Far out cosmology: Hubble constant confusion (Introduction)

by David Turell , Thursday, November 29, 2018, 22:37 (2184 days ago) @ David Turell

The current expansion rate of the universe, named for Ed Hubble since he discovered the expanding universe, is not corroborated by two studies:

https://gizmodo.com/expanding-universe-mystery-deepens-1830664922

"One currently unexplained cosmological mystery is the “Hubble tension,” where various measurements of the universe’s expansion seem to disagree. As the story surrounding this tension gets murkier, others have begun to come up with new ideas that could explain it.

"The universe is expanding; the space between galaxies is growing. A constant named after astronomer Edwin Hubble describes how quickly this expansion occurs. Scientists now have several methods for determining the value of Hubble’s constant, but these methods have produced two values that don’t agree. For some methods, which rely on using the light from supernova and pulsing stars called Cepheid variables to determine their changing distance, it appears that objects move away from the Earth 73 kilometers per second faster for every 3.26 million additional light-years, also called a megaparsec. For other measuring methods, which rely on the electromagnetic radiation that reaches us from the early universe called the cosmic microwave background, the value is around 67 kilometers per second per megaparsec.

"Experimental errors alone don’t seem to explain the discrepant values. Attempts to explain away the difference without new physics don’t seem to hold up to scrutiny. Even so, the difference between the values isn’t at the “five-sigma” level of experimental precision required to say that the values are truly discrepant.

"But the story has gotten murkier. Most recently, a new result from scientists running the Dark Energy Survey has muddied the waters. Using measurements from supernovae, they in fact measured a Hubble constant of 67.7 kilometers per second per megaparsec, closer to the early universe measurement.

***

"..two independent teams of theoretical physicists happened to release papers addressing this tension just after the DES result came out. Both propose tweaks to our understanding of the universe’s early history. One paper reduces the tension between the two values by modifying when the period of recombination—the era a few hundred thousand years after the Big Bang when the first neutral hydrogen atoms began to form—began and ended. Another introduces “early dark energy,” some force in charge of driving the universe apart during an earlier time that has since shut off.

"Physicists already believe there are two phases of the universe expanding—one right after the Big Bang when it expanded quickly, called inflation, and the current era. “What we are saying is something similar might have happened at another time in the history of the universe,” Vivian Poulin from Johns Hopkins University told Gizmodo.

"Both of the ideas are in their infancy—they’ve only been posted in the arXiv physics preprint server, meaning that they haven’t been vetted by peer review. Additionally, both came out too soon after the DES result to cite it—and if that work holds, the theorizing might be for naught. "

Comment: All the studies use certain estimates. The mystery will clear hen those estimates are more refined.