Status Updates From Physical Cosmology (Princet...

Completed Chapter 7: "The History of the Universe: Scenarios."

Completed Chapter VI: "A Child's Garden of Cosmological Models."

Completed Chapter V: "The Cosmic Microwave Background and the Primeval Fireball Hypothesis."

Completed Chapter 4: "The Mean Mass Density of the Universe."

Completed Chapter 3: "Hubble's Constant and the Cosmic Time Scale."

Completed Chapter 2: "Homogeniety and Isotrophy of the Universe."

Completed Chapter 1: "The Golden Age of Cosmology 1912-1950,"

Completed all front works, forewords, prefaces, and Introduction

The Primeval Fireball hypothesis is as well established as any of the conventional tenets of cosmology, including the hypothesis of the expansion of the Universe. This is not to say that either hypothesis is valid beyond reasonable doubt, or even to deny that there are clouds on the horizon in either case, only that both have appreciable observational support and are reasonable, fertile bases for further discussion.

Methodically going through possible explanations for the extra mass apparently present in gravitationally bound clusters of galaxies, Peebles considers hydrogen snow. The problem is that it would evaporate if it weren't in large chunks, and a calculation shows they'd in fact need to be at least 10 km in diameter.

I just can't get those giant intergalactic hydrogen snowballs out of my mind...

As is often the case this brilliant trick was "discovered" a number of times. Gunn and Peterson had the good fortune to have made the suggestion at the right time and place, at Caltech, when Schmidt had just obtained the spectrum of 3C9 in which for the first time one could see the Ly α emission line, and they were thus able to apply the test and make people pay attention to it. For this reason it bears their names.

In cosmology the reliance on physical simplicity, pure thought and revealed knowledge is carried well beyond the fringe because we have so little else to go on. By this desperate course we have arrived at a few simple pictures of what the Universe may be like.