The
anthropic principle in its most basic form states that any valid theory of the
universe must be consistent with our existence as carbon-based human beings at this particular time and place in the universe. Attempts to apply this principle to develop scientific explanations in
cosmology have led to some confusion and much controversy. Critics call it a
truism.
Origin
The term "anthropic principle" was first proposed in 1973 by
Brandon Carter during the
symposium "Confrontation of Cosmological Theories with Observational Data" in
Kraków celebrating Copernicus’ 500th birthday, as if to proclaim that humanity does hold a special place in the
universe after all.
1 In his contribution "Large Number Coincidences and the Anthropic Principle in Cosmology" Carter remarks: "Although our situation is not necessarily
central, it is inevitably privileged to some extent" (IAUS 63 (1974) 291).
Proponents and versions
Proponents of the anthropic principle suggest that we live in a
fine-tuned universe, i.e. a universe that appears to be "fine-tuned" to allow the existence of
life as we know it. If any of the basic
physical constants were different, then life as we know it would not be possible. Papers have been written arguing that the anthropic principle would explain the physical constants such as the
fine structure constant, the number of
dimensions in the universe, and the
cosmological constant.
The three primary versions of the principle, as stated by Barrow and Tipler (1986), are:
- Weak anthropic principle (WAP): "The observed values of all physical and cosmological quantities are not equally probable but they take on values restricted by the requirement that there exist sites where carbon-based life can evolve and by the requirements that the Universe be old enough for it to have already done so."
- Strong anthropic principle (SAP): "The Universe must have those properties which allow life to develop within it at some stage in its history."
- Final anthropic principle (FAP): "Intelligent information-processing must come into existence in the Universe, and, once it comes into existence, it will never die out."
The weak version has been criticized as an argument by lack of imagination for assuming no other forms of life are possible (see also carbon chauvinism). Furthermore, the range of constants allowing evolution of carbon-based life may be much less restricted than proposed (Stenger, "Timeless Reality"). The strong version is also criticized as being neither testable nor falsifiable, and unnecessary. The final version is discussed in more detail under
final anthropic principle; Barrow and Tipler state that, although it is a physical statement, it is nevertheless "closely connected with moral values".
Proponents of the
intelligent design conjecture assert support from the anthropic principle. On the other hand, the existence of alternate universes is suggested for other reasons and the anthropic principle provides additional support for their existence. Assuming some possible universe would be capable of supporting intelligent life, some actual universes must do so, and ours clearly is one of those. However, alternatives of the intelligent design conjecture are not limited to proposing the existence of alternate universes. Also,
it has been argued that the anthropic principle as conventionally stated actually
undermines the intelligent design conjecture (discussed in more detail under
fine tuning).
The Anthropic Cosmological Principle
In 1986, the controversial book
The Anthropic Cosmological Principle by
John D. Barrow and
Frank J. Tipler (Oxford University Press) was published. In this book Barrow, a cosmological scientist, pioneered what he called the
anthropic principle in order to deal with the seemingly incredible coincidences that allow for our presence in a universe that appears to be perfectly set up for our existence. Everything from the particular energy state of the
electron to the exact level of the
weak nuclear force seems to be tailored for us to exist. The existence of carbon-based life in this universe is contingent upon several independent variables; and were any of these variables to take a slightly different value, carbon-based life could not exist. The anthropic principle implies that our ability to ponder cosmology at all is contingent on
all the correct variables being in place. According to critics, this is simply a
tautology, a very elaborate way of saying
if things were different, they would be different. This weak anthropic principle is a truism that says nothing and explains nothing because in order for us to be here to ponder the universe, it had to be such that we can exist.
Brandon Carter presented his ideas about the anthropic principle in a 1974 publication of the
International Astronomical Union. Later, in 1983, he claimed that, in its original form, the principle was meant only to caution astrophysicists and cosmologists of possible errors in the interpretation of astronomical and cosmological data unless the biological constraints of the observer were taken into account. In 1983 he also included the warning that the inverse was true for evolutionary biologists; Carter claimed that in interpreting the evolutionary record, one must take into account the astrophysical restraints of the process. Working with this in mind, Carter concluded that the evolutionary chain probably could include only one or two highly improbable links given the available time interval. A. Feoli and S. Rampone ("Is the Strong Anthropic Principle Too Weak," 1999) argued that the estimated size of our universe and number of planets allows a higher bound, indicating no evidence for intelligent design in evolution.
There was renewed scientific interest in the anthropic principle in the late-1990s motivated by observational
cosmology and theoretical work in
quantum gravity. The theoretical work involved attempting to unify gravity with the other forces. While there were a number of promising developments, they all seemed to suffer from the problem that the fundamental physical constants seemed to be unconstrained. The observational motivation came from cosmological observations which gave firm values for quantities such as the matter density of the universe. Contrary to expectations, the value was not zero, but 0.7, which is a non-obvious value.
Recent publications (2004) by
Stephen Hawking suggest that our universe is much less
special than the proponents of the anthropic principle claim it is. According to Hawking, there is a 98% chance that a universe of a type as ours will come from a
Big Bang. Further, using the basic wavefunction of the universe as basis, Hawking's equations indicate that such a universe can come into existence without relation to anything prior to it, meaning that it could come out of nothing. As of 2004, however, these publications and the theories in them are still subject to scientific debate, and in the past, Hawking himself has asked, "What is it that breathes fire into the
equations and makes a universe for them to describe?...Why does the universe go to all the bother of existing?" (Hawking, 1988).
Anthropic principle in string theory
String theory predicts a large number of possible universes, called the backgrounds or vacua. The set of these of vacua is often called the
anthropic landscape or simply the
landscape. Some physicists argue that the existence of a large number of vacua puts the anthropic reasoning on firm ground. Others, most notably
Peter Woit and
Lubos Motl argue that this is not predictive.
M-theory attempts to deal with this problem.
Anthropic bias and anthropic reasoning
In 2002,
Nick Bostrom asked "Is it possible to sum up the essence of observation selection effects in a simple statement?" He concluded that it might be, but that:
:Many
anthropic principles are simply confused. Some, especially those drawing inspiration from Brandon Carter's seminal papers, are sound, but... they are too weak to do any real scientific work. In particular, I argue that existing methodology does not permit any observational consequences to be derived from contemporary cosmological theories, in spite of the fact that these theories quite plainly can be and are being tested empirically by astronomers. What is needed to bridge this methodological gap is a more adequate formulation of how observation selection effects are to be taken into account.
His Self-Sampling Assumption is "that you should think of yourself as if you were a random observer from a suitable reference class." This he expands into a model of
anthropic bias and anthropic reasoning under the uncertainty introduced by not knowing your place in our
universe - or even who "we" are. This may also be a way to overcome various
cognitive bias limits inherent in the humans doing the observation and sharing models of our universe using
mathematics, as suggested in the
cognitive science of mathematics.
See also
References
- Hawking, Stephen W. (1988). A Brief History of Time, p.174. New York: Bantam Books. Order: ISBN 0-553-34614-8.
External links
¹ The principle had, however, been invoked before then, e.g. in 1957, R.H. Dicke wrote:
The age of the Universe "now" is not random but conditioned by biological factors ... [changes in the values of the fundamental constants of physics] would preclude the existence of man to consider the problem. (R.H. Dicke,
Principle of Equivalence and Weak Interactions, Rev.Mod.Phys. 29, 355 (1957).) Even earlier statements of the principle may be found in
Alfred Russel Wallaces book Mans Place in the Universe, which was first published in 1903. For example: "such a vast and complex universe as that which we know exists around us, may have been absolutely required ... in order to produce a world that should be precisely adapted in every detail for the orderly development of life culminating in man." (pp. 256-7 in the 1912 edition).
It also has analogs in, e.g.,
Karl Marxs theory of historical materialism: "The first premise of all human history is, of course, the existence of living human individuals. Thus the first fact to be established is the physical organisation of these individuals and their consequent relation to the rest of nature." ('The German Ideology'',
ch. 1)
It is also invoked to salvage
string theory.
Category:Philosophy
Anthropic Cosmological Principle, The
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