Full Idea
Physical necessity might turn out to be necessity in the highest degree. But that's a question which I don't wish to prejudge.
Gist of Idea
Physical necessity may be necessity in the highest degree
Source
Saul A. Kripke (Naming and Necessity lectures [1970], Lecture 2)
Book Reference
Kripke,Saul: 'Naming and Necessity' [Blackwell 1980], p.99
A Reaction
Presumably necessity 'in the highest degree' is 'metaphysical' necessity, but Kripke is a bit coy about that. This is the germ of modern scientific essentialism.