The anthropic principle simply states that there are several universal constants and that these constants take on their values according to the requirement that carbon based life can evolve at some point during the universe's history. The universe must be old enough that this has already occurred.
Perhaps rather than being an argument on its own, apologists use the anthropic principle (or more precisely a straw man version of it) to further bolster the fine-tuning argument and argument from design.
Brandon Carter, the British Cosmologist who proposed this principle in 1976, has gone further by stating that "the Universe must have those properties which allow life to develop within it at some stage in its history."
Astronomer and Minister Hugh Ross counts more than 100 constants, at a probability of about 1 chance in 10138 against their lining up as they have in our universe. The probability that each of these constants has lined up in a "life friendly" way, without the intervention of an outside intelligence, is astronomically small. With such a low probability of a "life friendly" universe, the only reasonable explanation for our existence is that God has "fine tuned" these attributes specifically to accommodate human life.
There are several versions of the anthropic principle. The two major variations being: "strong" and "weak". The strong anthropic principle (SAP) can also be divided into two other variations, "participatory" and "final".
Weak anthropic principle (WAP)
The weak anthropic principle states that in a universe that is large or infinite in space and/or in time, the conditions necessary for the development of intelligent life will be met only in certain regions that are limited in space and time. The intelligent beings in these regions should therefore not be surprised if they observe that their locality in the universe satisfies the conditions that are necessary for their existence." (Steven Hawking. A Brief History of Time)
Strong anthropic principle (SAP)
This form states that a universe "must have those properties which allow life to develop within it at some stage of its history." (John Barrow and Frank Tipler, The Anthropic Cosmological Principle)
Participatory anthropic principle (PAP)
This form states that a universe cannot come into being without observers (Barrow and Tipler). The implication is that these observers must be sentient.
Final anthropic principle (FAP)
This form states that intelligences must evolve within a universe and that once evolved will not die out.
The FAP has also been dubbed "the Completely Ridiculous Anthropic Principle (CRAP)" by author and skeptic Martin Gardner.
- p1. There is some kind of special significance to human life and or the human frame of reference.
- p2. From the human frame of reference we seem to observe a number of 'constants' that are necessary for human life to be sustained
- a. Goldilocks zone
- b. Oxygen level
- c. Strength of gravity fields
- d. Etc
- p3. It is far too improbable for all the necessary 'constants' to occur by chance
- c1. Therefore the universe was specifically made this way
- c2. Therefore God
Straw man argument
The proper scientific usage of the anthropic principle in physics and cosmology, is a cautionary statement against making unwarranted assumptions based on the observer's frame of reference. Directly it refers to the tautology that the universe must be able to support life because we are here to observe this fact. Or more broadly, that anything we do observe in the universe must necessarily be skewed by our limited frame of reference from within the very system we are trying to observe.
One of the rules that defines over arching laws of nature, is that they cannot be frame dependent. Einstein's law of relativity must hold true on the other side of the galaxy, just as it does here, otherwise it cannot be called a true law of nature.
An example of the anthropic principle in action would be that we are able to observe red shift in the stars surrounding us. This means that they are all moving away from us. A credulous or egocentric observer might therefore conclude we are at the center of the universe. This is an unwarranted assumption. If however the universe were 'inflating' rather than simply expanding from a single point then another observer would see the same thing from any other position of observation within the universe. On closer inspection we see that the red shift of the stars exponentially increases with the distance the star is from us. It appears the stars are all moving away from us, but in fact they are all really moving away from each other.
The theistic usage of the term anthropic principle is almost diametrically opposed to its proper scientific usage. Rather than acting as a cautionary statement against weighting our conclusions based on our frame of reference, it argues that because of our observable frame of reference there must be a god.
False premise p1: Frames of reference
The entire argument hinges on the human frame of reference being statistically significant. There is however no evidence to support this premise. The only significance to our personal existence or frame of reference, is the significance that we choose to grant it post hoc.
The chances of getting a royal flush (A♠ K♠ Q♠ J♠ 10♠) in poker is 649,740 to 1. It is interesting to note though, that there are four suits and therefore, four possible royal flushes in a deck of cards. That means that the chances of getting any specific random poker hand of five cards (K♥ J♣ 8♣ 7♦ 3♠) is actually four times more unlikely than getting a royal flush. However we simply do not grant any statistical significance to this hand in the games rules.
The fundamental core of this argument is a case of the theist being dealt a random poker hand, and then proclaiming after the fact, “Wow! The chances of me getting this specific hand of cards is 2,598,960 to 1. It must have been divine intervention."
False premise p2: Constants
The second false premise is related to the so called constants. It is entirely possible that there are factors that make the possibilities of life in the universe statistically improbable, but reviewing the list of given reasons at some apologetics sites, their importance in the probability equation is questionable at best.
- Goldilocks Zone – Proponents of the argument claim that earth had to be exactly a certain distance from the sun to seed life. This is not necessarily the case. Some forms of bacteria can thrive in conditions ranging from -5°C ice sheets to 400°C underwater volcanic vents. Pressures up to 400 bar. Salt concentrations up to 10 times higher than regular sea water. The reason we see the life we do is because it has evolved to fit the environment. If a planet was further away from, or closer to the sun, it doesn't mean life couldn't exist, just that it would be different to the life we observe now. Additionally, it is possible that our solar system is a fairly typical system. That when a star system forms it does so under strict physical laws. A gas cloud of a certain size will form a certain sized star, with certain sized planets, at certain orbital distances. Similar to the way Plateau–Rayleigh instability causes a droplet of water followed by several smaller after drops at certain distances due to the waters surface tension verses gravitational pull.
- Oxygen Levels – The oxygen level within earth's atmosphere fluctuates. As there is more plant life the oxygen levels rise, the carbon dioxide level inversely goes down. When this happens plants have less to live on and some of those plants die off. When this happens the oxygen level goes back down and the carbon dioxide level goes up again allowing the plants to reproduce more and regain vitality. This is called a dynamic equilibrium. The system balances itself. It is also worth mentioning that some animals require more oxygen and others less. The level of oxygen is not a constant. And the current level of oxygen being fixed, isn't necessary for life to exist, just extremely fragile life that has evolved within the current environment. Furthermore it is worth noting that on the website referenced, carbon dioxide level is listed as a separate 'constant' rather than a counterpoint to oxygen in a further attempt to try and make the universe appear even more complicated than it really is.
- Gravity Fields – Even something as apparently fixed and transcendental as the strength of gravity is not necessarily a set constant. Recent unified field theories in physics and cosmology propose that at high enough energies, the strong nuclear, weak nuclear, electromagnetic and gravity forces, all converge to become a single unified force. As the universe cooled after the big bang and the four forces separated, mass and energy collapsed to a state where the outward push of the nuclear forces was in a stable equilibrium with the inward pull of gravity. We even observe some cases where one of the forces fails, such as in white dwarf or neutron stars, and the matter and energy compress further under the force of gravity until once again the remaining forces are in equilibrium. The universe is not dependent on the current strength of gravity being fixed.
False premise p3. Statistical probability
A royal flush is considered statistically significant. It has a probability of 649,740 to 1, which whilst being improbable means if you play 649,740 hands of poker, you should statistically get a royal flush at some point. Given the flaws with the first 2 premises that:
- p1. The only statistical significance to human life or the human frame of reference is what we arbitrarily apply to it post hoc
- p2. That the alignment of the necessary 'constants' is far less improbable than apologists would like to argue they are
Although the conditions for life similar to that on earth may still be improbable, given that there are 400 billion stars in our milky way galaxy, and that there are 100 billion galaxies in the observable universe, that is a staggering number of 'poker hands' the universe has to play with. That doesn't even take into account hypothetical theories about multiverses or an oscillating big bang/big crunch universe. Of course the proper usage of the anthropic principle tells us that while it may be statistically improbable, its isn't statistically impossible given that we have at least one example of life in the universe occurring. A further fallacy of the anthropic principle is the assumption that any of the physical constants of our universe can be changed independently of all other constants and laws. How do we know that altering one constant, assuming that this could, in fact, be done, wouldn't change all of the other natural properties of the system undermining the basic assumption of the anthropic priniciple.
Affirming the consequent
Arguments from the anthropic principle commit the fallacy of placing the consequent ahead of the antecedent, or affirming the consequent. In plain English, it means the tail is wagging the dog. The features of humanity have evolved as a result of our environment, rather than our environment being tailored to suit us.
Douglas Adams c.1998:
- "Imagine a puddle waking up one morning and thinking, 'This is an interesting world I find myself in, an interesting hole I find myself in, fits me rather neatly, doesn't it? In fact it fits me staggeringly well, must have been made to have me in it!' This is such a powerful idea that as the sun rises in the sky and the air heats up and as, gradually, the puddle gets smaller and smaller, it's still frantically hanging on to the notion that everything's going to be alright, because this world was meant to have him in it, was built to have him in it; so the moment he disappears catches him rather by surprise. I think this may be something we need to be on the watch out for."
The SAP and its variants assume that human observers are required for the existence of the universe. This is a common misrepresentation of the "Copenhagen interpretation" of quantum mechanics. It is taken from the mental experiment called Schrödinger's cat. A cat is placed in a sealed box into which poison will be pumped when the nucleus of a certain atom decays. According to the Copenhagen interpretation, the atom exists as both decayed and undecayed (superpositioned) until a measurement is made. Since the atom must exist in this superpositioned state, the cat must exist in the same state until the box is opened. Note that the cat does not cease to exist, nor does the atom's nucleus. They simply exist in an unobserved state. The 'wave forms' that represent the experiment's possibilities have not collapsed into a single 'choice'. If we accept the most mystical interpretation of quantum mechanics, the universe would still exist without human intelligence. It would simply exist in an unobserved state.
Other counter arguments
- Because we don't know of other universes with different constants, attempting to list the constants that can somehow vary is little more than speculation. There is no reason to assume that any "constant" can be changed. Furthermore, assuming it is somehow a knob that can be turned by a god effectively makes the anthropic principle assume its conclusion.
- While the odds of a universe's fundamental constants having a specific set of values may be very low, the odds of them having some value is 1.0 (100%). It may be that life exists in our universe because it happened to form, by chance, with a set of universal constants that support life. In other words, humanity exists because of a lucky roll of the dice, so to speak.
- It is possible that terrestrial life is not the only form of life possible in our universe. For example, creatures on another planet might pass on their genes via a mechanism other than the DNA double helix. In other words, it is possible that our universe's constants are friendly to a broad variety of life forms, and therefore it is wrong to assume that they have been 'tailored' to suit just humans.
- Similarly, it is possible that the universe's constants could have varied quite a bit, and still allow earth-style life to form. In other words, a broad variety of universes might be friendly to life as we know it. Indeed, if one of the "constants" is the amount of matter in the universe, why would a god choose a value that was clearly much higher than it needed to be to create life?
- The strong, participatory, and final anthropic principles presuppose that life had to exist in our universe. This is an unwarranted assumption. If our universe could not support life, it would not contain life. There is no reason to suppose that our universe was "intended" or "supposed to" contain life.
- The underlying principles of the universe are not known. Without knowing these principles, applying odds to the settings of the Universal constants is disingenuous. A probability analysis with a sample size of one is meaningless. Since we do not know how many 'settings' are possible for each constant, we cannot assign valid odds for different 'settings'.
- It can be shown that the chances of a universe having "life friendly" universal constants, low though they may be, are higher than the chances of the existence of a supernatural creator. As Michael Ikeda and Bill Jefferys point out in their paper "The Anthropic Principle Does Not Support Supernaturalism" a self referential loop occurs when a supernatural entity is assumed as a creator. Each iteration of the loop decreases the chances of a supernatural entity's involvement in the settings of the universal constant.
- It is unknown whether this is the only iteration of "The Universe". If other universes exist or if this universe has oscillated through a series of Big Bangs and Big Crunches, the universal constants may have been reset many times. Given enough universes and/or Bangs, our "life friendly" settings would inevitably occur.
- Most physicists do not accept the most mystical interpretation of quantum mechanics. Instead they view 'wave form collapse' and 'superpositioning' as an extremely useful and accurate description of poorly understood processes.
- With the SAP, apologists are positing a God of the gaps. The SAP and its variants take as fact what most cosmologists take as speculation. Cosmologists are making highly educated guesses about how the universe works. No-one currently knows how the Universe started or what underpins it. No-one even knows IF the universe started, or if it has always existed. This gap in our knowledge may provide a place for a god to exist, but humankind has examined other holes into which God was supposed to have climbed. In each case we have found nothing there but nature. It is a good bet that this gap houses fascinating things, but no God.
- The same argument can be applied to many entities within our universe, such as bacteria, black holes, or spaghetti bolognaise. For instance: we seem to observe a number of "constants" that are necessary for black holes to be formed and sustained. It is far too improbable for all the necessary "constants" to occur by chance. Therefore, the universe was specifically made this way so that black holes could exist.
Notwithstanding the obvious fact that the universe really isn't very congenial towards life, as 99.999% of the observed universe is uninhabitable, Vic Stenger in his book God: The failed hypothesis, quotes a private communication with Martin Wagner in which he points out that:
- "In fact, the whole argument from fine-tuning ultimately makes no sense. As my friend Martin Wagner notes, all physical parameters are irrelevant to an omnipotent God. 'he could have created us to live in a hard vacuum if he wanted.'"
- Anthropic Principle: The Design Is In The Details – Apologist POV
- The anthropic principle and the big bang: natural or supernatural? - Skeptical POV
- The Anthropic Principle Does Not Support Supernaturalism – Skeptical POV
- Wikipedia:Anthropic principle – Wikipedia article
- Wikipedia:Schrödinger's cat - Erwin Schrödinger's thought experiment regarding quantum indeterminacy.
- Wikipedia:Copenhagen interpretation – Key feature of quantum mechanics regarding particles described by wave function.
- Wikipedia:Unified field theory – Theory regarding the relationship between the 4 main forces in the universe.