Cosmology - A very short introduction

Over winter break I've read this book by Peter Coles, so I am writing here what my impressions about it. First of all I must say I am again impressed by the good quality of the collection "A very short introduction..." by Oxford University Press. These books are able to provide a good introduction and overview on many different topics, providing just enough details to get an idea, and avoiding obscure jargon. That said let's talk business, the book.

It opens with an historic overview of our conception of the cosmos, and of the methods used by mankind to investigate it. Then it presents in one chapter the main ideas of general relativity: Eistein's revolution, the equivalence principle, the curvature of space and its connection with gravity, completing the chapter with a paragraph on black holes. Chapter 3 ("First principles") introduces the cosmological principles (i.e. the universe is assumed to be homogeneous and isotropic on large scales), and--by using the Friedmann models to unravel the evolution of the universe--the idea of singularities and the open/flat/closed universe. Chapter 4 ("The expanding universe") describes Hubble's law (v=H_0 * d) and its observation with the Doppler's (red)shift. Then he explains why the measurement of H_0 is difficult, and how one can infer from its value the age of the universe (around 15 billion years). Chapter 5 is fully dedicated to the Big Bang theory, and its experimental evidence from the cosmic microwave background. The CMB also provides insight for the understanding of nucleosynthesis and bariogenesis (when considered along with our knowledge of the standard model of particle physics...). In chapter 6 ("what's the matter with the universe?") Coles introduces the main role played by Omega in cosmology (Omega = "ratio of the actual density of matter in the universe to the critical value that marks the line dividing between eternal expansion and ultimate recollapse"). Omega and H_0 are not provided by the Friedmann's model or by the BigBang theory: equations work for whatever values they assume. Their determination is still nowadays a hot topic, related to old (cosmological constant) and new (dark energy) topics. The origin of "Cosmic structures" (chapter 7) or large-scale structures (i.e. how galaxies are distributed) can be investigated by studying the CMB precious insights about their formation. "So why is the microwave background not smooth after all? The answer is intimately connected to the origin of large-scale structures and, as ever in cosmology,gravity provides the connection." The concluding chapter 8 ("A theory of everything?") illustrates how crucial has been quantum mechanics in all this picture, and how the link between standard model and gravity is still missing.