On the Renormalisation Group Explanation of Universality

It is commonly claimed, both by physicists and philosophers that the universality of critical phenomena is explained through particular applications of the Renormalisation Group (RG). This paper has three aims: (i) to clarify the nature of the explanation of universality; (ii) to discuss the physics of such renormalisation group explanations; (iii) to examine the extent to which universality is thus explained. The derivation of critical exponents proceeds via a real-space or a field-theoretic approach to the RG. Following Mainwood (2006) I argue that these approaches ought to be distinguished: while the real-space approach fails adequately to explain universality, the field-theoretic approach succeeds in the satisfaction of this goal