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The anthropic principle, also known as the "observation selection effect", is the hypothesis, first proposed in 1957 by Robert Dicke, that the range of possible observations that could be made about the universe is limited by the fact that observations could happen only in a universe capable of developing intelligent life. Proponents of the anthropic principle argue that it explains why the universe has the age and the fundamental physical constants necessary to accommodate conscious life, since if either had been different, no one would have been around to make observations. Anthropic reasoning is often used to deal with the idea that the universe seems to be finely tuned for the existence of life.

There are many different formulations of the anthropic principle. Philosopher Nick Bostrom counts them at thirty, but the underlying principles can be divided into "weak" and "strong" forms, depending on the types of cosmological claims they entail. The weak anthropic principle (WAP), as defined by Brandon Carter, states that the universe's ostensible fine tuning is the result of selection bias (specifically survivorship bias). Most such arguments draw upon some notion of the multiverse for there to be a statistical population of universes from which to select. However, a single vast universe is sufficient for most forms of the WAP that do not specifically deal with fine tuning. Carter distinguished the WAP from the strong anthropic principle (SAP), which considers the universe in some sense compelled to eventually have conscious and sapient life emerge within it. A form of the latter known as the participatory anthropic principle, articulated by John Archibald Wheeler, suggests on the basis of quantum mechanics that the universe, as a condition of its existence, must be observed, thus implying one or more observers. Stronger yet is the final anthropic principle (FAP), proposed by John D. Barrow and Frank Tipler, which views the universe's structure as expressible by bits of information in such a way that information processing is inevitable and eternal.

Source: Anthrophic principle - Wikipedia

In essence, when theists marvel at the remarkable fine-tuning of the fundamental constants of the universe, which enables the existence of intelligent conscious life, and suggest that this remarkable phenomenon demands an explanation (such as an intelligent designer), proponents of the anthropic principle often argue differently. They suggest that such fine-tuning isn't actually surprising—after all, we inevitably find ourselves in a universe capable of supporting life because, otherwise, we wouldn't be here to ponder it. If circumstances were different, we wouldn't exist, but since we do, it's not unexpected that the universe possesses conditions conducive to our existence.

Does this effectively counter the fine-tuning argument for God's existence? How do Christian proponents of this argument address such objections?


Note: Personally, I don't think so. See Does the "sniper analogy" undermine the Anthropic Principle objection to the fine-tuning argument for God's existence?

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  • Rather than answer, I will simply note that this looks suspiciously similar to christianity.stackexchange.com/questions/94341. 🙂
    – Matthew
    Commented Apr 1 at 17:25
  • @Matthew Are you suggesting that the anthropic principle and the puddle analogy are conceptually equivalent? If so, how?
    – Mark
    Commented Apr 1 at 19:45
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    They're related. The Anthropic Principle (which is purely philosophical) says there are infinite universes with no intelligent life, and us. The puddle argument says that a universe with intelligent life will necessarily "look" fine-tuned. A refutation to both is that merely being able to produce intelligent life is still extremely unlikely to produce the universe we actually inhabit.
    – Matthew
    Commented Apr 1 at 20:28
  • The strong and final anthropic principles (and maybe the weak one as well) seem a lot to me like attempts to sneak an intentional deity into an atheistic system.
    – Jed Schaaf
    Commented May 5 at 11:58

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The arguments of the Weak Anthropical Principle against Fine Tuning critically depend on the existence of an effectively infinite number of universes in which there can be "survivors". If there is only one universe then the existence of life in it is truly astonishing, whether or not we were here and able to observe it, and whether or not we could observe its non-existence. Having a throw of a thousand coins all come up heads is expected if you are allowed to toss them trillions of times, but astonishing if that is the only time you can toss them.

Arguers of the WAP have removed the need for God - who they see as an unnecessary construct and supported by little evidence. But to do so they have had to invent billions of universes of constructs supported by absolutely no evidence at all. Occam would consider God to be the more plausible hypothesis.

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    There's also the problem that, even if infinite universes exist, the probability of intelligent life inhabiting one with the diversity of life present in ours is quite small. If you liken the search space to "out of all living organisms, select one at random" and the WAP as specifying that only those picks that happen to be human bother to contemplate fine-tuning, our universe is like the one where you not only chose a human, but one who is a billionaire.
    – Matthew
    Commented Apr 1 at 17:29
  • @Matthew would you like to quote the specific source where you learned about these calculations?
    – Mark
    Commented Apr 1 at 20:09
  • @Mark, alas, I don't recall. (Also, what "calculations"?) However, it's obvious when you look at all the improbable steps necessary for Common Descent to explain observed reality (e.g. the eye evolving dozens of times). Where is the argument that intelligent life requires life to be as diverse as we observe, or to "re-evolve" certain features many, many times?
    – Matthew
    Commented Apr 1 at 20:38
  • @Matthew The calculation of the probability of an universe like ours existing even if a multiverse as required by the WAP is granted. WAP advocates claim that an universe like ours should be expected (otherwise intelligent conscious beings like us would not be here to think about it). But you are saying that even if that multiverse is granted, we shouldn't expect an universe like ours. I would like to see the math.
    – Mark
    Commented Apr 1 at 21:38
  • @Mark I think that DJ is getting at the point that the extra requirement of life actually existing is even more improbable than a universe that is merely finely tuned to support life. You could probably find estimates of the probability of life evolving, and then tack this on to the probability of a fine tuned universe without life.
    – user65254
    Commented Apr 1 at 22:08
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A straightforward definition of the anthropic principle is given here by geophysicist Professor Bob White:

"The universe is extremely finely balanced. The anthropic principle, which is a subject of scientific study, is concerned with some of these incredibly precisely tuned parameters that make life possible." God, the Big Bang & Bunsen Burning Issues, p.146, Ed. Nigel Bovey, Authentic, 2008

Whether weak or strong, a principle cannot suffer from logical fallacies. Only conclusions arrived at, based on principles, can either be illogical or logical. Any principle in the universe can be considered and conclusions arrived at that either the principle substantiates God as creator of this universe, or not. For the purpose of this answer I would like to quote sample reasoning from two camps. First, someone who does not believe in God but is erudite in explaining cosmological theories:

John Gribbin, in this book, arrived at an interesting conclusion. He does not believe in God or even in "members of a technologically advanced civilization in another part of the Multiverse" (p 195). But he quotes Harrison in an article published in the Quarterly Journal of the Royal Astronomical Society:

"The superior beings who created our universe inhabited a universe not greatly unlike our own. They were not only intelligent but intelligible, and were perhaps similar to our distant descendants who might also create universes. How these superior beings created our universe and how their own was created now becomes comprehensible issues open to inquiry.

The intelligence required to do the job may be superior to ours, but it is a finite intelligence reasonably similar to our own, not an infinite and incomprehensible God... This provides the best resolution yet to the puzzle Albert Einstein used to raise, that 'the most incomprehensible thing about the Universe is that it is comprehensible.' The Universe is comprehensible to the human mind because it was designed, at least to some extent, by intelligent beings with minds similar to our own." In Search of the Multiverse John Gribbin, p198 Allen Lane / Penguin, 2009

That is interesting. There's nothing wrong with exploring possibilities, and that's what all the theories about the universe do. Of course, some non-believers are a touch anxious that they are not seen to be 'allowing for' God in any of this.

Here, now, is a quote from an astrophysicist, Rev. Dr. Rodney Holder, giving a different view of the anthropic principle:

“Scientific discoveries, such as the fine-tuning of the universe, feed my faith and deepen my appreciation of God. For example, the universe in its initial phase – the first fraction of a second from the Big Bang – had to be set up in a very special way in order for stars, galaxies and ultimately life to form. Cosmologist Fred Hoyle did some major work on the nuclear reactions that go on inside stars to form all the chemical elements out of the simplest building block, which is hydrogen. He discovered that there needs to be a very fine balance of the forces in nature in order to make carbon, and then to make oxygen without destroying the carbon. Although he didn’t believe in God, Hoyle said that his work led him to the conclusion that there was a super-intellect behind physics, chemistry and biology, and that there are no blind forces worth speaking about in nature...

“Right back at the beginning, the universe needed to be very close to that knife-edge in order for stars, galaxies and planets to form. The mass-energy needed to be what it was to within 1 part in 10\60 (that’s ten with sixty noughts after it). That kind of accuracy would be the same as firing a gun from one end of the universe to the other (some 10 billion light years away) and hitting a coin you were aiming at. The question is, Was that a lucky shot or are you a brilliant marksman. Likewise, is the fine balance of the universe a lucky happenstance or is there a brilliant designer behind it? I believe that there’s a brilliant designer behind it.” God, The Big Bang & Bunsen Burning Issues pp 169-70, Ed. Nigel Bovey, Authentic, 2008

Now, you may think Gribbin is being logical in his conclusions, and that Holder (and, by implication, Hoyle) are being illogical. That might say more about one's idea of logic than it does about the anthropic principle. The facts of the astoundingly unlikely emergence of stars, building blocks for life, and all of those elements combining on just one planet in the universe (that we know of, so far) cannot be called 'illogical'. But the fact that conclusions as to God being at back of that clash hopelessly with conclusions that no God is 'needed'. And can we ever get away from the fact of intelligence in the universe? My answer is that the anthropic principle is sound. Our motives for trying to use the principle one way or another may be suspect, but that is actually a sign of intelligence.

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  • Excellent point! It is certainly worth noting that the anthropic principle is little more than a statement of the obvious, and as such, there is nothing really wrong with the principle per se.
    – user65254
    Commented Apr 4 at 18:27
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I assume that many of you are familiar with the watchmaker's argument of William Paley. Essentially, it is a version of the teleological argument for theism that claims that an object like a watch with all of it's perfectly synching mechanisms cannot fail but to be understood as having been designed with purpose.

In some sense, using the anthropic principle to object to intelligent design is a bit like stumbling upon a complicated mechanical piece like a watch and claiming "the fact that all of the pieces seem finely tuned should not be surprising because the watch does exist as brute force fact; if they were not perfectly tuned, then the thing in question would not exist in the first place". Though this is true, it merely pushes the argument one layer back from the issue of fine tuning or design to the issue of existence itself. The fact that a ponderable, pondered universe exists is an amazing fact that demands explanation as to existence even if one does not want to attribute significance to the details of it's inner workings. Thus, the anthropic principle fails to accomplish what objectors to fine tuning ultimately desire, to remove the necessity of the hypothesis of a designer in scientific explanations of the natural world.

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The anthropic argument cuts two ways. The given facts and the two lines of reasoning mentioned in the question can in their essence be stated as:

  • Something can only be observed if it happens.
  • Now we can have some theory: The observation is made but the event is so unlikely that we call it a miracle (the fine-tuning argument).
  • Or we can have some other theory: The unlikely event could only have been observed under the right conditions for the observer to exist so that the universe's existence is declared as some sort of unavoidable destiny, given it is observed. It is either observed so it had to exist, or it is not observed and does not exist.

Both theories are a posteriori given the observation is a bit lame in explaining the possible origin or probability of an observation. In a way it is similar to the probabilistic fallacy of the kind:

There is life in the universe, or there is not. So there is a 50/50 probability.

Here it is rather easy to see that this is false reasoning. Another more subtle but related analogy is the concept of a confidence interval:

Before a confidence interval is calculated, the interpretation for a 95% confidence interval means that if we were to repeat the sampling and interval calculation process many times (theoretically, an infinite number of times), about 95% of those confidence intervals would contain the true population mean.
However, once the confidence interval is calculated from a specific sample, a common misinterpretation arises: There is a 95% probability that this specific interval contains the true mean. However, this is not correct in frequentist statistics. In frequentist terms, the interval either contains the true mean or it does not.

The main point is that there is no probability attached to this specific event after the interval has been realized. Maybe the most similarity is shared with the sleeping Beauty problem. In a nutshell:

Some researchers are going to put you to sleep. During the two days that your sleep will last, they will briefly wake you up either once or twice, depending on the toss of a fair coin (Heads: once; Tails: twice). After each waking, they will put you back to sleep with a drug that makes you forget that waking. When you are first awakened, to what degree ought you believe that the outcome of the coin toss is Heads?

This example is more subtle. If you modify the Sleeping Beauty example with not a fair coin but a coin with a small (1 per gazillion) probability of heads, it captures the probabilistic essence of the anthropic argument discussion and it can give some intuition.

In conclusion, probabilistic theories or models leading to different outcomes about the probability of the occurrence of an event, after it has occurred simply have different assumptions. The question of which assumptions are appropriate typically ends in a philosophical debate, or a fit-for-purpose modeling debate. Generally, an objective probabilistic model can only be selected a priory, otherwise intentional cherry-picking is difficult to rule out. Theist or Atheist perspectives can in the context of antropic argument discussion be likened to choosing a Bayesian or the Frequentist perspective.

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Wolves lost by 5 goals to 1 against Manchester City last Saturday. What were the chances they would lose 5, 1? Well, before it happened you could have gone into a bookmakers and placed a bet on that result.

It should be no surprise that you cannot go into a bookmakers today and bet that the result was 5, 1.
It has already happened. It is actually no surprise Wolves would lose.. the chances of losing were close to 100%. But the chance they lost 5, 1 last Saturday is now 100%.

If you go into the bookmakers to place a bet, the bookmakers will now refuse your bet. You cannot make bets on historical events.

It seems to me all Anthropological Principle arguments are logically invalid.. it happened, therefore the chances of it happening are 100%. It is just a play with the laws of probability after the event has happened and claiming the probability of it happening were 100% because that is what happened.

The arguments are false arguments. They tell us precisely NOTHING about how likely an event would occur before it happened.

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    But isn't that what the Anthropic Principle is all about? That because it has already happened, there's no point in arguing that it was unlikely. ¶ Or by "arguments are logically invalid" do you mean arguments against the Anthropic Principle are meaningless? Commented May 7 at 13:46
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    @RayButterworth - my understanding of AP theories are they are logically invalid because they confuse the probability that something has already happened (everything is 100%) with the likelihood that they could happen before they happened, which, in the case of the universe as we know it and life as we know it is imo 0% by pure chance without God's intervention. AP theories seem to be no more than a con-trick, conflating post-event probability (100%) with prior-event possibility. Commented May 8 at 5:59
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    @Matthew - Yes, of course, I agree. And my post is seeking to draw attention to the trickery and shenanigans of AP theories in their obfuscation of pre and post event probability. Commented May 8 at 6:00
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    @RayButterworth - the argument of AP theories seems to be v similar to this logically invalid argument: 1. The universe exists. 2. The chance the universe came into existence is 100% (true). 3. The chance the universe would come into existence is therefore 100%. 4. Therefore the existence of the universe therefore needs no explanation, it was always bound to happen. Commented May 8 at 6:11
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    @RayButterworth - us theists want to have two possible scenarios for the existence of the universe: 1. It just happened by chance (because there is no God) or 2. God did it. AP theories seem to be attempts to ignore possibility 2 altogether. Commented May 8 at 6:28

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