{
  "id": 8922569,
  "title": "Einstein’s equivalence principle put to two new tests",
  "url": "https://urgent.news/2026/09/21/einsteins-equivalence-principle-put-to-two-new-tests",
  "topic": "science",
  "section": "Science",
  "published": "2026-09-21T13:00:49.000Z",
  "source": {
    "name": "Physics World",
    "slug": "physics-world",
    "url": "https://physicsworld.com/a/einsteins-equivalence-principle-put-to-two-new-tests/"
  },
  "original_language": "en",
  "account": "Scientists have conducted two new tests of Albert Einstein's equivalence principle, which is a cornerstone of his general theory of relativity. The principle states that all objects fall at the same rate regardless of their mass or composition.\n\nThe first test was performed on the China Space Station, using a cold atom interferometer to measure the acceleration of two different isotopes of rubidium. The researchers found that the difference in the acceleration between the two isotopes was extremely small, with an uncertainty of 2.8 x 10^-8. This test is the most precise to date, and could help refine our understanding of general relativity.\n\nIn a separate study conducted on Earth, physicists used a cold atom interferometer to measure the quantum phase of an object in freefall. They confirmed that the effect of gravity on the object's quantum phase is consistent with the predictions of the equivalence principle. This research demonstrates that the principle holds not only in the macroscopic world, but also in the quantum realm.",
  "summary": "The theory of general relativity still holds, according to new space-based and laboratory experiments The post Einstein’s equivalence principle put to two new tests appeared first on Physics World .",
  "key_points": [
    "Einstein's equivalence principle tested in two new experiments",
    "First test on China Space Station with rubidium isotopes",
    "Second study on Earth confirms principle in quantum realm"
  ],
  "editors_take": null,
  "illustration": null,
  "coverage": {
    "outlets": 1,
    "also_reported_by": []
  },
  "ai_generated": true,
  "disclaimer": "Summaries, key points and the editor’s take are written by software from other outlets’ reporting and may contain errors — always check the linked original."
}