Magazine article Science News

The Past According to Planck: Cosmologists Got a Lot Right: New Analysis Confirms Basic Ideas about Universe's Properties, but Some Unsolved Puzzles Linger

Magazine article Science News

The Past According to Planck: Cosmologists Got a Lot Right: New Analysis Confirms Basic Ideas about Universe's Properties, but Some Unsolved Puzzles Linger

Article excerpt

A new analysis of the universe's first light has cosmologists simultaneously patting themselves on the back and scratching on their chalkboards. The results, obtained from the Planck satellite and posted online in February in a set of papers at arXiv.org, largely support the theoretical framework that cosmologists employ to describe the universe. But there are also some puzzling findings, hinted at in previous research, that could signal undiscovered physical phenomena.

"The old model of the universe is doing remarkably well," says Shaun Hotchkiss, a cosmologist at the University of Sussex in Brighton, England. "But everything that was anomalous in the past is still anomalous." The Planck results also have a lot to say about inflation, the theorized period just after the Big Bang in which the universe swelled rapidly.

Cosmologists can describe the universe reasonably well with a model based on six quantities, including the universe's expansion rate and the density of ordinary matter. The Planck mission has chimed in with four years of measurements of the cosmic microwave background, or CMB, the universe's first light. It was emitted about 380,000 years after the Big Bang.

The latest data support the standard cosmological model and pin down five of the six numbers with 1 percent precision, says Planck project scientist Charles Lawrence. Those numbers describe a universe that started with a brief episode of inflation and since has been guided by a combination of regular matter, an invisible substance called dark matter, and dark energy, which causes space to stretch apart at an ever-increasing rate.

Yet the results include discrepancies that also showed up in Planck's 2013 data release and other microwave background observations, particularly the number of galaxy clusters. Planck detects subtle temperature variations in the CMB, which reflect quantum fluctuations in the early universe that got amplified by inflation into regions of varying density. Over time, mass in the high-density regions should have clumped together to form intricate galaxy clusters. But Planck data suggest there should be more clusters than scientists observe. The tension warrants further study but not any new theories just yet, Hotchkiss says.

Physicists are also pondering the expansion rate of the universe, known as the Hubble constant. Planck data indicate that objects located a mega-parsec (about 3.3 million light-years) away from each other move apart at roughly 68 kilometers per second. …

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