In Just Six Numbers, Martin Rees provides a tour of the universe and the delicately tuned values that govern it. Rees argues that, were some values of the universe (the strength of gravity, for example) slightly different, intelligent life would not be possible. As Rees demonstrates, the odds that all six of the crucial numbers he mentions should have values that are life-permitting is extraordinarily small, and therefore this remarkable find cries out for some sort of explanation.
The cosmological evidence roughly outlined by Rees has led to a renewed interest in the argument from design for the existence of God. If God purposely created the universe to support life, then we can understand why the values governing it are conducive to life. However, Rees offers a different interpretation. Rees argues that there might be a large (perhaps infinite) number of other universes that exist separate from our own. What we call the ‘universe’ is really just a small portion of the entire cosmos. This so-called ‘Multiverse’ model eliminates the mystery of why the universe seems so fortuitously life-permitting. Only in the small subset of actual universes that are compatible with life can life arise. Of course, we inhabit a life-permitting universe- because we must!
So, why should we accept the multiverse hypothesis rather than the design hypothesis? Unfortunately, on this point Rees is almost entirely silent. He never once argues that the multiverse model is superior or the design hypothesis deficient. Therefore, the evidence provided throughout the book is at least compatible with either interpretation.
Moreover, Rees does not provide much of a defense of the multiverse hypothesis, which has been critiqued in many ways. For example, the hypothesis that an infinite number of universes exist completely separate from our own seems to be an ad hoc and complicated hypothesis which we should therefore be hesitant to accept. Another problem is that multiverse models don’t necessarily eliminate the need for a designer anyways, because the models often require extensive fine-tuning to work in the first place.
The only objection that Rees tries to counteract is the claim that the multiverse model is unscientific. He claims that there are at least potential ways that the model could be confirmed or disconfirmed in the future. I think Rees is correct about this, but this does not give us any positive reason to accept the multiverse interpretation.
Most of Just Six Numbers deals with cosmology, and this discussion is very interesting. However, I found the author’s writing style to be a bit dry. For a more entertaining and engaging discussion, I would recommend Cosmic Jackpot by Paul Davies. If Rees spent more time defending his multiverse interpretation, this book might be worth a read. As it stands, however, there are much better books out there on this subject.