Dark Side of the Universe: Dark Matter, Dark Energy, and the Fate of the Cosmos

This is a terrific astronomy/cosmology book with a focus on providing an overview and update on what is known and ( & not known) about dark matter and dark energy. It's a beautiful, large format book that is well laid out and printed on high quality paper with lots of beautifully drawn, textbook quality figures (drawn by James Symonds), data, and pictures, all at a bargain price. The book is well organized and comprehensive, and Nicolson writes clearly and concisely for the literate general reader, often throwing in helpful analogies. I am an engineer and astronomically literate, and I learned a lot from this book. Dark matter is invariably described as forming a 'halo' (ring) around a galaxy extending far beyond the visible stars. I knew from college physics that the motion of a particle inside a spherical shell of matter is completely unaffected by the gravity of the shell, because the gravitational pull from all the little pieces of mass in the shell cancel out everywhere inside. So prior to this book, I was always puzzled as to how a galactic dark matter 'halo', (supposedly) far outside the visible part of the galaxy, was able to flatten the rotation curve of visible stars in the galaxy? Nicolson is not adverse to including a simple equation now and then, and he does this in his clear explanation of how dark matter speeds up star rotation speeds in the outer parts of a galaxy. The equation shows the average rotational speed of a star about the galaxy center depends on the ratio (mass 'inside orbit'/radius of orbit). Hence to flatten galaxy velocity rotation profiles, it is only necessary that mass inside star orbits increase linearly with radius. This requires nothing more (Nicolson explains) than dark matter density that falls off as (1/radius^2), because the volume of a sphere increases as (radius^3). In other words flat galaxy velocity curves are not caused by the 'outside' halo of dark matter, but by an increasing density of dark matter toward the center of the galaxy. It is the dark matter through which the stars are orbiting, that is 'inside' their orbits, that speeds up their rotation. Only after reading this book did I understand this. There is the occasional lapse in the book, for example, the mass of a muon (page 59) is described as approximately 400 times that of an electron (it's closer to 200 times), and a surprising omission is that there is no figure showing measured galaxy velocity rotation curves, one of the strongest pieces of evidence supporting the existence of dark matter. But minor quibbles aside, this is an excellent book for those wanting to understand the latest research, data, and thinking in cosmology. Highly recommended.

This book is a detailed overview of the contemporary ideas in cosmology, the meandering history of their conception and development, and the experimental observations supporting and sometimes contradicting them including the most contemporary experiments and collaborations up to 2006 and the future experiments planned. The emphasis is on concepts and how astronomical observations support or refute theories, formulas are used very rarely, the narrative is illustrated with numerous beautiful diagrams, photographs and pictures from state of the art telescopes. Theoretical highly speculative ideas in cosmology are also given some discussion. Big part of the book would be accessible to anyone that had a general physics course, but it contains a wealth of detailed information tailored to people that actually would want to work in the area like physics students specializing in cosmology and astronomy students and they will be able to pick up much more from that book than laymen. I've read the book in 3 days but most of the material wasn't new to me, a beginner reader would probably need 1-2 weeks. At the end, the reader will gain a very clear conceptual understanding of the main picture in contemporary cosmology and which observations agree/disagree with it. I HIGHLY recommend this book before or during any course in cosmology, dark matter or dark energy. If you want to be more informed than your adviser, read that book :) Chapter 1 introduces the reader to general astronomy - types and lives of stars, galaxies, clusters - and a basic understanding of light spectrum and redshift necessary to understand astronomical observations. Chapter 2 is an introduction to general cosmology: the expanding Universe, Hubble time, redshift, microwave background. The author gives a very clear account of observations that support the current Big Bang theory. A very understandable short story of the different stages in the cosmic evolution is given, including nucleosynthesis and recombination. Chapter 3 discusses astronomical evidence from galaxies and clusters supporting the dark matter hypothesis. All main points are there from optical observations of Coma cluster in 1933, through the rotation curves of spiral galaxies obtained from radio emission of their neutral hydrogen clouds to the contemporary observations of X-ray emitting gas allowing to map the mass distribution in galaxy clusters and large eliptical galaxies and the most recent observations of weak gravitational lensing in clusters. Mentioned is the 'dark galaxy' of swirling hydrogen gas without stars in it which was observed in 2005. The author points out problems of the dark matter scenario - the observations of planetary nebulae in some eliptical galaxies in 2003 suggest they don't contain much dark matter, the inferred profiles of dark matter halos in many galaxies do not show the expected cusps at the center, and the observed number of small satelite galaxies in galaxies disagrees with the expectat

Iain Nicolson has done a wonderful job of presenting many of the facts and hypotheses about cosmology to the layman (and to the interested high school student). The book starts with some fundamentals of astronomy. We then proceed to a discussion of Big Bang cosmology. And we learn all about the Hubble expansion, as well as observed evolution of the visible universe, comparison of the time since the Big Bang to the lifetimes of the oldest stars. In addition, we're told about Big Bang nucleosynthesis (this is one topic I would have wanted to see discussed in more detail), and evidence of the Big Bang from the cosmic microwave background. After this, we learn about the existence of dark matter in spiral galaxies and galaxy clusters. But what's the dark matter made of? One possibility is "MACHOs," (MAssive Compact Halo Objects). However, the author explains that MACHOs alone can not account for the dark matter in our own galaxy, much less for the dark matter elsewhere. It turns out that we need to look for non-baryonic sources of dark matter. And that means "WIMPs," (Weakly-Interacting Massive Particles). It also means wondering about whether dark matter is all that cold. Next, we look at an interesting hypothesis: maybe Newtonian gravitation breaks down at high accelerations! Most physicists think this idea is wrong, and so far (as this book shows), the evidence for it is not all that favorable. That brings us back to looking for those WIMPs. And we see some of the ideas for detecting them including Super-Kamiokande (a water-based neutrino detector) and atmospheric Cerenkov telescopes. Nicolson's next topic is the inflationary model of cosmic expansion. And there is a section on the growth of cosmic microwave background density fluctuations, including results from the BOOMERanG balloon experiments and the WMAP mission. Now comes something relatively new and exciting. In the past ten years, we've seen that data from supernovae indicate that the expansion of our universe is accelerating. And that leads to a search for the driver of this expansion, which most folks call "dark energy." That in turn brings up questions about whether there needs to be a "multiverse" to explain what otherwise would be an unusual set of coincidences about the properties of our own visible universe. In addition, it means questions about the history of dark energy in our own universe. And there is a discussion of possible outcomes: eternal accelerating expansion (where gravity loses), a "Big Crunch," (where gravity wins) or a "Big Rip," (where the repulsive force destroys everything). I highly recommend this book.

DARK SIDE OF THE UNIVERSE: DARK MATTER, DARK ENERGY, AND THE FATE OF THE COSMOS is a pick not just for college-level science collections strong in astronomy, but for the general-interest lending library catering to non-scientist readers. It offers up a history and survey of how ideas about nature and the universe have developed, using key discoveries and scientific rationale to consider the evolution of theories on dark matter and describing how astronomers explore the remote cosmos to gain evidence supporting or refuting these theories. Any with an interest beyond the solar system will find this a fascinating expose, packed with color astronomy photos throughout.

We used to believe that the entire universe consisted of the kind of matter and energy that we were familiar with in our daily lives, but when astronomers actually tried to calculate the actual mass of the universe, they found that there was not enough observable mass to account for all the observed gravitational effects. How to account for this discrepancy? Dark matter! Dark matter? But what exactly is this stuff? Physicists have postulated several different forms of dark matter, with such whimsical acronyms as MACHOs (massive compact halo objects) and WIMPs (weakly interacting massive particles). Astronomers and physicists continue to debate the nature of dark matter, and Iain Nicolson brings us the debate and the science and people behind it in "Dark Side of the Universe: Dark Matter, Dark Energy, and the Fate of the Cosmos". While dark matter seemed to offer a stopgap solution to missing matter, it came up short in explaining the observed accelerating expansion of the universe. Such an acceleration requires a nearly flat universe with a mass+energy density equal to a certain critical density. Even with dark matter the density of the known universe is roughly one-quarter the critical density, implying the existence of an additional form or forms of as-yet-unknown energy, i.e. dark energy. Iain Nicolson explores all these ideas and more in a compelling narrative that is accessible to the intelligent lay reader without omitting important details. More knowledgeable readers will find some familiar material, but Nicolson brings his considerable experience and insight to the subject so that the familiar becomes wondrously new again and even the most up-to-date reader finishes the book with a greater understanding and appreciation for both the people and the science exploring some of the biggest questions known to humankind.