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Evidence record

What is the universe expanding into?

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.

  • A judgement, not a fact: 14
  • Source checked: 54
  • 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If something here is wrong, misquoted, out of date or unfair, write to support@unknownoceans.com and give the claim number, which does not change.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 question that the standard model answers by rejecting its premise: in general relativity expansion is distance growing between things, not motion into a surrounding space. The page then turns to what is open inside that answer: the expansion rate, the size and shape of the whole, the far future and the beginning.

  • The universe is expanding

    Established

    Galaxies recede in proportion to their distance, and the microwave background fits a universe that was once hot and dense and has cooled as it expanded. How fast it expands today is disputed; that it expands is not.

  • Expansion needs a space outside the universe to expand into

    Open

    The page rejects this. In general relativity expansion is the growth of distances between things, and needs no outside; whether anything lies beyond everything is not a question an observation can reach.

  • The universe has a centre and an edge

    Open

    A uniform expansion looks the same from every point, so nothing observed marks a centre. Whether the whole is finite is not known: searches for a universe that wraps around set only a floor under its size.

How the question is labelled

Claim: Cosmic expansion

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

Claim: Expansion

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

The question

Claim: The honest answer begins by rejecting the picture the question assumes.

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

The page’s own framing of its answer, which follows from the account of expanding space in claims 24 to 26.

  • Context

    Expanding space: the root of all evil?section 2.4

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

    The source reads: They illustrate that the universe does not expand into previously existing empty space; it consists of expanding space.

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

Claim: Expansion is not motion outward through space.

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

    Expanding space: the root of all evil?section 2.1

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

    The source reads: The distance between observers at rest with respect to the cosmic fluid increases with time.

  • Qualifies

    Expanding space: the root of all evil?section 2.1

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

    The source reads: We can imagine attaching a Minkowski frame to each point in the Hubble flow.

    Locally, the same paper says, the expansion can be read as ordinary motion: objects receding with a velocity proportional to distance. That is an approximation for regions much smaller than the Hubble radius, not a description of the whole.

What this does not establish

A statement about how general relativity describes the universe as a whole. Over small regions the expansion can be described as galaxies moving apart, and Francis and others say that picture is valid locally.

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

Claim: It is space itself growing between things.

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

    Expanding space: the root of all evil?section 2.1

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

    The source reads: Perhaps a better description, in simple terms, is to suggest that more space appeared

What this does not establish

Expanding space is a way of describing the mathematics, and Francis and others call the difference between space stretching and more space appearing "largely semantic". It is not a force acting on anything.

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

Claim: That resolves the question as asked, and leaves several harder ones standing.

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 its own structure: the premise is answered in the first section, and the open questions follow.

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

Claim: Hear that the universe is expanding and it is easy to picture an explosion: matter flying outward, an edge somewhere, empty space beyond it.

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

Corrected

24 September 2026. Previously: “Almost everyone who hears that the universe is expanding pictures an explosion: matter flying outward, an edge somewhere, empty space beyond it.” "Almost everyone" is a claim about what people believe, and no cited source measures it. Rewritten as the page addressing the reader.

Claim: That picture is wrong in a specific and interesting way, and understanding why is more rewarding than the question it replaces.

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.

That the explosion picture is wrong follows from claims 24 to 26; that the correction is rewarding is the page’s judgement.

  • Context

    Expanding space: the root of all evil?section 2.4

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

    The source reads: They illustrate that the universe does not expand into previously existing empty space; it consists of expanding space.

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

Why the question assumes too much

Claim: Why the question assumes too much

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

Distant galaxies are receding, and the further away, the faster

Claim: Distant galaxies are receding, and the further away, the faster

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

Every distance-ladder measurement since, including those on this page, is a measurement of this relation; the dispute is over its slope, not its existence.

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

Claim: Edwin Hubble reported in 1929 that galaxies recede at speeds roughly proportional to their distance.

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.

What this does not establish

Hubble’s paper was not read; the claim rests on Davis and Lineweaver’s account of it. Hubble converted redshifts into velocities; Davis and Lineweaver point out that in general relativity redshift is not a velocity in the special-relativistic sense.

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

Claim: A uniform expansion produces exactly that relation, and it produces it identically from every point, so no observer is at a centre and there does not have to be one.

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

    Expanding space: the root of all evil?section 2.4

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

    The source reads: They show how a homogeneous expansion inevitably results in velocity being proportional to distance, and also gives an intuition for how the expansion of the universe looks the same from every point in the universe.

What this does not establish

That the universe is uniform on large scales is an assumption of the model, the cosmological principle, and the observations are consistent with it. It is not a proof that no centre exists beyond what can be seen.

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

Claim: An explosion would have 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.

Follows from the picture set out in the opening: an explosion flies outward from a point, which is what a uniform expansion does not need (claim 12).

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

The early universe left a signature and we have measured it

Claim: The early universe left a signature and we have measured it

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 Measurement of Excess Antenna Temperature at 4080 Mc/sp. 420

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

    The source reads: we compute the remaining unaccounted-for antenna temperature to be 3.5° ± 1.0° K at 4080 Mc/s

  • 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: from times prior to 380 000 years after the Big Bang, defining the last-scattering surface observed via the CMB

Later work looked for

The microwave background has been measured continuously since; Planck 2018 is the full-mission result and nothing since disputes that the radiation is there.

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

Claim: What Penzias and Wilson reported in 1965 was an excess: 3.5 kelvin of antenna noise they could not account for, isotropic, unpolarised and free of seasonal variation.

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 Measurement of Excess Antenna Temperature at 4080 Mc/spp. 419–420

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

    The source reads: have yielded a value about 3.5° K higher than expected. This excess temperature is, within the limits of our observations, isotropic, unpolarized, and ... free from seasonal variations (July, 1964-April, 1965).

  • Supports

    A Measurement of Excess Antenna Temperature at 4080 Mc/sp. 420

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

    The source reads: we compute the remaining unaccounted-for antenna temperature to be 3.5° ± 1.0° K at 4080 Mc/s

What this does not establish

The figure carried an uncertainty of one kelvin, and "isotropic" and "unpolarised" were within the limits of their observations, which ran from July 1964 to April 1965.

Corrected

24 September 2026. Previously: “isotropic, unpolarised and the same all year.” The letter says "free from seasonal variations" over July 1964 to April 1965, ten months rather than a year.

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

Claim: They offered no explanation of their own, and pointed instead at the letter printed alongside theirs for a possible one.

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.

Their note added in proof does rule one explanation out, radio sources of known types, but proposes none.

  • Supports

    A Measurement of Excess Antenna Temperature at 4080 Mc/sp. 420

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

    The source reads: A possible explanation for the observed excess noise temperature is the one given by Dicke, Peebles, Roll, and Wilkinson (1965) in a companion letter in this issue.

Corrected

24 September 2026. Previously: “They offered no explanation, and pointed instead at the letter printed alongside theirs.” They did point to an explanation: the companion letter’s, which they call "a possible explanation". They offered none of their own.

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

Claim: That letter proposed black-body radiation left over from a hot, dense early universe and cooled by its expansion.

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.

Dicke, Peebles, Roll and Wilkinson present their conclusions as tentative, and their own radiometer had not yet produced a result.

  • Supports

    Cosmic black-body radiationp. 415

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

    The source reads: Could the universe have been filled with black-body radiation from this possible high-temperature state? If so, it is important to notice that as the universe expands the cosmological redshift would serve to adiabatically cool the radiation

  • Supports

    Cosmic black-body radiationp. 416, Conclusions

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

    The source reads: we tentatively assume that the measurements of Penzias and Wilson (1965) do indicate black-body radiation at 3.5° K

Corrected

24 September 2026. Previously: “That one said what it was: radiation from a hot dense early universe, left over from the moment the plasma recombined and space went transparent.” The letter proposes an interpretation and calls its conclusions tentative; it did not say what the signal was. The recombination epoch is the standard model’s dating, now in its own sentence (claim 18).

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

Claim: In the standard model the radiation dates from about 380,000 years after the Big Bang, when the plasma recombined and the universe went transparent.

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 parameterssection 8, Conclusions

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

    The source reads: the 6-parameter ΛCDM model provides an 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

    Eternal inflation and its implicationssection 1 (iii)

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

    The source reads: The cosmic background radiation was released about 300,000 years after the big bang, after the universe cooled enough so that the opaque plasma neutralized into a transparent gas.

  • Supports

    Cosmic black-body radiationFigure 1 caption

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

    The source reads: Matter remains in thermal equilibrium with the ... until the plasma recombines

What this does not establish

The date is a model value: it comes from fitting the standard cosmological model to the data. Guth’s 2007 review gives the older round figure of 300,000 years.

Corrected

24 September 2026. Previously: “” The recombination dating was attributed to the 1965 letter; it is now given as the standard model’s, with Planck’s figure.

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

Claim: The pattern of its tiny variations is now measured to extraordinary precision, and it encodes the composition, geometry and age of the universe.

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: baryon density Ωbh2 = 0.0224± 0.0001 ... The angular acoustic scale is measured to 0 .03 % precision

What this does not establish

The composition and age are inferred by fitting a model, and Planck calls the late-universe parameters model-dependent. The precision is the precision of that fit.

Later work looked for

Planck 2018 remains the reference full-sky measurement; a Crossref query for the Atacama Cosmology Telescope’s 2025 parameters did not return, and nothing else found changes it.

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

Claim: The age comes out at 13.80 billion years, give or take 23 million.

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 parametersTable 2, TT,TE,EE+lowE+lensing, 68 % limits

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

    The source reads: Age [Gyr] ... 13 .797± 0.023

    13.797 billion years rounds to 13.80; the uncertainty is 0.023 billion, which is 23 million years.

What this does not establish

The age is inferred within the standard cosmological model, and the uncertainty is a 68 per cent interval. A different model would give a different age.

Later work looked for

Crossref, 2024 on: nothing found that revises the Planck age; the ACT query did not return.

Corrected

24 September 2026. Previously: “The age comes out at 13.80 billion years, give or take about 20 million.” The cited Planck column gives 13.797 ± 0.023 billion years; 23 million is 15 per cent more than "about 20", outside the rounding an "about" allows.

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

Claim: The geometry is flat to within measurement error once the microwave background is combined with galaxy surveys,

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 7.3, eq. 47b

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

    The source reads: to give ΩK = 0.0007± 0.0019 (68 %, TT,TE,EE+lowE +lensing+BAO). (47b) The joint results suggests our Universe is spatially flat to a 1 σ accuracy of 0.2 %.

  • Supports

    Planck 2018 results. VI. Cosmological parameterssection 1

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

    The source reads: with the addition of baryon acoustic oscillation (BAO) measurements from galaxy surveys

What this does not establish

Flat to within the measurement means curvature smaller than about 0.2 per cent, not zero. A slightly curved universe is not ruled out.

Later work looked for

DESI DR2 combined with the microwave background also finds no significant curvature (cited on "Is the universe infinite?"); the page stands.

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

Claim: though Planck’s temperature and polarisation spectra on their own lean slightly closed, and adding its lensing measurement pulls them back toward flat.

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 7.3, eq. 46b

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

    The source reads: an apparent detection of curvature at well over 2 σ. The 99 % probability region for the TT,TE,EE +lowE result is −0.095 < ΩK <−0.007

  • Supports

    Planck 2018 results. VI. Cosmological parameterssection 7.3, eq. 47a

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

    The source reads: Closed models predict substantially higher lensing ... (which is consistent with a flat model) pulls parameters back into consistency with a spatially flat universe to well within 2σ

What this does not establish

Planck reports the pull toward a closed universe as not robust to how the polarisation likelihood is modelled, and traces it to the same features that drive other mild anomalies in its data.

Later work looked for

The pull has been argued to come from the likelihood and the curvature prior (Efstathiou and Gratton 2020, cited on "Is the universe infinite?"); the page says only that the spectra lean, which Planck reports.

Corrected

24 September 2026. Previously: “though the microwave background on its own leans slightly closed.” The lensing measurement is also microwave background data, and Planck reports that adding it pulls the result back to within two sigma of flat. The lean belongs to the temperature and polarisation spectra alone.

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

Expansion has no centre and needs no outside

Claim: Expansion has no centre and needs no outside

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

  • Supports

    Expanding space: the root of all evil?section 2.4

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

    The source reads: how the expansion of the universe looks the same from every point in the universe. They illustrate that the universe does not expand into previously existing empty space

What this does not establish

What general relativity describes; it assumes the universe is uniform on large scales. It says nothing about whether anything lies outside, only that expansion does not require it.

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

Claim: In general relativity the distance between observers at rest with respect to the matter filling the universe grows with time: they separate without moving through anything.

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

    Expanding space: the root of all evil?section 2.1

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

    The source reads: The distance between observers at rest with respect to the cosmic fluid increases with time.

What this does not establish

The observers are idealised ones at rest with respect to the cosmic fluid. Real galaxies, and we, also move through space: the microwave background shows our own motion, as the paper notes.

Corrected

24 September 2026. Previously: “General relativity describes the geometry of space intrinsically, distances between points can grow without those points moving through anything, and without the space being embedded in a larger space.” The cited paper states expanding space as the growth of distance between observers at rest in the cosmic fluid; it says nothing about intrinsic geometry or embedding. Narrowed to what it states.

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

Claim: The universe does not expand into previously existing empty space.

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

    Expanding space: the root of all evil?section 2.4

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

    The source reads: They illustrate that the universe does not expand into previously existing empty space; it consists of expanding space.

What this does not establish

What the standard description says. It cannot be confirmed by looking outside, because there is no outside to look at.

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

Claim: It consists of expanding space.

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

    Expanding space: the root of all evil?section 2.4

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

    The source reads: They illustrate that the universe does not expand into previously existing empty space; it consists of expanding space.

What this does not establish

Expanding space is a description of the mathematics, not a detectable substance; the next paragraph says how far it can be pushed.

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

Claim: How hard that picture can be leaned on is argued about among cosmologists, because expanding space is a framework and not a mechanism, and reading it as a force is where the confusion usually starts.

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.

Francis and others defend expanding space as a valid framework against critics who would drop it; the argument is about its use, not about the equations.

  • Supports

    Expanding space: the root of all evil?abstract

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

    The source reads: the concept of expanding space in explaining the increasing separation of galaxies has recently come under fire as a dangerous idea whose application leads to the development of confusion and the establishment of misconceptions

  • Supports

    Expanding space: the root of all evil?section 2.4

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

    The source reads: But using these analogies to visualise a mechanism like a frictional or viscous force is taking the analogy too far.

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

Claim: The geometry underneath the argument is not in dispute.

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

    Expanding space: the root of all evil?abstract

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

    The source reads: We also demonstrate how arguments against the concept in general have failed thus far, as they imbue expanding space with physical properties not consistent with the expectations of general relativity.

  • Supports

    Expanding space: the root of all evil?section 2.2, quoting Peacock (2006)

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

    The source reads: the total volume of a closed universe is a well-defined quantity that increases with time, so of course space is expanding.

What this does not establish

Both sides of the argument Francis and others describe work within general relativity; the dispute is over interpretation and teaching.

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

Numbers that refuse to agree

Claim: Numbers that refuse to agree

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

How fast it is expanding

Claim: How fast it is expanding

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

Claim: Two methods for measuring the current expansion rate disagree.

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

One of the two is not a direct measurement of today’s rate but a prediction from the early universe under the standard model. How large the disagreement is depends on which local measurement is used (claims 35 to 37).

Later work looked for

Crossref, 2024 on, "Hubble tension distance ladder", and the rival papers cited on "Why do two measurements of the universe disagree?": the Chicago-Carnegie program finds 70.39 and the Cepheid team disputes it; page updated.

Corrected

24 September 2026. Previously: “Two independent methods for measuring the current expansion rate disagree at a level that is hard to attribute to chance.” The significance is the Cepheid team’s figure, and another local team finds a value consistent with the standard model. The strength of the disagreement is now attributed rather than asserted.

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

Claim: Planck, working forward from the early universe under the standard model, gives 67.36 plus or minus 0.54 kilometres per second per megaparsec.

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 3.1, eq. 14

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

    The source reads: H₀ = (67.36± 0.54) km s⁻¹ Mpc⁻¹ (68 %, TT,TE,EE +lowE+lensing)

    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: H0 = (67.36± 0.54) km s−1Mpc−1 (68 %, TT,TE,EE +lowE+lensing)

  • 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

What this does not establish

A model-dependent inference, as Planck says, not a direct measurement of today’s rate.

Later work looked for

Crossref, 2024 on: nothing that replaces Planck’s value as the early-universe reference.

Corrected

24 September 2026. Previously: “Planck, working from the early universe, gives” Planck’s value is inferred assuming the standard model, which it calls model-dependent. That is the crux of the dispute and the reader needs it.

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

Claim: Cepheids and supernovae in the nearby universe give 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 Uncertaintyabstract

    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

The same team’s 2024 JWST cross-check gives 73.2 plus or minus 0.9 from the full HST set; the figure stands.

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

Claim: That team puts the gap at five sigma and reports no sign that measurement error or any of its analysis variations explains 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.

What this does not establish

The five sigma is the Cepheid team’s own figure, and only for the variations it considered.

Later work looked for

Crossref, 2024 on: a rival local measurement finds no tension (claim 36); the significance is attributed.

Corrected

24 September 2026. Previously: “The second team puts the gap at five sigma and reports finding no analysis choice that closes it.” Closer to the paper’s own words, which limit the claim to the variations it considered.

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

Claim: Not every local measurement agrees with it.

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 (σSN), based on the TRGB method alone

    Notation restored: The subscript, lost in PDF text extraction, restored from the arXiv PDF as rendered (v3, page 1), read 2026-09-24. The text as extracted reads: Our current best (highest precision) estimate is H0 = 70.39 ± 1.22 (stat) ± 1.33 (sys) ± 0.70 (σSN ), based on the TRGB method alone

  • Qualifies

    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 ΔH₀ ∼2.5 km s⁻¹ Mpc⁻¹ between the CCHP JWST program and the full HST sample is entirely consistent with differences in sample selection.

    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: We show that ∆H0 ∼2.5 km s−1 Mpc−1 between the CCHP JWST program and the full HST sample is entirely consistent with differences in sample selection.

Other readings

The Cepheid team argues the lower local value is a product of which supernovae were in the smaller sample, and that its own distances agree with the rival methods galaxy by galaxy.

Corrected

24 September 2026. Previously: “” The page reported the Cepheid team’s result as the local value. A rival team using a different calibration gets a lower one; the brief requires the disagreement to be reported with who holds each side.

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

Claim: The Chicago-Carnegie Hubble Program, calibrating the supernovae with red giant stars instead of Cepheids, gets 70.39, with a larger uncertainty, and reports no need for new physics.

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

    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: (1) Tip of the Red Giant Branch (TRGB) stars, (2) JAGB (J-Region Asymptotic Giant Branch) stars, and (3) Cepheids. ... Our current best (highest precision) estimate is H₀ = 70.39 ± 1.22 (stat) ± 1.33 (sys) ± 0.70 (σSN), based on the TRGB method alone

    Notation restored: The subscript, lost in PDF text extraction, restored from the arXiv PDF as rendered (v3, page 1), read 2026-09-24. The text as extracted reads: (1) Tip of the Red Giant Branch (TRGB) stars, (2) JAGB (J-Region Asymptotic Giant Branch) stars, and (3) Cepheids. ... Our current best (highest precision) estimate is H0 = 70.39 ± 1.22 (stat) ± 1.33 (sys) ± 0.70 (σSN ), based on the TRGB method alone

    The three parts add in quadrature to about 1.94, against 1.04 for the Cepheid result.

  • 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 results are consistent with the current standard ΛCDM model, ... without the need for the inclusion of additional new physics.

What this does not establish

The uncertainty is quoted in three parts, 1.22 statistical, 1.33 systematic and 0.70 from the supernovae, larger in total than the Cepheid result’s 1.04. The program also measures with a second kind of star, which gives lower values from fewer galaxies.

Later work looked for

The rival result itself, found by the currency search; it is the newest in the dispute cited here.

Corrected

24 September 2026. Previously: “” Added the rival measurement.

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

Claim: The Cepheid team answers that the difference comes from 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 ΔH₀ ∼2.5 km s⁻¹ Mpc⁻¹ between the CCHP JWST program and the full HST sample is entirely consistent with differences in sample selection.

    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: We show that ∆H0 ∼2.5 km s−1 Mpc−1 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 H0section 5, Conclusion

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

    The source reads: We show that different values found for H0 based solely on JWST can be traced to differences in the small samples of SN hosts (and their SNe) and anchors selected for early JWST observations.

    The paper names the anchor galaxies as well as the supernova hosts.

What this does not establish

The reply addresses the Chicago-Carnegie program’s earlier JWST subsample; the page does not settle which side is right.

Corrected

24 September 2026. Previously: “” Added the Cepheid team’s reply, so the dispute is reported from both sides.

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

Whether the universe is finite

Claim: Whether the universe is finite

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

Claim: A flat universe can be infinite in extent or finite with a non-trivial topology, like a shape that wraps around on itself.

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.

What this does not establish

What geometry permits. Which of these the universe is, if any, is what the rest of the passage says is unsettled.

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

Claim: Planck searched the microwave background for the matched circles such a shape would print on the sky and found none.

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

None at scales below the diameter of the last scattering surface. Circles from a larger shape would not fall on the visible sky at all.

Later work looked for

Crossref, 2023 on: the COMPACT collaboration (2023) reanalysed what circle searches constrain; the page now carries it (claim 43).

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

Claim: For a cubic torus, that puts the largest sphere fitting inside the cube the space repeats at a radius of more than 97 per cent of the distance to the surface of last scattering.

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

For the cubic torus only; for a slab-shaped space the same search gives 56 per cent. The fundamental domain is the cube that repeats to make the torus.

Later work looked for

Crossref, 2023 on: COMPACT (2023) shows the bound does not carry over to most other shapes; page updated (claim 43).

Corrected

24 September 2026. Previously: “Planck searched the microwave background for the matched circles such a shape would print on the sky and found none, which puts the smallest sphere that would fit inside a cubic torus at more than 97 per cent of the distance to the surface of last scattering.” The bound is on the largest sphere that fits inside the torus’s fundamental domain, and on its radius; "the smallest sphere that would fit inside" described a different quantity.

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

Claim: A lower bound on the size, not an answer, and only for the shapes tested:

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 search setting a floor with no ceiling, and from its having tested two shapes.

Corrected

24 September 2026. Previously: “A lower bound on the size, not an answer.” Planck’s bound was calculated for two shapes; COMPACT (2023) shows it does not transfer to most others.

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

Claim: later work found that in all but the simplest shapes the shortest loop around the universe can miss us and be shorter than the diameter of that surface by a factor of 2 to at least 6.

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.

What this does not establish

A calculation of what the absence of circles allows, for the orientable flat shapes. The loop through our own location is still bounded above 98.5 per cent of that diameter.

Corrected

24 September 2026. Previously: “” Added the COMPACT collaboration’s result, which limits how far Planck’s bound generalises.

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

Beyond the horizon

Claim: Beyond the horizon

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

What is beyond the observable universe

Claim: What is beyond the observable universe

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

Claim: We can only see out to the distance light has had time to travel, and in practice only as far as the surface where the universe went transparent.

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.

What this does not establish

Light is the limit named here; Davis and Lineweaver note the particle horizon proper lies beyond the last scattering surface.

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

Claim: Beyond that, the standard model assumes more of the same,

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

    Expanding space: the root of all evil?section 2.1

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

    The source reads: The adoption of the cosmological principle, in that the Universe is homogeneous and isotropic, restricts the form of the underlying geometry of the Universe

  • Qualifies

    Planck 2015 results. XVIII. Background geometry and topology of the universesection 7, Conclusions

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

    The source reads: Although the evidence thus far corroborates the conventional wisdom that we live in the simplest FLRW Universe, this is likely to be only an approximation vastly beyond the Hubble scale.

What this does not establish

An assumption of the model, not a finding. The Planck collaboration itself expects it to be only an approximation far beyond what we see.

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

Claim: and the assumption cannot be checked.

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

Follows from claim 46: nothing beyond the horizon can have sent us a signal to check it against.

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

Claim: Receding faster than light is not what puts a region out of reach, which is the point at which this usually goes wrong.

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.

What this does not establish

Within the general-relativistic model Davis and Lineweaver use; in it, what sets the reach of observation is the horizons, not the recession speed.

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

Claim: Everything beyond redshift 1.46 recedes superluminally,

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.

What this does not establish

The redshift is calculated for the model Davis and Lineweaver use, 30 per cent matter and 70 per cent dark energy; different parameters move it a little.

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

Claim: and such objects are observed routinely,

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

The 2004 count of hundreds is superseded: DESI DR2 alone lists over 1.2 million quasars beyond redshift 1.77; page updated.

Corrected

24 September 2026. Previously: “and hundreds of such galaxies have been observed,” "Hundreds" was Davis and Lineweaver’s count in 2004. It is out of date by four orders of magnitude (claim 53).

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

Claim: because light that starts out in a superluminal region can end up in a slower one and reach us:

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.

What this does not establish

How light behaves in the model Davis and Lineweaver use: it depends on the Hubble sphere receding faster than the photons just outside it.

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

Claim: one survey’s latest catalogue alone holds over 1.2 million quasars beyond redshift 1.77.

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.

What this does not establish

A count from one survey’s second data release, built for measuring baryon acoustic oscillations; it is not a census of all such objects.

Later work looked for

The newest count found; DESI DR2 is the latest release cited on this page.

Corrected

24 September 2026. Previously: “” Replaces the 2004 figure of hundreds with a current count from a source the page already cites elsewhere.

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

Claim: The limit that is permanent is the event horizon, a different boundary and a nearer one:

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.

What this does not establish

Most models consistent with the observations have an event horizon; one with no dark energy would not. Nearer means nearer than the particle horizon, the edge of what we can see.

Corrected

24 September 2026. Previously: “What is permanently beyond reach is whatever lies outside the event horizon, a different boundary and a nearer one.” Galaxies outside the event horizon are still visible by light they sent long ago, so "whatever lies outside" it is not beyond reach. What is out of reach is what happens there now (claim 55).

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

Claim: nothing that happens beyond it now will ever be seen from here, though galaxies beyond it are still visible by light they sent long ago.

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.

What this does not establish

Holds in models with an event horizon, which include the standard one with dark energy; the horizon’s distance depends on the model’s parameters.

Corrected

24 September 2026. Previously: “” Says what the event horizon limits, in the source’s terms.

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

What happens in the far future

Claim: What happens in the far future

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

Claim: The long-term fate depends on the behaviour of dark energy, which is not understood.

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

    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: the main ingredients of ΛCDM, namely inflation, dark energy, and dark matter are not understood at any fundamental level

  • Supports

    Phantom Energy: Dark Energy with w < -1 Causes a Cosmic Doomsdayabstract

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

    The source reads: Cosmologists have long wondered whether the Universe will ... re-collapse and end with a Big Crunch, or expand forever, becoming increasingly cold and empty.

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

Claim: If it is a true constant, expansion continues and the observable universe empties out.

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

    Rapidly descending dark energy and the end of cosmic expansionintroduction

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

    The source reads: dark energy takes the form of a positive cosmological constant, in which case the current period of accelerated expansion will endure indefinitely into the future

  • Supports

    Phantom Energy: Dark Energy with w < -1 Causes a Cosmic Doomsdaysecond page

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

    The source reads: galaxies disappear beyond the horizon, and the Universe becomes increasingly dark. Still, structures that are currently gravitationally bound, such as the Milky Way and perhaps the Local Group, remain unaffected.

What this does not establish

A prediction of the model, not an observation. Bound structures such as our own galaxy stay together; it is the view beyond them that empties.

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

Claim: If it is not a constant, other outcomes remain possible: bound structures torn apart if its density grows, or a recollapse if it decays below zero.

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

    Phantom Energy: Dark Energy with w < -1 Causes a Cosmic Doomsdayfirst page, on phantom energy; abstract

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

    The source reads: the energy density of phantom energy increases with time ... The phantom energy rips apart the Milky Way ... before the death of the Universe in a “Big Rip”

  • Supports

    Phantom Energy: Dark Energy with w < -1 Causes a Cosmic Doomsdaysecond page

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

    The source reads: if w < −1 persists, then the fate of the Universe is quite fantastic

  • Supports

    Rapidly descending dark energy and the end of cosmic expansionabstract

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

    The source reads: a scalar field ϕ evolving down a monotonically decreasing potential V(ϕ) that passes sufficiently below zero ... The currently observed accelerated expansion will cease; soon thereafter, expansion will come to end altogether; and the universe will pass into a phase of slow contraction.

What this does not establish

Scenarios in particular models: the tearing apart needs dark energy whose density grows, and the recollapse needs a field whose potential falls below zero. Neither is observed.

Corrected

24 September 2026. Previously: “If it changes with time, other outcomes (including a tearing apart of bound structures, or a recollapse) remain possible.” Uncited, and the condition was loose: Caldwell and others’ Big Rip needs a dark energy whose density grows, which a constant equation of state below minus one gives; the recollapse Andrei and others describe needs a field decaying below zero. Both papers are now cited and the conditions stated.

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

Claim: Which of those is live has moved recently.

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.

Introduces the DESI result and the corrections to it in claims 61 to 65.

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

Claim: The Dark Energy Spectroscopic Instrument finds its baryon acoustic measurements fit better with an equation of state that evolves than with a constant: preferred at 3.1 sigma combined with the microwave background, and between 2.8 and 4.2 sigma with supernovae added, depending on which supernova sample is used.

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 significances are the collaboration’s, and they come from combinations: DESI’s measurements on their own prefer evolving dark energy at 1.7 sigma in its Table VI. The upper end has since come down (claims 63 and 64).

Later work looked for

Crossref and arXiv, 2025 on, "evolving dark energy supernova DESI": DES’s recalibration (November 2025) and Union3.1 (January 2026) bring the supernova combinations to 3.2 to 3.4; page updated.

Corrected

24 September 2026. Previously: “preferred at 3.1 sigma against the microwave background,” The 3.1 sigma is for DESI and the microwave background combined, not DESI tested against it.

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

Claim: The collaboration states the alternative itself, which is an unknown systematic error in one or more of the data sets.

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

    DESI DR2 results. II. Measurements of baryon acoustic oscillations and cosmological constraintsabstract

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

    The source reads: Unless there is an unknown systematic error associated with one or more datasets, it is clear that ΛCDM is being challenged by the combination of DESI BAO with other measurements and that dynamical dark energy offers a possible solution.

Corrected

24 September 2026. Previously: “an unknown systematic error in one of the data sets.” The abstract says "one or more datasets".

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

Claim: Corrections to the supernova samples since have narrowed that range: a 2026 reanalysis puts all three at 3.2 to 3.4 sigma,

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

A preprint. The narrowing brought the low end up as well as the high end down, so the preference did not simply weaken.

Later work looked for

The newest result found in the currency search.

Corrected

24 September 2026. Previously: “” The page gave DESI’s March 2025 range as current. Recalibrations of all three supernova samples since have moved it.

Claim 63 · checked 24 September 2026 · AI-assisted audit

Claim: and the team behind the sample that gave 4.2 now reports 3.2, which it calls a weak preference.

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

    The Dark Energy Survey Supernova Program: A Reanalysis Of Cosmology Results And Evidence For Evolving Dark Energy With An Updated Type Ia Supernova Calibrationabstract

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

    The source reads: Our results hold a significance of 3.2σ, reduced from 4.2σ for DES-SN5YR, to reject the null hypothesis that the data are compatible with the cosmological constant. ... Using generally accepted thresholds for model preference, our updated data exhibits only a weak preference for evolving dark energy.

    Notation restored: The mathematical italic σ of the PDF text set as the ordinary letter, as the arXiv PDF renders it, read 2026-09-24. The text as extracted reads: Our results hold a significance of 3.2𝜎, reduced from 4.2𝜎 for DES-SN5YR, to reject the null hypothesis that the data are compatible with the cosmological constant. ... Using generally accepted thresholds for model preference, our updated data exhibits only a weak preference for evolving dark energy.

What this does not establish

The 3.2 combines the recalibrated supernovae with DESI and microwave background data from Planck, ACT and SPT, a slightly different combination from DESI’s.

Later work looked for

Union3.1 (January 2026) gives 3.4 for the same recalibrated sample with Planck alone.

Corrected

24 September 2026. Previously: “” Added the Dark Energy Survey’s own recalibration of the sample behind the 4.2.

Claim 64 · checked 24 September 2026 · AI-assisted audit

Claim: George Efstathiou has argued that a small offset between supernova samples could bring the most discrepant one into line with a constant.

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

    Evolving dark energy or supernovae systematics?abstract

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

    The source reads: A comparison of SN common to both the DES5Y and Pantheon+ compilations shows evidence for an offset of ∼ 0.04 mag. between low and high redshifts. Systematics of this order can bring the DES5Y sample into good agreement with the Planck ΛCDM cosmology and Pantheon+.

What this does not establish

The argument was made against DESI’s first-year results and the original supernova sample, before the recalibrations in claims 63 and 64; the Dark Energy Survey rejected it, and Efstathiou replies in the same paper.

Corrected

24 September 2026. Previously: “” The page reported the preference without the published case that it is a supernova calibration effect.

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

What happened at the beginning

Claim: What happened at the beginning

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

Claim: Our description runs backwards reliably to about a second, where nucleosynthesis begins, and then it stops.

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

The Particle Data Group review gives the extrapolation back to about one second, where the light elements began to form.

What this does not establish

"Stops" means detailed tracing stops. Inflation and the origin of matter are expected to have happened earlier; the review says there are no standard models for them.

Later work looked for

The August 2025 revision of the same chapter carries the same wording at section 24.6.

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

Claim: The Particle Data Group puts the boundary there and says why: nothing from the epochs before it, the quark-hadron transition or electroweak symmetry breaking, has left a relic anyone has identified, so cosmology cannot be traced in detail any earlier.

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

    Review of Particle Physics, chapter 24: Big Bang Nucleosynthesissection 24.6

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

    The source reads: BBN still marks the boundary between the established and the speculative in Big Bang cosmology. It might appear possible to push the boundary back to the quark-hadron transition

  • Supports

    Review of Particle Physics, chapter 24: Big Bang Nucleosynthesissection 24.6

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

    The source reads: or electroweak symmetry breaking

  • Supports

    Review of Particle Physics, chapter 24: Big Bang Nucleosynthesissection 24.6

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

    The source reads: however, so far no observable relics of these epochs have been identified, either theoretically or observationally. Thus, although the Standard Model provides a precise description of physics up to the Fermi scale, cosmology cannot be traced in detail before the BBN era.

Later work looked for

The August 2025 revision keeps the passage word for word.

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

Claim: “The Big Bang” names the earliest state we can describe, not an explanation of how it came to be.

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

The page’s reading of the term, following from the boundary the Particle Data Group draws (claim 68).

Claim 69 · checked 24 September 2026 · AI-assisted audit

Inflation, and what follows from it

Claim: Inflation, and what follows from it

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

Inflation, and what it implies

Claim: Inflation, and what it implies

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

Claim: A brief period of extremely rapid expansion in the first instants would explain the universe’s uniformity and flatness,

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

  • Supports

    Eternal inflation and its implicationssection 1 (iii) and (iv)

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

    The source reads: The degree of uniformity in the universe is startling. ... inflation takes over and stretches the

    Guth’s section 1 sets out the uniformity of the microwave background, and then the flatness problem, as successes of inflation.

What this does not establish

That inflation would explain these is what its proponents argue; Guth’s review is a case for it, not a neutral survey. It is proposed, and the specific mechanism is not known.

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

Claim: and the statistical pattern of fluctuations in the microwave background matches its predictions well.

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: The primordial fluctuations are consistent with Gaussian purely adiabatic scalar perturbations characterized by a power spectrum with a spectral index ns = 0.965± 0.004, ... with the predictions of slow-roll, single-field, inflation.

What this does not establish

Consistent with, not proof of: a match to inflation’s predictions does not rule out other origins for the same pattern.

Later work looked for

Crossref, 2024 on: nothing found that revises Planck’s spectral index or its consistency with slow-roll inflation.

Claim 73 · checked 24 September 2026 · AI-assisted audit

Claim: Planck finds the fluctuations consistent with slow-roll single-field inflation and the universe flat to high accuracy.

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: with the predictions of slow-roll, single-field, inflation. Combined with BAO, we find that the Universe is spatially flat to high accuracy

Later work looked for

Crossref, 2024 on: nothing found that changes it.

Claim 74 · checked 24 September 2026 · AI-assisted audit

Claim: Many versions of inflation imply that it never stops everywhere, producing regions beyond our horizon with potentially different properties.

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

    Eternal inflation and its implicationsabstract

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

    The source reads: The mechanisms that lead to eternal inflation in both new and chaotic models are described.

  • Supports

    Eternal inflation and its implicationssection 3

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

    The source reads: apparent laws of physics at low energies could differ dramatically

What this does not establish

A consequence of the models, not an observation. Different properties in other regions depend on combining eternal inflation with a theory, such as string theory’s landscape, that allows many vacua.

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

Claim: Guth, one of the physicists who first proposed inflation, calls those regions unobservable in the same paper that argues for them.

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

    Eternal inflation and its implicationsabstract

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

    The source reads: pocket universes produced by eternal inflation are unobservable, it is argued that eternal inflation has real consequences

  • Supports

    Eternal inflation and its implicationssection 1 and reference 1

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

    The source reads: Since the proposal of the inflationary model some 25 years ago [1–4] ... Guth, A H 1981

Corrected

24 September 2026. Previously: “Guth, who wrote the mechanism down,” Guth’s review credits the proposal of inflation to four papers, his own 1981 paper first. "Wrote the mechanism down" credited him alone, and eternal inflation itself was found by Steinhardt and Vilenkin.

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

Claim: The general framework has strong observational support.

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, resting on Planck’s results (claims 73 and 74). Guth, who proposed inflation, gives the same judgement as his opinion.

  • 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: with the predictions of slow-roll, single-field, inflation

  • Context

    Eternal inflation and its implicationssection 1

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

    The source reads: In my opinion, the evidence that our universe is the result of some form of ... is very solid.

What this does not establish

Planck also says inflation is not understood at any fundamental level, and consistency with its predictions is not a detection of it.

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

Claim: The specific models, and their multiverse implications, do not.

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 Guth’s own account: the other regions are unobservable (claim 76), and how to make predictions from them is unresolved.

  • Supports

    Eternal inflation and its implicationssection 3

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

    The source reads: we do not even know how to define probabilities

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

The question dissolves rather than resolves

Claim: The question dissolves rather than resolves

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 heading of the page’s own conclusion, argued in claims 80 to 82.

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

Claim: Asking what the universe expands into may be like asking what is north of the North Pole: a grammatically valid question built on a spatial intuition that does not apply.

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.

An analogy, offered as a possibility ("may be"). It follows from the account of expanding space in claims 24 to 26.

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

Claim: Expanding space is the staple of almost all cosmological teaching, and this is the answer that comes with 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

    Expanding space: the root of all evil?abstract

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

    The source reads: While it remains the staple of virtually all cosmological teaching, the concept of expanding space in explaining the increasing separation of galaxies has recently come under fire

  • Supports

    Expanding space: the root of all evil?section 2.4

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

    The source reads: They illustrate that the universe does not expand into previously existing empty space; it consists of expanding space.

What this does not establish

Francis and others’ description of teaching in 2007, not a survey of it. The same sentence records that the concept has been attacked.

Claim 81 · checked 24 September 2026 · AI-assisted audit

Claim: It is worth noticing that it is an answer about our concepts, not about the universe.

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

The page’s own reading: the answer reframes the question rather than reporting an observation of an outside.

Claim 82 · checked 24 September 2026 · AI-assisted audit

What was read