Mary-Jane Rubenstein. Worlds Without End: The Many Lives of the Multiverse. Columbia University Press, 2014.

Richard J. Evans. Altered Pasts: Counterfactuals in History. Little Brown, 2014.

David Waltham. Lucky Planet: Why the Earth is Exceptional and What That Means for Life in the Universe. Icon Books, 2014.

These three books examine in very different ways the question of the 'plurality of worlds' and the uniqeness, or otherwise, of Earth's place in the universe.

Mary-Jane Rubenstein is a professor of religion, with a deep interest in science and philosophy and in her book she traces the history of ideas about the multiverse. She shows that these have much deeper roots than we normally suppose, starting with Greek speculations about other kosmoi, self-contained worlds, perhaps separated by special voids, perhaps having no special relationship one to another. These ideas were revived in modern forms by figures such as Nicholas of Cusa and Giordano Bruno. These speculations intrigued and troubled the theological imagination in perhaps equal measure.

She takes us through the various supposed hierarchies of multiverse, from the regions of our own “megaverse” beyond the observation horizon; through to separate bubble universes crystallising out of “inflation space”, the alternate worlds of the many worlds interpretation of quantum mechanics, along with separate 'brane' worlds floating in a higher dimensional space, cyclic universes, universes being born through black holes, all the way up to Max Tegmark’s multiverses of separate mathematical systems. This is usually presented, as in here, as the “ultimate” multiverse, but there seems no reason, having gone this far, one should not assume that “mathematical” multiverses are just one set in a much larger ensemble of multiverses based on quite different principles.

Such theories have often been regarded as pure metaphysical speculation, but one of them, devised by Laura Mersini-Houghton, does predict that the pre universe state will leave traces on the cosmic background radiation, which does indeed appear to have been found. This theory involves, in a very oversimplified way, a pre-geometrical cosmic 'bath' or 'sea', in which forces of attraction and repulsion vie, and from which universes bubble up. If attraction wins, the universe collapses back into the sea, if repulsion, it can inflate into a proper universe. Though this universe (or is it actually itself a multiverse) is now separate from this “underlying reality” and has lost most of the information about it, quantum entanglement means there is some sort of faint ghostly connection between the various bubbles and the “ocean”.

The attraction of ideas about the multiverse for science is that it can be used to explain why the universe has the precise conditions that it does, without involving a designer, (which in turn leads to endless regress, what designed the designer and so on). The implications are rather deeper than is often thought. The universe of the designer, such as the Abrahamic God is essentially a manufactured article, a thing; the universe born out of the pre-cosmic sea is something more analogous to an organism.

Of course we still have to account for the origin of the pre-cosmic ocean and the physics which sustains it. Presumably that along with physics, mathematics, information etc. has assembled upwards from something much simpler.

One issue which is not entirely resolved by the various theories is whether the various megaverses generated by the multiverse are infinite, and even if they are, does that infinity incorporate all possibilities or just some. The former case suggests that they will encompass all possible histories, including the various alternate histories which intrigue historians and are the subject of Richard J Evans’ book.

Evans is not here writing his own alternate history, rather he is writing a critical history of speculations about alternate histories. Most of these tend to argue that history is an accident, change one thing and you change another. Evans notes that many of them are essentially wishful thinking style histories and the largest number seem to be essentially reactionary ones, where the world somehow does not enter what are perceived to be the complexities of the modern world; or otherwise dystopias which come about if your friends don’t win. Evans argues that many of the scenarios invented by counter factual historians are, to say the least, implausible, that people and events being what there are there are limitations.

There is not going to be an alternate world in which Cardinal Richard Dawkins becomes Pope. There may be a world where a person with that name becomes Pope, but that person would not be in any sense the same person as the one we know as Richard Dawkins, because he must have had an entirely different history going back generations. As it progresses history winnows out possible alternate worlds. Which takes one back to Rubenstein’s discussion of the difference between limited and unlimited infinities?

Following in the footsteps of Brownlee and Ward’s Rare Earth David Waltham pours cold water on the belief that earth-like biospheres are abundant in the galaxy and that if we only sit at a radio telescope long enough we will detect the broadcasts of ET-TV. On the contrary Waltham argues that the earth is the lucky exception, perhaps the only place in the entire visible universe that good luck and the right moon allowed complex life to develop and sustain itself. While there will be other rich biospheres, these will lie well beyond the observation horizon. Waltham argues that the earth had an exceptionally lucky geological and climatological history, and that there were numerous occasions when things could have gone badly wrong leading to global extinction.

The arguments I suspect need specialist knowledge to comment on in detail, and perhaps life is a good deal more diverse and adaptable that Waltham gives it credit for. However the possibility that we living breathing human beings and out fellow social mammals are the only source of consciousness and value in the cosmos, and the enormous implications of that need to be taken very seriously indeed. – Peter Rogerson.

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