73 of 74 people found the following review helpful:
5.0 out of 5 stars
history, contemporary observations and theory explained in words, January 11, 2008
This review is from: Dark Side of the Universe: Dark Matter, Dark Energy, and the Fate of the Cosmos (Hardcover)
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 expectations based on dark matter simmulations of galaxy formation.
Chapter 4 is about a possible dark matter candidate - MAssive Compact Halo Objects (MACHO) - which gravitational microlensing observations suggest can't comprise more than 20% of the dark matter halo in our Galaxy and hence can't account for the total amount of dark matter.
Chapter 5 is about another dark matter candidate - the neutrinos. Discussed are the experiments confirming the neutrino oscillations which show neutrinos have small masses. Constraints from cosmological observations of the microwave background fluctuations and recent surveys on the large scale structure show that if neutrinos are indeed only 3 types, they don't have enough mass to explain the necessary amount of dark matter in the Universe. The reader is introduced to the ideas of hot and cold dark matter of which only the latter is shown to produce enough large scale structure compatible with observations. The chapter concludes with Weakly Interacting Massive Particles (WIMPs) as viable candidates for dark matter and guesses of what these particles could be from highly speculative extensions of Standard model like Supersymmetry, Kaluza-Klein particles, axions and other blah blah blah ....
Chapter 6 is devoted to the MOdified Newtonian Dynamics (MOND) as an alternative to dark matter. The chapter starts with giving the complete list of observations that disagree with the cold dark matter simmulations. Then MOND is introduced, with its characteristic acceleration separating the Newtonian regime from the MOND regime. The successes of MOND are listed - the spectacular fit to rotation curves with only one fitting parameter, the Tully-Fisher relation - as well its discrepancy with the data from galaxy clusters and the recent observation of 'dark galaxy' in 2005.
Chapter 7 describes the numerous experimental collaborations searching for dark matter WIMPs through direct detection of nuclear recoils when a WIMP hits a nucleus or indirect gamma ray detection from WIMP annihilation. The expected crossections, types of detectors and experimental difficulties are listed. Mentioned is the controversial result of DAMA collaboration and some hints of WIMP annihilation, although inconclusive, from gamma ray observations across our Galaxy. The main proof of dark matter existence, its detection, has yet to come.
Chapter 8 is about the matter-energy content of the Universe, being constrained by the observational data from the cosmic microwave background(CMB). The idea of inflation was posed in the early 1980's to resolve the problem with the finely tunned matter density and the approximate isotropy of the microwave background. Inflation leads to flatness and to big part of the density in the Universe not in the form of baryons. These two stipulations were made before their experimental confirmation in 1990's when the COBE satelite measured the fluctuations in the microwave background. It turned out, the fluctuations in CMB are way too weak to lead to the currently observed large scale structure unless there is a big amount of dark matter uncoupled to baryons and photons. The latest data in CMB comes from the WMAP satelite launched in 2001. The first peak in CMB power spectrum constraints the spatial curvature of Universe which turns out to be flat. The heights and positions of the peaks in the power spectrum fix the ratio of baryonic to dark matter and the total amount of matter. The matter content from CMB is in agreement with the baryon density from the Big Bang nucleosynthesis theory.
Chapter 9 is about using type Ia supernovae to measure the expansion history of the Universe. The reader will learn about the different types of supernovae and why only type Ia can be used as a standard candle. Difficulties in calibrating the supernovae and making sure the supernova from the distant past have the same properties as the contemporary ones are emphasized. The supernova data shows the universe recently entered a period of accelerated expansion which seems to require a nonzero cosmological constant.
Chapter 10 discusses the historical evolution of our cosmological models and how the conflict with observational data, mainly the ages of stars, the large scale structure and the missing nearly 70% of the critical density, finally lead to the idea of including the dark energy in the equation. That term was corroborated later with the supernova results in 1998.
Chapter 11 mainly discusses the nature of the dark energy term and is highly speculative since we don't have a clue what it is and where it comes from. It could be vaccuum energy in the form of cosmological constant or time evolving dark energy in terms of quintessence and phantom fields. The coincidence 'problem', why is the dark energy density similar to the matter density at the current time, is pointed out. Possible crazy 'solutions' are the anthropic principle, multiverse, buble universes, oscillating universes blah blah blah ... The exact nature of the dark energy will determine the future fate of the Universe, be it Big Cool, Crunch, Bounce or Rip Off.
Chapter 12 describes the most contemporary experiments/collaborations and some future ones designed to further constraint the parameters in the standard cosmological model, LCDM. The latest detailed data from CMB contains some yet unexplained correlations in it which may be due to distortions in CMB when it passes through clusters on its way to us. Lyman alpha forest, baryon oscillations, weak gravitational lensing are just some of the few possible techniques mentioned to further constraint our understanding of Cosmos.
Help other customers find the most helpful reviews
Was this review helpful to you? Yes
No
34 of 34 people found the following review helpful:
5.0 out of 5 stars
An enlightening book about some dark subjects, May 4, 2007
This review is from: Dark Side of the Universe: Dark Matter, Dark Energy, and the Fate of the Cosmos (Hardcover)
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.
Help other customers find the most helpful reviews
Was this review helpful to you? Yes
No
25 of 25 people found the following review helpful:
5.0 out of 5 stars
Beautiful, Comprehensive Review of Modern Cosmological Thinking and Research, February 6, 2008
This review is from: Dark Side of the Universe: Dark Matter, Dark Energy, and the Fate of the Cosmos (Hardcover)
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.
Help other customers find the most helpful reviews
Was this review helpful to you? Yes
No
