{
  "annotation_id": "f87757dc-9748-4334-a950-18d9095ec271",
  "date_created": "2026-03-02T18:01:07.598000Z",
  "date_modified": "2026-03-02T18:01:07.598000Z",
  "file_hash": "72208ef4765c34854fadbb1e12f28ffe9dcb4fd5e2f59a083333e0a623e787ed",
  "private": false,
  "record": {
    "abstract": "One of the questions in the cosmology courses is the cooling mechanism of\ncosmic fluid during it expansion according to classical concepts of the\nthermodynamics. In this short pedagogical paper, we quote the questions and\ngive a natural approach dealing with this problem by measuring the dispersion\nvelocity of the particles in the cosmic fluid by a comoving observer. We show\nthat the thermal motion of the particles in the cosmic fluid deviates from the\nHubble flow and follows the geodesics governed by the gravity of the\nhomogeneous universe. The dynamics of the \"thermal peculiar velocity\" of the\nparticles leads in an expanding universe, momentum of the particles relax by\nthe inverse of the expansion factor and the result is losing the energy of\nparticles, hence cooling the universe.",
    "arxiv_id": "physics/0603087",
    "authors": [
      "Sohrab Rahvar"
    ],
    "categories": [
      "physics.ed-ph",
      "astro-ph"
    ],
    "title": "Cooling in the Universe",
    "url": "https://arxiv.org/abs/physics/0603087"
  },
  "schema_id": "dorsal/arxiv",
  "source": {
    "execution_id": "727fa928-0081-4285-aa80-299962a1009d",
    "id": "arXiv Dataset IDs",
    "type": "Model",
    "variant": "snapshot-2026-03-01",
    "version": "0.1.0"
  },
  "user_id": 1000002
}