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The Cosmic Cocktail: Three Parts Dark Matter

by Katherine Freese
Princeton University Press, Princeton, New Jersey, 2014
264 pp., illus. 15 col., 73 b/w. Trade, $29.95
ISBN: 978-0-691-15335-3.

Reviewed by Christopher B. Germann
Marie Curie Fellow 'CogNovo'
Plymouth University, Cognition Institute


In nine compact chapters, Katherine Freese addresses the perhaps most fundamental question humankind can ask: What is the Universe made of? This question takes the reader deep into the peculiar abysses of astroparticle physics. In order to introduce the topic, she reminds us that, according to current theorizing, ordinary atomic matter constitutes only ≈ 5% of the observable Universe. The remaining 95% consist of dark matter (≈ 26%) and dark energy (≈ 69%), which are hitherto completely mysterious to scientists. These values are in themselves astonishing because they indicate numerically how limited our epistemic understanding regarding the fundamental ontology of the Universe really is. The physical presence of dark matter is currently purely hypothetical. Its existence is logically inferred from its attractive gravitational effects on ordinary matter (i.e., gravitational lensing). By contrast, as Freese points out, dark energy is an unidentified repulsive anti-gravitational form of energy that is assumed to accelerate the expansion of the Universe. Evidence for its effects is primarily based on spectroscopic measurements of distant supernovae and their associated photometric redshifts.

According to Freese, the field of astroparticle physics is still in its infancy stage, and there exists a wide future scope for potentially paradigm changing discoveries whose significance might be comparable to the second Copernican revolution or the shift from the geocentric to the heliocentric worldview. She is optimistic that science will be able to solve the riddle of dark matter in the foreseeable future. However, dark energy, which is stipulated to be ubiquitous, is a different animal. Freese emphasises that science is not even close to answering any questions concerning its nature. Dark matter is at least theoretically detectable, and it can, therefore, be investigated experimentally by probing for a new type of subatomic particle. However, researchers are groping in utter darkness when it comes to dark energy. Nevertheless, our scientific perspective on reality is literally expanding. According to Freese, the angular resolution of telescopes is increasing faster than Moore's law would prognosticate, namely by about a factor of 10 every two or three years. Following the author's line of thought, it is interesting to note that researchers in related domains observe similar exponential trajectories whose combinatorial synergies are difficult to predict a priori, for instance, computational algorithms for image analysis are steadily evolving unprecedented levels of sophistication and high-performance computing enables ever more powerful analyses and simulations of increasingly big-data scenarios.

The book puts the main focus of attention on the quest for dark matter detection that is one of the hottest topics in contemporary science. This shadowy component cannot be directly detected with current methods, primarily because it does not interact with light, hence the eponymous nomenclature. Freese describes the various experimental approaches physicists employ to search for it in a concise and accessible way. Furthermore, she describes her career as a women in this predominantly patriarchal disciplinary territory and how she deals effectively with MACHOs (Massive Astrophysical Compact Halo Object) and WIMPs (Weakly Interacting Massive Particles). In this context, she finally presents her own co-invention: a DNA-based method for the detection of dark matter [1]. This truly interdisciplinary hybrid-approach to dark matter detection has the potential to enable nanometre resolution for tracking of WIMPs. If it works (which has yet to be demonstrated), this extremely sensitive detector would outperform all of the existing technologies available today, and Freese and et al would take a leading position in the highly competitive field. The following quote from the book exemplifies her enthusiasm: "Now we have come full circle. It is an intriguing prospect that we can use the DNA created from stardust to search for astrophysical dark matter particles" (p.179). At present, the physics community attempts to cross-validate experimental results by methodological triangulation: 1) by the creation of dark matter particles in the particle accelerator complex at CERN, 2) by direct detection in sub-terrestrial laboratories, and 3) by indirect detection via products resulting from particle (WIMP) annihilations. The stated objective is to obtain convergent evidence from independent sources in order to shed light on the long-standing dark matter conundrum.

In addition to presenting the 21st century view of the Universe, the book chronicles the history of the exploration of dark matter. Freese expounds why Edwin Hubble's discovery of the expansion of the Universe [3] was crucial for the development of the discipline. Extending his line of research, the 2011 Noble Price in physics was awarded "for the discovery of the accelerating expansion of the Universe through observations of distant supernovae" [4]. In other terms, the Universe is expanding at an exponentially increasing velocity. Fascinatingly, although Freese is not very explicit on this point, current mathematical models postulate that its acceleration is not limited to the speed of light because this speed limit only applies to objects within space-time. By contrast, the metric expansion of space-time itself is not bound to this maximum. This is a very astonishing extrapolation, to say the least.

Another topic Freese discusses is the genesis of the Universe (Big Bang theory). However, she does not address the inherent deep philosophical questions concerning universal causation (e.g., the Aristotelian "unmoved mover" and the associated problem of infinite causal regress). Instead, she puts focus on reductionist experimental research programs. For example, she delineates the workings of the Large Hadron Collider at Europe's CERN research centre, the most powerful particle accelerator in the world, and she reviews the recent ground-breaking experimental discovery of the Higgs Boson (a new elementary particle), which had been theoretically predicted since 1964 [2]. This empirical triumph of atomism was rewarded with the 2013 Nobel Prize in physics [5]. Freese points out that the questions concerning the nature of the macro-scale of the Universe and the micro-scale of atoms are tightly interwoven.

To conclude, the cosmic cocktail has profound effects on the reader because it raises awareness to the fact that physics is currently unable to account for the bigger proportion of the constituents of the Universe. Its well-balanced ingredients contain a mixture of cutting-edge science enriched with a measure of history of cosmology and infused with oftentimes sparklingly amusing autobiographical details. This unique blend is rounded off with several intriguing pictorial bindings. Straight up! Taken together, the cosmic cocktail provides a rich taster of some of the core areas of modern astronomy and particle physics, and it is a comprehensive primer for the general educated layperson who is interested in the recipe of the cosmos. It leaves the reader wondering what the future of physics has in store. Until then, the dark side of the Universe remains an enigma to all great minds on spaceship earth.


[1] Drukier, A., Freese, K., Lopez, A., Spergel, D., Cantor, C., Church, G., Sano, T. (2015). "New Dark Matter Detectors using DNA or RNA for Nanometer Tracking". Instrumentation and Methods for Astrophysics. http://arxiv.org/pdf/1206.6809v2.pdf.

[2] Higgs, P. (1964). "Broken Symmetries and the Masses of Gauge Bosons". Physical Review Letters, 13(16), 508-509. https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.13.508.

[3] Hubble, E (1929). "A relation between distance and radial velocity among extra-galactic nebulae". PNAS, 15(3), 168-173. http://www.pnas.org/content/15/3/168.full.pdf.

[4] "The Nobel Prize in Physics 2011". Nobelprize.org. Nobel Media AB 2014. 10 Feb 2015. http://www.nobelprize.org/nobel_prizes/physics/laureates/2011/.

[5] "The Nobel Prize in Physics 2013". Nobelprize.org. Nobel Media AB 2014.10 Feb 2015. http://www.nobelprize.org/nobel_prizes/physics/laureates/2013/.

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