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Evidence record

Why do two good measurements of the universe disagree?

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: 55
  • A judgement, not a fact: 14
  • Presented as open: 1

If something here is wrong, misquoted, out of date or unfair, write to support@unknownoceans.com and give the claim number, which does not change.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 measurement question with a physics question behind it: two methods for one number disagree, and the page weighs whether a measurement is wrong or the standard model of cosmology is incomplete. The measurement side is itself contested between research teams.

  • Both routes measure the same quantity

    Contested

    Both aim at the present expansion rate, but the early-universe value is inferred through the standard model, so a gap can mean a wrong measurement or a wrong model. The page says so.

  • Both measurements are good

    Contested

    The title’s "good" is the SH0ES and Planck teams’ own assessment. A rival local ladder (CCHP) gets a lower value, and the SH0ES team attributes that to sample selection.

  • The universe is expanding, at a rate that can be expressed as one number today

    Established

    The Hubble constant is the present expansion rate; every source on the page takes it as the quantity measured.

How the question is labelled

Claim: The tension

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

Claim: The tension

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

The question

Claim: Two ways of measuring how fast space is expanding have been getting more precise for twenty years, and further apart.

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.

  • Supports

    A comprehensive measurement of the local value of the Hubble constant with 1 km/s/Mpc uncertainty from the Hubble Space Telescope and the SH0ES teamsection 1.1, The SH0ES Program

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: The result was a 5% measurement of H₀, 74.2 ± 3.6 km s⁻¹ Mpc⁻¹ ... was consistent with a value of H₀ = 71.9 ± 2.6 determined from WMAP and ΛCDM alone

    Notation restored: Subscript and superscripts restored as the arXiv version of the paper (2112.04510) typesets them: the 0 after H is lowered and set small, the −1 after s and after Mpc raised, read from glyph positions 2026-09-24. The text as extracted reads: The result was a 5% measurement of H 0, 74.2± 3.6 km s−1 Mpc−1 ... was consistent with a value of H 0 = 71.9± 2.6 determined from WMAP and ΛCDM alone

  • Supports

    A comprehensive measurement of the local value of the Hubble constant with 1 km/s/Mpc uncertainty from the Hubble Space Telescope and the SH0ES teamsection 1.2, The Hubble Tension

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: The first release of CMB data from the ESA Planck mission (Planck Collaboration et al. 2014) yielded H₀ = 67.2 ± 1.2 in the context of ΛCDM, a then 2 σ reduction relative to WMAP and a difference of 3 σ from the results of R11 and F12.

    Notation restored: Subscript and superscripts restored as the arXiv version of the paper (2112.04510) typesets them: the 0 after H is lowered and set small, the −1 after s and after Mpc raised, read from glyph positions 2026-09-24. The text as extracted reads: The first release of CMB data from the ESA Planck mission (Planck Collaboration et al. 2014) yielded H 0 = 67.2± 1.2 in the context of ΛCDM, a then 2 σ reduction relative to WMAP and a difference of 3 σ from the results of R11 and F12.

  • Supports

    A comprehensive measurement of the local value of the Hubble constant with 1 km/s/Mpc uncertainty from the Hubble Space Telescope and the SH0ES teamabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: Our baseline result from the Cepheid–SN Ia sample is H₀ = 73.04 ± 1.04 km s⁻¹ Mpc⁻¹, which includes systematic uncertainties

    Notation restored: Subscript and superscripts restored as the arXiv version of the paper (2112.04510) typesets them: the 0 after H is lowered and set small, the −1 after s and after Mpc raised, read from glyph positions 2026-09-24. The text as extracted reads: Our baseline result from the Cepheid–SN Ia sample is H 0 = 73.04± 1.04 km s−1 Mpc−1, which includes systematic uncertainties

  • Supports

    Planck 2018 results. VI. Cosmological parametersabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: Assuming the base- ΛCDM cosmology, the inferred (model-dependent) late-Universe parameters are: Hubble constant H₀ = (67.4±0.5) km s⁻¹ Mpc⁻¹

    Notation restored: Subscripts and superscripts restored as the arXiv PDF (1807.06209v4) typesets them, read from glyph positions 2026-09-24; the abstract on arXiv gives H_0 and Ω_m the same way. The text as extracted reads: Assuming the base- ΛCDM cosmology, the inferred (model-dependent) late-Universe parameters are: Hubble constant H0 = (67.4±0.5) km s−1Mpc−1

  • Supports

    A comprehensive measurement of the local value of the Hubble constant with 1 km/s/Mpc uncertainty from the Hubble Space Telescope and the SH0ES teamsection 1.1

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026

    The source reads: Indications of any tension between the early and late Universe at that time were < 2σ in significance

What this does not establish

"Twenty years" is approximate: the SH0ES programme began in 2005, and the gap passed three standard deviations only with Planck’s first data in 2013. "Further apart" is in standard deviations; in the rival red-giant calibration the local value is lower.

Later work looked for

Crossref, 2022 on, "Hubble tension" and "Chicago-Carnegie Hubble Program JWST": SH0ES (Riess and others 2024) still finds the gap; the CCHP team (Freedman and others 2025, and its erratum, which does not touch H0) finds 70.39 and no need for new physics. The page now attributes the five-sigma figure to SH0ES and reports the disagreement.

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

Claim: One method reads the expansion rate off the infant universe, the other measures it directly in nearby galaxies.

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.

"Reads off" is shorthand: the early-universe value is inferred through the standard model, as the page says later.

  • Supports

    In the realm of the Hubble tension: a review of solutionsabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field

    The source reads: The most statistically significant tension is the 4σ to 6σ disagreement between predictions of the Hubble constant, H0, made by the early time probes in concert with the “vanilla” ΛCDM Cosmological model, and a number of late time, model-independent determinations of H0 from local measurements of distances and redshifts.

Later work looked for

Crossref, 2022 on, "Hubble tension review solutions": nothing read that reverses the review; the SH0ES and CCHP papers of 2024 and 2025 show the measurement side still contested.

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

Claim: Both have shrunk their error bars.

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.

  • Supports

    A comprehensive measurement of the local value of the Hubble constant with 1 km/s/Mpc uncertainty from the Hubble Space Telescope and the SH0ES teamsection 1.1, The SH0ES Program

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: The result was a 5% measurement of H₀, 74.2 ± 3.6 km s⁻¹ Mpc⁻¹ ... was consistent with a value of H₀ = 71.9 ± 2.6 determined from WMAP and ΛCDM alone

    Notation restored: Subscript and superscripts restored as the arXiv version of the paper (2112.04510) typesets them: the 0 after H is lowered and set small, the −1 after s and after Mpc raised, read from glyph positions 2026-09-24. The text as extracted reads: The result was a 5% measurement of H 0, 74.2± 3.6 km s−1 Mpc−1 ... was consistent with a value of H 0 = 71.9± 2.6 determined from WMAP and ΛCDM alone

  • Supports

    A comprehensive measurement of the local value of the Hubble constant with 1 km/s/Mpc uncertainty from the Hubble Space Telescope and the SH0ES teamabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: Our baseline result from the Cepheid–SN Ia sample is H₀ = 73.04 ± 1.04 km s⁻¹ Mpc⁻¹, which includes systematic uncertainties

    Notation restored: Subscript and superscripts restored as the arXiv version of the paper (2112.04510) typesets them: the 0 after H is lowered and set small, the −1 after s and after Mpc raised, read from glyph positions 2026-09-24. The text as extracted reads: Our baseline result from the Cepheid–SN Ia sample is H 0 = 73.04± 1.04 km s−1 Mpc−1, which includes systematic uncertainties

  • Supports

    Planck 2018 results. VI. Cosmological parametersabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: Assuming the base- ΛCDM cosmology, the inferred (model-dependent) late-Universe parameters are: Hubble constant H₀ = (67.4±0.5) km s⁻¹ Mpc⁻¹

    Notation restored: Subscripts and superscripts restored as the arXiv PDF (1807.06209v4) typesets them, read from glyph positions 2026-09-24; the abstract on arXiv gives H_0 and Ω_m the same way. The text as extracted reads: Assuming the base- ΛCDM cosmology, the inferred (model-dependent) late-Universe parameters are: Hubble constant H0 = (67.4±0.5) km s−1Mpc−1

What this does not establish

From ±3.6 (ladder, 2009) to ±1.04, and from WMAP’s ±2.6 to Planck’s ±0.5.

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

Claim: The gap between them has not closed,

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

What this does not establish

The gap between the Cepheid ladder and Planck. A rival team’s red-giant ladder lands nearer the middle; see claims 52 and 53.

Later work looked for

Crossref, 2022 on, "Hubble tension" and "Chicago-Carnegie Hubble Program JWST": SH0ES (Riess and others 2024) still finds the gap; the CCHP team (Freedman and others 2025, and its erratum, which does not touch H0) finds 70.39 and no need for new physics. The page now attributes the five-sigma figure to SH0ES and reports the disagreement.

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

Claim: and that is either a mistake nobody has found or physics nobody has written down.

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 two readings set out in the section on where the fault could be.

Other readings

The review also names unexpected large-scale structure as a third kind of answer, and the CCHP team reads its own lower ladder value as leaving no gap that needs new physics.

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

Claim: A disagreement of about eight per cent does not sound like a crisis.

Kind
Present-day figure. A count, survey or report finding, as the named source gives it.
Review
Source checked. The cited passage was read, and it says this.

  • Supports

    Planck 2018 results. VI. Cosmological parametersabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: Assuming the base- ΛCDM cosmology, the inferred (model-dependent) late-Universe parameters are: Hubble constant H₀ = (67.4±0.5) km s⁻¹ Mpc⁻¹

    Notation restored: Subscripts and superscripts restored as the arXiv PDF (1807.06209v4) typesets them, read from glyph positions 2026-09-24; the abstract on arXiv gives H_0 and Ω_m the same way. The text as extracted reads: Assuming the base- ΛCDM cosmology, the inferred (model-dependent) late-Universe parameters are: Hubble constant H0 = (67.4±0.5) km s−1Mpc−1

  • Supports

    A comprehensive measurement of the local value of the Hubble constant with 1 km/s/Mpc uncertainty from the Hubble Space Telescope and the SH0ES teamabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: Our baseline result from the Cepheid–SN Ia sample is H₀ = 73.04 ± 1.04 km s⁻¹ Mpc⁻¹, which includes systematic uncertainties

    Notation restored: Subscript and superscripts restored as the arXiv version of the paper (2112.04510) typesets them: the 0 after H is lowered and set small, the −1 after s and after Mpc raised, read from glyph positions 2026-09-24. The text as extracted reads: Our baseline result from the Cepheid–SN Ia sample is H 0 = 73.04± 1.04 km s−1 Mpc−1, which includes systematic uncertainties

    73.04 against 67.4 is a gap of 5.6, which is 8.4 per cent of the Planck value and 7.7 per cent of the SH0ES one.

  • Supports

    A comprehensive measurement of the local value of the Hubble constant with 1 km/s/Mpc uncertainty from the Hubble Space Telescope and the SH0ES teamsection 1.2

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026

    The source reads: a difference of ∼ 9%

    SH0ES described the 2016 gap (73.2 against 66.9) as about nine per cent.

Later work looked for

Crossref, 2023 on, "Hubble constant JWST Cepheids SH0ES" and "Chicago-Carnegie Hubble Program": Riess and others 2024 report 73.2 ± 0.9 from the full HST set and JWST cross-checks that agree with it; Freedman and others 2025 get 70.39 from red giants. The Cepheid figure stands; the page now reports the rival value where it discusses the check.

Corrected

24 September 2026. Previously: “A disagreement in the fourth significant figure does not sound like a crisis.” 67.4 and 73.04 differ in the first significant figure, not the fourth. The gap is about eight per cent.

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

Claim: This one is.

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 five-sigma difference SH0ES reports and the review’s description of a serious crisis.

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

Claim: Two entirely different routes to the same number keep arriving at different answers, and each route is now precise enough that the difference cannot be shrugged off as luck.

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 comprehensive measurement of the local value of the Hubble constant with 1 km/s/Mpc uncertainty from the Hubble Space Telescope and the SH0ES teamabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: We find a 5σ difference with the prediction of H0 from Planck CMB observations under ΛCDM, with no indication that the discrepancy arises from measurement uncertainties or analysis variations considered to date.

  • Supports

    Planck 2018 results. VI. Cosmological parametersabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: Assuming the base- ΛCDM cosmology, the inferred (model-dependent) late-Universe parameters are: Hubble constant H₀ = (67.4±0.5) km s⁻¹ Mpc⁻¹

    Notation restored: Subscripts and superscripts restored as the arXiv PDF (1807.06209v4) typesets them, read from glyph positions 2026-09-24; the abstract on arXiv gives H_0 and Ω_m the same way. The text as extracted reads: Assuming the base- ΛCDM cosmology, the inferred (model-dependent) late-Universe parameters are: Hubble constant H0 = (67.4±0.5) km s−1Mpc−1

  • Supports

    A comprehensive measurement of the local value of the Hubble constant with 1 km/s/Mpc uncertainty from the Hubble Space Telescope and the SH0ES teamabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: Our baseline result from the Cepheid–SN Ia sample is H₀ = 73.04 ± 1.04 km s⁻¹ Mpc⁻¹, which includes systematic uncertainties

    Notation restored: Subscript and superscripts restored as the arXiv version of the paper (2112.04510) typesets them: the 0 after H is lowered and set small, the −1 after s and after Mpc raised, read from glyph positions 2026-09-24. The text as extracted reads: Our baseline result from the Cepheid–SN Ia sample is H 0 = 73.04± 1.04 km s−1 Mpc−1, which includes systematic uncertainties

What this does not establish

Luck here means a statistical fluctuation. Ruling that out does not rule out a systematic error, which is what the rest of the page weighs.

Later work looked for

Crossref, 2022 on, "Hubble tension" and "Chicago-Carnegie Hubble Program JWST": SH0ES (Riess and others 2024) still finds the gap; the CCHP team (Freedman and others 2025, and its erratum, which does not touch H0) finds 70.39 and no need for new physics. The page now attributes the five-sigma figure to SH0ES and reports the disagreement.

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

Two numbers, two methods

Claim: Two numbers, two methods

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

The early-universe route gives 67

Claim: The early-universe route gives 67

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

    Planck 2018 results. VI. Cosmological parametersabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: Assuming the base- ΛCDM cosmology, the inferred (model-dependent) late-Universe parameters are: Hubble constant H₀ = (67.4±0.5) km s⁻¹ Mpc⁻¹

    Notation restored: Subscripts and superscripts restored as the arXiv PDF (1807.06209v4) typesets them, read from glyph positions 2026-09-24; the abstract on arXiv gives H_0 and Ω_m the same way. The text as extracted reads: Assuming the base- ΛCDM cosmology, the inferred (model-dependent) late-Universe parameters are: Hubble constant H0 = (67.4±0.5) km s−1Mpc−1

What this does not establish

A model-dependent inference under base ΛCDM, as the Planck paper labels it, not a direct measurement of the present.

Later work looked for

arXiv and Crossref, 2020 on, "CMB Hubble constant" and "ACT DR6": the Atacama Cosmology Telescope DR6 with Planck (arXiv:2503.14452, abstract) gives 68.22 ± 0.36, the same early-universe side of the gap; nothing that changes the claim.

Claim 12 · checked 24 September 2026 · AI-assisted audit

Claim: The Planck satellite mapped the light released when the universe was about 380,000 years old.

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

    Planck 2018 results. VI. Cosmological parameterssection 8, Conclusions

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: astonishingly accurate description of the Universe from times prior to 380 000 years after the Big Bang, defining the last-scattering surface observed via the CMB

  • Supports

    Planck 2018 results. VI. Cosmological parametersabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: We present cosmological parameter results from the final full-mission Planck measurements of the cosmic microwave background

Later work looked for

arXiv and Crossref, 2020 on, "CMB Hubble constant" and "ACT DR6": the Atacama Cosmology Telescope DR6 with Planck (arXiv:2503.14452, abstract) gives 68.22 ± 0.36, the same early-universe side of the gap; nothing that changes the claim.

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

Claim: The pattern of hot and cold spots in that light encodes the contents and geometry of the early universe, and running the standard cosmological model forward from it predicts today’s expansion rate.

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

    Planck 2018 results. VI. Cosmological parametersabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: A combined analysis gives dark matter densityΩch2 = 0.120± 0.001 ... The joint constraint with BAO measurements on spatial curvature is consistent with a flat universe

  • Supports

    Planck 2018 results. VI. Cosmological parametersabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: Assuming the base- ΛCDM cosmology, the inferred (model-dependent) late-Universe parameters are: Hubble constant H₀ = (67.4±0.5) km s⁻¹ Mpc⁻¹

    Notation restored: Subscripts and superscripts restored as the arXiv PDF (1807.06209v4) typesets them, read from glyph positions 2026-09-24; the abstract on arXiv gives H_0 and Ω_m the same way. The text as extracted reads: Assuming the base- ΛCDM cosmology, the inferred (model-dependent) late-Universe parameters are: Hubble constant H0 = (67.4±0.5) km s−1Mpc−1

What this does not establish

The parameters are extracted by fitting the six-parameter model to the maps; the expansion rate today is a consequence of that fit, not something the maps show directly.

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

Claim: The 2018 result: a Hubble constant of 67.4 plus or minus 0.5 kilometres per second per megaparsec.

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

    Planck 2018 results. VI. Cosmological parametersabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: Assuming the base- ΛCDM cosmology, the inferred (model-dependent) late-Universe parameters are: Hubble constant H₀ = (67.4±0.5) km s⁻¹ Mpc⁻¹

    Notation restored: Subscripts and superscripts restored as the arXiv PDF (1807.06209v4) typesets them, read from glyph positions 2026-09-24; the abstract on arXiv gives H_0 and Ω_m the same way. The text as extracted reads: Assuming the base- ΛCDM cosmology, the inferred (model-dependent) late-Universe parameters are: Hubble constant H0 = (67.4±0.5) km s−1Mpc−1

What this does not establish

Inferred assuming base ΛCDM. Published in Astronomy & Astrophysics in 2020 as part of the 2018 release.

Later work looked for

arXiv and Crossref, 2020 on, "CMB Hubble constant" and "ACT DR6": the Atacama Cosmology Telescope DR6 with Planck (arXiv:2503.14452, abstract) gives 68.22 ± 0.36, the same early-universe side of the gap; nothing that changes the claim.

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

Claim: The paper adds that it finds "no compelling evidence for extensions to the base-ΛCDM model".

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.

The same abstract reports a significant, 3.6σ, tension with local measurements of the Hubble constant, and says simple extensions that partly resolve it are not favoured by the Planck data.

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

The nearby route gives 73

Claim: The nearby route gives 73

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 comprehensive measurement of the local value of the Hubble constant with 1 km/s/Mpc uncertainty from the Hubble Space Telescope and the SH0ES teamabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: Our baseline result from the Cepheid–SN Ia sample is H₀ = 73.04 ± 1.04 km s⁻¹ Mpc⁻¹, which includes systematic uncertainties

    Notation restored: Subscript and superscripts restored as the arXiv version of the paper (2112.04510) typesets them: the 0 after H is lowered and set small, the −1 after s and after Mpc raised, read from glyph positions 2026-09-24. The text as extracted reads: Our baseline result from the Cepheid–SN Ia sample is H 0 = 73.04± 1.04 km s−1 Mpc−1, which includes systematic uncertainties

Later work looked for

Crossref, 2023 on, "Hubble constant JWST Cepheids SH0ES" and "Chicago-Carnegie Hubble Program": Riess and others 2024 report 73.2 ± 0.9 from the full HST set and JWST cross-checks that agree with it; Freedman and others 2025 get 70.39 from red giants. The Cepheid figure stands; the page now reports the rival value where it discusses the check.

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

Claim: The other method does not assume a model of the early universe at all.

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

    In the realm of the Hubble tension: a review of solutionsabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field

    The source reads: The most statistically significant tension is the 4σ to 6σ disagreement between predictions of the Hubble constant, H0, made by the early time probes in concert with the “vanilla” ΛCDM Cosmological model, and a number of late time, model-independent determinations of H0 from local measurements of distances and redshifts.

Later work looked for

Crossref, 2022 on, "Hubble tension review solutions": nothing read that reverses the review; the SH0ES and CCHP papers of 2024 and 2025 show the measurement side still contested.

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

Claim: It builds a ladder: measure distances to nearby Cepheid variable stars by geometry, use Cepheids to calibrate type Ia supernovae in galaxies that contain both, then use those supernovae to reach far enough that the expansion dominates.

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.

Later work looked for

Crossref, 2023 on, "Cepheid metallicity distance scale" and "JWST Cepheids SH0ES": JWST remeasurements (Riess and others 2024) confirm the HST Cepheid photometry; nothing that changes how the ladder is described.

Corrected

24 September 2026. Previously: “measure distances to nearby Cepheid variable stars by parallax” SH0ES anchors its Cepheids with three geometric methods, not parallax alone: Gaia parallaxes, masers in NGC 4258 and eclipsing binaries in the Large Magellanic Cloud.

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

Claim: The 2022 measurement, using Hubble Space Telescope observations of Cepheids in the host galaxies of 42 supernovae, gives 73.04 plus or minus 1.04.

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 comprehensive measurement of the local value of the Hubble constant with 1 km/s/Mpc uncertainty from the Hubble Space Telescope and the SH0ES teamabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: We report observations from the Hubble Space Telescope (HST) of Cepheid variables in the host galaxies of 42 Type Ia supernovae (SNe Ia) used to calibrate the Hubble constant (H₀).

    Notation restored: Subscript and superscripts restored as the arXiv version of the paper (2112.04510) typesets them: the 0 after H is lowered and set small, the −1 after s and after Mpc raised, read from glyph positions 2026-09-24. The text as extracted reads: We report observations from the Hubble Space Telescope (HST) of Cepheid variables in the host galaxies of 42 Type Ia supernovae (SNe Ia) used to calibrate the Hubble constant (H 0).

  • Supports

    A comprehensive measurement of the local value of the Hubble constant with 1 km/s/Mpc uncertainty from the Hubble Space Telescope and the SH0ES teamabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: Our baseline result from the Cepheid–SN Ia sample is H₀ = 73.04 ± 1.04 km s⁻¹ Mpc⁻¹, which includes systematic uncertainties

    Notation restored: Subscript and superscripts restored as the arXiv version of the paper (2112.04510) typesets them: the 0 after H is lowered and set small, the −1 after s and after Mpc raised, read from glyph positions 2026-09-24. The text as extracted reads: Our baseline result from the Cepheid–SN Ia sample is H 0 = 73.04± 1.04 km s−1 Mpc−1, which includes systematic uncertainties

Later work looked for

Crossref, 2023 on, "Hubble constant JWST Cepheids SH0ES" and "Chicago-Carnegie Hubble Program": Riess and others 2024 report 73.2 ± 0.9 from the full HST set and JWST cross-checks that agree with it; Freedman and others 2025 get 70.39 from red giants. The Cepheid figure stands; the page now reports the rival value where it discusses the check.

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

Claim: The uncertainty is quoted including systematics.

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 comprehensive measurement of the local value of the Hubble constant with 1 km/s/Mpc uncertainty from the Hubble Space Telescope and the SH0ES teamabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: Our baseline result from the Cepheid–SN Ia sample is H₀ = 73.04 ± 1.04 km s⁻¹ Mpc⁻¹, which includes systematic uncertainties

    Notation restored: Subscript and superscripts restored as the arXiv version of the paper (2112.04510) typesets them: the 0 after H is lowered and set small, the −1 after s and after Mpc raised, read from glyph positions 2026-09-24. The text as extracted reads: Our baseline result from the Cepheid–SN Ia sample is H 0 = 73.04± 1.04 km s−1 Mpc−1, which includes systematic uncertainties

Later work looked for

Crossref, 2023 on, "Hubble constant JWST Cepheids SH0ES" and "Chicago-Carnegie Hubble Program": Riess and others 2024 report 73.2 ± 0.9 from the full HST set and JWST cross-checks that agree with it; Freedman and others 2025 get 70.39 from red giants. The Cepheid figure stands; the page now reports the rival value where it discusses the check.

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

Claim: The distance ladder, rung by rung

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

Claim: Geometry

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

Corrected

24 September 2026. Previously: “Parallax” The first rung is three geometric anchors, of which parallax is one.

Claim: Nearby Cepheids get their distances from parallaxes measured by the Gaia satellite, from masers in the galaxy NGC 4258, and from eclipsing binary stars in the Large Magellanic Cloud.

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

Later work looked for

Crossref, 2023 on, "Cepheid metallicity distance scale" and "JWST Cepheids SH0ES": JWST remeasurements (Riess and others 2024) confirm the HST Cepheid photometry; nothing that changes how the ladder is described.

Corrected

24 September 2026. Previously: “A nearby star shifts against the background as Earth moves around the Sun.” The rung was described as parallax alone, which no cited source described; the SH0ES paper names three geometric anchors, and the step now says what it uses.

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

Claim: Geometry alone gives the distance.

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

    In the realm of the Hubble tension: a review of solutionssection 2.2, Late

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field

    The source reads: The most often utilized approach is to use geometry (e.g. parallax) to calibrate the luminosities of specific star types (e.g. pulsating Cepheid variables and exploding Type Ia supernovae or SNIa) which can be seen at great distances where their redshifts measure cosmic expansion.

What this does not establish

Each anchor has its own measurement uncertainties; geometric means no stellar physics is needed to turn the measurement into a distance.

Later work looked for

Crossref, 2023 on, "Cepheid metallicity distance scale" and "JWST Cepheids SH0ES": JWST remeasurements (Riess and others 2024) confirm the HST Cepheid photometry; nothing that changes how the ladder is described.

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

Claim: Cepheid variables

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

Claim: These stars pulse with a period that tracks their true brightness.

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

What this does not establish

The relation depends slightly on the star’s metallicity, which is one of the systematics the page discusses.

Later work looked for

Crossref, 2023 on, "Cepheid period-luminosity relation metallicity": work refines the relation’s dependence on metallicity (the page raises it as a candidate systematic); nothing that changes the relation itself.

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

Claim: Calibrate that relation on those stars and a Cepheid’s brightness becomes a distance anywhere it can be seen.

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.

What this does not establish

Cepheids can be measured to about 10 to 40 megaparsecs, the review says, which is why the ladder needs another rung.

Later work looked for

Crossref, 2023 on, "Cepheid metallicity distance scale" and "JWST Cepheids SH0ES": JWST remeasurements (Riess and others 2024) confirm the HST Cepheid photometry; nothing that changes how the ladder is described.

Corrected

24 September 2026. Previously: “Calibrate that relation on the parallax stars and a Cepheid’s brightness becomes a distance anywhere it can be seen.” Follows the first rung, which now names all three geometric anchors.

Claim 28 · checked 24 September 2026 · AI-assisted audit

Claim: Type Ia supernovae

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

Claim: In galaxies close enough to contain measured Cepheids, the supernovae get calibrated in turn.

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

    In the realm of the Hubble tension: a review of solutionssection 2.2, Late

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field

    The source reads: The most often utilized approach is to use geometry (e.g. parallax) to calibrate the luminosities of specific star types (e.g. pulsating Cepheid variables and exploding Type Ia supernovae or SNIa) which can be seen at great distances where their redshifts measure cosmic expansion.

Later work looked for

Crossref, 2023 on, "Cepheid metallicity distance scale" and "JWST Cepheids SH0ES": JWST remeasurements (Riess and others 2024) confirm the HST Cepheid photometry; nothing that changes how the ladder is described.

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

Claim: At more than a billion times the Sun’s luminosity, they can be seen at great distances.

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

    In the realm of the Hubble tension: a review of solutionssection 2.2

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field

    The source reads: SNIa exceed a billion solar luminosities

  • Supports

    In the realm of the Hubble tension: a review of solutionssection 2.2, Late

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field

    The source reads: The most often utilized approach is to use geometry (e.g. parallax) to calibrate the luminosities of specific star types (e.g. pulsating Cepheid variables and exploding Type Ia supernovae or SNIa) which can be seen at great distances where their redshifts measure cosmic expansion.

Later work looked for

Crossref, 2023 on, "Cepheid metallicity distance scale" and "JWST Cepheids SH0ES": JWST remeasurements (Riess and others 2024) confirm the HST Cepheid photometry; nothing that changes how the ladder is described.

Corrected

24 September 2026. Previously: “They are bright enough to be seen across a large fraction of the observable universe.” "A large fraction of the observable universe" is not in any cited source; the review gives their luminosity and says they are seen at great distances.

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

Claim: The expansion

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

Claim: Far enough out, a galaxy’s recession dominates its own motion, and distance against redshift gives the rate directly.

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.

Later work looked for

Crossref, 2023 on, "Cepheid metallicity distance scale" and "JWST Cepheids SH0ES": JWST remeasurements (Riess and others 2024) confirm the HST Cepheid photometry; nothing that changes how the ladder is described.

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

The gap is now larger than the errors

Claim: The gap is now larger than the errors

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

Later work looked for

Crossref, 2022 on, "Hubble tension" and "Chicago-Carnegie Hubble Program JWST": SH0ES (Riess and others 2024) still finds the gap; the CCHP team (Freedman and others 2025, and its erratum, which does not touch H0) finds 70.39 and no need for new physics. The page now attributes the five-sigma figure to SH0ES and reports the disagreement.

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

Claim: Five or six units apart, with quoted uncertainties of half a unit and one.

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

    Planck 2018 results. VI. Cosmological parametersabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: Assuming the base- ΛCDM cosmology, the inferred (model-dependent) late-Universe parameters are: Hubble constant H₀ = (67.4±0.5) km s⁻¹ Mpc⁻¹

    Notation restored: Subscripts and superscripts restored as the arXiv PDF (1807.06209v4) typesets them, read from glyph positions 2026-09-24; the abstract on arXiv gives H_0 and Ω_m the same way. The text as extracted reads: Assuming the base- ΛCDM cosmology, the inferred (model-dependent) late-Universe parameters are: Hubble constant H0 = (67.4±0.5) km s−1Mpc−1

  • Supports

    A comprehensive measurement of the local value of the Hubble constant with 1 km/s/Mpc uncertainty from the Hubble Space Telescope and the SH0ES teamabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: Our baseline result from the Cepheid–SN Ia sample is H₀ = 73.04 ± 1.04 km s⁻¹ Mpc⁻¹, which includes systematic uncertainties

    Notation restored: Subscript and superscripts restored as the arXiv version of the paper (2112.04510) typesets them: the 0 after H is lowered and set small, the −1 after s and after Mpc raised, read from glyph positions 2026-09-24. The text as extracted reads: Our baseline result from the Cepheid–SN Ia sample is H 0 = 73.04± 1.04 km s−1 Mpc−1, which includes systematic uncertainties

Later work looked for

Crossref, 2023 on, "Hubble constant JWST Cepheids SH0ES" and "Chicago-Carnegie Hubble Program": Riess and others 2024 report 73.2 ± 0.9 from the full HST set and JWST cross-checks that agree with it; Freedman and others 2025 get 70.39 from red giants. The Cepheid figure stands; the page now reports the rival value where it discusses the check.

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

Claim: In 2009 the two routes gave 74.2 and 71.9, each uncertain by more than the gap between them,

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.

  • Supports

    A comprehensive measurement of the local value of the Hubble constant with 1 km/s/Mpc uncertainty from the Hubble Space Telescope and the SH0ES teamsection 1.1, The SH0ES Program

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: The first SH0ES results (Riess et al. 2009, hereafter R09) ... The result was a 5% measurement of H₀, 74.2 ± 3.6 km s⁻¹ Mpc⁻¹ ... was consistent with a value of H₀ = 71.9 ± 2.6 determined from WMAP and ΛCDM alone

    Notation restored: Subscript and superscripts restored as the arXiv version of the paper (2112.04510) typesets them: the 0 after H is lowered and set small, the −1 after s and after Mpc raised, read from glyph positions 2026-09-24. The text as extracted reads: The first SH0ES results (Riess et al. 2009, hereafter R09) ... The result was a 5% measurement of H 0, 74.2± 3.6 km s−1 Mpc−1 ... was consistent with a value of H 0 = 71.9± 2.6 determined from WMAP and ΛCDM alone

    The gap between 74.2 and 71.9 is 2.3; the quoted uncertainties are 3.6 and 2.6.

Corrected

24 September 2026. Previously: “Twenty years ago both numbers carried uncertainties larger than the gap,” "Twenty years ago" (2006) is not what the sources describe; the SH0ES history gives the 2009 pair, where each uncertainty exceeded the gap. The early-universe value then came from WMAP, not Planck.

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

Claim: and it was reasonable to expect the two to converge as the measurements improved.

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 two values then agreeing within their uncertainties.

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

Claim: They improved.

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.

  • Supports

    A comprehensive measurement of the local value of the Hubble constant with 1 km/s/Mpc uncertainty from the Hubble Space Telescope and the SH0ES teamabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: Our baseline result from the Cepheid–SN Ia sample is H₀ = 73.04 ± 1.04 km s⁻¹ Mpc⁻¹, which includes systematic uncertainties

    Notation restored: Subscript and superscripts restored as the arXiv version of the paper (2112.04510) typesets them: the 0 after H is lowered and set small, the −1 after s and after Mpc raised, read from glyph positions 2026-09-24. The text as extracted reads: Our baseline result from the Cepheid–SN Ia sample is H 0 = 73.04± 1.04 km s−1 Mpc−1, which includes systematic uncertainties

  • Supports

    Planck 2018 results. VI. Cosmological parametersabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: Assuming the base- ΛCDM cosmology, the inferred (model-dependent) late-Universe parameters are: Hubble constant H₀ = (67.4±0.5) km s⁻¹ Mpc⁻¹

    Notation restored: Subscripts and superscripts restored as the arXiv PDF (1807.06209v4) typesets them, read from glyph positions 2026-09-24; the abstract on arXiv gives H_0 and Ω_m the same way. The text as extracted reads: Assuming the base- ΛCDM cosmology, the inferred (model-dependent) late-Universe parameters are: Hubble constant H0 = (67.4±0.5) km s−1Mpc−1

  • Supports

    A comprehensive measurement of the local value of the Hubble constant with 1 km/s/Mpc uncertainty from the Hubble Space Telescope and the SH0ES teamsection 1.1, The SH0ES Program

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: The result was a 5% measurement of H₀, 74.2 ± 3.6 km s⁻¹ Mpc⁻¹ ... was consistent with a value of H₀ = 71.9 ± 2.6 determined from WMAP and ΛCDM alone

    Notation restored: Subscript and superscripts restored as the arXiv version of the paper (2112.04510) typesets them: the 0 after H is lowered and set small, the −1 after s and after Mpc raised, read from glyph positions 2026-09-24. The text as extracted reads: The result was a 5% measurement of H 0, 74.2± 3.6 km s−1 Mpc−1 ... was consistent with a value of H 0 = 71.9± 2.6 determined from WMAP and ΛCDM alone

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

Claim: They did not converge.

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

What this does not establish

True of the Cepheid ladder against Planck. The CCHP red-giant ladder lands between them; see claim 52.

Later work looked for

Crossref, 2022 on, "Hubble tension" and "Chicago-Carnegie Hubble Program JWST": SH0ES (Riess and others 2024) still finds the gap; the CCHP team (Freedman and others 2025, and its erratum, which does not touch H0) finds 70.39 and no need for new physics. The page now attributes the five-sigma figure to SH0ES and reports the disagreement.

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

Claim: The SH0ES team puts the difference at five standard deviations,

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

What this does not establish

Five sigma measures how unlikely the gap is as a fluctuation if both uncertainties are right. It says nothing about whether a systematic error is hiding in either.

Later work looked for

Crossref, 2022 on, "Hubble tension" and "Chicago-Carnegie Hubble Program JWST": SH0ES (Riess and others 2024) still finds the gap; the CCHP team (Freedman and others 2025, and its erratum, which does not touch H0) finds 70.39 and no need for new physics. The page now attributes the five-sigma figure to SH0ES and reports the disagreement.

Corrected

24 September 2026. Previously: “The difference is currently around five standard deviations,” The five-sigma figure is the SH0ES team’s, comparing its value with Planck. A rival ladder (CCHP 2025) gives a smaller gap, so the figure is attributed rather than stated as the current state of the field.

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

Claim: which is the threshold particle physicists use to call something a discovery rather than a fluctuation.

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

    Statistics (Review of Particle Physics, chapter 40)section 40.3.2

    Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work

    The source reads: Often in particle physics the level of significance where an effect is said to qualify as a discovery is Z = 5, i.e., a 5σeffect

What this does not establish

A convention, and the review itself says a physicist’s belief in a new effect depends on more than the p-value.

Later work looked for

Checked the 2025 revision of the review, the current one; the convention is unchanged.

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

Where the fault could be

Claim: Where the fault could be

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

Claim: They improved.

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.

  • Supports

    A comprehensive measurement of the local value of the Hubble constant with 1 km/s/Mpc uncertainty from the Hubble Space Telescope and the SH0ES teamabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: Our baseline result from the Cepheid–SN Ia sample is H₀ = 73.04 ± 1.04 km s⁻¹ Mpc⁻¹, which includes systematic uncertainties

    Notation restored: Subscript and superscripts restored as the arXiv version of the paper (2112.04510) typesets them: the 0 after H is lowered and set small, the −1 after s and after Mpc raised, read from glyph positions 2026-09-24. The text as extracted reads: Our baseline result from the Cepheid–SN Ia sample is H 0 = 73.04± 1.04 km s−1 Mpc−1, which includes systematic uncertainties

  • Supports

    Planck 2018 results. VI. Cosmological parametersabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: Assuming the base- ΛCDM cosmology, the inferred (model-dependent) late-Universe parameters are: Hubble constant H₀ = (67.4±0.5) km s⁻¹ Mpc⁻¹

    Notation restored: Subscripts and superscripts restored as the arXiv PDF (1807.06209v4) typesets them, read from glyph positions 2026-09-24; the abstract on arXiv gives H_0 and Ω_m the same way. The text as extracted reads: Assuming the base- ΛCDM cosmology, the inferred (model-dependent) late-Universe parameters are: Hubble constant H0 = (67.4±0.5) km s−1Mpc−1

  • Supports

    A comprehensive measurement of the local value of the Hubble constant with 1 km/s/Mpc uncertainty from the Hubble Space Telescope and the SH0ES teamsection 1.1, The SH0ES Program

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: The result was a 5% measurement of H₀, 74.2 ± 3.6 km s⁻¹ Mpc⁻¹ ... was consistent with a value of H₀ = 71.9 ± 2.6 determined from WMAP and ΛCDM alone

    Notation restored: Subscript and superscripts restored as the arXiv version of the paper (2112.04510) typesets them: the 0 after H is lowered and set small, the −1 after s and after Mpc raised, read from glyph positions 2026-09-24. The text as extracted reads: The result was a 5% measurement of H 0, 74.2± 3.6 km s−1 Mpc−1 ... was consistent with a value of H 0 = 71.9± 2.6 determined from WMAP and ΛCDM alone

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

Claim: They did not converge.

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

What this does not establish

True of the Cepheid ladder against Planck. The CCHP red-giant ladder lands between them.

Later work looked for

Crossref, 2022 on, "Hubble tension" and "Chicago-Carnegie Hubble Program JWST": SH0ES (Riess and others 2024) still finds the gap; the CCHP team (Freedman and others 2025, and its erratum, which does not touch H0) finds 70.39 and no need for new physics. The page now attributes the five-sigma figure to SH0ES and reports the disagreement.

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

Whether something is wrong with one of the measurements

Claim: Whether something is wrong with one of the measurements

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

Claim: The obvious candidate is an unknown systematic in the distance ladder:

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; the review discusses measurement errors on both sides and says no single proposed error survives the data.

  • Supports

    In the realm of the Hubble tension: a review of solutionssection 2.2.3, Systematics

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field

    The source reads: it is challenging to devise a single error that would suffice and we are not aware of a specific proposal that is not ruled out by the data

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

Claim: crowding in the fields where Cepheids are measured, the metallicity dependence of the period-luminosity relation, or supernova corrections that differ between star-forming and quieter host galaxies.

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.

Corrected

24 September 2026. Previously: “or supernova standardisation drifting with the age of the host galaxy.” The cited paper addresses host star formation and mass (after Rigault and others), not host age. Host-age effects have been proposed elsewhere, but no cited source was read for them.

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

Claim: Each of these has been tested hard: the 2022 SH0ES paper alone runs nearly seventy variants of its analysis.

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.

Corrected

24 September 2026. Previously: “Each of these has been hunted hard and independently.” "Independently" was not carried by the cited sources for these particular systematics; the SH0ES paper’s own tests are what was read.

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

Claim: Alternative rungs, including tip-of-the-red-giant-branch distances and gravitational lensing time delays, have been used to route around the suspect steps,

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.

What this does not establish

The CCHP paper was read as an abstract only.

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

Claim: and this is where the two camps part.

Kind
Disputed. A contested point, where the page reports a side or the disagreement.
Review
A judgement, not a fact. Reviewed for whether it is fairly put and follows from the checked claims. No source can confirm it.

  • Supports

    Status Report on the Chicago-Carnegie Hubble Program (CCHP): Measurement of the Hubble Constant Using the Hubble and James Webb Space Telescopesabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: Our current best (highest precision) estimate is H₀ = 70.39 ± 1.22 (stat) ± 1.33 (sys) ± 0.70 (σ_SN), based on the TRGB method alone, with a total of 24 SN Ia calibrators from both HST and JWST data.

    Notation restored: Subscripts and symbols restored from the arXiv PDF (v3), whose abstract renders them as H0 = 70.39 ± 1.22 (stat) ± 1.33 (sys) ± 0.70 (σSN), read 2026-09-24. The text as extracted reads: Our current best (highest precision) estimate is $H_0$ = 70.39 $\pm$ 1.22 (stat) $\pm$ 1.33 (sys) $\pm$ 0.70 ($\sigma_{SN}$), based on the TRGB method alone, with a total of 24 SN Ia calibrators from both HST and JWST data.

  • Supports

    Status Report on the Chicago-Carnegie Hubble Program (CCHP): Measurement of the Hubble Constant Using the Hubble and James Webb Space Telescopessection 16, Summary and Conclusions

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: Our current best estimate of H0 is 70.39 ± 1.22 (stat) ± 1.33 (sys) ± 0.70 ... This value falls between that obtained from studies of the CMB, from BAO measurements calibrated by BBN, and the SHoES value, all without significant tension.

  • Supports

    A comprehensive measurement of the local value of the Hubble constant with 1 km/s/Mpc uncertainty from the Hubble Space Telescope and the SH0ES teamsection 7.2

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026

    The source reads: we cite the mean of the two (72.53 ± 0.95 km s⁻¹ Mpc⁻¹) as representative of the combination of Cepheids and TRGB

    Notation restored: Subscript and superscripts restored as the arXiv version of the paper (2112.04510) typesets them: the 0 after H is lowered and set small, the −1 after s and after Mpc raised, read from glyph positions 2026-09-24. The text as extracted reads: we cite the mean of the two (72.53± 0.95 km s−1 Mpc−1) as representative of the combination of Cepheids and TRGB

Other readings

SH0ES holds that every alternative rung agrees with its Cepheids; CCHP holds that its red-giant and carbon-star distances give a lower value with no need for new physics.

Corrected

24 September 2026. Previously: “and the disagreement has proved stubborn rather than fragile.” One-sided. The SH0ES team finds the alternative rungs agree with its Cepheids; the CCHP team, using red giants, finds a value near 70 consistent with the standard model. Both sides are now reported.

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

Claim: The SH0ES team finds red giants agree with its Cepheids, giving 72.53 in combination.

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

    A comprehensive measurement of the local value of the Hubble constant with 1 km/s/Mpc uncertainty from the Hubble Space Telescope and the SH0ES teamabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: We demonstrate consistency with measures from HST of the TRGB between SN Ia hosts and NGC 4258, and include them simultaneously to yield 72.53 ± 0.99 km s⁻¹ Mpc⁻¹.

    Notation restored: Subscript and superscripts restored as the arXiv version of the paper (2112.04510) typesets them: the 0 after H is lowered and set small, the −1 after s and after Mpc raised, read from glyph positions 2026-09-24. The text as extracted reads: We demonstrate consistency with measures from HST of the TRGB between SN Ia hosts and NGC 4258, and include them simultaneously to yield 72.53± 0.99 km s−1 Mpc−1.

What this does not establish

Section 7.2 gives 72.53 ± 0.95 in the text and the abstract 72.53 ± 0.99; the page quotes the central value only.

Later work looked for

Crossref, 2023 on, "Hubble constant JWST Cepheids SH0ES" and "Chicago-Carnegie Hubble Program": Riess and others 2024 report 73.2 ± 0.9 from the full HST set and JWST cross-checks that agree with it; Freedman and others 2025 get 70.39 from red giants. The Cepheid figure stands; the page now reports the rival value where it discusses the check.

Corrected

24 September 2026. Previously: “” Added so that the red-giant check is reported with who ran it and what it gave.

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

Claim: The Chicago-Carnegie team, measuring red giants with the Hubble and James Webb telescopes, gets 70.39 and calls it consistent with the standard model;

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.

What this does not establish

70.39 carries ±1.22 statistical, ±1.33 systematic and ±0.70 from the supernovae; JWST data alone give 68.81 (red giants) and 67.80 (carbon stars).

Later work looked for

Crossref, 2023 on, "Hubble constant JWST Cepheids SH0ES" and "Chicago-Carnegie Hubble Program": Riess and others 2024 report 73.2 ± 0.9 from the full HST set and JWST cross-checks that agree with it; Freedman and others 2025 get 70.39 from red giants. The Cepheid figure stands; the page now reports the rival value where it discusses the check.

Corrected

24 September 2026. Previously: “” Added: a published, independent red-giant ladder disagrees with the SH0ES reading of the same kind of check, and the page reported only one side.

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

Claim: SH0ES puts the difference down to which supernovae each sample happens to include.

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

    JWST Validates HST Distance Measurements: Selection of Supernova Subsample Explains Differences in JWST Estimates of Local H0abstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: We show that Delta(H0)~2.5 km/s/Mpc between the CCHP JWST program and the full HST sample is entirely consistent with differences in sample selection.

  • Supports

    JWST Validates HST Distance Measurements: Selection of Supernova Subsample Explains Differences in JWST Estimates of Local H0Figure 5 caption

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: The CCHP and SH0ES subsamples selected for JWST observations produce a large difference of 3–4 km s⁻¹ Mpc⁻¹ in H0 a priori owing to selection. The HST Cepheid and JWST distance measurements themselves are in good agreement.

    Notation restored: Subscript and superscripts restored as the arXiv version (2408.11770) typesets them, read from glyph positions 2026-09-24. The text as extracted reads: The CCHP and SH0ES subsamples selected for JWST observations produce a large difference of 3–4 km s−1 Mpc−1 in H0 a priori owing to selection. The HST Cepheid and JWST distance measurements themselves are in good agreement.

What this does not establish

The SH0ES team’s own analysis of the other team’s sample. It also reports JWST red-giant, carbon-star and Cepheid values of 72.1 to 73.4 on a larger combined sample.

Other readings

CCHP does not accept that sample selection explains its lower value.

Corrected

24 September 2026. Previously: “” Added with the CCHP result, so the SH0ES response is reported too.

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

Claim: Six lensed quasars, analysed without any distance ladder at all, gave 73.3 in 2019.

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

    H0LiCOW XIII. A 2.4 per cent measurement of H0 from lensed quasars: 5.3 sigma tension between early and late Universe probesabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: a joint analysis of six gravitationally lensed quasars with measured time delays ... we find H₀ = 73.3 (+1.7/−1.8) km s⁻¹ Mpc⁻¹, a 2.4% precision measurement

    Notation restored: Notation restored as the arXiv PDF (1907.04869) typesets it, read from glyph positions 2026-09-24: the 0 after H lowered, the −1 after s and Mpc raised, and the uncertainty set as +1.7 raised over −1.8 lowered, written here as (+1.7/−1.8). The text as extracted reads: a joint analysis of six gravitationally lensed quasars with measured time delays ... we find H0 = 73.3+1.7 −1.8 km s−1 Mpc−1, a 2.4% precision measurement

What this does not establish

Assumes flat ΛCDM for the conversion to H0, and specific forms for the lensing galaxies’ mass (see the next claim).

Later work looked for

Crossref and arXiv, 2020 on, "TDCOSMO Hubble constant": TDCOSMO IV (2020) and TDCOSMO 2025 revisit the same lenses with looser mass models; the page now reports both.

Corrected

24 September 2026. Previously: “Six lensed quasars, analysed without any distance ladder at all, gave 73.3.” Dated, because later analyses of the same lenses give different values.

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

Claim: That precision leaned on assumptions about the lensing galaxies’ mass, and a 2025 analysis of eight lenses that loosened them gave 71.6, uncertain by three or four units either way.

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

    TDCOSMO IV: Hierarchical time-delay cosmography, joint inference of the Hubble constant and galaxy density profilesabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: describing deflector mass density profiles by either a power-law or stars plus standard dark matter halos. The mass-sheet transform (MST) that leaves the lensing observables unchanged is considered the dominant source of residual uncertainty in H₀.

    Notation restored: Subscript restored from the arXiv PDF (v3), whose abstract renders it as 𝐻0, read 2026-09-24. The text as extracted reads: describing deflector mass density profiles by either a power-law or stars plus standard dark matter halos. The mass-sheet transform (MST) that leaves the lensing observables unchanged is considered the dominant source of residual uncertainty in $H_0$.

  • Supports

    TDCOSMO 2025: Cosmological constraints from strong lensing time delaysabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: We present cosmological constraints from 8 strongly lensed quasars ... Our uncertainties are maximally conservative by accounting for the mass-sheet degeneracy in the deflectors' mass density profiles.

  • Supports

    TDCOSMO 2025: Cosmological constraints from strong lensing time delaysabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: In the flat Λ cold dark matter (CDM), we find H₀ = 71.6 +3.9/−3.3 km s⁻¹ Mpc⁻¹.

    Notation restored: Greek letter, subscript and superscripts restored from the arXiv PDF (v4), whose abstract renders it as H0 = 71.6 +3.9 −3.3 km s−1 Mpc−1, read 2026-09-24; the upper and lower errors are written after a slash. The text as extracted reads: In the flat $\Lambda$ cold dark matter (CDM), we find $H_0=71.6^{+3.9}_{-3.3}$ km s$^{-1}$ Mpc$^{-1}$.

What this does not establish

TDCOSMO IV (2020) found 74.5 +5.6/−6.1 from seven lenses with the mass models freed, and says this does not invalidate the 2019 assumptions; the 2025 value is +3.9/−3.3, and 4.6 per cent precision when non-time-delay lenses are added.

Corrected

24 September 2026. Previously: “” Added: the 2019 lensing value was presented as settled, and later work by the same collaboration shows its precision depended on mass-model assumptions.

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

Whether the model between the two is wrong

Claim: Whether the model between the two is wrong

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

Claim: The early-universe number is not a direct measurement of today’s expansion.

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

    In the realm of the Hubble tension: a review of solutionsabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field

    The source reads: The most statistically significant tension is the 4σ to 6σ disagreement between predictions of the Hubble constant, H0, made by the early time probes in concert with the “vanilla” ΛCDM Cosmological model, and a number of late time, model-independent determinations of H0 from local measurements of distances and redshifts.

  • Supports

    Planck 2018 results. VI. Cosmological parametersabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: Assuming the base- ΛCDM cosmology, the inferred (model-dependent) late-Universe parameters are: Hubble constant H₀ = (67.4±0.5) km s⁻¹ Mpc⁻¹

    Notation restored: Subscripts and superscripts restored as the arXiv PDF (1807.06209v4) typesets them, read from glyph positions 2026-09-24; the abstract on arXiv gives H_0 and Ω_m the same way. The text as extracted reads: Assuming the base- ΛCDM cosmology, the inferred (model-dependent) late-Universe parameters are: Hubble constant H0 = (67.4±0.5) km s−1Mpc−1

Later work looked for

Crossref, 2022 on, "Hubble tension review solutions": nothing read that reverses the review; the SH0ES and CCHP papers of 2024 and 2025 show the measurement side still contested.

Claim 57 · checked 24 September 2026 · AI-assisted audit

Claim: It is a prediction, produced by evolving the standard model of cosmology forward for 13.8 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.

  • Supports

    A comprehensive measurement of the local value of the Hubble constant with 1 km/s/Mpc uncertainty from the Hubble Space Telescope and the SH0ES teamsection 1

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026

    The source reads: The value of H₀ may be determined locally with measurements of distances and redshifts, and it can also be predicted from a cosmological model calibrated in the early Universe

    Notation restored: Subscript and superscripts restored as the arXiv version of the paper (2112.04510) typesets them: the 0 after H is lowered and set small, the −1 after s and after Mpc raised, read from glyph positions 2026-09-24. The text as extracted reads: The value of H 0 may be determined locally with measurements of distances and redshifts, and it can also be predicted from a cosmological model calibrated in the early Universe

  • Supports

    Planck 2018 results. VI. Cosmological parameterssection 8

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026

    The source reads: to the present day at an age of 13.8 billion years

What this does not establish

13.8 billion years is itself a Planck ΛCDM value, from the same fit.

Corrected

24 September 2026. Previously: “It is a prediction, produced by evolving the standard model of cosmology forward for thirteen billion years.” Planck gives the present age as 13.8 billion years; "thirteen billion" understated it.

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

Claim: If that model is missing something, the prediction can be precise and wrong.

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 early value being a model-dependent inference.

  • Supports

    In the realm of the Hubble tension: a review of solutionsabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field

    The source reads: The most statistically significant tension is the 4σ to 6σ disagreement between predictions of the Hubble constant, H0, made by the early time probes in concert with the “vanilla” ΛCDM Cosmological model, and a number of late time, model-independent determinations of H0 from local measurements of distances and redshifts.

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

Claim: The review that classifies the proposals sorts them into early dark energy, late dark energy, extra relativistic degrees of freedom, extra interactions, modified gravity and six other families, and cites more than a thousand papers doing 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

    In the realm of the Hubble tension: a review of solutionsabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field

    The source reads: We include more than 1000 references

  • Supports

    In the realm of the Hubble tension: a review of solutionsabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field

    The source reads: these categories: Early Dark Energy, Late Dark Energy, Dark energy models with 6 degrees of freedom and their extensions, Models with extra relativistic degrees of freedom, Models with Extra Interactions, Unified cosmologies, Modified gravity, Inflationary models, Modified recombination history, Physics of the critical Phenomena, and Alternative proposals.

Later work looked for

Crossref, 2022 on, "Hubble tension review solutions": nothing read that reverses the review; the SH0ES and CCHP papers of 2024 and 2025 show the measurement side still contested.

Corrected

24 September 2026. Previously: “modified gravity and a dozen other families” The review has eleven categories; five are named on the page, so six others, not a dozen.

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

Claim: None has made a strong case.

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

    In the realm of the Hubble tension: a review of solutionsabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field

    The source reads: While no specific proposal makes a strong case for being highly likely or far better than all others

What this does not establish

A 2021 review. Later proposals are not covered by it.

Corrected

24 September 2026. Previously: “None of them is comfortable: some improve the fit only by paying for the degrees of freedom they add, and most fixes for the expansion rate break something else that the same data constrains.” The review says some proposals are "formally successful, improving the fit ... in light of their additional degrees of freedom", which the page read as the opposite. "Most fixes break something else" was stronger than the review, which says successful models are "often" at odds with other probes.

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

Claim: Models that ease the tension on Planck’s data alone often disagree with other probes, and many ease it by widening the error bar rather than by moving the number.

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

    In the realm of the Hubble tension: a review of solutionssection 15, Summary and Conclusions

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field

    The source reads: these a priori successful cosmological models are often not in agreement with additional cosmological probes ... Moreover, the Hubble constant tension is alleviated due to an increase in the error bars of H0, rather than by an increase in the Hubble constant itself

  • Supports

    In the realm of the Hubble tension: a review of solutionsabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field

    The source reads: In many cases, reduced tension comes not simply from a change in the value of H0 but also due to an increase in its uncertainty due to degeneracy with additional physics

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

Claim: Two ways the tension resolves

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

Claim: A measurement problem

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

Claim: Some step in the distance ladder, or in the Planck analysis, carries an error nobody has found.

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

  • Supports

    In the realm of the Hubble tension: a review of solutionsabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field

    The source reads: demands a hypothesis with enough rigor to explain multiple observations

  • Supports

    In the realm of the Hubble tension: a review of solutionssection 2.2.3, Systematics

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field

    The source reads: it is challenging to devise a single error that would suffice and we are not aware of a specific proposal that is not ruled out by the data

What this does not establish

The review knows of no single proposed error that survives the data; an answer of this kind may need several unrelated errors.

Other readings

CCHP’s reading is that the local value is lower than SH0ES finds, which narrows the gap without new physics.

Claim 65 · checked 24 September 2026 · AI-assisted audit

Claim: Would be unglamorous,

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.

A judgement about how the answer would be received, not about which answer is right.

Claim 66 · checked 24 September 2026 · AI-assisted audit

Claim: and is how the 1980s dispute over this number, 50 against 100, ended: in the middle.

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.

  • Supports

    In the realm of the Hubble tension: a review of solutionssection 2.2.3

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field

    The source reads: might argue for a true value of H₀ “in the middle”, e.g. ∼ 70 km s⁻¹ Mpc⁻¹, as the easiest to accommodate, as was the resolution of the 1980’s debate between 50 and 100

    Notation restored: Subscript and superscripts restored as the arXiv PDF (2103.01183) typesets them, read from glyph positions 2026-09-24. The text as extracted reads: might argue for a true value of H0 “in the middle”, e.g.∼ 70 km s−1 Mpc−1, as the easiest to accommodate, as was the resolution of the 1980’s debate between 50 and 100

What this does not establish

The review adds that the analogy breaks down: the old dispute was between measurements of the same kind at the same distances, and pointed straight at systematics.

Corrected

24 September 2026. Previously: “Would be unglamorous and is historically the way most such disagreements have ended.” "Most such disagreements" had no source. The review supports one precedent, the 1980s dispute, and the page now names it.

Claim 67 · checked 24 September 2026 · AI-assisted audit

Claim: Has survived a decade of deliberate searching by the team that made the measurement, though a rival team’s red-giant distances land nearer the middle.

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.

What this does not establish

"A decade" counts from Planck’s first release in 2013, when the gap reached three standard deviations.

Later work looked for

Crossref, 2022 on, "Hubble tension" and "Chicago-Carnegie Hubble Program JWST": SH0ES (Riess and others 2024) still finds the gap; the CCHP team (Freedman and others 2025, and its erratum, which does not touch H0) finds 70.39 and no need for new physics. The page now attributes the five-sigma figure to SH0ES and reports the disagreement.

Corrected

24 September 2026. Previously: “Has survived a decade of deliberate attempts to find it, using independent methods.” Independent methods do not all agree: the CCHP red-giant ladder gives about 70. Attributed, with the other side stated.

Claim 68 · checked 24 September 2026 · AI-assisted audit

Claim: A physics problem

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

Claim: The standard model of cosmology is incomplete, and the early-universe prediction inherits the gap.

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

  • Supports

    In the realm of the Hubble tension: a review of solutionsabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field

    The source reads: The most statistically significant tension is the 4σ to 6σ disagreement between predictions of the Hubble constant, H0, made by the early time probes in concert with the “vanilla” ΛCDM Cosmological model, and a number of late time, model-independent determinations of H0 from local measurements of distances and redshifts.

  • Supports

    In the realm of the Hubble tension: a review of solutionsabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field

    The source reads: While no specific proposal makes a strong case for being highly likely or far better than all others

What this does not establish

Proposed, not shown: no specific model makes a strong case, the review says.

Other readings

The measurement reading in the other column.

Claim 70 · checked 24 September 2026 · AI-assisted audit

Claim: Would mean that a model which fits almost every other probe is incomplete.

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

    In the realm of the Hubble tension: a review of solutionssection 15

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field

    The source reads: The ΛCDM cosmological model, a simple and elegant framework, has been found to provide a very good fit to almost all of the observational probes available until present

Later work looked for

Crossref, 2021 on, "ΛCDM tensions": the Planck paper itself notes smaller tensions (lensing amplitude, galaxy clustering), and DESI baryon-acoustic results since 2024 have been read by their authors as hints of evolving dark energy; neither was read in full here, and "almost every" allows for them.

Corrected

24 September 2026. Previously: “Would be the first crack in a model that has otherwise fitted everything for twenty-five years.” Overstated: the model does not fit everything (Planck itself reports smaller tensions), and "first crack" was a claim no source made.

Claim 71 · checked 24 September 2026 · AI-assisted audit

Claim: No proposed fix has yet made a strong case over the others.

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

    In the realm of the Hubble tension: a review of solutionsabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field

    The source reads: While no specific proposal makes a strong case for being highly likely or far better than all others

What this does not establish

As of the 2021 review.

Corrected

24 September 2026. Previously: “Every proposed fix so far costs more in fit elsewhere than it buys here.” Contradicted by the cited review, which says some proposals are formally successful and improve the fit; what it does say is that none makes a strong case.

Claim 72 · checked 24 September 2026 · AI-assisted audit

What is actually unresolved

Claim: What is actually unresolved

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

Which it is

Claim: Which it is

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

Claim: Nobody knows.

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

    A comprehensive measurement of the local value of the Hubble constant with 1 km/s/Mpc uncertainty from the Hubble Space Telescope and the SH0ES teamabstract, last sentence

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026

    The source reads: The source of this now long-standing discrepancy between direct and cosmological routes to determining H₀ remains unknown

    Notation restored: Subscript and superscripts restored as the arXiv version of the paper (2112.04510) typesets them: the 0 after H is lowered and set small, the −1 after s and after Mpc raised, read from glyph positions 2026-09-24. The text as extracted reads: The source of this now long-standing discrepancy between direct and cosmological routes to determining H 0 remains unknown

  • Supports

    In the realm of the Hubble tension: a review of solutionsabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field

    The source reads: While no specific proposal makes a strong case for being highly likely or far better than all others

Claim 75 · checked 24 September 2026 · AI-assisted audit

Claim: That sentence is the reason this question is on this site rather than in a textbook: it is not a gap in public understanding, it is a gap in the field’s.

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.

SH0ES calls the source of the discrepancy unknown; the review says no proposal makes a strong case.

  • Supports

    A comprehensive measurement of the local value of the Hubble constant with 1 km/s/Mpc uncertainty from the Hubble Space Telescope and the SH0ES teamabstract, last sentence

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026

    The source reads: The source of this now long-standing discrepancy between direct and cosmological routes to determining H₀ remains unknown

    Notation restored: Subscript and superscripts restored as the arXiv version of the paper (2112.04510) typesets them: the 0 after H is lowered and set small, the −1 after s and after Mpc raised, read from glyph positions 2026-09-24. The text as extracted reads: The source of this now long-standing discrepancy between direct and cosmological routes to determining H 0 remains unknown

Claim 76 · checked 24 September 2026 · AI-assisted audit

Claim: What would settle it is more independent routes to the same number.

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 review calls for additional probes and for broadening the measurements.

Claim 77 · checked 24 September 2026 · AI-assisted audit

Claim: Gravitational-wave sirens, which measure distance directly from the physics of a merger without any ladder at all, are one such route:

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.

Corrected

24 September 2026. Previously: “Gravitational-wave sirens, which measure distance directly from the physics of a merger without any ladder at all, are the most promising:” "The most promising" was a ranking no cited source made. A 2018 forecast of two per cent from sirens within five years has not been met.

Claim 78 · checked 24 September 2026 · AI-assisted audit

Claim: the first, in 2017, gave a value consistent with both camps and an uncertainty far too wide to choose between 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.

  • Supports

    A gravitational-wave standard siren measurement of the Hubble constantabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: We determine the Hubble constant to be 70.0 (+12.0/−8.0) km s⁻¹ Mpc⁻¹ ... This is consistent with existing measurements (Planck Collaboration et al. 2016; Riess et al. 2016), while being completely independent of them

    Notation restored: Notation restored as the paper’s LaTeX abstract on arXiv (1710.05835) sets it, 70.0^{+12.0}_{-8.0} km s^{-1} Mpc^{-1}, read 2026-09-24; the uncertainty is written here as (+12.0/−8.0). The text as extracted reads: We determine the Hubble constant to be 70.0+12.0 −8.0 km s−1 Mpc−1 ... This is consistent with existing measurements (Planck Collaboration et al. 2016; Riess et al. 2016), while being completely independent of them

Later work looked for

arXiv and Crossref, 2018 on, "standard siren Hubble constant GWTC-3": the 2023 GWTC-3 analysis of 47 events gives 68 +12/−7 with GW170817, still far too wide to decide; page now cites it.

Claim 79 · checked 24 September 2026 · AI-assisted audit

Claim: There are not yet enough of 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.

  • Supports

    Constraints on the Cosmic Expansion History from GWTC-3section 6, Conclusions

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Astronomical observation · Measurement

    The source reads: using these 47 GW events, our results are still dominated by the systematic effects induced by the assumptions made about the GW source population. ... In the future, with significantly more both bright and dark sirens it will be possible to make robust measurements of H0

What this does not establish

Its combined value with GW170817 is 68, with an uncertainty of +12 and −7 or −8 (the arXiv abstract and PDF differ), far too wide to decide between 67 and 73.

Later work looked for

arXiv and Crossref, 2018 on, "standard siren Hubble constant GWTC-3": the 2023 GWTC-3 analysis of 47 events gives 68 +12/−7 with GW170817, still far too wide to decide; page now cites it.

Claim 80 · checked 24 September 2026 · AI-assisted audit

How it ends

Claim: How it ends

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

What a resolution would look like

Claim: What a resolution would look like

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

Claim: If it is a systematic, the fix will be dull and specific: a recalibration, a better treatment of one population of stars, and the two numbers will slide together over a few years.

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.

A possibility, in the section of the page that says so.

What this does not establish

A projection, not a finding. The review doubts a single error could do it; see the next sentence.

Claim 83 · checked 24 September 2026 · AI-assisted audit

Claim: It may take more than one:

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.

  • Supports

    In the realm of the Hubble tension: a review of solutionssection 2.2.3, Systematics

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field

    The source reads: it is challenging to devise a single error that would suffice and we are not aware of a specific proposal that is not ruled out by the data

Corrected

24 September 2026. Previously: “” Added: the sentence before implied one fix would do, and the cited review says no single proposed error survives the data.

Claim 84 · checked 24 September 2026 · AI-assisted audit

Claim: the 2021 review of the tension knew of no single proposed error that the data had not already ruled out.

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

    In the realm of the Hubble tension: a review of solutionssection 2.2.3, Systematics

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field

    The source reads: it is challenging to devise a single error that would suffice and we are not aware of a specific proposal that is not ruled out by the data

What this does not establish

As of 2021.

Claim 85 · checked 24 September 2026 · AI-assisted audit

Claim: If it is physics, it will show up in other places at once, because a change to the model moves more than one number.

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 review’s point that a solution must explain multiple observations, and that models which fix the Hubble constant often disagree with other probes.

  • Supports

    In the realm of the Hubble tension: a review of solutionsabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field

    The source reads: demands a hypothesis with enough rigor to explain multiple observations

  • Supports

    In the realm of the Hubble tension: a review of solutionssection 15, Summary and Conclusions

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field

    The source reads: these a priori successful cosmological models are often not in agreement with additional cosmological probes ... Moreover, the Hubble constant tension is alleviated due to an increase in the error bars of H0, rather than by an increase in the Hubble constant itself

Corrected

24 September 2026. Previously: “If it is physics, the change is to the early universe rather than to the nearby one, and it will show up in other places at once.” The cited review classifies late-time proposals (late dark energy, modified gravity) alongside early-time ones and names both among its best options; saying the change must be early was a side the review does not take.

Claim 86 · checked 24 September 2026 · AI-assisted audit

Claim: That is the useful property of this kind of tension.

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.

Claim 87 · checked 24 September 2026 · AI-assisted audit

Claim: A real crack is never local.

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.

A figure of speech for the sentence before, not a law.

Claim 88 · checked 24 September 2026 · AI-assisted audit

What was read