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The Philosophy of Cosmology
Chamcham, Silk, Barrow, Saunders, eds.

Cambridge, 2017, 514 pages

Reviewed by T. Nelson

C osmology is uncovering lots of unresolved issues in the philosophy of science. They're important: they determine how we decide whether a theory is good enough, whether it makes sense to say, as some physicists have started doing, that the laws of physics transcend the universe itself, or that big bang was a creation event, or even whether evidence is really necessary when all we can get is the math.

Does it make any sense, for example, to have a deterministic theory of quantum mechanics that is constructed from non-deterministic, random events? Many physicists think it does not, but so far no viable explanation has emerged.

Thus, philosophy is not an exercise in wordplay mixed with overly complicated writing. Or at least, it's not just that. It's a process of thinking that, when successful, can reveal hidden assumptions in our reasoning. Can we assume, for example, that the value of pi is the same in all possible worlds, or is it a product of our particular three-dimensional space? Philosophers ask the question, and somebody else figures out the answer.

In short, science tells us what must be true, and philosophy tells us what cannot or need not be true. If one were feeling cynical, one might say philosophy is gloomy, badly written science and science is optimistic, badly written philosophy. Like matter and antimatter, when they come together they can shed light, or at least radiation, on the subject.

This collection of articles starts out great. Claus Beisbart writes “[T]he question is whether we can know that we have reached the limits of what we can know.” [p. 68]. Chris Smeenk phrases it as a pair of questions:

To what extent do observations of the early universe provide multiple, independent constraints on the physics underlying inflation? And has inflation made it possible to identify new physical features of the early universe that can be checked independently? (p.207)

His answer is that the challenges are insurmountable, because eternality undermines any evidence taken to support inflation.

That's a solid question and a daring answer that goes to the heart of the philosophy of science. But for the most part what we get here is a lot of basic astrophysics and not much actual philosophy.

The advantage of a multi-author book is that you can skip the bad ones, or one in particular where the author rewrites a famous quote to indulge in virtue-signaling, and focus on the scientific and philosophical articles. There are some great ones here.

An example is “Why Boltzmann Brains do not Fluctuate into Existence from the de Sitter Vacuum” by Boddy, Carroll, and Pollack. A Boltzmann brain is simply the idea that time-dependent thermal fluctuations (for which Boltzmann is justifiably famous for studying) will, over a long enough time, create an intelligent brain just by random chance. Needless to say, this idea causes problems.

The authors say the term ‘fluctuation’ has been equivocated to mean three entirely different things: vacuum fluctuations, Boltzmann fluctuations, and measurement-induced fluctuations. They conclude that quantum states in any horizon patch do not undergo dynamical fluctuations of any sort, including into Boltzmann brains. This is a very clever argument.

Some of the later articles are a little far out. Carlo Rovelli says that entropy is essentially a fiction. S.E. Rugh & H. Zinkernagel calculate that, due to relativistic effects, the center of the Earth is actually two years younger than the outside. And another author uses Bayes's theorem to come up with a new proof of the existence of God (although it's actually nearly the same as Leibniz's).

aug 19, 2017; updated aug 26, 2017