{
  "abstract": "We review the conceptual and theoretical status of twin-universe models, from Sakharov's early ideas on baryogenesis, CPT symmetry, and reversed arrows of time to recent quantum-cosmological scenarios involving pair-created entangled universes. Particular attention is given to the distinction between Sakharov-type cosmological symmetry, modern bimetric theories of gravity, and speculative models involving negative mass sectors. We summarize the main consistency conditions faced by bimetric gravity, including the Boulware-Deser ghost, Higuchi-type bounds, covariant conservation laws, and no-go results for positive- and negative-mass sectors. We then examine the Janus cosmological model and related black-hole replacement proposals, emphasizing the difference between heuristic twin-universe narratives and fully specified relativistic field theories. We argue that while twin-universe ideas remain a fertile framework for questions about the arrow of time, matter-antimatter asymmetry, and the quantum origin of the universe, models combining bimetric gravity, negative mass, dark-sector phenomenology, and alternatives to Kerr black holes face a substantial burden of mathematical and observational proof.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": "Journal reference: Inference Vol. 8, NO. 4 / September 2026",
  "arxiv": "2609.26834",
  "author_total": 1,
  "authors": [
    {
      "name": "Jean-Pierre Luminet"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/dy0wmbbmk2xzv.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.26834",
  "fulltext_url": null,
  "id": "dy0wmbbmk2xzv",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.26834",
  "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"
    ],
    [
      "arxiv",
      "physics.gen-ph"
    ],
    [
      "openalex",
      "3103|Cosmology and Gravitation Theories"
    ]
  ],
  "openalex": "W7214405934",
  "pdf_url": "https://arxiv.org/pdf/2609.26834",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-02",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/dy0wmbbmk2xzv.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:26:45Z",
      "native_id": "2609.26834",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.26834"
    }
  ],
  "subjects": [
    {
      "field": "physics",
      "origin": "arxiv:gr-qc",
      "subfield": "gravitation"
    }
  ],
  "title": "Twin Universes and Bimetric Gravity: From Sakharov's Cosmological Symmetry to Modern Speculations on Negative Mass",
  "title_text": "Twin Universes and Bimetric Gravity: From Sakharov's Cosmological Symmetry to Modern Speculations on Negative Mass",
  "type": "preprint",
  "updated_at": "2026-10-30T12:26:45Z",
  "url": "https://research.draconitic.com/paper/dy0wmbbmk2xzv",
  "venue": "arXiv",
  "versions": []
}