In part 1, part 2, and part 3 of this review, I reviewed the physics in the book The Grand Design by Stephen Hawking and Leonard Mlodinow. In this last part I want to look at the book’s implications for religion.

The book seeks to address three questions: Why is there something rather than nothing? Why do we exist? Why this particular set of laws and not some other? These are, of course, big questions. Many people will recognize these questions as those on which sophisticated religious apologists have pinned their hopes as being the last remaining mysteries which science cannot answer and for which god is the only answer. What the book argues is that this hope, like similar hopes before it, has been dashed, and that what is called M-theory and the no boundary condition have eliminated any need for god.

It is important to realize that M-theory was not invented in order to eliminate god from the universe, any more than Darwin and Wallace’s theory of natural selection was deliberately created to eliminate god from the creation of species. Questions of god’s existence play no part in the normal workings of scientists. Despite what some religious people think, scientists do not spend their time trying to find ways to make religious people sad. Scientific theories rise and fall on the basis of how good they are in relation to empirical evidence and data, and their implications for theology are at best an incidental by-product or afterthought. As Hawking says, the “multiverse idea is not a notion invented to account for the miracle of fine-tuning. It is a consequence of the no-boundary condition as well as many other theories of modern cosmology.” (p. 164)

In his books, Hawking refers to god a lot. I suspect that this is partly a publicity ploy. He knows how to market himself by pushing people’s buttons and whenever an eminent scientist talks of god, people listen and buy their books. The very last sentence of his A Brief History of Time was, “If we find the answer to [why it is that we and the universe exist], it would be the ultimate triumph of human reason – for then we would know the mind of God.” This sentence has been widely quoted and led to hope among religious people that the world’s most famous living scientist was religious, though those who know him said that he was not a believer and that his use of the word god is in the same sense as Einstein used it, as a label for the laws of nature, not in any sense the way that religious people use the term as some kind of entity that actually exists and can do things. In reading that earlier book, it was not clear to me whether he believed in the existence of a god-like entity or not. I got the sense that he was using the word god in both real and metaphorical senses but tellingly, God was not listed in the index, the way that other people mentioned in the book were.

What his latest book does is definitely eliminate any hope that Hawking believes in god. As the authors say, “Some would claim the answer to these questions is that there is a God who chose to create the universe that way… We claim, however, that it is possible to answer these questions purely within the realm of science, and without invoking any divine beings.” (p. 172) This probably explains why this time around, religious dignitaries have been quick to dismiss him. Woo master Deepak Chopra, who has made a career out of mixing quantum physics with religious ideas to create a ghastly mess of confusion that religious people like because they think that god is hidden somewhere in his fog of words, is of course disappointed with Hawking’s conclusion.

Cosmologist Sean Carroll has a nice three-minute video that I’ve shown before that summarizes some of the points made in this review.

Of course, theologians and philosophers will rightly claim that Hawking has not proved that god does not exist. But that is a cheap point since science can never prove the non-existence of anything, whether it be god or Santa Claus or unicorns. What science has shown (even before Hawkng’s book) is that god is an unnecessary concept. As Steven Weinberg says, “One of the great achievements of science has been, if not to make it impossible for intelligent people to be religious, then at least to make it possible for them not to be religious.”

I would actually put it in a shorter and stronger form than Weinberg. Science can never prove that there is no god but it has shown that there is no need for god. Disbelief in god is far more intellectually coherent than belief and thus should be the natural choice for any thinking person.

Although I said that there would be only four parts to the review, I have some final thoughts on the book and Hawking’s views that I will add as a coda tomorrow.

In part 1 of this review I discussed the main issues raised by the book and in part 2 I said that the book by Hawking and Mlodinow argued that M-theory and the no boundary condition can provide answers to the three big questions: Why is there something rather than nothing? Why do we exist? Why this particular set of laws and not some other?

To understand what lies at the basis of M-theory, we need to appreciate a key difference between classical physics (which describes the large-scale structure of the everyday world we live in and from which we draw our intuitions about how the world works) and quantum mechanics (which describes the microscopic atomic and subatomic world).

What classical physics says is that if we release an object at some point A, it will subsequently wander off on some trajectory (or path) that depends on its initial state of motion and the forces that act on it. This is what enables good football quarterbacks to throw passes to receivers with such accuracy. If the ball is poorly thrown on a windy day and/or we stop observing the ball, we may not know or be able to predict which path the ball will take or where it will land but our classical intuition tells us that it will go along some specific path that is determined by the initial throw and the wind conditions.

But quantum mechanics has this counter-intuitive idea that once we stop observing the object, the object takes every conceivable path simultaneously. This means that there is no unique location for the object at any given time, that it is everywhere at the same time and could eventually end up anywhere at all. Another way to say it is that an object has many different histories. This is what boggles most people’s (including scientists’) minds about quantum theory but we have to learn to live and work with it (i.e., develop ‘quantum intuition’, so to speak) because this theory is phenomenally successful and there seems to be no getting around it at this time. Some people are working on developing alternative theories that do not have its strange features but have not had much success so far.

Now if we detect the object at some later time to be at some point B, this eliminates some of the potential paths we started with because they would not have resulted in the object ending up where we detected it. So the act of detection picks out a subset of the initial set of possible histories, limiting the ones of interest to those that began at point A at the specified time and ended at B at the later time, which still includes an infinite number of paths or histories. An elaborate mathematical machinery (called the ‘sum over histories’ or more technically ‘path integrals’) has been created to add up all the possible paths the particle could have taken in going from A to B. The calculated results correctly predict the empirical observations, which is why scientists have confidence in quantum theory despite its counter-intuitive features.

What M-theory does is take this key idea of quantum mechanics and apply the ‘sum over histories’ approach to the universe as a whole. Building on the idea of the inflationary universe (see part 9 and part 13 of my series Big Bang for Beginners for more details), since the net energy of the universe is zero, there is no restriction on the number of new universes that can ‘pinch’ off from previously existing universes. Since the Heisenberg uncertainty principle states that you can never have truly empty and inert space (p. 113) but that space constantly has particles coming into existence and disappearing again, any one of those fluctuations in space could form the seed of a quantum fluctuation that triggers the birth of a new universe.

So universes are being created all the time and there are a vast number of possible histories of the universe, of the order of 10⁵⁰⁰. They each have their own forms of matter and their own laws. According to the ‘sum over histories’ in quantum mechanics, all these universes exist simultaneously, giving rise to the name ‘multiverse theory’. When we observe our universe, we are picking out just those histories that could produce the present state we see. As Hawking and Mlodinow state:

Quantum physics tells us that no matter how thorough our observation of the present, the (unobserved) past, like the future, is indefinite and exists only as a spectrum of possibilities. The universe, according to quantum physics, has no single past, or history. (p. 82)
…
We seem to be at a critical point in the history of science, in which we must alter our conception of goals and of what makes a physical theory acceptable. It appears that the fundamental numbers, and even the form, of the apparent laws of nature are not determined by logic or physical principle. The parameters are free to take on many values and the laws to take on any form that leads to a self-consistent mathematical theory, and they do take on different values and forms in different universes. (p. 143)

Given the staggeringly large number of possible histories, it was almost inevitable that one of those universes would have the properties that ours has. It is like rain. If you pick a point on the ground, the probability of it being hit by a raindrop is infinitesimally small. But in a rainstorm, there is such a huge number of drops that it is inevitable that at least one will hit the ground there.

Hawking and Mlodinow’s book does not shy away from making strong claims, such as that the theory they describe has to be the right one. “M-theory is the only candidate for a complete theory of the universe… M-theory is the unified theory Einstein was hoping to find.” (p. 181, emphasis in original.)

That seems hubristic to me. If the history of science teaches us anything it is that theories, however successful at any given time, tend to be later replaced by other theories as the questions that need to be addressed change. However obviously important they may seem, is usually a mistake to think that the questions that concern us now will be the same questions that future generations care about. Also the theory of supersymmetry, which is central to M-theory though not necessarily to the idea of multiverses, has been around since 1970 or so, with none of the exotic partner particles it predicts having been detected as yet. The theory’s supporters are pinning their hopes on the Large Hadron Collider that has just started operations, hoping that its energies will be sufficient to produce these particles.

In the last part of this review, I will look at the implications of M-theory for religion and give some of my reactions to other features of the book.

In part 1 of this review, I argued that the lack of a unified theory of gravity and quantum mechanics is what has stymied scientists in their attempt to understand the origins of our universe and even what came ‘before’, assuming that the question even makes sense. M-theory and the no boundary condition is what Hawking proposes as the candidate for a unified theory that can address the physics of the early universe.

M-theory is not an elegant theory expressed in a single equation (like Newton’s law of gravity) or even a few equations (like Maxwell’s equations of electromagnetism) but instead consists of a patchwork of theories, each with its domain of application, and overlapping with other theories so that the whole space of nature is covered. Hawking argues that this patchwork feature may not be due to our lack of imagination or inventiveness but intrinsic to the nature of the laws of science.
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