Cosmic expansion overdrive
An old tension resurfaced in the summer quiet. The "SH0ES-Planck tension" was first in the news a year ago
, and this is about two cosmology experiments measuring how fast the universe is expanding and finding somewhat different results. Now they are joined in the controversy by three more experiments (and increasingly facepalm-worthy names).
In brief, the SH0ES experiment ("Supernovae H0 for the Equation of State") looks at stars whose brightness we can tell exactly and measures how fast they move apart as space grows larger. The rate that it finds is 10% faster than that by Planck, the high-profile satellite telescope which analyzes the cosmic microwave background - the first and oldest light, that shone when the universe was only 400,000 years old.
Now, a couple of months ago the Dark Energy Survey popped up and took sides. This telescope spent the last five years looking at hundreds of millions of galaxies, in an effort to find out more about dark energy (codename for said expansion of universe accelerating with time). It also announced its own measurement of the current expansion rate - and it is in the ballpark of Planck's results.
But then, in July the H0LiCOW experiment ("H0 Lenses in COSMOGRAIL’s Wellspring" - just don't ask, okay?) came with results of its own - and agreeing with the SH0ES' numbers.
Only days apart, a heavyweight in cosmological observations helpfully decided to settle the matter. That was none other than the legendary Hubble telescope itself. It turns out that all this time its people had been preparing their own measurement. And, obligingly, its result falls between
the numbers of the other two teams...
Some physicists (and particularly some media outlets) see adventure in this "tension". The conservative view however is that the distances and times involved in such measurements are large enough to justify uncertainties and miscalculations, and that the numbers might easily converge a few more telescopes down the road.