Book Review: A Fortunate Universe by Geraint F. Lewis and Luke A. Barnes

Introduction 

Throughout A Fortunate Universe: Life in a Finely Tuned Cosmos, astronomers Geraint F. Lewis and Luke A. Barnes discuss the claim that our universe is governed by laws and constants which appear to be finely tuned for the existence of life. While those familiar with apologetics may recognize this concept from the fine-tuning argument for the existence of God, Lewis and Barnes present the fine tuning of the universe from a strictly scientific perspective, and it is only in the final chapter that the philosophical and theological implications are discussed.

Lewis and Barnes open the book with a conversation, and it is through this conversation that they introduce the concept of fine tuning. In general, fine tuning takes place with respect to a specific outcome which itself is highly sensitive to the initial conditions. To say that the universe is finely tuned for life is to say that it is overwhelmingly more probable that life would not exist had the physical laws or constants been even slightly different.

The rest of the introduction covers a wide range of topics, but three points deserve special mention. First, the majority of changes to the initial conditions of the universe result in clear cases of non-life, and therefore no precise definition of life is needed. Second, the anthropic principle is insufficient to answer the question of why life exists. Third, the practice of science is a complicated process involving theories and experiments, predictions and data, ultimately resulting in increasingly accurate models of the physical world.

At this point, a disclaimer is warranted. A Fortunate Universe becomes quite technical at times. In order to avoid getting lost in the details, this review will focus on the conclusions that the authors reach with respect to these technical discussions.

Fine Tuning: The Science

Lewis and Barnes quickly dive into a discussion of the foundation of the physical world: subatomic particles. Following a survey of the underlying principles of particle physics, they provide a taste of life’s improbability by exploring the outcomes of the universe had the masses of various subatomic particles been different. Whether we consider quarks, electrons, the Higgs boson, or any number of theoretical supersymmetric particles, the slightest of alterations almost always result in universes devoid of the type of chemical reactions required for life.

Next, Lewis and Barnes dive into a discussion of the four fundamental forces: gravity, electromagnetism, the strong nuclear force, and the weak nuclear force. The relative strengths of these forces are dictated by their respective coupling constants. Within quantum field theory, these coupling constants effectively indicate the probability that, given an interaction occurs, a force particle will be exchanged. When adjustments are made to these coupling constants, the resulting universe is almost always life-prohibiting. For example, adjusting the strengths of the weak force, strong force, or gravitational force results in dramatically different nuclear reactions in the early universe. Furthermore, many adjustments result in elements common to life becoming radioactive, which itself would be detrimental to life in the universe.

Moving forward, Lewis and Barnes discuss the importance of energy and entropy for life in the universe. For the purposes of this discussion, entropy is defined as, “useful free energy,” where a low-entropy condition contains a large amount of said useful free energy. According to the second law of thermodynamics, whenever energy flows within the universe, the total entropy of the universe never decreases. In other words, the amount of usable energy in the universe decreases over time. Thus, a life-permitting universe requires a low-entropy initial condition. Furthermore, within low-entropy universes like ours, alterations to the aforementioned coupling constants tend to preclude star formations, and therefore life, altogether.

Lewis and Barnes then dive head-first into the world of General Relativity with discussions of spacetime curvature, geodesics, and the like. What immediately follows is an introduction to dark matter, dark energy, the Cosmic Microwave Background, and more. Ultimately, life can only exist within a universe containing a similar mixture of dark energy and matter to our universe. Furthermore, the shape of our universe is within 1% of being perfectly flat as we observe it today, which means that at the earliest moments of the universe, it must have been flat to one part in 10⁵⁵, a difficult number to comprehend. Yet life can only exist in a similarly flat universe.

Next, Lewis and Barnes transition to the topic of symmetry in the physical world. More specifically, life depends on there being an asymmetry between the amount of matter and antimatter in the universe. In addition, there must be an asymmetry to time itself in order for life to function at all. Whether time is related to the expansion of the universe (cosmological time) or the increasing of entropy (thermodynamic time), its asymmetry is a direct consequence of the initial conditions of the universe.

The prospects of life in the universe become even more dim as Lewis and Barnes proceed to even more abstract discussions including: the number of macroscopic physical dimensions, computational properties found in simulations of life, and even the underlying mathematical comprehensibility of the universe to begin with. The conclusion of this endeavor: the universe’s physical laws themselves must be fine-tuned in order to allow life.

Fine Tuning: The Response

The final third of the book is dedicated to analyzing various responses to the fine tuning of the universe. In total, Barnes and Lewis address fifteen unique objections to fine-tuning. In the interest of keeping this review at a reasonable length, a full discussion of these objections cannot be included. A simple list will have to suffice:

1. It’s Just a Coincidence.
2. We’ve Only Observed One Universe
3. Low-Probability Events Happen All the Time
4. Fine-Tuning Has Been Disproved
5. Evolution Will Find a Way
6. How Can the Universe Be ‘Fine-Tuned’ When It Is Mostly Inhospitable To Life?
7. This Universe Is Just As Unlikely As Any Other Universe
8. How Do We Know What Would Happen In Other Universes?
9. Fine-Tuners Turn Only One Dial at a Time
10. Why Think That Life is Special?
11. We Don’t Even Have a Good Definition of Life
12. There Could Be Other Forms of Life
13. The Anthropic Principle Explains Our Existence
14. Whence the Possibilities?
15. Whence the Probabilities?

With respect to each of the above responses, Lewis and Barnes provide an explanation of the objection, a short answer, and a long answer. In each case the objection is found wanting.

In the final chapter Lewis and Barnes return to the conversation that began between the two of them in the beginning of the book, and here they address a few last responses to fine tuning. Ultimately, two views are left up to debate for Lewis and Barnes: one is the multiverse, the other is God. Within this conversation, Lewis favors the former. In response, Barnes points out the odd result that given a multiverse, we are most likely Boltzmann Brains. Barnes, however, believes God is the more likely explanation. God, says Barnes, is a necessary being, which is something that cannot be said about the physical universe. In response, Lewis raises several objections including, most notably, the problem of evil. The pair ultimately reach a standstill, leaving the conclusion up to the reader to decide.

Final Thoughts

Overall, A Fortunate Universe is a necessary read for anyone interested in the fine-tuning of the universe, regardless of religious worldview. Lewis and Barnes managed to write a technically sound survey of some of the most complex topics in all of physics, while still keeping the discussions accessible to the layman. That, alone, is no small feat, but they also managed to squeeze in witty asides along the way, making this book as enjoyable as it was thought-provoking. While this is, first and foremost, a book about physics, Lewis and Barnes showed an impressive command of the philosophical, and even theological, literature surrounding the implications of fine-tuning, making this book an important read for scientists, philosophers, and theologians alike.