Evidence record

Is time fundamental?

Every sentence on the exploration belongs to at least one claim below. Each says what kind of statement it is, what it rests on, what the evidence does not establish, and how far it was checked. Nothing here is a score, and none of it is a verdict on a belief or a theory.

Last checked 24 September 2026.

Source checked: 42
Presented as open: 4
A judgement, not a fact: 6

If something here is wrong, misquoted, out of date or unfair, write to support@unknownoceans.com and give the claim number, which does not change.

What the question takes for granted

A question in the foundations of physics that no experiment currently reaches. The two theories disagree about what time is, the most direct way of combining them yields an equation with no time in it, and the page reports three responses without taking a side.

Quantum theory and general relativity treat time in incompatible ways
Established
Both reviews the page cites begin from this. Isham calls it a fundamental conflict; Anderson calls the two notions of time mutually incompatible.
Quantising general relativity is the right route to a quantum theory of gravity
Contested
The equation the page is built around comes from quantising general relativity directly. Isham doubts that this is the right way to formulate the theory, and asks whether time should instead emerge from something very different. The page reports this as its third response.
The question of whether time is fundamental has an answer physics could find
Open
The page says no experiment discriminates between the positions and that the case is argued on coherence. It does not claim more.

How the question is labelled

Claim: The equation with no clock

Kind: Framing. Signposting. It asserts nothing a source could check.

Claim: Time itself

Kind: Framing. Signposting. It asserts nothing a source could check.

The question

Claim: Write down the most natural equation for quantum gravity and time does not appear in it.

Kind: What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review: Source checked. The cited passage was read, and it says this.

Supports
Canonical Quantum Gravity and the Problem of Timesection 5.1.5, The Wheeler-DeWitt Equation, problem 4
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field
The source reads: One of the hardest problems is to decide what the Wheeler-DeWitt equation means in physical terms. In particular, the notions of ‘time’ and ‘time-evolution’ must be introduced in some way.
Supports
Canonical Quantum Gravity and the Problem of Timesection 5.1.5
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field
The source reads: It is the heart of the Dirac constraint quantisation approach to the canonical theory of quantum gravity

What this does not establish

"Most natural" is the page’s word for quantising general relativity directly. It is not the only route: Isham describes approaches that identify a time before quantising, and doubts that this equation is the right formulation (claim 36).

Claim 3 · checked 24 September 2026 · AI-assisted audit

Claim: Nobody agrees what that means.

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

Supports
Canonical Quantum Gravity and the Problem of Timesection 7, Conclusions
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: Unfortunately, there is no universally-agreed way of interpreting the ensuing Wheeler-DeWitt equation; certainly none of the ideas produced so far is satisfactory.
Supports
Forget timesection VII, Conclusion
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Argument
The source reads: I also see well that the view I present here is far from being uncontroversial. Several authors maintain the idea that the notion of time is irreducible, and cannot be eliminated from fundamental physics.
Qualifies
The solution to the problem of time in quantum gravity also solves the time of arrival problem in quantum mechanicsabstract
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Argument
The source reads: We introduced with coauthors some years ago a solution to the problem of time in quantum gravity which consists in formulating the quantum theory in terms of real clocks.
Some groups describe their own proposal as a solution; the page reports this in claim 33.

Later work looked for

Crossref, 2012 on, "problem of time quantum gravity review": Anderson’s 2012 review treats the problem as open and many-sided, Gambini and Pullin (2022) describe their real-clock proposal as a solution, and papers in 2026 are still proposing new clocks for it; nothing that shows agreement.

Claim 4 · checked 24 September 2026 · AI-assisted audit

Claim: Quantum mechanics treats time as an external parameter.

Kind: What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review: Source checked. The cited passage was read, and it says this.

Supports
Canonical Quantum Gravity and the Problem of Timesection 2.1, Time in Conventional Quantum Theory
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field
The source reads: Time is not a physical observable in the normal sense since it is not represented by an operator. Rather, it is treated as a background parameter which, as in classical physics, is used to mark the evolution of the system.

What this does not establish

How standard quantum theory is formulated. Isham adds that no physical clock can track this parameter perfectly.

Later work looked for

How the theory is formulated; not a finding later work revises.

Claim 5 · checked 24 September 2026 · AI-assisted audit

Claim: General relativity treats it as part of a dynamical geometry.

Kind: What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review: Source checked. The cited passage was read, and it says this.

Supports
Canonical Quantum Gravity and the Problem of Timesection 2.2, Time in a Diff(M)-invariant Theory
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field
The source reads: The calculation of the value of an interval of proper time involves the spacetime metric ... it has a meaning only after the equations of motion have been solved

What this does not establish

"Dynamical" means the geometry is solved for along with everything else rather than fixed in advance.

Later work looked for

How the theory is formulated; not a finding later work revises.

Claim 6 · checked 24 September 2026 · AI-assisted audit

Claim: Combining them produces a description in which time has no separate role,

Kind: What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review: Source checked. The cited passage was read, and it says this.

Supports
Canonical Quantum Gravity and the Problem of Timesection 1.2, Preliminary Remarks
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field
The source reads: This stands against the simple Newtonian picture of a fixed time parameter, and tends to produce quantisation schemes that apparently lack any fundamental notion of time at all.

What this does not establish

Isham’s words are "tends to produce": the direct quantisation does, and schemes that pick out a time before quantising are built to avoid it.

Claim 7 · checked 24 September 2026 · AI-assisted audit

Claim: and whether that is a deep truth or a technical artefact is unresolved.

Kind: Open question. Something the page says is not known.
Review: Presented as open. The page says this is unresolved, and the review found that it is.

Supports
Canonical Quantum Gravity and the Problem of Timesection 7, Conclusions
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: the main task is to decide whether ‘time’ should preserve the basic role it plays in classical general relativity
Supports
Forget timesection I
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Argument
The source reads: I am aware that the answer I outline here is only one among many possibilities.

Later work looked for

Crossref, 2012 on, "problem of time quantum gravity": still an active research problem (Anderson 2012; new proposals in 2022 and 2026); nothing that settles it.

Claim 8 · checked 24 September 2026 · AI-assisted audit

Claim: In quantum mechanics, time is the thing the state evolves with respect to, supplied from outside the system.

Kind: What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review: Source checked. The cited passage was read, and it says this.

Supports
Canonical Quantum Gravity and the Problem of Timesection 2.1, Time in Conventional Quantum Theory
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field
The source reads: in Newtonian physics, time–the parameter with respect to which change is manifest–is external to the system itself. This is reflected in the special status of time in conventional quantum theory

What this does not establish

The outside is an idealisation. For the universe as a whole there is nothing outside to supply the time, which is where the problem begins.

Later work looked for

How the theory is formulated; not a finding later work revises.

Claim 9 · checked 24 September 2026 · AI-assisted audit

Claim: In general relativity there is no outside.

Kind: What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review: Source checked. The cited passage was read, and it says this.

No external time parameter, and, applied to the universe, no system outside it to supply one.

Supports
Forget timesection III
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Argument
The source reads: In general relativity, there isn’t a preferred and observable quantity that plays the role of independent parameter of the evolution, as there is in non-relativistic mechanics.
Supports
Canonical Quantum Gravity and the Problem of Timesection 1.2, Preliminary Remarks
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field
The source reads: Newtonian time is a fixed structure, external to the system: a concept that is manifestly incompatible with diffeomorphism-invariance and also with the idea of constructing a quantum theory of a truly closed system (such as the universe itself).

What this does not establish

A statement about the theory’s structure. Clocks in general relativity still measure proper time along their own paths.

Claim 10 · checked 24 September 2026 · AI-assisted audit

Claim: Time is part of the geometry, and the geometry is what is supposed to be quantised.

Kind: What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review: Source checked. The cited passage was read, and it says this.

Supports
Canonical Quantum Gravity and the Problem of Timesection 2.2
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field
The source reads: This causes no problem in the classical theory, but difficulties arise in any theory in which the geometry of spacetime is subject to quantum fluctuations and therefore has no fixed value.

What this does not establish

"Supposed to be" is exact: quantising the geometry is a programme, not a finished theory.

Claim 11 · checked 24 September 2026 · AI-assisted audit

The mismatch

Claim: The mismatch

Kind: Framing. Signposting. It asserts nothing a source could check.

The two theories use time differently

Claim: The two theories use time differently

Kind: What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review: Source checked. The cited passage was read, and it says this.

Supports
Canonical Quantum Gravity and the Problem of Timeabstract
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field
The source reads: This problem originates in the fundamental conflict between the way the concept of ‘time’ is used in quantum theory, and the role it plays in a diffeomorphism-invariant theory like general relativity.

What this does not establish

A heading that summarises claims 14 to 18.

Claim 13 · checked 24 September 2026 · AI-assisted audit

Claim: The Schrödinger equation describes how a state changes with time, where time is a parameter attached to a clock that is not part of the quantum system.

Kind: What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review: Source checked. The cited passage was read, and it says this.

Supports
Canonical Quantum Gravity and the Problem of Timesection 2.1, point 1
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field
The source reads: it is treated as a background parameter which, as in classical physics, is used to mark the evolution of the system. In particular, it provides the parameter t in the time-dependent Schrödinger equation
Qualifies
Canonical Quantum Gravity and the Problem of Timesection 2.1
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field
The source reads: such a time is truly an abstraction in the sense that no physical clock can provide a precise measure of it

What this does not establish

The clock is an idealisation. Isham shows that no physical clock can track the parameter perfectly, so the clock outside the system is part of the background assumed, not an instrument in it.

Claim 14 · checked 24 September 2026 · AI-assisted audit

Claim: General relativity has no preferred time coordinate.

Kind: What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review: Source checked. The cited passage was read, and it says this.

Supports
Forget timesection III
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Argument
The source reads: The relativistic coordinate t is a freely chosen label with no direct physical interpretation. This is a well known consequence of the invariance of the Einstein equations under general changes of coordinates.

What this does not establish

What is missing is a time coordinate the theory prefers. Clocks still measure proper time along their own paths.

Claim 15 · checked 24 September 2026 · AI-assisted audit

Claim: Choosing one is a choice of description, and the physics must not depend on it.

Kind: What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review: Source checked. The cited passage was read, and it says this.

Supports
Canonical Quantum Gravity and the Problem of Timesection 2.2
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field
The source reads: the equations of general relativity transform covariantly under changes of spacetime coordinates, and physical results are meant to be independent of choices of such coordinates

What this does not establish

This is a property of the classical theory. How to keep it in a quantum theory is the problem the page goes on to describe.

Claim 16 · checked 24 September 2026 · AI-assisted audit

Claim: Bringing the two together means quantising a theory whose own equations say the time labelling is arbitrary.

Kind: What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review: Source checked. The cited passage was read, and it says this.

The group Isham names is the diffeomorphisms of spacetime, which include every relabelling of time.

Supports
Canonical Quantum Gravity and the Problem of Timesection 1.2
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field
The source reads: The prime source of the problem of time in quantum gravity is the invariance of classical general relativity under the group

What this does not establish

The arbitrariness belongs to the classical equations; the quantum theory inherits it only if it is quantised directly.

Claim 17 · checked 24 September 2026 · AI-assisted audit

Claim: Done directly, the result is a constraint equation rather than an evolution equation.

Kind: What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review: Source checked. The cited passage was read, and it says this.

Supports
Canonical Quantum Gravity and the Problem of Timesection 2.3, category II
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field
The source reads: the constraints are imposed at a quantum level as restrictions on allowed state vectors and with time being identified only after this step
Supports
Canonical Quantum Gravity and the Problem of Timesection 2.3, category II
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field
The source reads: the most important of the operator constraints is a functional differential equation for ... known as the Wheeler-DeWitt equation (5.1.171). The notion of time has to be recovered in some way from the solutions to this central equation.
Qualifies
Canonical Quantum Gravity and the Problem of Timesection 2.3, category I
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field
The source reads: an internal time is identified as a functional of the canonical variables, and the canonical constraints are solved, before the system is quantised. The aim is to reproduce something like a normal Schrödinger equation with respect to this choice of time.

What this does not establish

Only for the route that quantises first. Schemes that choose a time first aim at an ordinary evolution equation.

Corrected

24 September 2026. Previously: “Bringing the two together means quantising a theory whose own equations say the time labelling is arbitrary, and the result is a constraint equation rather than an evolution equation.” Only the direct route gives a constraint equation. Isham’s first category of schemes identifies a time before quantising and aims at a Schrödinger evolution equation.

Claim 18 · checked 24 September 2026 · AI-assisted audit

The equation itself

Claim: The equation itself

Kind: Framing. Signposting. It asserts nothing a source could check.

Claim: The constraint was written down in 1967 by Bryce DeWitt, following work by John Wheeler.

Kind: Historical claim. A statement about the past that historical evidence can test.
Review: Source checked. The cited passage was read, and it says this.

Isham credits the equation to Wheeler’s papers of 1962 and 1964, DeWitt’s 1967 paper and Wheeler’s of 1968.

Supports
Canonical Quantum Gravity and the Problem of Timesection 5.1.5 and the reference list
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: is the famous Wheeler-DeWitt equation [Whe62, Whe64, DeW67a, Whe68] ... DeWitt, B. (1967a), ‘Quantum theory of gravity. I. The canonical theory’, Phys. Rev. 160, 1113–1148.
Context
Quantum Theory of Gravity. I. The Canonical TheoryCrossref record
Cited · Link answered, 19 October 2026 · Catalogue record only, 24 September 2026
The source reads: Journal: Physical Review Volume: 160 Pages: 1113-1148 Published: 1967-08-25

What this does not establish

DeWitt’s paper itself was not read, only its bibliographic record. Wheeler also published on it in 1968, so "following" describes the earlier papers, not all of his.

Claim 20 · checked 24 September 2026 · AI-assisted audit

Claim: Applied to the whole universe it says that the quantum state is annihilated by the operator that would have generated time evolution.

Kind: What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review: Source checked. The cited passage was read, and it says this.

The canonical Hamiltonian of general relativity is built from the constraints, so a state that satisfies them is left unchanged by it. Isham’s treatment assumes a closed (spatially compact) universe.

Supports
Canonical Quantum Gravity and the Problem of Timesection 5.1.2, The Imposition of the Constraints
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field
The source reads: has a rather remarkable implication for the putative Schrödinger equation ... since if the state ... satisfies the constraint equations ... we see that it has no time dependence at all!
Supports
The solution to the problem of time in quantum gravity also solves the time of arrival problem in quantum mechanicssection 1, Introduction
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Theory · Argument
The source reads: In such systems the Hamiltonian is a linear combination of the constraints, and therefore all Dirac observables are constants of the motion

What this does not establish

A formal statement about the canonical theory of a spatially closed universe. Whether it describes the real universe depends on that theory being right.

Claim 21 · checked 24 September 2026 · AI-assisted audit

Claim: Read literally, the state does not change.

Kind: What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review: Source checked. The cited passage was read, and it says this.

Supports
Canonical Quantum Gravity and the Problem of Timesection 5.1.2
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field
The source reads: This so-called ‘frozen formalism’ caused much confusion when it was first discovered since it seems to imply that nothing happens in a quantum theory of gravity.

What this does not establish

"Read literally" matters. Isham reports that the frozen formalism is now understood as the absence of an external time, not as a world in which nothing happens.

Claim 22 · checked 24 September 2026 · AI-assisted audit

Claim: That is the problem of time, and it arrives immediately, from taking general relativity's indifference to the time coordinate and quantising it in the obvious way.

Kind: What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review: Source checked. The cited passage was read, and it says this.

Supports
Canonical Quantum Gravity and the Problem of Timesection 5.1.2
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: These days, this situation is understood to reflect the absence of any external time parameter in general relativity
Supports
Canonical Quantum Gravity and the Problem of Timesection 1.2
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: The prime source of the problem of time in quantum gravity is the invariance of classical general relativity under the group
Context
Problem of Time in Quantum Gravityabstract
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: Emphasis in this Review is on the Problem of Time being multi-faceted and on the nature of each of the eight principal facets. Namely, the Frozen Formalism Problem

What this does not establish

The frozen state is the problem in its most direct form. The reviews treat the problem of time as wider than this one face of it (claims 25 to 27).

Later work looked for

Crossref, 2012 on, "problem of time quantum gravity review": Anderson (2012) still names the frozen formalism first among the facets; nothing that changes it.

Claim 23 · checked 24 September 2026 · AI-assisted audit

Claim: The equation has severe mathematical problems of its own and is not regarded as a finished theory.

Kind: What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review: Source checked. The cited passage was read, and it says this.

"Severe" is the page’s summary of Isham’s list: no preferred operator ordering, infinities that need regularising, boundary conditions that are usually not checked, and no agreed physical meaning.

Supports
Canonical Quantum Gravity and the Problem of Timesection 5.1.5, problems 1 to 3
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: The ordering chosen in (5.1.171) is a simple one but there is no particular reason why it should be correct. ... likely to produce ... singularities when acting on a wide variety of possible state functionals. Thus regularisation will almost certainly be needed.
Supports
Canonical Quantum Gravity and the Problem of Timesection 7, Conclusions
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: there is no universally-agreed way of interpreting the ensuing Wheeler-DeWitt equation; certainly none of the ideas produced so far is satisfactory

Later work looked for

Crossref, 2012 on, "Wheeler-DeWitt equation" and "problem of time quantum gravity review": Anderson (2012) lists constraint closure among the open facets; nothing that presents the equation as finished.

Claim 24 · checked 24 September 2026 · AI-assisted audit

Claim: The problem it exposes is not confined to that formulation.

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

Type I schemes pick out a time before quantising and never write the Wheeler-DeWitt equation, and they meet problems of time of their own.

Supports
Canonical Quantum Gravity and the Problem of Timesection 7, Conclusions
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: In theories of type I, time is defined internally at a classical level ... This approach is relatively uncontroversial at a conceptual level but it runs into severe technical problems including obstructions to global existence, and local non-uniqueness.
Context
Problem of Time in Quantum Gravityabstract
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: Emphasis in this Review is on the Problem of Time being multi-faceted and on the nature of each of the eight principal facets.

Corrected

24 September 2026. Previously: “The problem it exposes has outlived every attempt to dismiss it as an artefact of that particular formulation.” "Every attempt" was carried by nothing cited, and it sat badly with the page’s own third response, which reports Isham doubting the equation. What the sources carry is narrower: Isham locates the problem in the two theories’ frameworks rather than in one equation, and a later review finds it has several distinct facets. Anderson’s review was added as a source.

Claim 25 · checked 24 September 2026 · AI-assisted audit

Claim: Isham traced it to an inconsistency between the basic frameworks of the two theories,

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

Supports
Canonical Quantum Gravity and the Problem of Timesection 7, Conclusions
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: the problems encountered in unravelling the concept of time in quantum gravity are grounded in a fundamental inconsistency between the basic conceptual frameworks of quantum theory and general relativity

Claim 26 · checked 24 September 2026 · AI-assisted audit

Claim: and Anderson’s 2012 review counts eight facets of it, the frozen state being one.

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

Supports
Problem of Time in Quantum Gravityabstract
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: Emphasis in this Review is on the Problem of Time being multi-faceted and on the nature of each of the eight principal facets. Namely, the Frozen Formalism Problem
Supports
Problem of Time in Quantum Gravitysection 4, The Problem of Time Possesses Other Facets
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: it has become more common to suggest or imply that the POT is the Frozen Formalism Problem. However, a more long-standing point of view ... is that the POT contains a number of further facets. Furthermore, it is not even a case of then having to address around eight facets

What this does not establish

Eight is Anderson’s count of the principal facets. He notes that it has become common to treat the problem as the frozen formalism alone, and argues against that.

Claim 27 · checked 24 September 2026 · AI-assisted audit

The responses

Claim: The responses

Kind: Framing. Signposting. It asserts nothing a source could check.

What to do with an equation with no time in it

Claim: What to do with an equation with no time in it

Kind: Framing. Signposting. It asserts nothing a source could check.

Claim: One response is that time is emergent: the fundamental description is timeless, and what we experience as evolution is a correlation between parts of a system, one of which can be used as a clock for the others.

Kind: Hypothesis. A proposed explanation, not an established one.
Review: Source checked. The cited passage was read, and it says this.

Supports
Canonical Quantum Gravity and the Problem of Timesection 2.3, category III.2, the conditional probability interpretation
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field
The source reads: In certain cases, one of the observables is regarded as defining an instant of time (i.e., it represents a physical, and therefore imperfect, clock) at which the other variable is measured
Supports
Forget timeabstract
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Argument
The source reads: I propose to interpret mechanics as a theory of relations between variables, rather than the theory of the evolution of variables in time.

What this does not establish

A position, stated as one. Isham’s third category holds that time has at most a phenomenological status; none of the schemes in it is established.

Claim 30 · checked 24 September 2026 · AI-assisted audit

Claim: This is Rovelli’s position,

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

Supports
Forget timesection I
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Argument
The source reads: The answer I defend is that we must forget the notion of time altogether, and build a quantum theory of gravity where this notion does not appear at all.

Claim 31 · checked 24 September 2026 · AI-assisted audit

Claim: and his thermal time hypothesis, which makes the flow we notice an artefact of the statistical state the world happens to be in, is a proposal within it rather than a result.

Kind: Hypothesis. A proposed explanation, not an established one.
Review: Source checked. The cited passage was read, and it says this.

Supports
Forget timesection VI, Recovery of time
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Argument
The source reads: The “thermal time hypothesis” is the idea that what we call “time” is the thermal time of the statistical state in which the world happens to be, when described in terms of the macroscopic parameters we have chosen.
Supports
Forget timesection VI
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Argument
The source reads: This observation leads us to the following hypothesis.

What this does not establish

Rovelli reports that the hypothesis works in some cases, such as recovering cosmological time from the background radiation; that is a consistency check, not a test.

Claim 32 · checked 24 September 2026 · AI-assisted audit

Claim: Gambini and Pullin, building the same idea on real quantum clocks, describe their version as a solution to the problem of time.

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

Supports
The solution to the problem of time in quantum gravity also solves the time of arrival problem in quantum mechanicsabstract
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Argument
The source reads: We introduced with coauthors some years ago a solution to the problem of time in quantum gravity which consists in formulating the quantum theory in terms of real clocks. It combines Page and Wootters’ relational proposal with Rovelli’s evolving constants of the motion.
Supports
The solution to the problem of time in quantum gravity also solves the time of arrival problem in quantum mechanicssection 1, Introduction
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Argument
The source reads: Physical time arises from observing a (quantum) clock.

What this does not establish

"Describe" is deliberate: this is the authors’ own account of their proposal. The page does not report the problem as solved.

Corrected

24 September 2026. Previously: “” The currency search found a group that presents a version of the first response as solved. The page now reports the claim and whose it is, alongside its statement that nobody agrees.

Claim 33 · checked 24 September 2026 · AI-assisted audit

Claim: Another is that the formalism is incomplete and a correct theory of quantum gravity will restore a notion of time, by identifying one before quantising rather than after.

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

Supports
Canonical Quantum Gravity and the Problem of Timesection 2.3, category I
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: This category is the most conservative of the three since its central assumption is that the construction of any coherent quantum-theoretical structure requires something resembling the external, classical time of standard quantum theory.

Claim 34 · checked 24 September 2026 · AI-assisted audit

Claim: A third is that the equation itself is the wrong starting point.

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

Supports
Canonical Quantum Gravity and the Problem of Timesection 7, Conclusions
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: there is no real justification for extending the Dirac approach to constraint generators that are quadratic functions of the momentum variables

Corrected

24 September 2026. Previously: “A third is that the problem is an artefact of quantising a theory in that particular way.” Isham doubts the equation, not the problem. His conclusions trace the problem of time to the two theories’ frameworks and find it already in simple models, so the response he states is about the formulation.

Claim 35 · checked 24 September 2026 · AI-assisted audit

Claim: Isham, reviewing the whole field, allowed that the Wheeler-DeWitt equation “may be completely the wrong way of formulating a quantum theory of gravity”.

Kind: Quotes a source. The words of a named text, checked against the source.
Review: Source checked. The cited passage was read, and it says this.

Isham’s lectures survey ten schemes for dealing with the problem of time, in three categories.

Supports
Canonical Quantum Gravity and the Problem of Timesection 7, Conclusions
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: although it may be heretical to suggest it, the Wheeler-DeWitt equation–elegant though it be–may be completely the wrong way of formulating a quantum theory of gravity

Corrected

24 September 2026. Previously: “Isham, reviewing the whole field, allowed that the Wheeler-DeWitt equation, elegant though it be, may be completely the wrong way of formulating a quantum theory of gravity.” Isham’s own words were printed without quotation marks.

Claim 36 · checked 24 September 2026 · AI-assisted audit

Claim: Two positions

Kind: Framing. Signposting. It asserts nothing a source could check.

Claim: Time is emergent

Kind: Hypothesis. A proposed explanation, not an established one.
Review: Source checked. The cited passage was read, and it says this.

Supports
Forget timesection I
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Argument
The source reads: The notion of time familiar to us may then be reconstructed in special physical situations, or within an approximation

What this does not establish

A position with named defenders, not a result.

Claim 38 · checked 24 September 2026 · AI-assisted audit

Claim: Fundamental description relates variables to each other, not to a clock

Kind: Hypothesis. A proposed explanation, not an established one.
Review: Source checked. The cited passage was read, and it says this.

Supports
Forget timeabstract
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Argument
The source reads: I propose to interpret mechanics as a theory of relations between variables, rather than the theory of the evolution of variables in time.

What this does not establish

What the emergent view proposes, in Rovelli’s formulation.

Claim 39 · checked 24 September 2026 · AI-assisted audit

Claim: The clock is a physical subsystem, so time is relational

Kind: Hypothesis. A proposed explanation, not an established one.
Review: Source checked. The cited passage was read, and it says this.

Supports
Forget timesection III.1, Back to Galileo and Newton
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Argument
The source reads: Thus, it is true also in non-relativistic mechanics that what we measure is only relative evolution between variables.
Supports
The solution to the problem of time in quantum gravity also solves the time of arrival problem in quantum mechanicssection 1, Introduction
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Theory · Argument
The source reads: Physical time arises from observing a (quantum) clock.

What this does not establish

The inference is the emergent view’s; those who hold time fundamental do not draw it.

Claim 40 · checked 24 September 2026 · AI-assisted audit

Claim: Has to explain why the emergent time behaves so uniformly

Kind: This page’s reading. A judgement the page makes from the evidence. Others read it differently.
Review: A judgement, not a fact. Reviewed for whether it is fairly put and follows from the checked claims. No source can confirm it.

The page’s summary of the burden the emergent view carries. Rovelli names recovering the familiar notion of time as the problem it then faces.

Context
Forget timesection VI, Recovery of time
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Argument
The source reads: If we formulate the fundamental theory of nature in a timeless language, we have then the problem of recovering the familiar notion of time.

Claim 41 · checked 24 September 2026 · AI-assisted audit

Claim: Time is fundamental

Kind: Hypothesis. A proposed explanation, not an established one.
Review: Source checked. The cited passage was read, and it says this.

Supports
Forget timesection I
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Argument
The source reads: Other authors have argued that the notion of time is irreducible, and cannot be left out of a fundamental description of Nature in the way I propose.

What this does not establish

A position with named defenders, not a result. Rovelli cites Smolin for it.

Claim 42 · checked 24 September 2026 · AI-assisted audit

Claim: Some approaches to quantum gravity keep a preferred slicing

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

A slicing, or foliation, divides spacetime into a sequence of moments of space.

Supports
Canonical Quantum Gravity and the Problem of Timesection 4.2.4, Mean Extrinsic Curvature Time
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: One of the few definitions of internal time that has been studied in depth is one in which spacetime is foliated by hypersurfaces of constant mean intrinsic curvature.
Supports
Canonical Quantum Gravity and the Problem of Timesection 2.2
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: General relativity could be forced into a Newtonian framework by assigning special status to some particular foliation of

Later work looked for

Crossref, 2020 on, "preferred foliation quantum gravity": approaches with a preferred foliation are still being developed (for example matrix models with a preferred foliation, 2021); nothing that changes it.

Claim 43 · checked 24 September 2026 · AI-assisted audit

Claim: Would mean relativity’s indifference to time labelling is not fundamental

Kind: What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review: Source checked. The cited passage was read, and it says this.

Isham completes the sentence: the invariance of general relativity is reduced to the transformations that leave the chosen foliation alone.

Supports
Canonical Quantum Gravity and the Problem of Timesection 2.2
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field
The source reads: insisting on preserving the special foliation generates a type of symmetry breaking in which the

What this does not establish

What a preferred slicing would cost, as Isham describes it. Whether nature has one is open.

Claim 44 · checked 24 September 2026 · AI-assisted audit

Claim: Sits awkwardly with the success of general relativity

Kind: This page’s reading. A judgement the page makes from the evidence. Others read it differently.
Review: A judgement, not a fact. Reviewed for whether it is fairly put and follows from the checked claims. No source can confirm it.

The page’s judgement. Isham reports little support for a special foliation; Rovelli argues that general relativity’s success is the reason to take its treatment of time seriously.

Context
Canonical Quantum Gravity and the Problem of Timesection 2.2
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: Thus there is not much support for the idea of focussing on a special foliation associated with a contingent feature of the actual universe in which we happen to find ourselves.
Context
Forget timesection VII
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Argument
The source reads: The best guide is provided by the theories of the world that have proven empirically effective

Claim 45 · checked 24 September 2026 · AI-assisted audit

Whether any of this is testable

Claim: Whether any of this is testable

Kind: Framing. Signposting. It asserts nothing a source could check.

Claim: No experiment discriminates between the positions,

Kind: Open question. Something the page says is not known.
Review: Presented as open. The page says this is unresolved, and the review found that it is.

Supports
Forget timesection I
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Argument
The source reads: Until our theoretical and experimental investigations tell us otherwise, I think that what is important is to put the alternatives clearly on the table, and extensively discuss their rationale and consistency.
Supports
Quantum-Spacetime Phenomenologysection 2.1.4
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: The possibility of comparing a full quantum-gravity theory directly to experiments appears to be for a still distant future

Later work looked for

Crossref, 2020 on, "Lorentz invariance violation gamma-ray burst" and "quantum gravity phenomenology review": bounds keep tightening, but none bears on whether time is fundamental; nothing that changes it.

Claim 47 · checked 24 September 2026 · AI-assisted audit

Claim: and the obstacle is not only the energy scale.

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

Supports
Canonical Quantum Gravity and the Problem of Timesection 7, Conclusions
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: most of the problems of time in quantum gravity are not associated with the existence of ultraviolet divergences in the weak-field perturbative quantisation

Claim 48 · checked 24 September 2026 · AI-assisted audit

Claim: Isham’s point is that most of the problem is not tied to the high-energy behaviour of quantum gravity at all, since the interpretative difficulties turn up already in finite-dimensional minisuperspace models.

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

Supports
Canonical Quantum Gravity and the Problem of Timesection 7, Conclusions
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: most of the problems of time in quantum gravity are not associated with the existence of ultraviolet divergences in the weak-field perturbative quantisation; in particular, many interpretative difficulties arise already in infinity-free, minisuperspace models.
Supports
Canonical Quantum Gravity and the Problem of Timesection 1.3
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: many of the specific problems of time are not connected with the pathological short-distance behaviour of the theory, and appear in an authentic way in these finite-dimensional model systems

Claim 49 · checked 24 September 2026 · AI-assisted audit

Claim: The case is argued on coherence rather than data.

Kind: This page’s reading. A judgement the page makes from the evidence. Others read it differently.
Review: A judgement, not a fact. Reviewed for whether it is fairly put and follows from the checked claims. No source can confirm it.

Follows from claim 47. Rovelli, arguing one side, says the alternatives are to be weighed on their rationale and consistency.

Context
Forget timesection I
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Argument
The source reads: put the alternatives clearly on the table, and extensively discuss their rationale and consistency

Claim 50 · checked 24 September 2026 · AI-assisted audit

Claim: The nearest thing is a testing programme for quantum spacetime in general, not for this question.

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

Supports
Quantum-Spacetime Phenomenologysection 1.2.3
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: our best chance for uncovering non-classical properties of spacetime is to focus on the implications of spacetime quantization for the “Minkowski limit”
Supports
Quantum-Spacetime Phenomenologysection 1.4
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: by offering an opportunity to test quantum-gravity theories at a pure kinematical level, these “Lorentz-symmetry-test proposals” provided a path toward testability

What this does not establish

The review is about tests of spacetime structure, such as departures from Lorentz symmetry. It does not claim these tests bear on the problem of time.

Corrected

24 September 2026. Previously: “The nearest thing to a testing programme looks for Planck-scale effects where a tiny departure accumulates: photons from gamma-ray bursts crossing cosmological distances, and ultra-high-energy cosmic rays.” Following "No experiment discriminates between the positions", the sentence read as if this programme tested them. Amelino-Camelia’s review tests the structure of spacetime, mostly through Lorentz symmetry, and does not address whether time is fundamental.

Claim 51 · checked 24 September 2026 · AI-assisted audit

Claim: It looks for Planck-scale effects where a tiny departure accumulates: photons from gamma-ray bursts crossing cosmological distances, and ultra-high-energy cosmic rays.

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

Supports
Quantum-Spacetime Phenomenologysection 1.4
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: It started with some analyses of observations of gamma-ray bursts at sub-MeV energies ... quickly followed by the first discussions of Planck scale effects relevant for the analysis of ultra-high-energy cosmic rays
Supports
Quantum-Spacetime Phenomenologysection 1.5
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: Let me here use this cosmic-ray context also as an opportunity to discuss explicitly a first example of the type of “amplifier” that is inevitably needed in quantum-gravity phenomenology.
Supports
Quantum-Spacetime Phenomenologysection 3.8, In-vacuo dispersion for photons
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: this time-of-arrival-difference effect can be significant ... in the analysis of short-duration gamma-ray bursts that reach us from cosmological distances

Later work looked for

Crossref, 2020 on, "Lorentz invariance violation gamma-ray burst": gamma-ray burst analyses continue through 2025 with tighter bounds; the programme is as described.

Claim 52 · checked 24 September 2026 · AI-assisted audit

Claim: Amelino-Camelia, reviewing that work, grants that the regime where the effects would be dramatic, the quantum black hole, is the one hardest to get at.

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

Supports
Quantum-Spacetime Phenomenologysection 1.2.3
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: Surely, some very dramatic manifestations of spacetime quantization should be expected in what I labeled as the quantum-black-hole regime. But, as already stressed above, it is hard to even imagine managing to derive evidence of spacetime quantization from experimental access to that regime.

Claim 53 · checked 24 September 2026 · AI-assisted audit

The experience

Claim: The experience

Kind: Framing. Signposting. It asserts nothing a source could check.

Claim: A clock is a physical system inside the universe.

Kind: What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review: Source checked. The cited passage was read, and it says this.

Supports
Forget timesection III, Two clocks
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Argument
The source reads: Consider a clock at rest on the surface of the Earth and a clock on a satellite in orbit around the Earth. ... Each measures the proper time along its own worldline, in the Earth gravitational field.

What this does not establish

Rovelli’s example is two clocks in the Earth’s gravitational field; the line states the general point.

Claim 55 · checked 24 September 2026 · AI-assisted audit

Claim: On the relational view, that makes time a relation rather than a stage.

Kind: Hypothesis. A proposed explanation, not an established one.
Review: Source checked. The cited passage was read, and it says this.

Supports
Forget timesection III
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Argument
The source reads: General relativity describes the relative evolution of observable quantities, not the evolution of quantities as functions of a preferred one.

What this does not establish

The relational view’s conclusion, not a result. Those who hold time fundamental reject it.

Corrected

24 September 2026. Previously: “A clock is a physical system inside the universe, which makes time a relation rather than a stage.” The line stated one side of the page’s open question as fact. It is the relational view’s conclusion, and is now attributed to it.

Claim 56 · checked 24 September 2026 · AI-assisted audit

Why time feels like something

Claim: Why time feels like something

Kind: Framing. Signposting. It asserts nothing a source could check.

Claim: Even if the physics turns out to be timeless, the experience of a moving present has to be accounted for by something, and that something is a brain in a universe with a thermodynamic gradient.

Kind: This page’s reading. A judgement the page makes from the evidence. Others read it differently.
Review: A judgement, not a fact. Reviewed for whether it is fairly put and follows from the checked claims. No source can confirm it.

The page’s own reading. Rovelli argues that the features of experienced time, its flow and its direction, emerge at the thermodynamic level; that a brain is what does the experiencing is the page’s assumption, not something a cited source shows.

Context
Forget timesection VI
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Argument
The source reads: I think that these features are not mechanical. Rather they emerge at the thermodynamical level.

Claim 58 · checked 24 September 2026 · AI-assisted audit

Claim: No established account connects the two levels.

Kind: Open question. Something the page says is not known.
Review: Presented as open. The page says this is unresolved, and the review found that it is.

The leading proposal is offered by its author as a hypothesis.

Supports
Forget timesection VI
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Argument
The source reads: This observation leads us to the following hypothesis.

Corrected

24 September 2026. Previously: “Nothing currently connects the two levels.” The page itself describes Rovelli’s thermal time hypothesis, which is offered as exactly such a connection. What is true is that no account is established, and that the proposal concerns the flow rather than the experience of it.

Claim 59 · checked 24 September 2026 · AI-assisted audit

Claim: Thermal time proposes where the flow comes from, not how it comes to be felt.

Kind: This page’s reading. A judgement the page makes from the evidence. Others read it differently.
Review: A judgement, not a fact. Reviewed for whether it is fairly put and follows from the checked claims. No source can confirm it.

The page’s reading of Rovelli’s section VI, which identifies which variable is time and why it flows, and says nothing about how that is experienced.

Context
Forget timesection VI
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Argument
The source reads: When we say that a certain variable is “the time”, we are not making a statement concerning the fundamental mechanical structure of reality. Rather, we are making a statement about the statistical distribution we use

Claim 60 · checked 24 September 2026 · AI-assisted audit

Claim: A timeless fundamental description and a lived present are not obviously in conflict,

Kind: This page’s reading. A judgement the page makes from the evidence. Others read it differently.
Review: A judgement, not a fact. Reviewed for whether it is fairly put and follows from the checked claims. No source can confirm it.

The page’s judgement. It follows the emergent view’s own claim (claim 30) that timelessness at the fundamental level leaves room for time at another.

Claim 61 · checked 24 September 2026 · AI-assisted audit

Claim: and nobody has shown how the second follows from the first.

Kind: Open question. Something the page says is not known.
Review: Presented as open. The page says this is unresolved, and the review found that it is.

Supports
Forget timesection VI
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Argument
The source reads: If we formulate the fundamental theory of nature in a timeless language, we have then the problem of recovering the familiar notion of time.

Claim 62 · checked 24 September 2026 · AI-assisted audit

What was read

Forget timeRovelli · arXiv:0903.3832v3 (FQXi essay, dated August 2008), read in full as rendered by ar5iv from the arXiv sourceRead in full, 24 September 2026 · Copyright; quoted brieflyMathematics in the ar5iv rendering is kept as LaTeX; excerpts avoid it.
Quantum Theory of Gravity. I. The Canonical TheoryDeWitt, Physical Review · Crossref record for 10.1103/PhysRev.160.1113Catalogue record only, 24 September 2026The APS page refused this environment (403). The record carries the author, title, journal, volume, pages and date only.
Canonical Quantum Gravity and the Problem of TimeIsham, NATO Advanced Study Institute lectures · arXiv:gr-qc/9210011, as rendered by ar5iv from the arXiv source; read sections 1.2, 2.1 to 2.3, 3.3.5, 4.2.4, 5.1.2, 5.1.5 and 7, and the reference listRead in full, 24 September 2026 · Copyright; quoted brieflyIsham uses em dashes; excerpts record them as en dashes. Some citations render as "?" in ar5iv, and excerpts avoid them.
Quantum-Spacetime PhenomenologyAmelino-Camelia, Living Reviews in Relativity · Living Reviews in Relativity 16 (2013) 5, the version of record as served in HTML by link.springer.com; the text saved for is-there-a-smallest-length, re-read here at sections 1.1 to 1.5, 2.1.4 and 3.8Read in full, 24 September 2026 · Open access; quoted briefly
Problem of Time in Quantum GravityAnderson, Annalen der Physik · arXiv:1206.2403v2 (16 August 2012), the preprint of Annalen der Physik 524 (2012) 757 to 786, read from the arXiv PDF: abstract and section 4 for the facets; Crossref record for the journal detailsRead in full, 24 September 2026 · arXiv non-exclusive licence to distribute; quoted briefly
The solution to the problem of time in quantum gravity also solves the time of arrival problem in quantum mechanicsGambini and Pullin, New Journal of Physics · arXiv:2204.08371v1, the preprint of the New Journal of Physics paper; read the abstract and introduction. The IOP version of record was not reachable from this environment.The cited passage was read, 24 September 2026 · CC BY 4.0 (version of record); quoted briefly