Proper time is an objective interval associated with that path. Changing the coordinates used to describe the journey does not change the interval. Different physical paths between the same departure and reunion events can, however, accumulate different proper times.
Changism calls the accumulated clock activity a proper count. Proper counts provide operational access to proper time; they do not create or exhaust the metric structure being measured. A faulty clock can misreport an interval, just as a faulty ruler can misreport a length.
The reunion matters. Once the clocks meet again, their accumulated difference can be compared at the same encounter. Comparing rates while the clocks remain far apart requires a specified procedure for relating stages of their histories, including the handling of transmitted signals. That procedure must distinguish propagation effects from what the clocks accumulated.
Changism interprets these results through organized physical activity rather than a substance that flows through clocks. This interpretation preserves differential ageing and the metric calculations that predict it. It supplies no additional clock-rate effect by itself.
What spacetime geometry represents
A spacetime model represents more than a collection of instrument readings. Its metric relates intervals along physical paths, while its causal structure constrains which events can be connected by signals. Coordinates let us describe this structure, but changing labels does not freely change the physical relations.
Changism therefore distinguishes the physical structure, its mathematical representation, and the measurements through which we investigate it. Calling a clock network a ledger describes how its records are coordinated. It does not imply that human bookkeeping manufactures the structure to which those records answer.
There is a further philosophical question about what a complete spacetime representation means. Does its inclusion of events establish that every represented occurrence exists equally, as a completed four-dimensional whole? Changism argues that this conclusion requires an additional account of actuality. It does not follow simply from drawing a diagram or changing coordinates.
An eternalist can accept real interactions and change throughout a history. The disagreement must address that stronger position. Changism’s refusal to infer a completed block automatically from the formalism does not refute every argument for eternalism.
The positive task for Changism is equally demanding. It must explain how its process account accommodates quantitative metric relations. Ordering interactions alone does not derive their durations, and the general derivation of metric scale remains an open question.
Local activity without a universal present
Relativity permits physically defined local activity without providing one observer-independent simultaneity relation for all distant events. Changism expresses its corresponding commitment as follows:
Ongoingness is locus-indexed. A process is ongoing at its own locus. Changism does not posit an invariant field-wide relation of co-ongoingness between spacelike-separated processes, nor a global present slice, preferred foliation, or master clock.
A locus is the specified physical setting of an activity; it need not be an isolated mathematical point. Saying that a detector registers a signal there does not place every distant process on the same cosmic present. Nor does the arrival of a signal make its source occurrence happen at reception.
Clock synchronization remains useful. A network can establish shared coordinates under a stated protocol, and a cosmological model can employ a common time parameter under its assumptions. Those achievements organize comparisons. They do not establish a universal present as an additional physical entity.
Quantum interactions and the limits of the ledger analogy
Quantum theory assigns probabilities to outcomes under specified preparations and measurements. Its mathematical success leaves questions about how states, interactions, and outcomes should be understood.
Changist writing explores relational quantum mechanics, associated with Carlo Rovelli, as one possible comparison. In the relational accounts examined there, state assignments and the values acquired in interactions are relative to physical systems. An observer can be a detector or another physical system; consciousness has no privileged role in producing the outcome.
The ledger analogy prompts useful questions: relative to which system is a state assigned, which interaction does the claim concern, and what predictions follow? A quantum state need not be a literal notebook stored inside that system. Relational quantum mechanics also makes a stronger claim than the familiar observation that different people possess different information about one agreed absolute result.
Consider a detector that interacts with a small system and retains a pointer reading. A second device later reads the pointer. The original interaction, the retained record, and the later comparison are distinct physical events. What the second device may infer about the first encounter depends on the chosen interpretation, the measurement arrangement, and the information that survives.
Decoherence can suppress accessible interference between alternatives under specified conditions. That helps explain why certain comparisons behave approximately classically. The stability of a comparison, the durability of a stored reading, and its fidelity to the alleged source still require separate examination.
Changism has not solved the measurement problem by calling collapse a ledger update. Nor do probabilistic predictions alone establish fundamental indeterminism. The fit between its account of completed occurrences and different versions of relational quantum mechanics remains a philosophical task. This comparison is optional: rejecting it would not by itself reject Changism’s account of time.
From local clocks to cosmic history
Cosmology reconstructs a history from received signals. Light is emitted, propagates through intervening structure, and interacts with an instrument. Calibration and modelling connect the resulting records to claims about sources, distances, and expansion.
The standard homogeneous and isotropic cosmological model, usually called FLRW, has a well-defined cosmic time associated with observers moving with its idealized cosmic matter flow. The model’s symmetry supports that common parameter. Its usefulness does not restore a Newtonian clock outside the universe.
The real universe also contains galaxies, clusters, filaments, and large underdense regions called voids. Standard cosmology already studies this structure and applies corrections for such effects as peculiar motions, gravitational lensing, source variation, and survey selection. A proposed alternative must be compared with that corrected account.
Three operations need distinguishing. A spatial average describes a chosen collection of regions. A clock comparison relates specified physical histories. An observational inference fits a model to received signals from a selected sample. Connecting them requires a model of geometry and propagation; they are not interchangeable merely because each can involve a rate.
What Relational Tempo Cosmology proposes
RTC asks whether regional evolution, physical clock comparisons, and the weighting of observations have been connected adequately when cosmologists infer a common expansion history.
Relational tempo names a family of proper-time comparisons between specified physical histories. Each comparison needs a reference and a rule connecting the events being compared. The term introduces no extra supply of time or independently established physical field. Large contrasts in matter density do not automatically produce large differences between clocks.
The programme draws on Thomas Buchert’s work on averaging in general relativity and on questions explored by David Wiltshire’s timescape cosmology. Averaging can reveal how changing regional volume shares affect a domain’s expansion. Timescape adds particular regional clock and observational assumptions. RTC must justify its own construction and calculate its consequences; it cannot inherit another model’s observational success by using related ideas.
Its central empirical proposal is the Homogeneous Ledger Misidentification Hypothesis. In accessible terms, a smooth cosmic history might represent some combination of regional evolution, calibration, and observational weighting inadequately, leaving a residual effect in the cosmological parameters inferred from the data. The proposed size ranges from a small correction to much stronger claims. Those possibilities must be tested separately.
One target is a material contribution to the Hubble tension, the disagreement between specified methods of inferring the present expansion rate. The comparison includes a direct distance ladder, which carries nearby luminosity calibrations out to distant supernovae, and inferences based on the cosmic microwave background. An inverse distance ladder supplies another constraint by combining relative distances with an early-universe ruler rather than the nearby luminosity calibration. The size of the discrepancy depends on the datasets and modelling choices compared.
RTC’s investigation of this target retains the hot early history as a constraint. Explaining some of the expansion-rate discrepancy would not establish that dark energy is unnecessary. Replacing the cosmological constant is a stronger undertaking requiring a consistent account of acceleration and the other observations it helps explain.
What a physical model must supply
A change of coordinates can redescribe the same universe without changing any observation. An RTC model needs a physical construction whose consequences can be calculated beyond such a relabelling.
It must specify regional geometry and matter, how those regions evolve, and how any averaging is performed. Additional assumptions needed to determine the evolution must be explicit. The model must then follow signals from source to receiver, connect them to physical standards, and calculate what a survey with its actual selection would record.
Changing weights in a spatial average does not, by itself, supply an extra clock ratio. Multiplying a published Hubble estimate by a chosen factor also bypasses the distance measurements and calibration chains that produced it. The proposed explanation must reach those observations through the full calculation.
RTC already provides a framework, conditional calculations, illustrative models, and designs for empirical comparison. The selected route has not yet supplied a complete physical model demonstrating the required contribution to the Hubble tension. Its needed observational effect, with a justified magnitude and uncertainty, remains to be calculated.
How the observations could decide
The test depends on which mechanism is proposed. A calibration explanation predicts that transporting a luminosity relation from nearby calibrators to a different source population introduces a bias. A geometrical explanation changes the physical distance and propagation relations used to interpret the observations. Their predicted effects across different methods need not be the same.
Gravitational-wave standard sirens are especially useful here. Their signals supply distance information without the Cepheid and supernova luminosity ladder. They still require waveform modelling, detector calibration, and redshift information, with uncertainties in orientation, host association, and motion handled appropriately.
A calibration proposal should predict the absolute distance offset between sirens and the affected ladder. A shared geometrical proposal should predict the related responses of electromagnetic and gravitational-wave observations after accounting for their different samples. A supernova trend accompanied by no siren trend could point towards source physics or calibration; it would not establish an RTC mechanism.
For the selected RTC calibration route, a mechanism that produces the needed difference between these methods has not yet been derived. Ordinary relativistic redshift corrections cannot simply be applied a second time. The same source-to-receiver redshift factor already affects received wavelengths and periods.
Several observations constrain the programme together.
| Observation | What it examines | What an RTC model must account for |
|---|---|---|
| Supernova distances | Brightness, redshift, and environmental patterns | Predicted residuals after source, dust, motion, lensing, and selection corrections |
| Standard sirens | Distances from gravitational-wave signals | The required absolute offset or shared environmental response without refitting each method separately |
| Acoustic rulers and the microwave sky | Linked early and late cosmological distances and spectra | Consistent ruler calibration, radial and transverse distances, and the full relevant microwave-background constraints |
| Redshift drift | Changes in a source’s measured redshift between observations | A predicted curve or environmental contrast over a stated interval of the receiver’s proper time |
| Structure growth and lensing | How matter gathers and deflects signals | Joint consistency with the proposed geometry and evolution, including ordinary lensing effects |
Redshift drift tests an evolving source-to-receiver relation. Looking along two directions does not give one receiver two different elapsed proper times. Any predicted directional contrast must come from the physical histories, paths, and selection involved. A calibration correction that leaves the expansion history unchanged may also leave the standard drift prediction unchanged.
Before testing a model, the programme must state the sign, size, conditions, and minimum explanatory contribution it requires. Parameters constrained by one set of observations should predict suitably reserved observations, with shared errors retained. Separate freely adjusted offsets for every dataset would surrender the common explanation.
A sufficiently precise null result can exclude an effect large enough to do the promised work. A less sensitive result supplies a bound. Success in one channel cannot cancel a decisive failure in another necessary prediction, and a surviving environmental correlation must still be compared with ordinary astrophysical effects and rival cosmological explanations.
What success would establish
A successful RTC construction would earn support for its physical model and the scope of the effect it predicts. It would not uniquely establish Changism’s ontology. Conversely, failure of an optional cosmological hypothesis would require withdrawing that physical claim while leaving the philosophical arguments to be assessed on their own merits.
The relationship between philosophy and physics is productive when each makes its contribution clear. Changism supplies questions about process, comparison, and representation. Physical models turn selected questions into calculations. Observations then determine how much explanatory work those models can do.
Read further
Begin with Changism, Volume I. Chapters 7–9 discuss relativity, spacetime, and quantum interpretation. Chapters 23–25 develop cosmological inference, RTC’s proposal, and its tests. Appendix C examines the comparison with relational quantum mechanics.
Continue with Relational Tempo Cosmology for the framework, mathematical constructions, competing explanations, and proposed tests. Searching for Time compares accounts of time and the different explanatory tasks they undertake. The Books pages explain the reading routes; Research provides the arguments and their stated limits.
Continue exploring: Time and Change introduces clocks, order, and measurement. Truth, Records, and Knowledge explains how physical records become evidence.
Chapter numbers refer to the second edition of Changism, Volume I.