With DES-Dovekie supernovae, DESI DR2 and cosmic-chronometer data, the light-speed parameter ε is -0.096 with uncertainties of about +0.125 and -0.114.

The paper

The paper's details are OpenAlex's; the citation count is OpenAlex's, 18 Oct 2026. The line on the paper is machine-written, as noted under Why it matters.

Why it matters

Written by Claude (claude-sonnet-5-5) on 18 Oct 2026 from the paper's abstract (as the publisher's record at Crossref publishes it) and its OpenAlex record. Machine-written context to help a reader: it is not evidence, it moves no number, and it may be wrong. The quoted sentence is the claim; where it stands is computed from the record. If it misreads the paper, tell the stewards.

The story so far

1. 1

   What the authors did

   The authors fitted a one-parameter varying-speed-of-light model to DESI DR2 BAO data, 31 cosmic-chronometer H(z) points and supernova samples (DES-Dovekie, Pantheon-plus), leaving the sound horizon free with no CMB or distance-ladder prior.

   Machine-written from the paper's abstract, as noted under Why it matters.

2. 2

   What they found

   • Replacing DES-Dovekie with Pantheon-plus gives ε = -0.048 with uncertainties of +0.142 and -0.122.
   • The varying-speed-of-light model improves the minimum χ² by only 1.05 relative to flat ΛCDM and is penalised by both AIC and BIC.
   • Allowing spatial curvature changes the degeneracy directions but still gives ε consistent with zero.

   Machine-written from the paper's abstract, as noted under Why it matters.

3. 3

   What has been checked on Ecdysis

   Exuvia registered the claim on 18 October 2026, with a test written from the paper. No check has been filed yet.

What would check it

How far it has been checked

1. 1
   The object itself, checked againverification · not yet

   Not yet: re-run the paper's analysis on its own data, where the authors have published it.

2. 2
   New instances of the constructionreproduction · not yet

   Not yet: the same construction run afresh.

3. 3
   The designrobustness tests and arguments · not yet

   Nothing yet: change the method or the data and see whether it holds (a robustness test), or argue that the method does not test what the claim says.

How sure is the record?

Share this finding

Ready-made posts, written from the record. You post them yourself, from your own account; nothing is ever posted for anyone.

Click a post's text to select all of it. Both posts give the claim's standing on the record, and the longer one says what the checks show and what they do not; the wording changes when the record does. The longer post quotes the paper first, then gives the machine-written headline, marked as such; edit it as you like. To cite the claim, see Cite this claim.

What would prove it wrong

Refuted if an independent replication of the analysis, using the DES-Dovekie, DESI DR2 and H(z) data sets with the same C(z)=1+εz/(1+z) model and priors (including r_d∈[120,180] Mpc and analytically profiled supernova intercept), yields a best‑fit ε whose 68 % confidence interval does not overlap the quoted interval [−0.210,+0.029].

The test as Exuvia registered it on 18 Oct 2026, written from the paper's words.

The wider literature

Other claims from the same paper

• uncheckedUsing Pantheon-plus supernovae instead of DES-Dovekie, the fitted light-speed variation parameter ε is -0.048 (+0.142, -0.122), a value that includes zero.“Replacing DES-Dovekie by Pantheon-plus gives $$\epsilon =-0.048^{+0.142}_{-0.122}$$ ϵ = - 0 . 048 - 0.122 + 0.142 .”
• uncheckedAdding a varying-speed-of-light term lowers the best-fit chi-squared by only 1.05 versus flat ΛCDM, and AIC and BIC both penalise the extra parameter.“The VSL extension improves the minimum $$\chi ^2$$ χ 2 by only $$1.05$$ 1.05 relative to flat $$\Lambda \textrm{CDM}$$ Λ CDM , and is penalized by both AIC and BIC.”

Headlines are machine-written from the paper's abstract, or from the quote and the paper's title where no abstract is open; each claim's own words are quoted beneath its headline.