{
  "id": "gr-qc/0508052",
  "version": "v2",
  "published": "2005-08-12T14:46:30.000Z",
  "updated": "2012-01-09T14:37:47.000Z",
  "title": "In an expanding universe, what doesn't expand?",
  "authors": [
    "Richard H. Price",
    "Joseph D. Romano"
  ],
  "comment": "8 pages, 9 eps figures",
  "categories": [
    "gr-qc"
  ],
  "abstract": "The expansion of the universe is often viewed as a uniform stretching of space that would affect compact objects, atoms and stars, as well as the separation of galaxies. One usually hears that bound systems do not take part in the general expansion, but a much more subtle question is whether bound systems expand partially. In this paper, a very definitive answer is given for a very simple system: a classical \"atom\" bound by electrical attraction. With a mathemical description appropriate for undergraduate physics majors, we show that this bound system either completely follows the cosmological expansion, or -- after initial transients -- completely ignores it. This \"all or nothing\" behavior can be understood with techniques of junior-level mechanics. Lastly, the simple description is shown to be a justifiable approximation of the relativistically correct formulation of the problem.",
  "revisions": [
    {
      "version": "v2",
      "updated": "2012-01-09T14:37:47.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "expanding universe",
      "affect compact objects",
      "undergraduate physics majors",
      "bound systems expand",
      "initial transients"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 8,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 689723,
      "adsabs": "2005gr.qc.....8052P"
    }
  }
}