Old-school cosmological calculations

By Tushna Commissariat

Doing away with complex calculations? (CC-BY-2.0/Boaz Arad)

The next time you need to quickly convert the redshift of some distant cosmic object to parsecs or kilometres, and find that your laptop and phone have both run out of charge (the horror!), the “Paper-and-pencil cosmological calculator” might be just the thing for you. More of a chart than a “calculator”, the new table – that is based on the ΛCDM cosmological model of the universe – has been drawn up by Sergey Pilipenko from the Lebedev Physical Institute in Moscow. And here’s the best bit – all the parameters that Pilipenko has plugged into his table are from the latest Planck results unveiled last month.

The calculator allows you to calculate for redshifts from z<0.1 to z <20 and includes eight different cosmological parameters, including the Hubble constant, the age of the universe, size of the object being observed and of course, the redshift and the respective distance in megaparsecs (Mpc). As Pilipenko points out in the paper, “In order to use the calculator, one needs to find a known value on a respective vertical scale. All the other values are situated on the same horizontal level.” So as the name suggests, all you need is a copy of the chart, a pencil and maybe a ruler to navigate the rows and you can quickly convert those pesky redshift values into parsecs. Pilipenko has also been kind enough to make public the code he used to build his calculator – take a look here.

For those of you who do not regularly carry out redshift conversions and are wondering what all the fuss is about (and why Google can’t be used), the issue arises thanks to the fact that many of the parameters involved change depending on the model you are using at the time and on the most up-to-date values of the parameters, as well as the huge numbers involved. While there are many such calculators available on the Internet, this is by far the simplest one we have come across, and could serve as quite a handy tool for researchers.