What to Read: The Fine-Tuning of the Universe for Intelligent life

I’ve spent a lot of time critiquing articles on the fine-tuning of the universe for intelligent life. I should really give the other side of the story. Below are some of the good ones, ranging from popular level books to technical articles. I’ve given my recommendations for popular cosmology books here.

Books – Popular-level

• Just Six Numbers, Martin Rees – Highly recommended, with a strong focus on cosmology and astrophysics, as you’d expect from the Astronomer Royal. Rees gives a clear exposition of modern cosmology, including inflation, and ends up giving a cogent defence of the multiverse.
• The Goldilocks Enigma, Paul Davies – Davies is an excellent writer and has long been an important contributor to this field. His discussion of the physics is very good, and includes a description of the Higgs mechanism. When he strays into metaphysics, he is thorough and thoughtful, even when he is defending conclusions that I don’t agree with.
• The Cosmic Landscape: String Theory and the Illusion of Intelligent Design, Leonard Susskind – I’ve reviewed this book in detail in a previous blog posts. Highly recommended. I can also recommend his many lectures on YouTube.
• Constants of Nature, John Barrow – A discussion of the physics behind the constants of nature. An excellent presentation of modern physics, cosmology and their relationship to mathematics, which includes a chapter on the anthropic principle and a discussion of the multiverse.
• Cosmology: The Science of the Universe, Edward Harrison – My favourite cosmology introduction. The entire book is worth reading, not least the sections on life in the universe and the multiverse.
• At Home in the Universe, John Wheeler – A thoughtful and wonderfully written collection of essays, some of which touch on matters anthropic.

I haven’t read Brian Greene’s book on the multiverse but I’ve read his other books and they’re excellent. Stephen Hawking discusses fine-tuning in A Brief History of Time and the Grand Design. As usual, read anything by Sean Carroll, Frank Wilczek, and Alex Vilenkin.

Books – Advanced

• The Cosmological Anthropic Principle, Barrow and Tipler – still the standard in the field. Even if you can’t follow the equations in the middle chapters, it’s still worth a read as the discussion is quite clear. Gets a bit speculative in the final chapters, but its fairly obvious where to apply your grain of salt.
• Universe or Multiverse (Edited by Bernard Carr) – the new standard. A great collection of papers by most of the experts in the field. Special mention goes to the papers by Weinberg, Wilczek, Aguirre, and Hogan.

Scientific Review Articles

The field of fine-tuning grew out of the so-called “Large numbers hypothesis” of Paul Dirac, which is owes a lot to Weyl and is further discussed by Eddington, Gamow and others. These discussions evolve into fine-tuning when Dicke explains them using the anthropic principle. Dicke’s method is examined and expanded in these classic papers of the field:

• Large number coincidences and the anthropic principle in cosmology, Carter (1974)
• The anthropic principle and the structure of the physical world, Carr and Rees (1979)
• The anthropic principle, Davies (1983)

A number of papers, while not discussing fine-tuning, are very relevant as they discuss how the macroscopic universe depends on the values of fundamental constants. Here are a few good examples.

• Dependence of macrophysical phenomena on the values of the fundamental constants, Press and Lightman (1983). Great fun to work through if you’re a physicist.
• The eighteen arbitrary parameters of the standard model in your everyday life, Cahn (1998)

Here are a few good review papers, arranged in order of increasing technical level.

• Understanding the Fine Tuning in Our Universe, Cohen (2008): A nice little introduction to the fine-tuning of nuclear binding and nucleosynthesis in stars. Aimed at teaching to undergraduate physics students.
• Numerical coincidences and ‘tuning’ in cosmology, Rees (2004)
• Why the universe is just so, Hogan (2000): an excellent overview and update of the field, and one of the first papers to extend anthropic constraints to grand unified theories.
• The Fine-Tuning of the Universe for Intelligent Life, Barnes (2012). Well … I like it. I wrote my paper because no one had systematically reviewed the important work done since Hogan’s review in 2000.
• Life at the Interface of Particle Physics and String Theory, Schellekens (2013): A very nice review, with the feature of being from the standpoint of a string theorist. Complementary to mine.
• Varying Constants, Gravitation and Cosmology, Uzan (2011): There is some overlap between the field of fine-tuning, and investigations of variations of fundamental constants in the actual universe, for obvious reasons – both must ask “what would happen if the fundamental constants were different?”. Uzan gives a good overview of this field.

Technical scientific articles

Here are some of the papers that have performed detailed calculations of specific fine-tuning cases, in chronological order.

Particle Physics Parameters

• Anthropic Considerations in Multiple-Domain Theories and the Scale of Electroweak Symmetry Breaking, Agrawal et al. (1998).
• Anthropic tuning of the weak scale and of mu/md in two-Higgs-doublet models, Barr and Khan (2007)
• Evidence for the multiverse in the standard model and beyond, Hall and Nomura (2008)
• Quark masses: An environmental impact statement, Jaffe et al. (2009)
• Effects of the variation of fundamental constants on Population III stellar evolution, Ekstrom et al. (2010)
• Viability of Carbon-Based Life as a Function of the Light Quark Mass, Epelbaum et al. (2013). This paper and the one above give the most recent updates on Hoyle’s classic carbon triple-alpha resonance fine-tuning. See also Schlattl el al.

Cosmology Parameters

• Anthropic bound on the cosmological constant, Weinberg (1987). The classic paper on anthropic limits on the cosmological constant. See also the updated calculations of Efstathiou, Peacock and Bousso et al, and the review paper of Bousso.
• On the dimensionality of spacetime, Tegmark (1997)
• Why is the Cosmic Microwave Background Fluctuation Level 10^-5?, Tegmark and Rees (1998)
• Dimensionless constants, cosmology, and other dark matters, Tegmark, Aguirre, Rees, and Wilczek (2006)

Philosophical articles and books

• Issues in the Philosophy of Cosmology, Ellis (2006). An excellent review of some of the philosophical issues raised by modern cosmology, including fine-tuning. See also “Philosophy of Cosmology” by Chris Smeenk.
• Universes, John Leslie – A tremendously clear exposition of what conclusions we can and should draw from fine tuning. Leslie loves a good analogy, and his choice of illustration is almost always excellent. Another must read.

Part of the reason why the fine-tuning of the universe for life is of such interest to philosophers is that it is often used as a premise in an argument for the existence of God.  A lot of the literature on the fine-tuning argument, pro and con, misses the mark by a large margin, in my opinion. Here are three of the best expositions of this argument.

• The Existence of God, Richard Swinburne (2004)
• The teleological argument: an exploration of the fine-tuning of the universe, Robin Collins (in The Blackwell Companion to Natural Theology, 2012). See also this article.
• Modern Physics and Ancient Faith, Stephen Barr (2006)

Unsurprisingly, such claims have not gone unchallenged. Here are some of the best responses.

• Does the Universe Need God?, Sean Carroll (2012) – A good, if brief, response to the arguments above. I recently presented fine-tuning with Carroll in the audience and he gave some good comments. I wouldn’t mind seeing him give an extended response.
• See also the books by Leonard Susskind and Alex Vilenkin (and, though I haven’t read them, Brian Greene and Stephen Hawking) for a defence of the multiverse as the correct explanation for fine-tuning.
• Probabilities and the Fine‐Tuning Argument: a Sceptical View, McGrew, McGrew and Vestrup – A critique of the fine-tuning argument for the existence of God based on skepticism as to the applicability of probabilities to hypothetical universes. At least two of the authors are theists. See also this paper by Bradley Monton (though I don’t think that the “old evidence” problem exists for Bayesian theories of probability.)

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