Appendix E - Historical milestones

Summary

This appendix contains a list of papers which, in the opinion of this author, played a crucial role in the development of inhomogeneous cosmological models. It must be stressed that, except for a few, the papers listed below have never been properly appreciated, and many of them are virtually unknown even today. The list is thus a call for historical justice (based on a personal assessment by this author) rather than a presentation of development of the field.

Lemaître (1933a) – the pioneering paper, and probably the most underappreciated one. The author introduced the Lemaître–Tolman model, and in addition presented or solved a few problems commonly associated now with names and papers younger by a whole generation. Examples: the definition of mass for a spherically symmetric perfect fluid, a proof that the Schwarzschild horizon is not a singularity (by a coordinate transformation to a system of freely falling observers), a preliminary statement of a singularity theorem illustrated by a Bianchi I model.

McVittie (1933) – presented a superposition of the Schwarzschild and FLRW metrics which is a perfect fluid solution. A remarkably bold and early entry, but the solution has still not been satisfactorily interpreted.

Dingle (1933) – a preliminary investigation of spherically symmetric shearfree perfect fluid solutions, later completed by Kustaanheimo and Qvist (1948). The paper is remarkable for the author's strong criticism of the cosmological principle and an explicit call for inhomogeneous models (see Appendix C).