Improved Hubble Data Provide Fresh Evidence for New Physics in the Universe

Here's the good news: Astronomers have made the most precise measurement to date of the rate at which the universe is expanding since the Big Bang.

Here's the possibly unsettling news: The new numbers remain at odds with independent measurements of the early universe's expansion, which could mean that there is something unknown about the makeup of the universe.

Is something unpredicted going on in the depths of space?

"The community is really grappling with understanding the meaning of this discrepancy," said Adam Riess, a Nobel Laureate and Bloomberg Distinguished Professor at Johns Hopkins University who leads a team of researchers using the Hubble Space Telescope to measure the expansion rate of the universe. He shared a Nobel Prize in 2011 for the discovery of the accelerating universe.

The team, which includes researchers from Hopkins and the Space Telescope Science Institute, has used the Hubble Space Telescope over the past six years to refine the measurements of the distances to galaxies, using stars as milepost markers. Those measurements are used to calculate how fast the universe expands with time, a value known as the Hubble constant.

Measurements made by the European Space Agency's Planck satellite, which maps the cosmic microwave background, predicted that the Hubble constant value should now be 67 kilometers per second per megaparsec (3.3 million light-years), and could be no higher than 69 kilometers per second per megaparsec. This means that for every 3.3 million light-years farther away a galaxy is from us, it is moving 67 kilometers per second faster. But Riess's team measured a value of 73 kilometers per second per megaparsec, indicating galaxies are moving at a faster rate than implied by observations of the early universe.

The Hubble data are so precise that astronomers cannot dismiss the gap between the two results as errors in any single measurement or method.

"Both results have been tested multiple ways," Riess explained. "Barring a series of unrelated mistakes, it is increasingly likely that this is not a bug but a feature of the universe."

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