Despite a new measurement, the debate over the universe’s expansion rages on
When it comes to the expansion rate of the universe, physicists have apparently agreed to disagree. Two types of measurements clash over how fast the cosmos is expanding (SN: 7/30/19). Now, a new estimate from the Atacama Cosmology Telescope, or ACT, further entrenches this disagreement. To tease out the properties of the universe, ACT observes light emitted shortly after the Big Bang, known as the cosmic microwave background. Those observations reveal that the universe is expanding a rate of about 67.9 kilometers per second for each megaparsec (about 3 million light-years), physicists report in two papers posted online and submitted to arXiv.org. The number aligns with that of an earlier cosmic microwave background experiment called Planck (SN: 7/24/18). “As an independent experiment, we see the same thing,” says cosmologist Simone Aiola of the Flatiron Institute in New York City. Located in the Atacama Desert in Chile, ACT observes the cosmic microwave background with...