Book Review: 'The Grand Design' by Stephen Hawking and Leonard Mlodinow

The Grand Design (2010)
Stephen Hawking (1942 - ) and Leonard Mlodinow (1954 -)

199 pages

“Why is there a universe, and why is the universe the way it is?” (p. 123)

Stephen Hawking and Leonard Mlodinow go right to the big picture in their new book The Grand Design. In a quick 200 pages they provide an overview of the development of theories to describe the natural world, from the creation stories of early civilizations, through the thought experiments of Greek scientists and philosophers, to the growth of the scientific method in the work of Newton and others, leading finally to the focus of their book, the modern theories that physicists are working on to try to unify the behavior of everything, from the very small to the very large.

The authors introduce the concept of models --- which are developed to describe observed behavior in nature --- and the role of the scientific method in evaluating these models. A physicist will study physical behavior through experimental observation and develop a model in order to describe that behavior and to predict future behavior. Over time the model will be subjected to tests that either support it as an accurate description of the physical behavior, or that demonstrate it is inadequate. When a model is contradicted by experimental observation, it must then either be enhanced, to account for the new observed behavior, or replaced by another model that more accurately reflects the behavior.

As an example, over many years Newton’s laws were found to accurately model the interaction of objects seen in nature; around the beginning of the 20th century, however, as physicists explored the behavior of particles at the atomic level, it was found that Newton’s laws no longer accurately applied. New, more accurate, models (quantum mechanics) were eventually developed to replace Newton’s laws at this tiny scale. Hawking and Mlodinow point out, however, that physicists "are still working to figure out the details of how Newton's laws emerge from the quantum domain" (p. 68). So, two models end up being used: the familiar Newton’s laws for the behavior of larger objects, and the models of quantum mechanics at the atomic scale.

The difficulty of reconciling these two different models for the interaction of objects into a single model is a part of the larger challenge described in the book of creating a single, unified ‘theory of everything’: a single theory that will describe all observed behavior between objects (that is, the four known forces of nature: gravity, electromagnetism, the weak nuclear force and the strong nuclear force). One such theory that the authors introduce is the so-called ‘M-Theory’, which rests on string theory, and represents one of the principal paths being followed by today’s physicists in their current search to find a unified theory.

Hawking and Mlodinow in fact conclude the book by arguing that “M-theory is the only candidate for a complete theory of the universe.” (p. 181). Their claim rests on the apparent (though still to be conclusively demonstrated) characteristic of M-theory to be fully consistent with the strong anthropic principle, which “suggests that the fact that we exist imposes constraints not just on our environment but on the possible form and content of the laws of nature themselves” (p. 155). Thus, the strong anthropic principle states that if the fundamental laws of nature were much different than they are observed to be, life would be impossible. (The weak anthropic principle is based on the idea that “our own knowledge of our existence imposes rules that select, out of all the possible environments, only those environments with the characteristics that allow life.,” (p. 154) for example, the distance of our planet from the sun.)

As interesting as the final chapters are on how M-Theory could be the unifying theory that describes how the universe came to exist, it is the authors extended discussion of models, and the scientific method used to develop and confirm them, that may be the most interesting aspect of their story. The authors’ discussion of the models of quantum mechanics drives home a critical point: a model is not a description of how a set of objects interact, but rather a way of describing the outcome of the interaction, and predicting the outcomes of future such interactions.

At the macro level of everyday experience it can be easy to conflate these two ideas. We throw a ball and, taking into account the forces that act on it --- friction and gravity --- we can predict where the ball will land. It is easy to begin to think that we can ‘see’ the pull of gravity on the ball, and to imagine, because we can accurately predict the effect of gravity on the ball, that we have any understanding of how gravity is actually exercising its effect on the ball. In reality, and as made clear by the authors, what we really have is the barest idea how gravity physically carries out its work; we only have a very accurate description of the result.

For me, although I have little understanding of quantum mechanics, this makes more palatable the idea that much of the models of quantum mechanics deal with probabilities. As the authors state it, “according to quantum physics … nature does not dictate the outcome of any process or experiment, even in the simplest of situations. Rather, it allows a number of different eventualities, each with a certain likelihood of being realized.” (p. 72) The idea that nature might not be deterministic is a difficult one to accept, and it is some consolation to remember that quantum mechanics is a model of the behavior observed in nature --- a very accurate model based on much testing, but still only a model. And I have the consolation of being in good company: “It is, to paraphrase Einstein, as if God throws the dice before deciding the result of every physical process. That idea bothered Einstein, and so even though he was one of the fathers of quantum physics, he later became critical of it.” (p.72)

---

Other of my book reviews: FICTION and NON-FICTION