by Lawrence Krauss, Basic Books, 04650337402.
Cosmology has a lot going for it at the moment. Unprecedented amounts of data characterizing the universe at almost every possible energy and lengthscale make it one of the richest scientific fields around. Theorists scramble to explain all of the disparate results, while experimentalists and observers push the limits of what, only a few years ago, was not thought possible. In the middle of all this activity, Lawrence Krauss’s book Quintessence(a re-edition of his 1989 Fifth Essence) arrives to assess what is going on.
There is a growing trend in astrophysical and particle cosmology to believe (or at least sell the idea) that cosmology is “solved”. Again and again researchers in the field say something like: “things are finally falling into place”,so that we now have a standard model for structure formation. Often this represents a very theoretical and prejudiced view in selecting which data to believe.
Krauss himself embraces the latest high-redshift supernova results and consequent evidence for a cosmological constant as a confirmation of the “new standard cosmological model” that he developed with collaborators in the mid-1980s. He is not alone in doing this, but such an attitude seriously compromises the evolution of the field.
It is the glaring inconsistencies and the conceptually inexplicable fixes that we should be trying to tackle. For example, we assume that the universe is homogeneous (and we know that the cosmic microwave background is very smooth), but when we look atthe distribution of luminous matter it is strongly clustered as far as we can see; we believe that galaxies follow the underlying distribution of mass, but when we try to compare catalogues of different galaxies we end up having to invoke biasing mechanisms to make them all consistent.
My view is that cosmology is opening up and complexifying, not closing down and focusing on an existing component theory. Having declared my prejudices when starting this book, the truth is that I enjoyed it a lot. Although Krauss does try to oversell the inflationary cosmology and the derived cold dark matter scenario, this theme does not dominate the narrative. He does a great job of explaining the existence of dark matter, critically assessing the different pieces of experimental evidence and ensuring that he can relate these results with understandable physical principles. Particularly impressive is his description of the cosmic virial theorem (relating the kinematics of systems of gravitating bodies with the overall underlying mass) and his careful attempts to explain freezeout and relic abundances.
Many of the fundamental concepts needed in contemporary cosmology are outlined in the book and I see it as a great source of explanations for a wider audience. It was inevitable that this book would be revised. When Krauss wrote The Fifth Essenceat the end of the 1980s, it was at the end of a decade of fruitless searches for cosmological relics (he relates the story of the “Cabrera Monopole”, which was never properly explained away).
The search for dark matter in the universe really took off in the 1990s, with bolometric and scintillation direct detection experiments being set up all over the world, the microlensing searches producing arguable evidence for clumped baryonic dark matter in our halo and the new weak lensing experiments mapping out the dark mass in clusters. Krauss systematically goes through these different technological advances, explaining why they happened and what scientific returns to expect. I particularly liked his description of the use of bolometric detectors in direct detection experiments, and his clear explanation of the phonon/ionization method used by the CDMS experiments at Berkeley. It conveys the beauty of experimental physics – how clever ideas and masterful work can really transcend physical limitations. Krauss has also done a reasonable job of avoiding the sociological folklore of characters and egos. He succumbs vary rarely, the most notable occasion being in his description of his work on WIMP detection and axions (and he likes Glashow’s quips).
The bottom line is that Lawrence Krauss has been able to give us a glimpse of an open,fascinating problem in physics that is far from being solved: the existence and essence of dark matter. The book can be read by the layperson but is also useful for scientists and non-specialists in cosmology.
