I was a little bemused to read this article by Stephen Battersby in NewScientist (8 December 2018, paywall) on the latest refinement of the coordinate system used by astronomers and others based on black holes:
To chart our place in the universe, astronomers have looked billions of light years away, to some of the most extraordinary objects in the cosmos: quasars. These intense beacons of light surrounding black holes in distant galaxies are being used to fix physical positions back here in the solar system. And not only will they help guide our travels to distant worlds, they will also help us learn more about our own. …
… in the 1990s, astronomers took a giant leap. Rather than relying on stars mere hundreds of light years away, they decided to look billions of light years away instead. Objects that distant don’t shift their position in the sky we see very fast, which made them ideal candidates as reference points. But to be clearly visible from so far away, they have to be bright, and the brightest beacons we know are quasars: the sites where supermassive black holes suck matter in and fire radiation out. A side benefit of using such heavy markers is that they don’t get pushed around easily. Being billions of times the mass of the sun, supermassive black holes tend to stay put at the centre of their galaxies.
What’s my problem? The Universe is allegedly continually expanding. That really renders attempts to absolutely establish position a bit of an exercise in futility for those of us who refuse to operate with error bars. (An error bar refers to the uncertainty of some measurement, the plus/minus of a given measured value.)
And, I’m sure, this coordinate system is nifty enough that it doesn’t really matter. It just strikes my funny bone a little oddly….
