In cosmology there is a number, called Hubble's Constant. It's named after Edwin Hubble, the man who first realised that the universe is expanding. The units don't matter but generally, the smaller the value, the older and bigger the universe is.
Hubble put the value at 500, but then with the equipment at his disposal he had no way of understanding just how big the universe is. Over the years the value has been worked downwards and until recently the accepted value was somewhere around 70.
The value relies on an understanding of a certain type of star, the Cepheid Variable and new data on these has led to a revaluing of the constant.
The proposed new value of Hubble's Constant is ... 42. Maybe Douglas Adams knew something we don't.
Had he lived, Douglas Adams would have been 60 today. And I think he would have been rather pleased.