How Fast Is the Universe Growing? The Measurement Dispute ✛ ✦
Bread baking offers an unexpected clue for cosmology. To find out how fast dough rises, you can measure its height with a ruler or calculate it from the temperature and properties of the yeast. So it is with the expansion of the universe: one method relies on observing actual galaxies and stellar explosions, determining how fast they're receding. Another analyzes the ancient light that cooled over 13.8 billion years, and computes the expected expansion from the cosmological 'recipe.' The result: 73 kilometers per second per 3 million light-years versus 67.
A 9% difference seems small, but the statistical odds that the methods agree are negligible — less than one in a million. Even after checking with the latest James Webb Telescope, the discrepancy persists. The cosmic 'oven' clearly works differently than we thought: maybe the dough rose faster at first and then slowed down? Or hidden dark energy and dark matter have unexpected properties.
Solving this could rewrite textbooks.
At one point, estimates of the expansion rate differed by a factor of two: some scientists gave 50, others 100 km/s/Mpc. It was the Hubble Space Telescope that helped refine the number.