{
  "abstract": "Quantum-gravitational spacetime foam varying in space and in time imprints, respectively, a transverse phase decoherence and an achromatic, stochastic arrival-time jitter on light from distant sources. We show that the jitter modifies the first-order temporal coherence $g^{(1)}(τ)$ and hence the observed spectrum, providing a spectroscopic probe of the temporal variation, complementary to existing imaging-channel constraints on the spatial variation. In the dynamical-foam limit, where the foam decorrelates within the light's coherence time, the spectrum splits into a coherent line core suppressed by $e^{-σ_ϕ^2}$, with $σ_ϕ^2$ the variance of the foam-induced phase jitter, and an incoherent pedestal, yielding a spectral shape-distortion bound on the foam exponent $α$. Three probes follow: the outright survival of broadband flux, the fractional width of a spectral line, and a chromatic deficit across a broadband continuum. Applied to the MeV emission lines of GRB\\,221009A we obtain $α\\gtrsim 0.63$, a weak, lever-arm-dominated floor. For the broadband CMB the foam induces an $e^{-σ_ϕ^2(ν)}$ deficit ($σ_ϕ^2 \\propto ν^2$); a fit to the COBE/FIRAS monopole spectrum reaches $α\\gtrsim 0.52$ ($95\\%$ CL), and next-generation spectrometers reach only $α\\gtrsim 0.54$--$0.55$ (forecast), limited by the foam--temperature degeneracy. The pedestal-independent line-width and CMB bounds are floors below the holographic value $α= 2/3$, consistent with and excluding no part of the imaging window reported for GRB\\,221009A; only the conditional TeV survival bound ($α\\gtrsim0.74$), which holds only for near-Planck-refresh foam ($τ_{\\rm foam}\\lesssim4\\times10^{-28}$\\,s), would exclude it --- and, with it, the window.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2610.26766",
  "author_total": 3,
  "authors": [
    {
      "name": "A. G. Kim"
    },
    {
      "name": "P. E. Nugent"
    },
    {
      "name": "L. Wang"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/ayn4s15bt850b.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2610.26766",
  "fulltext_url": null,
  "id": "ayn4s15bt850b",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2610.26766",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "http://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "gr-qc"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2610.26766",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-19",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/ayn4s15bt850b.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:30:52Z",
      "native_id": "2610.26766",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2610.26766"
    }
  ],
  "subjects": [
    {
      "field": "physics",
      "origin": "arxiv:gr-qc",
      "subfield": "gravitation"
    }
  ],
  "title": "Spectroscopy as a Probe of Spacetime Foam",
  "title_text": "Spectroscopy as a Probe of Spacetime Foam",
  "type": "preprint",
  "updated_at": "2026-10-30T12:33:41Z",
  "url": "https://research.draconitic.com/paper/ayn4s15bt850b",
  "venue": "arXiv",
  "versions": []
}