24 OCTOBER 1992, Page 29

Sheer ignorance

Sir: In his review of Julian Critchley's book (Books, 19 September), Alan Clark wrote:

'critical mass' — a nice analogy from physics (or is it astronomy?) for something that is on the point of either accelerating beyond the speed of light or disappearing into a black hole. [My emphasis]

It is symptomatic of the general igno- rance of science that this was allowed to pass. As everyone should know, critical mass is that required for nuclear fission to take place. Speeds involving accelerations past the speed of light are generally thought to have been ruled out by Albert Einstein.

Marc Read

Balliol College, Oxford