Evidence record

Is there a smallest length?

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: 35
Presented as open: 1
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If something here is wrong, misquoted, out of date or unfair, write to support@unknownoceans.com and give the claim number, which does not change.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 physics that may not have the shape it seems to. Thought experiments and most approaches to quantum gravity point to a limit on how finely space can be resolved, but the approaches disagree about whether that limit is a smallest length at all, and no experiment has yet selected between them.

Gravity and quantum mechanics together single out a scale where both must be revised
Established
Both field-level reviews the page cites take this as the starting point of the problem, and derive the Planck scale from the two theories alone.
A limit on resolution would be a smallest length
Contested
Hossenfelder’s review finds that in many approaches the bound is on products of spatial and temporal extensions rather than on a length, and calls "minimal length" somewhat misleading. The page raises this as its second possibility: that the question is wrong.
The question can be settled by experiment
Open
So far observations only bound the simplest models, and the reviews describe comparison of full theories with data as a distant prospect. The page does not claim more.

How the question is labelled

Claim: The bottom of the ruler

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

Claim: Smallest

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

The question

Claim: Physics has a scale at which its two great theories both stop working.

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.

The two theories are general relativity and quantum mechanics (as relativistic quantum field theory). Each works where the other can be neglected; at the Planck scale neither can be.

Supports
Quantum-Spacetime Phenomenologysection 1.2.1, The quantum-black-hole regime
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: the Compton and Schwarzschild radii are of the same order of magnitude and quantum mechanics cannot ignore gravitation but at the same time gravitation cannot ignore quantum mechanics
Supports
Quantum-Spacetime Phenomenologysection 1.1
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: is the Planck scale (Eₚ ∼ 10²⁸ eV). The effective-field-theory description evidently breaks down at energies E on the order of the Planck scale
Notation restored: Superscript exponents and the subscript p restored from the version of record as served in HTML by link.springer.com, which sets them with and , read 2026-09-24; also confirmed in the arXiv LaTeX source of 0806.0339v2. The text as extracted reads: is the Planck scale (E p ∼ 10 28 eV). The effective-field-theory description evidently breaks down at energies E on the order of the Planck scale

Later work looked for

Crossref, 2021 on, "quantum gravity phenomenology review": the multi-messenger review of Addazi and others (2022, abstract) still frames the Planck scale as where a quantum theory of gravity is needed; nothing that changes it.

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

Claim: Whether space is grainy there, or whether the question is wrong, is unsettled.

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
Minimal Length Scale Scenarios for Quantum Gravitysection 5.3, Is it possible that there is no minimal length?
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: These questions are presently very much under discussion; we mention them to show that the case is not as settled as it might have seemed
Supports
Minimal Length Scale Scenarios for Quantum Gravitysection 3.8, Summary of Motivations
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: it is somewhat misleading to speak of a ‘minimal length,’ since in many cases a bound on the length itself does not exist, but only on the powers of spatio-temporal distances

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

Claim: Combining gravity with quantum mechanics produces a length below which the usual ideas of distance appear to fail.

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
Minimal Length Scale Scenarios for Quantum Gravitysection 1, Introduction
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: We will see that almost all such approaches lead us to find that the possible resolution of structures is finite or, more graphically, that nature features a minimal length scale
Supports
Quantum-Spacetime Phenomenologysection 1.2.3, The quantum-spacetime regime
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: The nature of the quantum-gravity problem tells us in many ways that the ultimate description of spacetime structure is not going to be in terms of a smooth classical geometry.

What this does not establish

"Appear to" is the right strength: the reviews report strong indications, not a result, and Hossenfelder notes the scale need not be exactly the Planck length.

Later work looked for

Crossref, 2021 on, "minimal length quantum gravity" and "quantum gravity phenomenology review": no later review read that reverses the expectation; it remains an expectation, not a measurement.

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

Claim: Models inspired by the candidate theories predict observable consequences,

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
Quantum-Spacetime Phenomenologysection 1.8, Paradigm change and test theories of not everything
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: since it is de facto impossible to compare to data present full candidates for quantum gravity one ends up comparing to data the predictions of an associated “test theory”, a model that is inspired by some features we do understand
Supports
Quantum-Spacetime Phenomenologysection 2.1.4, Other proposals
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: In practice, at least for the next few decades, what will be compared to data will be simple test theories inspired by our understanding of the quantum-gravity problem or by the intuition obtained in the study of formal theories of quantum gravity.

What this does not establish

The review stresses that such a test theory has no guarantee of full compatibility with the theory that inspired it, so a negative result need not count against that theory.

Later work looked for

Crossref, 2021 on, "quantum gravity phenomenology review": Addazi and others (2022, abstract) describe the same search for Planck-scale signatures through phenomenological models; nothing that changes it.

Corrected

24 September 2026. Previously: “Several candidate theories predict observable consequences,” The review says the full candidate theories are too complex to yield testable predictions; what is compared with data are simpler test theories inspired by them.

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

Claim: and astronomical observations have already bounded the simplest of them past the Planck scale itself.

Kind: Observation. Something measured or seen, as the named source reports it.
Review: Source checked. The cited passage was read, and it says this.

Supports
Quantum-Spacetime Phenomenologysection 3.8, In-vacuo dispersion for photons
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Review of the field
The source reads: GRB 090510 was a truly phenomenal short burst [ 4 ] and the structure of its observation allows us to conservatively establish that the scale of in-vacuo dispersion, for the linear-effects (“ n = 1”) scenario, is higher than 1.2 times the Planck scale.
Supports
A limit on the variation of the speed of light arising from quantum gravity effectsabstract
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement
The source reads: this photon sets limits on a possible linear energy dependence of the propagation speed of photons (Lorentz-invariance violation) requiring for the first time a quantum-gravity mass scale significantly above the Planck mass

What this does not establish

The simplest means a speed that changes in proportion to energy. The quadratic case is not significantly constrained.

Later work looked for

Crossref and arXiv, 2013 on, "Lorentz invariance violation gamma-ray burst": the LHAASO analysis of GRB 221009A (2024, abstract) raises the linear bound to 10²⁰ GeV, about eight times the Planck energy (its abstract rounds this to ten); Xu and Ma (2016, abstract) read the Fermi delays as a variation below it. The page now reports both.

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

Claim: Take the constants that govern gravity, quantum mechanics and light, and there is only one way to combine them into a length.

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
Minimal Length Scale Scenarios for Quantum Gravitysection 2, A Minimal History
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: Yet, from these constants alone one cannot construct either a constant of dimension length or mass. ... But in 1899, Max Planck pointed out that adding Newton’s constant G to the universal constants c and ħ allows one to construct units of mass, length and time

What this does not establish

Only one way up to a pure number: the sources give the Planck length as an order of magnitude, and the review defines it as the square root of ħG in units where c is one.

Later work looked for

A matter of dimensional analysis; not a finding later work revises.

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

Claim: It comes out around ten to the minus thirty-five metres.

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
Quantum-Spacetime Phenomenologysection 1.1
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: ≡ 1/Ep ∼ 10⁻³⁵ m, the inverse of the huge Planck scale in natural units
Notation restored: Superscript exponent restored from the version of record as served in HTML by link.springer.com, which sets it with , read 2026-09-24; also confirmed in the arXiv LaTeX source of 0806.0339v2. The text as extracted reads: ≡ 1/Ep ∼ 10 −35 m, the inverse of the huge Planck scale in natural units

Later work looked for

A value fixed by the constants; not a finding later work revises.

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

Claim: That number is not a measurement.

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 Planck length is built from constants, not observed; the review treats it only as an estimate of where new effects would set in.

Supports
Minimal Length Scale Scenarios for Quantum Gravitysection 2
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: But back in Planck’s days their relevance was their universality, because they are constructed entirely from fundamental constants.
Qualifies
Quantum-Spacetime Phenomenologysection 1.6
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: Planck length, ∼ 10⁻³⁵ m only as a crude, very preliminary estimate
Notation restored: Superscript exponents restored from the version of record as served in HTML by link.springer.com, which sets them with , read 2026-09-24; also confirmed in the arXiv LaTeX source of 0806.0339v2. The text as extracted reads: Planck length, ∼ 10 −35 m only as a crude, very preliminary estimate

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

Claim: It is the scale at which nobody knows what they are talking about.

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 blunt way of putting what the review says: at that scale current theories do not give even a first approximation.

Supports
Quantum-Spacetime Phenomenologysection 1.2.1
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: an energy on the order of the Planck scale, then our current theories do not even give us a reliable first approximation of the outcome

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

Why the scale exists

Claim: Why the scale exists

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

Why something must change there

Claim: Why something must change there

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
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: We do not have at present enough information to deduce how our formalization of spacetime should change, but it must change.
Supports
Quantum-Spacetime Phenomenologysection 1.1
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: The expectation that the fundamental description of spacetime should not be given by a classical geometry is shared by a large majority of quantum-gravity researchers.

Later work looked for

Crossref, 2021 on, "quantum gravity phenomenology review": nothing read that changes the expectation.

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

Claim: Probing a smaller distance requires more energy, and enough energy in a small enough region makes a black hole.

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
Minimal Length Scale Scenarios for Quantum Gravitysection 3.1.2, The general relativistic Heisenberg microscope
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field
The source reads: Thus, the larger the energy, the better the particle can be focused. On the other hand, if the extension drops below 4 πGE , then a black hole is formed with radius 2 ωG .
Supports
Quantum-Spacetime Phenomenologysection 1.2.1
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field
The source reads: On one side, we have quantum mechanics, with its characteristic property that a rest energy M can only be localized within a region the size of the Compton wavelength
Qualifies
Minimal Length Scale Scenarios for Quantum Gravitysection 3.1.2
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: The Hoop conjecture is unproven, but we know from both analytical and numerical studies that it holds to very good precision

What this does not establish

A thought experiment, which Hossenfelder calls heuristic. It rests on the hoop conjecture, which is unproven for general configurations, and on gravity not weakening at high energies.

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

Claim: Beyond a point, trying to look closer makes the region you are looking at larger.

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
Minimal Length Scale Scenarios for Quantum Gravitysection 3.1.2
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field
The source reads: The important point to notice here is that the extension of the black hole grows linearly with the energy, and therefore one can achieve a minimal possible extension

What this does not establish

What grows is the horizon the probe would form, in an argument that combines two theories at the scale where the review says neither can be trusted alone.

Claim: That argument does not depend on any particular theory of quantum gravity,

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.

The argument uses only quantum mechanics and general relativity; the reviews set it beside, not inside, the candidate theories.

Supports
Minimal Length Scale Scenarios for Quantum Gravitysection 3.8
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: there are many indications, from thought experiments as well as from different approaches to quantum gravity, that lead us to believe in a fundamental limit to the resolution of structure
Supports
Quantum-Spacetime Phenomenologysection 1.2.1
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: Evidently we can get nowhere attempting to investigate this issue by just combining Footnote 2 somehow the Standard Model of particle physics and the general-relativistic classical description of gravitational phenomena.

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

Claim: which is why the Planck length is taken seriously as a boundary even though nothing is known about what lies at it.

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 1.1
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: especially if we are correct in expecting that the magnitude of the characteristic effects of the new theory should be set by the tiny Planck length
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: We do not have at present enough information to deduce how our formalization of spacetime should change, but it must change.
Qualifies
Minimal Length Scale Scenarios for Quantum Gravitysection 5, Discussion
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: We usually talk about the Planck mass because we know of no higher energy scale that is relevant to the physics we know, so it is the obvious candidate, but not necessarily the right one.

What this does not establish

The Planck length is the expected scale, not a proven one: in string theory the relevant scale is the string scale, and Hossenfelder calls the Planck mass the obvious candidate but not necessarily the right one.

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

It is being tested, from very far away

Claim: It is being tested, from very far away

Kind: Observation. Something measured or seen, as the named source reports it.
Review: Source checked. The cited passage was read, and it says this.

Supports
Quantum-Spacetime Phenomenologysection 3.8
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Review of the field
The source reads: But the present best constraints on quantum-spacetime-induced in-vacuo dispersion are derived from observations of gamma-ray bursts reported by the Fermi telescope.

What this does not establish

What is tested is a class of consequences, not the Planck scale itself.

Later work looked for

arXiv, 2013 on, "Lorentz invariance violation gamma-ray burst": LHAASO (2024, abstract) continues the tests with GRB 221009A.

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

Claim: If space were grainy, light of different energies might travel at very slightly different speeds.

Kind: Hypothesis. A proposed explanation, not an established one.
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 · Theory · Review of the field
The source reads: by introducing new “quantum features” (e.g., discreteness or noncommutativity of the spacetime coordinates) in spacetime structure, as some aspects of the “quantum-gravity problem” might invite us to do, Lorentz symmetry may be affected
Qualifies
Quantum-Spacetime Phenomenologysection 2.1.2, footnote 10
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: some authors (notably Refs. [ 478 , 479 ]) have observed that there could be ways to reconcile what is presently known about LQG with the presence of exact Lorentz symmetry in the quasi-Minkowski limit

What this does not establish

"Might" is right: not every grainy picture predicts it, and the review notes loop quantum gravity may be compatible with exact Lorentz symmetry.

Claim 19 · checked 24 September 2026 · AI-assisted audit

Claim: Over a few metres this is undetectable; over billions of light years, from a gamma-ray burst, it accumulates.

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
Quantum-Spacetime Phenomenologysection 3.8
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field
The source reads: in controlled Earth experiments, in which one perhaps could manage to study the propagation of photons of TeV energies, over distances of 10⁶ m, the in-vacuo dispersion would still induce, even for n = 1, only time delays of order ∼ 10⁻¹⁸ s.
Notation restored: Superscript exponents restored from the version of record as served in HTML by link.springer.com, which sets them with , read 2026-09-24; also confirmed in the arXiv LaTeX source of 0806.0339v2. The text as extracted reads: in controlled Earth experiments, in which one perhaps could manage to study the propagation of photons of TeV energies, over distances of 10 6 m, the in-vacuo dispersion would still induce, even for n = 1, only time delays of order ∼ 10 −18 s.
Supports
Quantum-Spacetime Phenomenologysection 3.8
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field
The source reads: the amplification is due primarily to the long propagation times, which essentially render the analysis sensitive to the accumulation [ 52 ] of very many minute Planck-scale effects

What this does not establish

A prediction of the energy-dependent models, if they are right; the review’s laboratory example is a thousand kilometres, and even that gives a delay of a billionth of a billionth of a second.

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

Claim: Observations of distant bursts have found photons of very different energies arriving within seconds of each other after travelling for billions of years,

Kind: Observation. Something measured or seen, as the named source reports it.
Review: Source checked. The cited passage was read, and it says this.

Supports
A limit on the variation of the speed of light arising from quantum gravity effectsmain text
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement
The source reads: Finally, the detection of multi-GeV photons <1 s from the onset of GRB 090510, and its known distance, allow us to tightly constrain Lorentz Invariance Violation (LIV).
Supports
Quantum-Spacetime Phenomenologysection 3.8, footnote 22
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Review of the field
The source reads: Sources at a distance of ∼ 10¹⁰ light years (∼ 10¹⁷ s) are not uncommon.
Notation restored: Superscript exponents restored from the version of record as served in HTML by link.springer.com, which sets them with , read 2026-09-24; also confirmed in the arXiv LaTeX source of 0806.0339v2. The text as extracted reads: Sources at a distance of ∼ 10 10 light years (∼ 10 17 s) are not uncommon.

Later work looked for

arXiv, 2013 on, "Lorentz invariance violation gamma-ray burst": LHAASO (2024, abstract) reports the same kind of observation for GRB 221009A at TeV energies; nothing that changes the claim.

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

Claim: which constrains the simplest versions of energy-dependent speed at or beyond the Planck scale.

Kind: Observation. Something measured or seen, as the named source reports it.
Review: Source checked. The cited passage was read, and it says this.

Supports
Quantum-Spacetime Phenomenologysection 3.8
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Review of the field
The source reads: The data for each one of these bursts has the strength of constraining the scale of in-vacuo dispersion, for the linear-effects (“ n = 1”) scenario, at better than 1/10 of the Planck scale.
Supports
Quantum-Spacetime Phenomenologysection 3.8
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Review of the field
The source reads: GRB 090510 was a truly phenomenal short burst [ 4 ] and the structure of its observation allows us to conservatively establish that the scale of in-vacuo dispersion, for the linear-effects (“ n = 1”) scenario, is higher than 1.2 times the Planck scale.

What this does not establish

For the linear case. The four Fermi bursts the review names each bound it at better than a tenth of the Planck scale; one of them, GRB 090510, above it.

Later work looked for

Crossref and arXiv, 2013 on, "Lorentz invariance violation gamma-ray burst": LHAASO (2024, abstract) raises the linear bound to 10²⁰ GeV, about eight times the Planck energy (its abstract rounds this to ten); Xu and Ma (2016, abstract) read the Fermi delays as a variation below it. The page now reports both.

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

Claim: Not everyone reads the bursts that way: one group finds a regularity in the Fermi delays that it takes as a variation at a few hundredths of the Planck 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.

3.6 × 10^17 GeV against a Planck energy of about 10^19 GeV (10^28 eV) is about three hundredths.

Supports
Light speed variation from gamma-ray burstsabstract
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Observational study: associations, not causes
The source reads: the GRBs observed by the Fermi Gamma-ray Space Telescope (FGST), we reveal a surprising regularity of the observed time lags between photons of different energies ... E_LV = (3.60 ± 0.26) × 10¹⁷ GeV is the Lorentz violation scale
Notation restored: LaTeX in the arXiv abstract rendered as Unicode, checked against the abstract as typeset in the arXiv PDF (v3), read 2026-09-24. The subscript LV is written after an underscore. The text as extracted reads: the GRBs observed by the Fermi Gamma-ray Space Telescope (FGST), we reveal a surprising regularity of the observed time lags between photons of different energies ... $E_{\rm LV}=(3.60 \pm 0.26) \times 10^{17}~ \rm GeV$ is the Lorentz violation scale
Context
Quantum-Spacetime Phenomenologysection 1.1
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: is the Planck scale (Eₚ ∼ 10²⁸ eV). The effective-field-theory description evidently breaks down at energies E on the order of the Planck scale
Notation restored: Superscript exponents and the subscript p restored from the version of record as served in HTML by link.springer.com, which sets them with and , read 2026-09-24; also confirmed in the arXiv LaTeX source of 0806.0339v2. The text as extracted reads: is the Planck scale (E p ∼ 10 28 eV). The effective-field-theory description evidently breaks down at energies E on the order of the Planck scale
Supports
Light speed variation from gamma-ray burstsconclusion
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Observational study: associations, not causes
The source reads: If such results are not due to statistical fluctuation, we consider these fascinating regularities as an indication for a linear form modification of light speed
Qualifies
Light speed variation from gamma-ray burstsdiscussion
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Observational study: associations, not causes
The source reads: It is also possible that the matter in the universe leads to a dispersion as expressed in Eq. (1), so the regularities indicate the consequence of matter effect on light speed in the universe

What this does not establish

It is one group’s reading, which its authors make conditional on the regularity not being a statistical fluctuation, and which they say could instead be an effect of matter on light speed. Its value lies below the bound the Fermi collaboration drew from GRB 090510.

Corrected

24 September 2026. Previously: “” A published analysis reads the Fermi burst delays as a detected variation below the Planck scale. The page reported only the bounds, so the rival reading is now named.

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

Claim: while the LHAASO observatory’s analysis of the brightest burst yet recorded puts the bound for the linear case at about eight times the Planck energy.

Kind: Observation. Something measured or seen, as the named source reports it.
Review: Source checked. The cited passage was read, and it says this.

Supports
Stringent Tests of Lorentz Invariance Violation from LHAASO Observations of GRB 221009Aabstract
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement
The source reads: the very early TeV afterglow of the brightest-of-all-time GRB 221009A ... the 95% confidence level lower limits on the QG energy scales are E_QG,1 > 10 times of the Planck energy E_Pl for the linear
Notation restored: LaTeX in the arXiv abstract rendered as Unicode, checked against the abstract as typeset in the arXiv PDF (v3) and the LaTeX source, read 2026-09-24. Subscripts are written after an underscore. The text as extracted reads: the very early TeV afterglow of the brightest-of-all-time GRB 221009A ... the 95% confidence level lower limits on the QG energy scales are $E_{\mathrm{QG},1}>10$ times of the Planck energy $E_\mathrm{Pl}$ for the linear
Supports
Stringent Tests of Lorentz Invariance Violation from LHAASO Observations of GRB 221009ASummary
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement
The source reads: Our limit on the linear modification of the photon dispersion relation is E_QG,1 > 1.0 × 10²⁰ GeV (E_QG,1 > 1.1 × 10²⁰ GeV), considering a subluminal (superluminal) LIV effect.
Notation restored: Superscript exponents restored from the arXiv LaTeX source of 2402.06009v3 (10^{20}, 10^{19}), read 2026-09-24. Subscripts are written after an underscore. The text as extracted reads: Our limit on the linear modification of the photon dispersion relation is EQG,1 > 1.0 × 1020 GeV (EQG,1 > 1.1 × 1020 GeV), considering a subluminal (superluminal) LIV effect.
1.0 × 10²⁰ GeV against the paper’s Planck energy of 1.22 × 10¹⁹ GeV is 8.2 times (9.0 for the superluminal case); the abstract rounds this to ten.
Supports
Stringent Tests of Lorentz Invariance Violation from LHAASO Observations of GRB 221009AIntroduction, first paragraph
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement
The source reads: 1.22 × 10¹⁹ GeV are predicted in many quantum gravity (QG) theories
Notation restored: Superscript exponents restored from the arXiv LaTeX source of 2402.06009v3 (10^{20}, 10^{19}), read 2026-09-24. Subscripts are written after an underscore. The text as extracted reads: 1.22 × 1019 GeV are predicted in many quantum gravity (QG) theories

What this does not establish

A 95 per cent confidence lower limit, from a single burst, and like every single-burst bound it rests on assumptions about when the source emitted. The abstract gives the linear limit as ten times the Planck energy; the body’s figure is about eight.

Later work looked for

Crossref, 2023 on, "Lorentz invariance violation GRB 221009A": other analyses of the same burst (JCAP and Physical Review D, 2023 and 2024) exist; none read that loosens the LHAASO limit.

Corrected

24 September 2026. Previously: “” Currency: the strongest linear bound is now LHAASO’s from GRB 221009A (2024), and it sits against the rival reading reported in the same sentence.

24 September 2026. Previously: “while the LHAASO observatory’s analysis of the brightest burst yet recorded puts the bound for the linear case at ten times the Planck energy.” Integrity pass: the full paper gives the linear 95 per cent lower limit as 1.0 × 10²⁰ GeV (1.1 × 10²⁰ for the superluminal case) against a Planck energy it takes as 1.22 × 10¹⁹ GeV, which is 8.2 (9.0) times; the abstract's 'ten times' rounds that up by a fifth.

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

Claim: That is a real experimental constraint on models of quantum gravity, obtained without any accelerator.

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 bound applies to test models of energy-dependent speed. The review warns that when the link from theory to model is heuristic, a negative result does not falsify the theory behind it.

Supports
Quantum-Spacetime Phenomenologysection 3.8
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: But the present best constraints on quantum-spacetime-induced in-vacuo dispersion are derived from observations of gamma-ray bursts reported by the Fermi telescope.
Qualifies
Quantum-Spacetime Phenomenologysection 1.4
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: if the results of the experiments are negative the theoretical ideas that motivated them are not falsified

Corrected

24 September 2026. Previously: “That is a real experimental constraint on quantum gravity,” What the bursts constrain is a test model of energy-dependent speed, not quantum gravity as such, and the review says a negative result need not count against the theories that motivated the model.

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

Claim: It pushes the simplest energy-dependent models past the scale they were built around.

Kind: Observation. Something measured or seen, as the named source reports it.
Review: Source checked. The cited passage was read, and it says this.

Supports
Quantum-Spacetime Phenomenologysection 3.8
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Review of the field
The source reads: I feel that at least the limit at 1.2 times the Planck scale is reasonably safe/conservative.
Supports
A limit on the variation of the speed of light arising from quantum gravity effectsmain text
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement
The source reads: Because of their short duration and cosmological distances GRBs are well-suited for constraining LIV

What this does not establish

For linear dependence on energy; the quadratic models are barely touched.

Later work looked for

arXiv, 2013 on, "Lorentz invariance violation gamma-ray burst": LHAASO (2024, abstract) puts the linear bound at 10²⁰ GeV, about eight times the Planck energy; the claim stands.

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

Claim: That is not the same as closing them out, because a single burst cannot separate a delay picked up on the way from one the source imposed.

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.

The review says a large sample of bursts at different distances would separate the two, because a propagation delay grows with distance in a predictable way.

Supports
Quantum-Spacetime Phenomenologysection 3.8
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: On a single observation of gamma-ray-burst events such at-the-source correlations are, in principle, indistinguishable from the effect we expect from in-vacuo dispersion

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

Claim: How you test a scale you cannot reach

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

Claim: Find an effect that accumulates

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

Claim: An error of one part in ten to the nineteen is invisible in a laboratory and adds up over a journey of ten billion years.

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.

One part in ten to the nineteen is a photon of about a billion electronvolts against the Planck energy of about 10^28 eV, in the linear model.

Supports
Quantum-Spacetime Phenomenologysection 3.8
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field
The source reads: in controlled Earth experiments, in which one perhaps could manage to study the propagation of photons of TeV energies, over distances of 10⁶ m, the in-vacuo dispersion would still induce, even for n = 1, only time delays of order ∼ 10⁻¹⁸ s.
Notation restored: Superscript exponents restored from the version of record as served in HTML by link.springer.com, which sets them with , read 2026-09-24; also confirmed in the arXiv LaTeX source of 0806.0339v2. The text as extracted reads: in controlled Earth experiments, in which one perhaps could manage to study the propagation of photons of TeV energies, over distances of 10 6 m, the in-vacuo dispersion would still induce, even for n = 1, only time delays of order ∼ 10 −18 s.
Supports
Quantum-Spacetime Phenomenologysection 3.8, footnote 22
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Review of the field
The source reads: Sources at a distance of ∼ 10¹⁰ light years (∼ 10¹⁷ s) are not uncommon.
Notation restored: Superscript exponents restored from the version of record as served in HTML by link.springer.com, which sets them with , read 2026-09-24; also confirmed in the arXiv LaTeX source of 0806.0339v2. The text as extracted reads: Sources at a distance of ∼ 10 10 light years (∼ 10 17 s) are not uncommon.
Supports
Quantum-Spacetime Phenomenologysection 1.1
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: is the Planck scale (Eₚ ∼ 10²⁸ eV). The effective-field-theory description evidently breaks down at energies E on the order of the Planck scale
Notation restored: Superscript exponents and the subscript p restored from the version of record as served in HTML by link.springer.com, which sets them with and , read 2026-09-24; also confirmed in the arXiv LaTeX source of 0806.0339v2. The text as extracted reads: is the Planck scale (E p ∼ 10 28 eV). The effective-field-theory description evidently breaks down at energies E on the order of the Planck scale

What this does not establish

The size of the effect is the model’s, not a measurement; no such error has been observed.

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

Claim: Use the universe as the apparatus

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

Claim: Gamma-ray bursts, distant blazars and the polarisation of light from distant radio galaxies have all been used to bound effects at or near the Planck scale.

Kind: Observation. Something measured or seen, as the named source reports it.
Review: Source checked. The cited passage was read, and it says this.

Supports
Quantum-Spacetime Phenomenologysection 3.8
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Review of the field
The source reads: studies of TeV flares from Mk 501 and PKS 2155-304 performed by the MAGIC [ 233 ] and HESS [ 285 ] observatories have established ... bounds on the scale of dispersion, for the linear-effects (“ n = 1”) scenario, at about 1/10 of the Planck scale
Supports
Quantum-Spacetime Phenomenologysection 3.12, Birefringence and observations of polarized radio galaxies
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Review of the field
The source reads: Using observations of polarized light from distant radio galaxies [ 395 , 261 , 262 , 158 , 342 , 495 ] one can comfortably achieve Planck-scale sensitivity (for “ n = 1” linear modifications of the dispersion relation) to birefringence effects following this strategy.
Supports
Quantum-Spacetime Phenomenologysection 3.8
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Review of the field
The source reads: But the present best constraints on quantum-spacetime-induced in-vacuo dispersion are derived from observations of gamma-ray bursts reported by the Fermi telescope.

Later work looked for

arXiv, 2013 on, "Lorentz invariance violation gamma-ray burst": later bursts (LHAASO 2024, abstract) extend the same approach; nothing that changes the claim.

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

Claim: Set bounds

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

Corrected

24 September 2026. Previously: “Rule things out” The observations bound the models rather than excluding them; the review puts ruling out even the linear case in the future conditional.

Claim: The constraints are negative results, and so far bounds like these are the only experimental grip anyone has on quantum gravity.

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
Quantum-Spacetime Phenomenologysection 2.2, Candidate effects
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: the theory proposals I briefly considered in Section 2.1.4 (all still lacking any experimental success) can only serve the purpose of inspiring some test theories suitable for comparison to data
Supports
Quantum-Spacetime Phenomenologysection 1.9, Sensitivities rather than limits
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: placing experimental bounds (“limits”) on the parameters of these test theories does deserve intrinsic interest

What this does not establish

A positive claim exists and is contested: one group reads the Fermi delays as a detection (claim 23).

Later work looked for

Crossref, 2016 on, "light speed variation gamma-ray bursts" and "quantum gravity phenomenology review": Xu and Ma (2016, abstract) claim a variation; LHAASO (2024, abstract) sets a bound above it. No detection is established.

Corrected

24 September 2026. Previously: “The constraints are negative results, and they are the only experimental grip anyone has on quantum gravity.” The astrophysical bounds are not the only ones (the review also covers laboratory and cosmic-ray bounds); what is true is that every experimental result so far is a bound.

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

The measurement that did it

Claim: The measurement that did it

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

Claim: In 2009 a gamma-ray burst whose light had been travelling for about seven billion years produced photons across a range of energies, and a space telescope recorded them.

Kind: Observation. Something measured or seen, as the named source reports it.
Review: Source checked. The cited passage was read, and it says this.

Seven billion years is the light-travel time for redshift 0.903 in the paper’s own cosmology, computed for this review (7.3 billion years); the paper gives the redshift and luminosity distance, not the travel time.

Supports
A limit on the variation of the speed of light arising from quantum gravity effectsmain text
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement
The source reads: On May 10th, 2009, T0 = 00:22:59.97 UT, the Gamma-ray Burst Monitor (GBM)5 and the Large Area Telescope (LAT)6 on-board Fermi triggered on the very bright short GRB 090510
Supports
A limit on the variation of the speed of light arising from quantum gravity effectsmain text
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement
The source reads: common redshift of z = 0.903±0.003, corresponding to a luminosity distance of dL = 1.8×10²⁸ cm (for a standard cosmology, [ΩΛ, ΩM, h] = [0.73, 0.27, 0.71])
Notation restored: Superscript exponent restored from the arXiv PDF of 0908.1832 as rendered, where the 28 is set raised and smaller, read 2026-09-24. The text as extracted reads: common redshift of z = 0.903±0.003, corresponding to a luminosity distance of dL = 1.8×1028 cm (for a standard cosmology, [ΩΛ, ΩM, h] = [0.73, 0.27, 0.71])

Later work looked for

arXiv, 2009 on, "GRB 090510": nothing read that revises the redshift or the detection.

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

Claim: A photon of 31 billion electronvolts arrived within a second of the lower-energy ones.

Kind: Observation. Something measured or seen, as the named source reports it.
Review: Source checked. The cited passage was read, and it says this.

Supports
A limit on the variation of the speed of light arising from quantum gravity effectsmain text
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement
The source reads: a single 31 GeV photon – the highest-energy photon detected from any GRB, coincides with the last GBM pulse at T0+0.829 s

What this does not establish

The paper’s most conservative limit counts from the start of any low-energy emission, a delay under 859 milliseconds.

Later work looked for

arXiv, 2009 on, "GRB 090510": nothing read that revises the photon’s energy or timing.

Claim 37 · checked 24 September 2026 · AI-assisted audit

Claim: Over that distance, that puts a limit on a linear energy-dependent variation in the speed of light at or beyond the Planck scale itself.

Kind: Observation. Something measured or seen, as the named source reports it.
Review: Source checked. The cited passage was read, and it says this.

Supports
A limit on the variation of the speed of light arising from quantum gravity effectsabstract
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement
The source reads: this photon sets limits on a possible linear energy dependence of the propagation speed of photons (Lorentz-invariance violation) requiring for the first time a quantum-gravity mass scale significantly above the Planck mass
Supports
A limit on the variation of the speed of light arising from quantum gravity effectsmain text
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement
The source reads: models with n > 1 are not significantly constrained by our results

What this does not establish

The most conservative of the paper’s limits is 1.19 times the Planck mass; the least conservative, which assumes the photon left with a particular spike, is over a hundred.

Later work looked for

Corrected

24 September 2026. Previously: “that puts a limit on any energy-dependent variation” The Fermi paper bounds only the linear case at the Planck scale and says models with a higher power of energy are not significantly constrained.

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

Claim: A single burst, about two seconds long,

Kind: Observation. Something measured or seen, as the named source reports it.
Review: Source checked. The cited passage was read, and it says this.

Supports
A limit on the variation of the speed of light arising from quantum gravity effectsmain text
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement
The source reads: we estimate the T90 (T50) duration of the event – the time within which 90% (50%) of the 50–300 keV event counts are collected – to be 2.1 s (0.2 s)

Later work looked for

arXiv, 2009 on, "GRB 090510": nothing read that revises the duration.

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

Claim: constraining a class of models of the structure of space at a scale no accelerator can reach.

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 summing up of the two claims before it.

Supports
A limit on the variation of the speed of light arising from quantum gravity effectsmain text
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement
The source reads: even our most conservative limit (Table 2; (a)) greatly reduces the parameter space for n=1 models
Supports
Quantum-Spacetime Phenomenologysection 1.1
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: We are presently unable to redo the same experiments having as “in state” two particles with energy of 10³⁰ eV (i.e., energy higher than the Planck scale)
Notation restored: Superscript exponents restored from the version of record as served in HTML by link.springer.com, which sets them with , read 2026-09-24; also confirmed in the arXiv LaTeX source of 0806.0339v2. The text as extracted reads: We are presently unable to redo the same experiments having as “in state” two particles with energy of 10 30 eV (i.e., energy higher than the Planck scale)

Corrected

24 September 2026. Previously: “constraining a theory about the structure of space at a scale no experiment can otherwise touch.” The burst constrains the linear models, not a theory; and the same passage names blazars and radio galaxies that also bound effects near the Planck scale, so "no experiment can otherwise touch" contradicted the page.

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

What might be there

Claim: What might be there

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

What grainy would mean

Claim: What grainy would mean

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

Claim: Some approaches describe space as built from discrete elements with a smallest area and volume.

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.

Loop quantum gravity is the main example; causal sets also start from discrete points.

Supports
Quantum-Spacetime Phenomenologysection 2.1.2, Loop Quantum Gravity
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: the quantum properties of spacetime in LQG, which appear to be primarily codified in a discretization of the area and volume observables
Supports
Minimal Length Scale Scenarios for Quantum Gravitysection 3.8
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: LQG and the simplified model for LQC give rise to bounds on the eigenvalues of the area and volume operator

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

Claim: Others keep space continuous and change what distance means at short scales.

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.

String theory limits resolution without discreteness, and noncommutative geometry limits how precisely coordinates can be jointly fixed.

Supports
Minimal Length Scale Scenarios for Quantum Gravitysection 5, Discussion
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: String theory is an example that documents that discreteness is not necessary for a limit to the resolution of structures
Supports
Quantum-Spacetime Phenomenologysection 2.1.3, Approaches based on spacetime noncommutativity
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: spacetime coordinates should not commute [ 211 , 391 , 374 , 384 , 70 , 98 ] among themselves, producing some limitations for the combined determination of more than one coordinate of a spacetime point/event

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

Claim: Others treat spacetime as emerging from something more fundamental.

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 2.1.4
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: This literature actually contains a variety of possible way through which gravity could be described not as a fundamental aspect of the laws of nature, but rather as an emergent feature.
Supports
Minimal Length Scale Scenarios for Quantum Gravitysection 1
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: Are space and time fundamental, or are they just good approximations that emerge from a more fundamental concept in the limits that we have tested so far?

What this does not establish

The reviews name emergent gravity as a family of proposals and ask the question; they do not describe one worked-out account.

Corrected

24 September 2026. Previously: “Others treat spacetime as emergent from something that is not spatial at all.” The reviews describe emergent gravity and ask whether spacetime emerges from something more fundamental; neither says what it emerges from is not spatial at all.

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

Claim: These are not variations on one picture.

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 the three families just named, which the reviews treat separately.

Supports
Minimal Length Scale Scenarios for Quantum Gravitysection 3.8
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: But we have also seen that these limits appear in different forms.

Claim 46 · checked 24 September 2026 · AI-assisted audit

Claim: They disagree about whether the question, how short can a length be, is even meaningful.

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.

Some approaches bound a length, some only products of distances and times, and in some discrete approaches there may be no finite limit at all.

Supports
Minimal Length Scale Scenarios for Quantum Gravitysection 3.8
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: it is somewhat misleading to speak of a ‘minimal length,’ since in many cases a bound on the length itself does not exist, but only on the powers of spatio-temporal distances
Supports
Minimal Length Scale Scenarios for Quantum Gravitysection 5
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: discreteness seems neither necessary nor sufficient for the existence of a minimal length scale

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

Which account is right

Claim: Which account is right

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

Claim: Trying to look closer eventually makes the thing you are looking at bigger.

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
Minimal Length Scale Scenarios for Quantum Gravitysection 3.1.2
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field
The source reads: The important point to notice here is that the extension of the black hole grows linearly with the energy, and therefore one can achieve a minimal possible extension

What this does not establish

The same thought experiment as claim 15, with the same dependence on the hoop conjecture.

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

Which theory, if any

Claim: Which theory, if any

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

Claim: No candidate theory of quantum gravity has an experimental result in its favour.

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
Quantum-Spacetime Phenomenologysection 2.2
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: the theory proposals I briefly considered in Section 2.1.4 (all still lacking any experimental success) can only serve the purpose of inspiring some test theories suitable for comparison to data

What this does not establish

The review is from 2013; the claimed variation in claim 23 is a contested reading of burst data, not a result for any one theory.

Later work looked for

Crossref, 2016 on, "quantum gravity phenomenology review" and "light speed variation gamma-ray bursts": Addazi and others (2022, abstract) still describe a search for indications; the Xu and Ma claim is contested by later bounds. Nothing that changes the claim.

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

Claim: The observations described above constrain possibilities without selecting one.

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
Quantum-Spacetime Phenomenologysection 1.4
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: a more mature phenomenology should also be able to discriminate between similar (but somewhat different) new-physics scenarios
Supports
Quantum-Spacetime Phenomenologysection 1.9
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: However, at the time of writing, the transition “from sensitivities to limits” is not yet complete.

Later work looked for

Crossref and arXiv, 2013 on, "Lorentz invariance violation gamma-ray burst": later work tightens the bounds (LHAASO 2024, abstract) without selecting a theory.

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

Claim: This is one of the largest open problems in fundamental physics,

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 ranking. The review describes the two pillars of physics as disconnected, which is what makes the problem fundamental.

Supports
Quantum-Spacetime Phenomenologysection 1.1
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: Our present description of the fundamental laws of Nature is based on two disconnected pieces

Corrected

24 September 2026. Previously: “This is the largest open problem in fundamental physics,” A ranking no source makes; the page now states it as one of the largest rather than the largest.

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

Claim: and it has been open, without an experimental foothold that discriminates between the candidates, for the better part of a century.

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.

More than 70 years in 2013, so more than eighty now.

Supports
Quantum-Spacetime Phenomenologysection 1.1
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: Therefore, we do have a genuine “quantum-gravity problem”, and this problem has been studied for more than 70 years
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: a more mature phenomenology should also be able to discriminate between similar (but somewhat different) new-physics scenarios

Claim 54 · checked 24 September 2026 · AI-assisted audit

What was read

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; read sections 1.1 to 1.9, 2.1, 2.2 opening, 3.8, 3.12 and 3.13 opening, and compared against arXiv:0806.0339v2Read in full, 24 September 2026 · Open access; quoted brieflyMathematics in the HTML is served as LaTeX or split across lines; excerpts keep the text as extracted.
A limit on the variation of the speed of light arising from quantum gravity effectsFermi GBM/LAT Collaborations, Nature · arXiv:0908.1832, the accepted manuscript (titled there "Testing Einstein’s special relativity with Fermi’s short hard γ-ray burst GRB090510"); read in full with Table 2. The Nature version of record was not reachable.Read in full, 24 September 2026 · Copyright; quoted brieflySuperscripts are lost in the text extraction, so excerpts avoid numbers written as powers.
Minimal Length Scale Scenarios for Quantum GravityHossenfelder, Living Reviews in Relativity · Living Reviews in Relativity 16 (2013) 2, the version of record as served in HTML by link.springer.com; read sections 1, 2, 3.1.1, 3.1.2, 3.8, 4.1, 5 and 6, and compared against arXiv:1203.6191v2Read in full, 24 September 2026 · Open access; quoted briefly
Light speed variation from gamma-ray burstsXu and Ma, Astroparticle Physics · arXiv:1607.03203v3, the accepted version of the Astroparticle Physics paper; abstract and full text readRead in full, 24 September 2026 · arXiv non-exclusive distribution licence; quoted brieflyExcerpts from the abstract keep the arXiv abstract’s LaTeX markup as served; a reader is shown it rendered.
Stringent Tests of Lorentz Invariance Violation from LHAASO Observations of GRB 221009ALHAASO Collaboration, Physical Review Letters · arXiv:2402.06009v3 (13 February 2026), abstract and full text, with its LaTeX source; Crossref record for the Physical Review Letters versionRead in full, 24 September 2026 · arXiv non-exclusive distribution licence; quoted brieflyExcerpts from the abstract keep the arXiv abstract’s LaTeX markup as served; a reader is shown it rendered.