ABSTRACT
When confronted by the elegance and simplicity of a physical law, we might be forgiven for overlooking the presence of a constant in the equation before us. Sometimes a physical constant might be imposed upon a law after experimental investigations—as in the case of the Newtonian constant of gravitation G. However, sometimes the reason for the addition of a constant to fundamental equations might seem to be less convincing. Einstein’s introduction of the cosmological constant into the field equations of the General Theory of Relativity (GTR) has often been criticised. The physicist de Sitter claimed in 1917 that the introduction of the constant into GTR ‘is somewhat artificial, and detracts from the simplicity and elegance’ of the original field equations, and recent writers, such as Abraham Pais and Stephen Hawking, emphasise the ad hoc character of the constant. 1 And Einstein himself is reported to have said that the constant was his greatest mistake—he had recommended getting rid of the constant in 1931. 2 In this chapter, we shall examine how the cosmological constant affected the development of GTR and assess the two criticisms above. I shall conclude that the introduction of the constant was neither ad hoc nor a blunder and furthermore that we can learn much about the status of fundamental laws from the history of the constant. We shall also find that the problem of the cosmological constant introduces us to another important area of debate within modern cosmology: does the universe obey a principle of anthropocentricity?
