The leftover glow from the Big Bang, as well as the galaxies that exist today, give us a way to measure the expanding Universe that’s very different from the standard cosmic distance ladder. Their results are mutually incompatible. Image credit: E.M. Huff, the SDSS-III team and the South Pole Telescope team; graphic by Zosia Rostomian.

New Dark Matter Physics Could Solve The Expanding Universe Controversy

Multiple teams of scientists can’t agree on how fast the Universe expands. Dark matter may unlock why.

There’s an enormous controversy in astrophysics today over how quickly the Universe is expanding. One camp of scientists, the same camp that won the Nobel Prize for discovering dark energy, measured the expansion rate to be 73 km/s/Mpc, with an uncertainty of only 2.4%. But a second method, based on the leftover relics from the Big Bang, reveals an answer that’s incompatibly lower at 67 km/s/Mpc, with an uncertainty of only 1%. It’s possible that one of the teams has an unidentified error that’s causing this discrepancy, but independent checks have failed to show any cracks in either analysis. Instead, new physics might be the culprit. If so, we just might have our first real clue to how dark matter might be detected.

The expanding Universe, full of galaxies and the complex structure we observe today, arose from a smaller, hotter, denser, more uniform state. Why the Universe expands at the rate it shows when you ask with different methods is hitherto unexplained. Image credit: C. Faucher-Giguère, A. Lidz, and L. Hernquist, Science 319, 5859 (47).

The expanding Universe has been one of the most important discoveries of the past 100 years, and it’s brought with it a revolution in how we conceive of the Universe. It was the key observation that led to the formulation of the Big Bang; it allowed…