The Anthropic Principle

Introduction
The Anthropic Principle is a speculative hypothesis that attempts to relate the structure of the universe to the underlying conditions that are necessary for the existence of observers. It was formulated in 1971 by the British astrophysicist Brandon Carter in an attempt to limit the Copernican Principle, which asserts that the earth does not occupy a privileged central position in the universe.

However, while the earth may not be special or privileged in every way, this does not mean that it cannot be privileged in any way. Indeed, Carter pointed out that our location in space is "necessarily privileged to the extent of being compatible with our existence as observers."

The Anthropic Principle is controversial because it implies a teleological linkage between the structure of the universe and the existence of human beings. Several theorists have taken this idea one step further by incorporating the Anthropic Principle into a larger design argument for the existence of God.

The Anthropic Principle makes this type of goal-directed argument possible by highlighting the various prerequisites for the existence of life. When these prerequisites are duly examined, a striking number of "cosmic coincidences" are discovered to exist between distant branches of physics. These "anthropic coincidences" are noteworthy because they are essential for the existence of life and because they require tremendous "fine-tuning" before they can be operational.

The gravitational constant (G), for instance, appears to be exceedingly fine-tuned for the existence of life. If it were slightly larger, stars would have burned too hot and much too quickly to support the fragile needs of life; but if it were slightly smaller, the intrastellar process of nuclear fusion would have never initiated, and life would have been incapable of arising here.

This same rationale can also be applied to the expansion rate of the nascent universe as well. This crucial factor is determined by the cooperative interplay between several distinct cosmic parameters, including the mass density of the universe, the explosive vigor of the Big Bang, and the strength of the gravitational constant. If the resulting cosmic expansion rate happened to be slightly greater than the presently observed value, life-supporting galaxies would have been unable to form; but if it were slightly smaller, the early universe would have collapsed back in on itself shortly after the Big Bang. Either way and no life forms would have been possible.

This is significant, because the various parameters that comprise the cosmic expansion rate also had to be fine-tuned to better than one part in 10⁶⁰ in order to generate a "flat" universe, so that normal Euclidian geometry (in which the sum of a triangle’s three angles add up to 180 degrees) could then become applicable. A similar degree of fine-tuning can be found throughout the remainder of nature’s fundamental parameters.

The challenge is to find a plausible explanation for this fine-tuning. According to the British mathematical physicist Roger Penrose, the odds that our biocentric universe could have accidentally evolved into its present fine-tuned configuration are an astounding one in 10 to the 10¹²³, which is a number so vast that it couldn’t be written on a piece of paper the size of the entire visible universe. This is why many theorists have posited the existence of a "supercalculating intellect" to account for this fine-tuning.

Others, however, have scoffed at this teleological interpretation of our cosmological history. They instead point out that this fine-tuning could have been generated randomly over billions of years if our universe turns out to merely be one of many. In this case, life would have evolved only in those regions that happened to possess the "correct" configuration of fundamental parameters, and we would then find ourselves living in this "special" region as a straightforward selection effect. Critics, however, charge that this position is question-begging by its very nature, since it gratuitously assumes the prior existence of these unexplained worlds.

Definitions
The Anthropic Principle comes in a variety of permutations, each with its own set of implications. The broadest and least controversial is known as the Weak Anthropic Principle (or WAP):

The WAP states that we never could expect to observe a universe that is significantly different from our own, because our existence depends on the prior existence of just such a universe. The WAP thus doesn’t try to explain how or why our universe came to be life-supporting. It merely notes that, while the universe is biocentric for unknown reasons, given our current existence it couldn’t possibly have been otherwise.

One of the advantages of the WAP is that it highlights the many diverse structural parameters that are necessary for the existence of life. Nevertheless, many people still find the WAP to be deeply unsatisfying, because it merely states what we already know to be true; namely, that the universe has to be structured in its present format before it can be capable of supporting carbon-based life. The WAP is thus incapable of explaining why the universe is structured in this biocentric manner. For this we need a more potent form of the Anthropic Principle, which has been dubbed the Strong Anthropic Principle (or SAP):

The key element of the SAP is the word "must." It means that the universe had to be life-supporting at some stage of its history. This possibility is suggested by the many astonishing "coincidences" between distant branches of physics that all work together, against all the odds, to make life possible. The conventional SAP, however, does not attempt to explain why the universe must be biocentric. It simply states that this must be so.

The SAP thus comes close to positing the existence of a cosmic Designer. This is because there doesn’t seem to be any other plausible way of explaining why the universe had to be life-supporting. It is for this reason that the physicist Heinz Pagels once quipped that the SAP is "the closest that some atheists can get to God."

One interpretation of the SAP makes note of the above inference by explicitly crediting a Designer for the earth’s many biocentric features. This interpretation can be called the Design-Centered Anthropic Principle (or DCAP):

A second interpretation of the SAP is derived from the findings of modern theoretical physics. Dubbed the Participatory Anthropic Principle (or PAP) by physicist John Wheeler, it states the following:

The PAP follows from the standard Copenhagen interpretation of quantum mechanics, in which some type of living consciousness is required to make events "real." According to this interpretation, due to Neils Bohr, there is no such thing as a concrete quantum reality until a living observer exists to collapse the appropriate quantum wave function. Without this act of observership, reality seems to be held in a paralyzing state of indecision.

Some theorists have gone so far as to argue that life is necessary to make the universe itself real. The physicist George Greenstein has conceived of a "symbiotic universe," in which both life and the universe exist in a classic state of symbiosis—the universe provides the physical foundation for the existence of life, and life symbiotically responds by imparting a concrete state of reality to the cosmos.

The problem with this conceptualization is that life didn’t evolve until billions of years after the Big Bang. In order for Greenstein’s theory to be plausible, then, a non-corporeal form of life had to have been responsible for observing the universe into being long ago. The only candidate for this role would be the "Ultimate Observer" spoken of by Barrow and Tipler, who alone would have been in a position to observe the entire universe into being.

The third version of the SAP has been dubbed the Final Anthropic Principle, or FAP:

According to the FAP, once life arises, it will survive forever and become infinitely knowledgeable as it strives to mold the universe to its will. The FAP thus has an obvious religious quality to it, because it states that there is a positive universal purpose to human life that cannot be thwarted by any possible power. In this sense it is somewhat analogous to the tenets of generic theism, particularly in its affirmation of an "afterlife." However, the FAP doesn’t tell us why intelligent life will continue to endure forever. It merely states that it will do so.

Anthropic Coincidences
It is important to distinguish between the Anthropic Principle and a curious set of physical facts known as "anthropic coincidences." The Anthropic Principle proper is a speculative hypothesis regarding the possible role of humanity in the cosmos, whereas the various anthropic coincidences are empirical observations that relate the apparent "fine-tuning" of the universe life. This, in turn, seems to provide some degree of empirical support for certain forms of the Anthropic Principle.

We have seen how the value of the gravitational constant G, the mass density of the universe, and the explosive vigor of the Big Bang have all seemingly been fine-tuned to cooperate with one another to generate a smoothly expanding universe of coherent galaxies, each containing an abundance of medium-sized biocentric stars like our own sun. Numerous other fine-tuned anthropic "coincidences" are also at work in the universe to make life possible. A partial list includes the following: 1) the values of nature’s fundamental constants, 2) the existence of three spatial dimensions, 3) the ratio of the electromagnetic force constant to the gravitational constant, 4) the mass ratio of the electron and proton, 5) the ratio of protons to electrons, 6) the cosmic entropy level, 7) the speed of light, 8) the age of the universe, 9) the mass excess of the neutron over the proton, 10) the initial excess of matter over anti-matter, and 11) the sun’s historical change in luminosity, which happened to coincide with the specific needs of earth-based life forms.

One of the most notable anthropic "coincidences" was discovered by the British astronomer Sir Fred Hoyle, a former atheist. Hoyle had been researching the intrastellar process of carbon synthesis when he stumbled upon a remarkable series of "coincidences" pertaining to the stepwise assembly of the carbon atom. To his great surprise, Hoyle discovered that the nuclear resonance levels of both carbon and its immediate precursors (helium and beryllium) were fine-tuned to work together to encourage carbon synthesis. He also found that oxygen’s nuclear resonance level is half a percent too low to encourage the nuclear conversion of carbon into oxygen.

The end result of this remarkable series of "coincidences" is that carbon is able to be manufactured inside dying stars in sufficient quantities to make organic life possible. Hoyle concluded from this that the universe is a "put up job," and that a "supercalculating intellect" had to have "monkeyed" with the basic parameters of physics and cosmology. Otherwise, one would never expect so many unrelated and improbable "coincidences" to seamlessly work together to generate a biocentric universe.

The Anthropic Design Argument
Given the many inter-coordinated steps that are required to generate a fine-tuned, biocentric universe, many theorists find it astonishing that any form of life could have evolved on this planet. There are simply too many ways in which cosmic evolution could have gone "wrong" with respect to life, particularly given the universality of the Second Law of Thermodynamics, which states that the total amount of disorder in the universe is always increasing. It is the Second Law that leads one to expect a non-biocentric outcome at each stage of the universe-building process, yet the "correct" biocentric result nevertheless happened at each bifurcation point.

It is the fine-tuning of nature’s fundamental constants at the Big Bang that probably enabled this to happen. Indeed, given brute fact of human existence, it is necessarily the case that the universe be fine-tuned enough for it to overcome the many thermodynamic hurdles that naturally exist on the way to life. This, in turn, seems to suggest a strong element of necessity in the universe’s underlying ability to generate life. Insofar as this is so, it constitutes evidence in favor of the Strong Anthropic Principle.

Moreover, since the general cosmic tendency is always towards an increased amount of disorder, some thinkers conclude that there had to have been some type of constraining force at work in the past. Otherwise, this predisposition towards an increased amount of disorder would likely have put the universe on a non-biocentric path long ago, despite the fact that order can sometimes be generated to an open thermodynamic system by adding energy to it.

Traditional cosmology has been unable to account for this mystery, except insofar as it has used the principle of cumulative selection to "explain" the successive preservation of small instances of order, each of which could have possibly been random in origin. The problem with this hypothesis is that the universe had to have evolved to a relatively advanced stage before any type of cumulative selection could have taken place.

It is for this reason that many find the Strong Anthropic Principle to be compelling. How else are we to explain the trillions of correct choices on the way to life, despite the Second Law, if it weren’t structurally necessary for the universe to evolve life at some point in its history?

The Weak Anthropic Principle is typically invoked to refute this conclusion. On this view, we shouldn’t be surprised at our own existence because we are merely experiencing a selection effect, since it isn’t possible for us to have observed a non-biocentric universe. While this may be so, it doesn’t necessarily follow that our existence isn’t surprising. In the same way that a condemned criminal facing a one hundred-man firing squad would naturally be surprised if all one hundred rifles misfired simultaneously, it is also appropriate for human beings to be astonished at their own existence.

A potent counterargument to this "anthropic" viewpoint has been provided by Everett’s Many Worlds Interpretation of Quantum Mechanics. According to this hypothesis, there are an infinite number of "compartments" or worlds in existence within a much larger "multiverse," each possessing its own randomly varying set of fundamental constants. We therefore shouldn’t be surprised at our own existence, because it is only natural for life to evolve in the one region of the multiverse that is capable of supporting its existence. This is a prime example of how the Weak Anthropic Principle can be used within a non-theistic worldview to account for the existence of life.

There are three problems with this Many Worlds approach, however. First, there is no evidence for any of these other possible worlds, nor can there be any such evidence in the future, since these alternative domains are believed to be utterly beyond our observational powers, even in principle. Secondly, this approach is question-begging by its very nature, since it assumes the prior, unexplained existence of the multiverse itself. Finally, the use of an infinite number of unobservable worlds just to explain the existence of our own world is an unprecedented violation of Ockham’s Razor, which states that the simplest explanation in any set of natural circumstances is probably the correct one.

Anthropic Explanations
Critics of the Anthropic Principle believe it to be scientifically sterile, since it doesn’t initially seem to explain much about the cosmos in which we live. Supporters of the Anthropic Principle, by contrast, believe that it holds the key to an intriguing relationship between the structure of the universe and the existence of human observers.

The size and age of the universe provide an excellent case in point. Prior to the advance of modern cosmological science, it was believed that both the physical and temporal dimensions of the universe were unrelated to the existence of living observers. Bertrand Russell, for instance, believed that the universe’s enormous size and age naturally rendered the concept of intelligent design implausible, since one would naturally expect a Deity to have created the best things in the world (e.g., human beings) first rather than last.

This naïve viewpoint has now been supplanted by our modern cosmological understanding of the universe. It is now known, for instance, that a certain minimum time frame is inherently required for the intrastellar synthesis of carbon by natural evolutionary pathways. The amount of time that is necessary for this outcome amounts to several billion years, and is roughly equivalent to the time required to synthesize carbon and other heavy elements inside dying red giant stars. During this entire carbon-making epoch, though, the universe itself has been relentlessly expanding.

Therefore, it is only in a universe that is sufficiently old, and hence sufficiently large, that carbon-based observers can evolve. The enormous size of the universe (approximately 15 billion light years) is thus directly related to the time required for intrastellar carbon synthesis, due to the ongoing cosmic expansion. This is a genuine "anthropic" explanation, because it links several aspects of the universe to the conditions necessary to generate living observers.

Anthropic vs. Biocentric
The Anthropic Principle is actually a philosophical misnomer, since it is primarily an argument about the centrality of biological life in general. As such, it could legitimately be called the "Biocentric Principle."

A separate argument is thus required to generate an Anthropic Principle from the biocentric evidence. The term "anthropos," however, is a reference to uniquely human life, so the possible existence of intelligent beings elsewhere would technically invalidate the Anthropic Principle as such. In order to allow for this possibility, it has been suggested that the Anthropic Principle be renamed the "Humanoid Principle."

Three distinct arguments are thus conflated within the Anthropic Principle itself: 1) a biocentric argument, which refers to the centrality of biological life forms in general, 2) a humanoid argument, which refers to the centrality of intelligent humanoid life, and 3) a specific "anthropic" argument, which argues for the exclusivity of earth-based intelligent life.

These conflations, however, are widely deemed to be irrelevant to the central thrust of the Anthropic Principle, since it is generally assumed that human life would be the ultimate "goal" of any cosmic intention to evolve earth-based life. It is also assumed that the possible existence of other humanoid life forms would not invalidate the Anthropic Principle itself. Instead, it would simply provide other cosmic loci by which the existence of our biocentric universe could be explained.

An Anthropocentric Argument
It is possible to extend the Anthropic Principle into a general anthropocentric argument (and possibly a humanoid argument) by noting three relatively uncontroversial aspects of human existence:

1. The entire universe is thought to be based on the same structural "recipe" that is required for human existence. In this limited structural sense human beings do indeed appear to be located at the "center" of the known universe.
2. The human brain is widely acknowledged to be the most complex physical structure ever discovered. In terms of sheer structural complexity, then, the human brain can also be considered to exist at the "center" of the known universe.
3. Human consciousness is widely believed to be the most advanced functional property ever observed in the cosmos. In terms of pure functional sophistication, then, the property of human consciousness can also be considered to exist at the "center" of the entire known universe.

This argument actually represents a moderate anthropocentric point of view, because it allows for the possible existence of other intelligent beings in the universe besides humans. Two additional requirements must first be met, however, before this line of argument can work within a general "anthropic" context: 1) human existence must inherently require a profound degree of cosmological fine-tuning, and 2) human life must be intrinsically desirable enough to at least partially justify the existence of our "anthropic" universe.

This moderate anthropocentric position is vulnerable to criticism, however, on two levels: 1) the overwhelming scope of evil on this planet seems to nullify the possible existence of a benevolent Creator, regardless of the ostensible centrality of the human race, and 2) it is possible that creatures who are more complex and sophisticated than human beings will eventually be discovered.

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