Martin Rees- Just Six Numbers

The idea that the fundamental forces which govern our Universe and fundamental constants such as: the strength of gravity, the electric charge on an electron and the density of matter, dark matter and dark energy in the Universe have been  some sense finely tuned to allow for our existence has been explored in the  Just Six Numbers written by Martin Rees who is the current (2022) UK Astronomer Royal. In this book Rees makes the point that, if any of these six numbers were very different, then the Universe couldn’t exist in its current form.

Rees’s six numbers are:


(1)The number of spatial dimensions we live in – 3

(2) The relative strength of the electrostatic to the gravitational force between two protons – This is a  very large number approximately  1036

(3) The fraction of mass converted to energy when hydrogen is fused to form helium – approximately 0.007.

(4) The average matter density of the  Universe, rather than being expressed in kilogrammes per cubic metre, it is expressed in units where the critical density (10-26  kilogrammes per cubic metre) is equal to one – approximately 0.32.

(5) The  average dark energy density of the Universe, also expressed in units where the critical density is equal to one – 0.68.

(6) The final number is a measure of how tightly bound the large clusters and supercluster of galaxies are. On the scale used in Rees’s book it has the value 10-5.