{
  "title": "Gravity train models compared",
  "description": "One-way travel times through a straight tunnel in the Earth, one row per model and path: our closed-form calculations for a uniform Earth and for a constant-gravity approximation, using NASA's Earth Fact Sheet radius 6371.000 km and surface gravity 9.820 m/s^2, and three figures reported, not recomputed, from Alexander Klotz's 2013 preprint (arXiv:1308.1342v1), including 38 min 11 s through the center with a seismic Earth model. Idealized: no friction, no air, Earth not rotating. Retrieved 2026-10-31. License CC BY 4.0 (our calculations and arrangement; NASA values are public facts).",
  "license": "CC BY 4.0",
  "license_url": "https://creativecommons.org/licenses/by/4.0/",
  "creator": "Puzzles, Charts & Dilemmas",
  "page": "https://puzzleschartsanddilemmas.com/thought-experiments/gravity-train/",
  "derived_from": [
    "NASA NSSDCA, Earth Fact Sheet (last updated 2024-11-15), volumetric mean radius 6371.000 km and surface gravity (mean) 9.820 m/s^2, https://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html",
    "Alexander R. Klotz, The Gravity Tunnel in a Non-Uniform Earth, arXiv:1308.1342v1 (2013 preprint), figures reported only, https://arxiv.org/abs/1308.1342"
  ],
  "method": "Compiled by Puzzles, Charts & Dilemmas from the data listed",
  "data_credit": [
    "NASA Earth Fact Sheet; Klotz 2013 preprint, arXiv:1308.1342"
  ]
}