Caption: E.A. Milne (1896--1950) (see also E.A. Milne (1896--1950): Biography) was an important 20th century cosmologist.

E.A. Milne originated the term cosmological principle in 1935 (Cormac O'Raifeartaigh, et al., 2017, p. 29) though the concept goes back to Isaac Newton (1643--1727) in Principia (1687) and maybe earlier (Wikipedia: Cosmological principle: Origin). Albert Einstein (1879--1955) used the cosmological principle (as a vastly simplifying assumption without using the term) in formulating early general relativistic cosmology and in his Einstein universe (presented 1917).

Of course, E.A. Milne (1896--1950) and other early users of the cosmological principle did NOT have modern evidence for it. For them, it was a vastly simplifying assumption for research in cosmology.

Factoids:

1. The photograph shown here of E.A. Milne was taken in 1939 by famous astronomer Subrahmanyan Chandrasekhar (1910--1995).

2. Milne in 1935 was the proposer of what is now called the Milne universe (AKA empty universe). In the Milne universe the cosmic scale factor increases linearly with cosmic time: i.e., a(t) = constant*t, where t is cosmic time (see Wikipedia: Milne model: Milne metric). So there is NO acceleration NOR deceleration of the expansion of the universe.

3. The E.A. Milne Centre for Astrophysics at the University of Hull (in Kingston upon Hull (usually called just Hull), East Riding of Yorkshire, England) was named in E.A. Milne's honor. He was born in Hull.

4. E.A. Milne would NOT have known poet Philip Larkin (1922--1985), who worked 1955--1985 at the University of Hull. But Philip Larkin was a friend of astronomer Alex Dalgarno (1928--2015) whom yours truly occasionaly used to see at Harvard-Smithsonian Center for Astrophysics (CfA) in 1991--1993. So yours truly has 2 degrees of separation to Philip Larkin and, since Alex Dalgarno certainly had contacts with Chandrasekhar, 3 degrees of separation to E.A. Milne.

5. E.A. Milne is NOT a relation of A.A. Milne (1882--1956), but one has to believe that he was amused by the similarity of their professional names.

6. Now what is cosmological principle and cosmological principle size scale?