'Serious gap' in cosmic expansion rate hints at new physics

From BBC - January 11, 2018

A mathematical discrepancy in the expansion rate of the Universe is now "pretty serious", and could point the way to a major discovery in physics, says a Nobel laureate.

The most recent results suggest the inconsistency is not going away.

Prof Adam Riess told BBC News that an unknown phenomenon, such as a new particle, might explain the deviation.

The difference is found when comparing precise measurements of the rate obtained in different ways.

However, the statistics are not yet at the threshold for claiming a discovery,

Prof Riess, who is based at Johns Hopkins University in Baltimore, Maryland, was one of three scientists who shared the 2011 Nobel Prize in Physics for discovering that the expansion rate of the Universe is accelerating.

This phenomenon was widely attributed to a mysterious, unexplained "dark energy" filling the cosmos.

Values holding

The unit of measurement used to describe the expansion is called the Hubble Constant, after 20th Century astronomer Edwin Hubble - after whom the orbiting space observatory is named.

Appropriately, Prof Riess has been using the Wide Field Camera 3 instrument on the Hubble telescope (installed during the last servicing mission to the iconic observatory) to help refine his measurements of the constant.

"The answer we get is 73.24. This is not very different to what people have gotten before measuring the Hubble constant. What is different is that the uncertainty has gotten quite a bit smaller," he said here at the 231st American Astronomical Society meeting in National Harbor, just outside Washington DC.

"The uncertainty has been dropping progressively over time, while the value has not been changing very much."

To calculate the Hubble Constant, Prof Riess and others use the "cosmic ladder" approach, which relies on known quantities - so-called "standard candles" - such as the brightness of certain types of supernova to calibrate distances across space.

However, a different approach uses a combination of the afterglow of the Big Bang, known as the Cosmic Microwave Background (CMB), as measured by the Planck spacecraft and a cosmological model known as Lambda-CDM.

The Hubble Constant obtained using these data is 66.9 kilometres per second per megaparsec. (A megaparsec is 3.26 million light-years, so it follows that cosmic expansion increases by 66.9km/second for every 3.26 million light-years we look further out into space).


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