I’m going to do the unthinkable: on a site entitled Research Reviews, I’ll actually be reviewing some research! Before you die of shock, let me assure you that I will not be reviewing what generally comes to mind when people think of “research” (no labs were harmed, or used, in the making of this research), and that of course you will be getting something for free out of it (the entire book Anthropic Bias: Observation Selection Effects in Science and Philosophy). Also, I will as is typical of this blog be reviewing certain topics in or relevant to the sciences, such as the anthropic principle and fine-tuning.
The Book: What it isn’t
The reviewed work here is the book Anthropic Bias: Observation Selection Effects in Science and Philosophy by Dr. Bostrom. Although it covers topics like multiverse cosmology and the anthropic principle, it differs in several ways from most books that deal with these subjects. First, it is not filled with equations and formulae as is Barrow & Tipler’s (in)famous The Anthropic Cosmological Principle nor is it sensationalist and overly simplistic like Krauss’ A Universe From Nothing or Schroeder’s The Hidden Face of God. It’s a work of scholarship, published by Routlege (an academic publishing company) as part of the series Studies in Philosophy. It’s not the kind of book you’ll find in bookstores nor would most, I think, find it light reading. Second, it deals with multiverse theory and the anthropic principle secondarily. The book is really a treatise on the best way to approach a particular kind of problem that we face in the sciences but are actually more likely to encounter in popular discourse. To illustrate the kind of problem this book concerns (observation selection effect bias), I’ll give two examples, one simple and the other simplistically summarized.
Anthropic Bias: Examples of bias from observation selection effects
Example 1: Extraterrestrial intelligent life must exist
This is one of several examples that Bostrom gives in his introduction, but I choose it because I have addressed this specific question here and I have found myself trying to explain the problems involved to an almost inevitably skeptical audience. Many people believe that even if it is incredibly unlikely for life to develop on any given planet, there must be a huge number of planets with life, including intelligent life, because there exists an astronomically (bad pun intended) large number of planets in the universe. Moreover, there are many of them even relatively nearby that are “Earth-like” and found in what astrobiologists, among others, call “habitable zones” (HZs). And after all, what are the chances that Earth is the only planet in the entire universe on which complex (including microscopic, multicellular organisms) or intelligent life arose?
Well, this final question approaches the right way to think about this issue. To estimate how many planets have life, all we need to do is take the number of favorable outcomes (planets with complex life) and divide by all the planets. Simple. Of course, if knew of any other planet with complex life, we wouldn’t be asking this question. But I don’t want to present my approach to this problem (although it is similar, in form and conclusion, to Bostrom’s). I want to give his:
“Let’s look at an example where an observation selection effect is involved: We find that intelligent life evolved on Earth. Naively, one might think that this piece of evidence suggests that life is likely to evolve on most Earth-like planets. But that would be to overlook an observation selection effect. For no matter how small the proportion of all Earth-like planets that evolve intelligent life, we will find ourselves on a planet that did (or we will trace our origin to a planet where intelligent life evolved, in case we are born in a space colony). Our data point—that intelligent life arose on our planet—is predicted equally well by the hypothesis that intelligent life is very improbable even on Earth-like planets as by the hypothesis that intelligent life is highly probable on Earth-like planets…
The impermissibility of inferring from the fact that intelligent life evolved on Earth to the fact that intelligent life probably evolved on a large fraction of all Earth-like planets does not hinge on the evidence in this example consisting of only a single data point. Suppose we had telepathic abilities and could communicate directly with all other intelligent beings in the cosmos. Imagine we ask all the aliens, did intelligent life evolve on their planets too? Obviously, they would all say: Yes, it did. But equally obvious, this multitude of data would still not give us any reason to think that intelligent life develops easily. We only asked about the planets where life did in fact evolve (since those planets would be the only ones which would be “theirs” to some alien), and we get no information whatsoever by hearing the aliens confirming that life evolved on those planets (assuming we don’t know the number of aliens who replied to our survey or, alternatively, that we don’t know the total number of planets). An observation selection effect frustrates any attempt to extract useful information by this procedure.”
Example 2: The Anthropic Principle
The anthropic principle is usually divided into classes (especially strong and weak) and is highly nuanced, so I will just keep things simple by approaching it as sort of an inverse of example 1. In the first example, we looked at the flawed reasoning that leads to the idea that complex life is likely abundant in the universe. The most frequent arguments involve a flawed inference from the fact that life arose here to how likely it is to arise elsewhere, because knowing only that it arose here is consistent both with the hypothesis that life arose only on Earth and the hypothesis that complex life is abundant in the universe.
Not long ago, back when Neil deGrasse Tyson was Carl Sagan, scientists in general had pretty high hopes for the Search for Extra-Terrestrial Intelligence (SETI). To some extent that hasn’t changed, but a combination of the complete failure of SET and an increased understanding of the sheer number of variables that have to be just for life to arise and evolve have prompted many scientists working in astrobiology to conclude that complex life is probably rare, that if intelligent life exists elsewhere we’re never going to know, or even that we are alone. The arguments for and against these and other beliefs about life in the universe are for another time. Here, I simply want to introduce a very simple definition of the anthropic principle as it is relevant here:
“The anthropic principle is the name given to the observation that the physical constants in the cosmos are remarkably finely tuned, making it a perfect place to host intelligent life. Physicists offer a “many-worlds” explanation of how and why this might be the case.
My feeling is that a misanthropic principle could also be applicable. I use this term to express the idea that the possible environments and biological opportunities in this apposite cosmos are so vast, varied and uncooperative (or hostile), either always or at some time during the roughly 3-to-4 billion years intelligent life requires to emerge, that it is unlikely for intelligence to form, thrive and survive easily.” (Alone in the Universe)
Because there are so many fundamental “parameters” (e.g., the cosmological constant, the four fundamental forces, etc.) don’t just appear to allow for life, but are instead “remarkably finely tuned” for it. Again, I don’t want to introduce too much of my take here so to quote from Bostrom:
“Another example of reasoning that invokes observation selection effects is the attempt to provide a possible (not necessarily the only) explanation of why the universe appears fine-tuned for intelligent life in the sense that if any of various physical constants or initial conditions had been even very slightly different from what they are then life as we know it would not have existed. The idea behind this possible anthropic explanation is that the totality of spacetime might be very huge and may contain regions in which the values of fundamental constants and other parameters differ in many ways, perhaps according to some broad random distribution. If this is the case, then we should not be amazed to find that in our own region physical conditions appear “fine-tuned”. Owing to an obvious observation selection effect, only such fine-tuned regions are observed. Observing a fine-tuned region is precisely what we should expect if this theory is true, and so it can potentially account for available data in a neat and simple way, without having to assume that conditions just happened to turn out “right” through some immensely lucky—and arguably a priori extremely improbable—cosmic coincidence.”
Popular Physics: What this book isn’t
Paul Davies is a physicist and author of a number of popular science books, including The Goldilocks Enigma and The Eerie Science. The first book is on fine-tuning and the anthropic principle, while the second is on life in the universe. In the second, Davies concludes with his own views, one as a scientists, one from a philosophical perspective, and one as a person. Wearing his “scientist hat”, he conclude, “my answer is that we are probably the only intelligent beings in the observable universe, and I would not be very surprised if the solar system contains the only life in the observable universe. I arrive at this dismal conclusion because I see so many contingent features involved in the origin and evolution of life, and because I have yet to see a convincing theoretical argument for a universal principle of increasing organized complexity…”
Both of Davies books are quite like many, some that agree and many that don’t, in that they offer glimpses into the nature of scientific research related to the origins of life, the finely-tuned parameters (or why they actually aren’t finely tuned, although this is a minority position), but don’t require any real background knowledge. Then there are books that are at least semi-popular, such as Penrose’s The Road to Reality or the aforementioned The Anthropic Cosmological Principle, but are largely inaccessible to most readers (my father received his undergraduate degree in physics from one an Ivy League college, is an extremely intelligent individual, and didn’t get much past chapter 1 of Barrow & Tipler’s book).
That’s one thing I find particularly delightful about Bostrom’s book. It is technical in that it tackles reasoning and logic in a highly nuanced way. Although examples are given frequently to illustrate logical implications or flaws in particular inferences, the questions and issues tackled are fleshed out completely without skimping over any issue related to the rational, logic, validity, or justifications for any arguments.
Philosophical Texts on Reasoning and Rationality: What this book is better than
Better yet is that this book deals with subjects like whether the cosmos is finely tuned for intelligent life and if so what this means. The book is fundamentally concerned with advancing a coherent, logical, and justifiable framework for addressing kinds of questions like those in the examples. I have many books with similar goals: Heuristics and Biases: The Psychology of Intuitive Judgment, Probability Theory: The Logic of Science, Acceptable Premises: An Epistemic Approach to an Informal Logic Problem, Abductive Reasoning- Logical Investigations into Discovery and Explanation, Against Coherence: Truth, Probability, and Justification, Bayesian Epistemology, The Algebra of Probable Inference, Abductive Cognition: The Epistemological and Eco-Cognitive Dimensions of Hypothetical Reasoning, Model-Based Reasoning in Science and Technology: Theoretical and Cognitive Issues, and many dozens more. I enjoyed many of them and found all to be useful, but would recommend few if any to the general reader. That’s because they aren’t just technical, but only technical. They are “dry”, not just because they demand the reader deal with sophisticated nuances, but because they introduce their subject matter as their subject matter.
Now, there’s nothing wrong with this. In fact, it’s very hard to write a book about something, especially an academic monograph, without talking almost exclusively about that something. Of course, most books on methods in the sciences, certain kinds of reasoning or logics, epistemology, etc., give plenty of examples. But they are of the kind that we find e.g., in Bostrom’s 5th chapter “The self-sampling assumption in science” where there are sections on SSA in thermodynamics or evolutionary biology. Few books are able to recognize how far two related subjects (in this case, fine-tuning and the anthropic principle), both the main topic of countless popular books, can serve to introduce and cover in no small detail something like a specific kind of abstract reasoning. Bostrom not only found such a perfect way to thoroughly introduce the reader to so abstract a topic, he proceeds to cover it in more detail with a variety of interesting examples, and then uses a popular and fascinating probability paradox (the doomsday argument, one of the paradoxes in Eckhardt’s Paradoxes in Probability Theory, which cites Bostrom here) as yet another way to flesh out still finer points of his approach.
Thank you, and please help yourself to our complimentary gift on your way out
To embarrass myself by quoting the children’s television show Reading Rainbow, “but you don’t have to take my word for it.” If you think that fine-tuning, multiverse theory, the anthropic principle, and scientific reasoning might be interesting topics, but you don’t want to spend the money, another great thing about this book is that it is available in FULL for free and LEGALLY (well, I think legally, as it is available from the book’s website). So please, help yourself:
Anthropic Bias – complete text