‘Serious gap’ in cosmic expansion rate hints at new physicsOctober 9, 2018
Image copyrightNASAImage caption
Artwork: The expansion of the Universe has been accelerating in the billions of years since the Big Bang
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 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.
This is not very different to what people have gotten before measuring the Hubble constant.
Image copyrightJHUImage caption
Prof Riess shared in the 2011 Nobel Prize in Physics for his work on the expansion of the Universe
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.
The Hubble Constant obtained using these data is 66.9 kilometres per second per megaparsec.
A level of five sigma is usually considered the threshold for claiming a discovery.
However, Prof Riess said that at the three sigma level “this starts to get pretty serious I would say”.
Indeed, a recent measurement of time delays in quasars that is completely independent of the cosmic distance ladder data gets very similar results to Prof Riess’s late Universe Hubble Constant.
Another possibility is that dark energy behaves in a different way now compared with how it did in the early history of the cosmos.
“One promising way is if we don’t have dark matter be so perfectly ‘collision-less’ but it could interact with radiation in the early Universe,” Prof Riess said.