The Probability of God: A Simple Calculation That Proves the Ultimate Truth (Anglais) Broché – 26 octobre 2004
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This is probably the most debated question in the history of mankind. Scholars, scientists, and philosophers have spent their lifetimes trying to prove or disprove the existence of God, only to have their theories crucified by other scholars, scientists, and philosophers. Where the debate breaks down is in the ambiguities and colloquialisms of language. But, by using a universal, unambiguous language—namely, mathematics—can this question finally be answered definitively? That’s what Dr. Stephen Unwin attempts to do in this riveting, accessible, and witty book, The Probability of God.
At its core, this groundbreaking book reveals how a math equation developed more than 200 years ago by noted European philosopher Thomas Bayes can be used to calculate the probability that God exists. The equation itself is much more complicated than a simple coin toss (heads, He’s up there running the show; tails, He’s not). Yet Dr. Unwin writes with a clarity that makes his mathematical proof easy for even the nonmathematician to understand and a verve that makes his book a delight to read. Leading you carefully through each step in his argument, he demonstrates in the end that God does indeed exist.
Whether you’re a devout believer and agree with Dr. Unwin’s proof or are unsure about all things divine, you will find this provocative book enlightening and engaging.
“One of the most innovative works [in the science and religion movement] is The Probability of God...An entertaining exercise in thinking.”—Michael Shermer, Scientific American
“Unwin’s book [is] peppered with wry, self-deprecating humor that makes the scienti?c discussions more accessible...Spiritually inspiring.”--Chicago Sun Times
“A pleasantly breezy account of some complicated matters well worth learning about.”--Philadelphia Inquirer
“One of the best things about the book is its humor.”--Cleveland Plain Dealer
“In a book that is surprisingly lighthearted and funny, Unwin manages to pack in a lot of facts about science and philosophy.”--Salt Lake Tribune
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More accurately, it formulates the existence of God as something that we may not be entirely certain of, and therefore depends on vague estimates of probabilities, which are subjective measures of one's predilections to believe arguments of one type or another. Thus, this book acknowledges the subjective character of the question, and instead of focusing too much on the AUTHOR'S probability of the existence of God, it provides the reader with the tools to calculate the READER'S probabiliity of the existence of God.
This is a perfect example of a situation where the usual notion of probability often taught (when you flip the coin a thousand times it comes up heads as often as it comes up tails, for instance) comes up short. This notion makes no sense when it comes to matters of fact, which cannot be repeated in experiment. For this, Unwin describes the Bayesian interpretation of probability, pioneered in the early 1900s, where probabilities measure rational belief.
Unwin's work here applies the Bayesian notion of probability to five classical arguments used in the debate over the existence of God. As such, he has added something new and interesting to the debate.
In execution, however, there are problems and fallacious arguments--a feature that can be beneficial in a classroom where these deficiencies can be debated and discussed. First, Unwin's choice of five arguments determines the resulting probability more than he would like to admit. If some arguments had been subdivided into subarguments, the probability would change, giving that argument more weight. Similarly, there are fairly abstract philosophical arguments that were not brought in at all, which may be good for most people who are suspicious of such abstract arguments (perhaps with good reason) but it is important to recognize that not all arguments for or against the existence of God are considered.
Furthermore, the most difficult issue of all problems with the bayesian approach to probability, the initial a priori probability, he skips over facilely by declaring it to be 1/2. This may perhaps be better defended than any other number, but the explanation here is lacking.
Unwin also has a rating system to deal with the effect of each evidence area on the overall probability of the existence of God, that is very coarse, as it must be in such situations (can you imagine anyone arguing that the existence of evil in the world, given that God exists, is 23% as opposed to 24%, for instance?) The representative percent probabilities (1/11, 1/3, 1/2, 2/3, 10/11) he gets is fairly influential over the resulting answer, more than Unwin would like to admit. He certanly doesn't get two decimal places of accuracy, as he claims.
Now there is structure to bayesian analysis that Unwin does not discuss. In a chain of evidence, evidence that favors a hypothesis cancels evidence that works against that hypothesis in a very precise way, so that given his choices of probabilities, he is bound to get fairly moderate numbers (especially since he made sure to have arguments that favor the existence of God and arguments against).
Now, beyond the math, I should also mention a few other criticisms:
1. Philosophers and theologians have brought a great deal of nuance to these arguments that Unwin does not acknowledge. To take one example, the problem of evil in the world is not necessarily stacked against a traditional theist as it at first appears, depending on to what extent you accept various explanations offered by theists.
2. As in any philosophical work, there are arguments Unwin makes that would not work for everyone. For instance, his use of the anthropic principle to explain the fruitfulness of our universe depends on the many-worlds interpretation of quantum mechanics, which from a scientific methodological viewpoint, is as metaphysical and unmotivated as the existence of God in the first place. Still, the fact that Unwin does not focus on the ANSWER but on the PROCESS the reader can use to find his or her own answer, ameliorates this consideration considerably, as long as the reader goes through this exercise.
3. Unwin compares two positions: the traditional monotheist position of the Abrahamic faiths against the materialistic version of modern atheism. Comparing many positions at once would make this story much more complicated, so it's easy to see why he didn't bother. But for many people, the competing theories are of a different kind.
5. The most compelling reasons for belief, for many people, often involve issues beyond rationality, such as personal encounters with the divine, or the influence of a community of belief. And it is not at all clear that these reasons are "bad" reasons that should be shunned in these considerations. But they are excluded from the start in Unwin's work.
Still, the fact that Unwin seeks to provide tools, not answer questions, makes this book valuable as a *beginning* of a conversation.
His description of faith as the extra-rational piece that goes beyond reason falls short of traditional understandings of faith. Faith is not the magical extra extent to which one believes something that one would not believe otherwise. It is a trust that one chooses to make when reason is there: "faith is a leap into the light, not a leap into darkness". Even if this were the case, it is hardly acceptable to posit faith and rationality as adding together--as if a particularly gullible individual who has very good reason to believe something could end up with a probability of higher than 100%! Yet this is the model he argues for, somewhat unconvincingly.
With all these disagreements aside, I recommend the book, not as a source of answers, but a way to start thinking about these questions for yourself, perhaps leading you to write another book that reflects your perspective on this question. After reading this book, I was upset at the problems I mentioned above, but decided to organize a group of students to read this together, not in spite of the problems, but perhaps because of them. It is a positive thing for discussions to be deeper, especially when one does not agree with the other side.
Beyond all of this, Unwin is a very clear writer, and explains concepts of probability, risk, and Bayesian analysis so that anyone can understand it. He is also chatty and pleasant to read, with a sense of dry wit that can be delightful or annoying, depending on your personal taste in humor.
Overall, I recommend this book highly, as a beginning, not an end, to discussion.
Do I regard the authors core argument for belief in a God as flawed for the reasons you have read? Yes. I do. But in the interest of restoring balance allow me to highlight the strengths of this book.
First, Dr. Unwin has presented a new and innovative way to look at belief in God. In an area where the standard arguments for theistic belief have become calcified and tedious, the author delivers a breath of fresh air through Bayesian probabilities. The mathematical framework of Bayesian probabilities also provides a badly needed field of commonality on which both sides can meet to debate the merits of the issues. The math is easy and accessible due to the effortless way the authors has with words.
Second, the provocative 67% probability figure has energized the debate and provoked a lot of interest in the issues, as evidenced not just by the flurry of reviews here on Amazon, but by the guest appearance of the author on NPR, as well as by all of the human-interest news items generated in the press. Most theistic books never manage a blip on the public radar, while the authors work is seismographic in comparison.
Third, the supporting material is worth the price of the book. The author challenges currently popular evidences for God, and his discussions on what it means to `exist', on quantum behaviors, and the bigotry of `Scaleism' are delightful!
In conclusion, The Probability of God is vibrant. It sparkles with wit and thought provoking arguments. Weather you are a believer in God or not, you will find something in this book the challenge you and engage your mind. If you don't agree with the author, run your own numbers. Cast your own criteria and see where the calculations lead. Dr. Unwin will show you how.
In spite of the fact that I am agnostic and have no particular belief in gods, I find myself in the unusual position of recommending that people buy this book which argues for the existence of God. That is how special this book is. I call this book is a recommended read.
Amazingly, the author achieves this feat without burdening the reader with heavy theology and abstract mathematics. Nor does he reduce man's search for the Divine to trivial arithmetic. Rather, he proposes an intriguing way to view the subject. It's also a thoroughly enjoyable read because he presents his case in an informal, conversational style and with a sense of humor that balances the gravity of the subject.
Perhaps the most appealing feature of the book is that it's basic ideas stay with you long after you've finished reading. For example, Dr. Unwin presents six "evidentiary areas" for estimating the probability that God truly exists; for example: the universal notion of good and evil, and life-saving events that defy physical explanation (miracles). He uses these concepts as a basis for developing a probabilistic argument that God exists; that is, the evidence suggests it's more likely he exists than he doesn't. Soon after finishing the book, I found myself playing with the numbers and applying them to my own ideas of evidence for and against the proposition that God exists. This is the stuff that stimulates great discussion around the dinner table or (God forbid) at happy hour.
The mathematical arguments are solid, but they are only tools for converting assumptions into consequences. I will not be so presumptuous as to judge the assumptions (although the fact that I assign only 2 stars is indicative of my OPINION that the assumptions are subjective and questionable); that task is for you as the reader. Rather, my intent in this review is to encourage you to focus on the author's construction of the ASSUMPTIONS. The mathematical calculations that follow are easily verified as completely sound; please be careful not to artificially inflate the value of the assumptions because of the correctness and elegance of the math.
Unwin starts with 13 core assumptions. I won't be specific with them, because I believe the specifics deserve to be consumed in their appropriate context, in the book. But here they are in basic terms:
1. As a starting point (representing complete ignorance), the probability of the existence of God is X1.
2,3. The recognition of goodness has a relative Y2 amount of evidence and offers a relative Z2 amount of support for the existence of God.
4,5. The existence of moral evil "" Y3 "" Z3.
6,7. The existence of natural evil "" Y4 "" Z4.
8,9. Intra-natural miracles "" Y5 "" Z5.
10,11. Extra-natural miracles "" Y6 "" Z6.
12,13. Religious experiences "" Y7 "" Z7.
All of these X, Y, and Z variables are assigned numerical values by Unwin. Then the mathematical principle of Bayes' Theorem is applied (correctly) to calculate the CONDITIONAL probability that God exists given that ALL ASSUMPTIONS ARE EXACTLY TRUE. I won't ruin your or the author's fun and reveal the answer, but I'll at least mention that it's not precisely 0 or precisely 1.
So, my suggestion is to read this book ONLY if you are willing to approach it with caution and use it as food for thought. You will be sorely disappointed if you are seeking a weapon to defend your pre-existing opinions. Please be aware that the author's conclusions should be measured based primarily on the validity of his assumptions.
If you're interested in learning how to better interpret assertions (like Unwin's calculated probability of God) in an objective way without being swayed by subjective or emotional persuasion, then I recommend the following books:
Damned Lies and Statistics: Untangling Numbers from the Media, Politicians, and Activists (by Joel Best, 2001); Trust Us, We're Experts!: How Industry Manipulates Science and Gambles with Your Future (by John Stauber and Sheldon Rampton, 2000); and an oldie but goodie, How to Lie with Statistics (by Darrell Huff, 1954).