Anthropic principle

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The anthropic principle (from the Greek anthropos "man"; AP for short ) states that the observable universe can only be observed because it has all the properties that enable the observer to live. If it were not suitable for the development of a life capable of consciousness, there would also be no one who could describe it.

Development of the term

The principle was conceptually introduced into the scientific discussion in 1973 by cosmologist Brandon Carter during the celebrations of Nicolaus Copernicus ' 500th birthday, although similar strategies of argument were also occasionally used before. It links the properties of the observable universe with the necessity of the existence of a conscious observer who is also able to recognize this universe. Anthropic principles, as they are mostly discussed in natural science , are supposed to offer “natural” explanations for facts in the universe that seem very improbable to an observer and therefore cannot be explained by chance or make a goal-oriented or purposeful ( teleological ) impression.

Because of Carter's ambiguous definition of the anthropic principle, there are dozens of different interpretations today. While the "trivial" form, namely that the necessity of the existence of an observer has to be taken into account when interpreting astronomical data, is well recognized, some other versions are scientifically and philosophically discussed. The various formulations of the anthropic principle that exist today can be distinguished according to teleological and non-teleological interpretations, which have an almost opposite intention. The weak anthropic principle formulated by Carter is regarded as non-teleological, since it only describes effects that come about through selective observation, while the strong anthropic principle also allows teleological interpretations due to its ambiguous definition. In natural science, non-teleological interpretations predominate, often even only non-teleological interpretations are considered to be scientifically meaningful, and the anthropic principle is even certified as having an almost anti-leological thrust.

Some common versions of the anthropic principle

Brandon Carter

Some passages in Carter's 1974 publication are considered to be the first concrete formulation of the anthropic principle:

  • General AP : "... what we can expect to observe must be restricted by the conditions that are necessary for our presence as observers."
  • Weak AP ( weak anthropic principle , WAP ): "... we must be ready to take into account the fact that our place in the universe is necessarily privileged in the sense that it is compatible with our existence as an observer."
  • Strong AP ( strong anthropic principle , SAP ): ".. the universe (and therefore the fundamental parameters on which it depends) must be such that it allows the emergence of observers in it in some phases."

Especially the uncertain meaning of the word “must” in the strong AP is responsible for the unclear interpretation of this principle, as it can be interpreted both as a requirement of the simple logical compatibility of the observation data with the observer existence and in a stronger teleological sense. Because of this teleological interpretability of the strong AP in this formulation, it is often accused of a speculative and unscientific character.

In 1983 Carter emphasized that the principle in its original form should only serve to warn astrophysicists and cosmologists of possible errors in the interpretation of astronomical and cosmological data if the biological boundary conditions of the observer were not taken into account.

John Leslie

John Leslie regards the anthropic principle as a tautology which, like the rules of inference , which are also tautologies, can be used to draw valid conclusions from empirical observations.

He formulates the anthropic principle in general:

  • Every intelligent living being that is can only find itself there where intelligent life is possible.

According to Leslie, the only difference between weak and strong AP is that the weak AP claims that intelligent life can only be found in areas within a given universe where observers can exist at all, while the strong AP focuses on multiple universes (or also refers to a single universe with causally independent regions) and claims that intelligent life can only be found in universes in which the existence of observers is possible.

Nick Bostrom

The philosopher Nick Bostrom asked in 2002:

“Is it possible to summarize the core ideas of the selective perception effect in one simple statement? [... It could be that] many of the anthropic principles are simply confused. Some, especially those who draw inspiration from Brandon Carter's foundational work, sound reasonable [...] but are too weak to do real scientific work. In particular, I contend that the existing methodology does not allow any observable consequences to be inferred from current cosmological theories, notwithstanding that these theories can be tested quite easily and are also tested empirically by astronomers . What is needed to bridge this methodological gap is a more adequate determination of how selective perception effects must be included. "

To implement his views, he defines the self -sampling assumptions :

  • Self Sampling Assumption (SSA) : One should conclude as if one were a random selection from the set of all observers in one's reference class.
  • Strong Self Sampling Assumption (SSSA) : One should conclude that the current observation time is a random selection from the set of all observer times in its reference class.

The SSA or SSSA allow, unlike other anthropic principles, to assign a probability to the observations possible in observable universes; usually those universes in which conscious observers cannot exist are excluded from observation without taking it into account. It is therefore actually no longer a purely anthropic principle, but in this respect has similarities with a synthesis of the anthropic and the Copernican principle proposed by the astrophysicist Richard Gott , the Copernican-anthropic principle.

This self-selection hypothesis Bostrom extended to a model of "anthropic bias" ( anthropic bias ) and anthropischem Close ( anthropic reasoning ). It takes into account the uncertainty regarding the meaning of the observation at a given observation time in the universe. The model tries to overcome existing limits through cognitive human bias. Since the exact determination of the reference class, i.e. H. the class of all entities , from which an observer can reasonably assume to be randomly selected, but is in many cases uncertain, Bostrom believes above all such evidence with the aid of anthropic principles to be credible, the results of which are as independent as possible of the choice of the reference class.

John Archibald Wheeler

A version of the AP comes from the physicist John Archibald Wheeler , which is often associated with the subjective idealism of George Berkeley .

  • Participatory anthropic principle (PAP): observers are necessary to create the universe.

In particular, a quantum mechanical phenomenon, the so-called reduction of the wave function during measurement, is associated with an observer in PAP . Roughly speaking, a measurement is interpreted as an observation of a conscious being, and the associated reduction in the wave function is understood as the “realization” of the world in a definite state. The observer would therefore be an essential part of the physical description of the world; only through his observation would the world assume “reality”.

The PAP is closely related to an interpretation of quantum mechanics , in particular to the so-called Copenhagen interpretation , which represents the reduction of the wave function in the measurement. For example, recent developments in the interpretation of quantum mechanics, which allow an objective description of the quantum mechanical measurement process in purely quantum mechanical terms, i.e. do not refer to a measurement apparatus that obeys classical laws as in the Copenhagen interpretation, are also relevant for the assessment of the PAP.

This principle is often accused of having an unscientific teleological character; B. Earman's critical review of the PAP .

Barrow & Tipler

In 1986 the controversial book The Anthropic Cosmological Principle by physicists John D. Barrow and Frank J. Tipler was published. In it the cosmologist John Barrow paved the way for what he called an anthropic principle. His aim was to find a way of dealing with the almost unbelievable coincidences that led to our presence in a universe that seems perfectly adjusted to our existence. Everything from the exact energy state of the electron to the extent of the weak interaction seems tailor-made to allow our existence. We seem to live in a universe that is dependent on a number of independent variables where a tiny change was enough to make it uninhabitable for any form of life. And yet we exist. The anthropic principle claims that the reason we are here and even consider these questions is because we have just the right values ​​for the variables.

The two versions of the weak and strong anthropic principle as formulated by John Barrow and Frank Tipler are:

  • weak anthropic principle (Engl. 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 for the existence of places at which carbon-based Life can develop, and by the requirement that the universe must be old enough that this process has already occurred. "
  • strong anthropic principle ( SAP) : "The universe must be such that it enables the development of life in a certain stage of its history."

In addition, Barrow and Tipler also postulated another principle, called the Final Anthropic Principle (FAP) , according to which the universe is structured in such a way that it should be possible in the future to achieve eternal life with technological means.

  • Final Anthropic Principle: "Intelligent information processing must arise in the universe, and once it has arisen it will never die out".

Tipler expanded this concept in 1994 in his book The Physics of Immortality to include the Omega point theory . Both the book and the theory, however, meet with strong criticism and rejection in the professional world in general because of the many extremely questionable and highly speculative assumptions.

Anti-Leological Interpretation

The intention of the non-teleological interpretation is to explain conditions in cosmology that are perceived as improbabilities through selection effects in possible observations, which are caused by the conditions necessary for the existence of the observer. In particular, in conjunction with many-worlds models or a universe assumed to be infinite (or at least sufficiently large), the anthropic principle is able to explain such apparently teleologically acting improbabilities non-teleologically, and thus has a pronounced anti-leological character. For example, in an infinite universe with spatially varying physical constants, an observer can only exist in such areas and therefore locally only observe those areas in which these constants permit conscious life. Even a universe that is predominantly hostile to life could appear "made" for life to an observer.

The current state of development of string theory includes the possibility to the probability of the coexistence of very many universes that are different according to natural law (typical estimates call the astronomical number of approx. 10,500 ). Should this still speculative possibility be substantiated, this would be a strong argument for the non-teleological interpretation that one of these many worlds happens to be “friendly to life”.

Teleological interpretation

The teleological interpretation of nature has appeared again sporadically in some scientific and popular science publications since the 1970s, but is mainly propagated in a more religious environment. Teleological explanations try to represent the universe guided by goal-oriented or purposeful principles or mechanisms, or also planned and guided by a divine being. The controversial participatory anthropic principle by John Archibald Wheeler is often cited as an example of a teleological anthropic principle .

Sometimes nowadays in some popular scientific publications, actually incorrectly and contrary to the original intention of this principle, the anthropic principle and the teleological explanation are equated. Particularly in creationist circles, the anthropic principle is mostly inadmissibly narrowed to the teleological interpretation. In its teleological interpretation, as it was also spread by John D. Barrow and Frank J. Tipler, the principle goes back to deep historical roots. Thus, for most philosophers and theologians, the world before Darwin was centered on humans. It was only through Charles Darwin's theory of evolution that today's predominant non-teleological view prevailed.

Criticism and defense of the anthropic principle

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The anthropic principle was criticized for its tautological character, since according to the rules of logic it must always be true. The answer is usually that the purpose of the anthropic principle is not to express its own content, but only to use it to provide evidence, for which tautologies are also permissible and useful. Despite its originally anti-iteleological intention, the anthropic principle, especially in its strong form, was accused of being teleological and unscientific. The naming “anthropic” has also been criticized, since “conscious observer” does not only include human observers, but any kind of intelligent observer.

Proponents of the anthropic principle point out that the universe appears so finely tuned to allow the existence of life as we know it, and that if any of the fundamental physical constants were to deviate from its value, that life would not be possible would. Works have been written that take the view that the anthropic principle is able to explain physical constants such as the fine structure constant , the number of dimensions of the universe and the cosmological constant . The proponents point out that these constants have no "obvious" values. The universe that we observe must be suitable for intelligent life to develop, otherwise we could not be here and observe it. Whether this fine-tuning and thus the anthropic principle is really necessary to explain life is, however, controversial. Opponents argue that this fine-tuning is only necessary if one assumes that conscious life is only possible as we know it. If this previously unjustifiable restriction were dropped, fine-tuning would not be necessary.

Another criticism of the anthropic principle is that theories that allow the anthropic principle as an argument are often not falsifiable . For example, in an infinite universe that obeys quantum mechanical laws, all possible processes would actually occur somewhere, however rare they may be. In particular, due to quantum mechanical fluctuations, the sudden emergence of so-called “freak observers”, who could experience all kinds of actual or even just hallucinated observations, would be inevitable. In principle, we couldn't even be sure that we weren't such a freak observer ourselves. So there would be no possible observation with which one could refute such a theory. One can escape this problem, however, by going over to statistical evidence, as is customary in scientific practice anyway. All observations are possible, but not all are equally frequent, and some events, such as the creation of a freak observer, are so extremely rare that they can be practically ruled out.

Although actually not a fundamental criticism of the validity of the anthropic principle, it is often objected that it often takes on a stopgap role by offering a possible explanation for circumstances for which science has so far lacked stronger explanations.

Anthropic and Copernican principles

It is interesting, also because of the imprecise definition of the anthropic principle, to consider the relationship between the anthropic principle and the Copernican principle , which denies that humans have an excellent position in the cosmos. The naming of the anthropic principle, albeit often criticized as ambiguous, seems to indicate a contradiction between the two principles.

In its non-teleological interpretation, the anthropic principle does not necessarily contradict the Copernican principle, since there can also be applications of the anthropic principle that presuppose a universe that is homogeneous as a whole and corresponds to the Copernican principle. However, the weak anthropic principle can e.g. B. can also be applied to universes that are predominantly hostile to life and only allow the existence of intelligent life forms such as humans in small, life-friendly "islands". Here, the weak anthropic principle can be used to explain the fact that intelligent observers can only observe life-friendly islands within the universe as selective observation. Since humans could only observe such special areas, they would have an epistemological special position in such a universe . So, contrary to the Copernican principle, they would at least be excellent observers, even if the human being does not occupy a special position here in the sense that the universe is specifically geared towards its existence. As part of his presentation of the Doomsday argument, the astrophysicist R. Gott proposed the anthropic-Copernican principle, which is a synthesis of both principles.

It is different with teleological interpretations of the anthropic principle. What is ultimately assumed here is a "mechanism" or principle that aligns the universe towards a specific goal. Depending on how strongly this goal is specifically directed towards the existence of man, such anthropic principles are therefore also in contradiction to the Copernican principle, provided that this is interpreted strictly anti-iteleologically. Is the Copernican principle defined "only" in the epistemological sense, i. That is, if only a special position of the human being as an observer in the existing universe is denied, the principles do not have to be fundamentally in contradiction to one another.

Application of anthropic principles

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Origin of Life

The anthropic principle is only needed as an argument for the emergence of (intelligent) life in our given universe if one assumes that some steps, which are absolutely necessary for the emergence of (intelligent) life, are very much on a given planet with suitable conditions are unlikely. This is currently still scientifically controversial, with a wide spectrum of opinions ranging from extremely unlikely (for the development of an intelligent civilization) to the opposite position, according to which life must inevitably arise under reasonably suitable environmental conditions.

If one assumes the emergence of life on a given planet as very unlikely, the weak anthropic principle with the assumption of an infinite (or very large) universe is often considered as a possibility to explain the emergence of life despite some possibly locally improbable evolutionary steps. In such an infinite (or very large) universe, the sheer number of suitable planets would outweigh the improbability of the development of life on an individually considered planet and life would therefore practically inevitably arise. This is particularly interesting since current astronomical observation data can be interpreted with an infinite, or at least very large, universe.

Conversely, conclusions can also be drawn about some properties of evolution from the fact of earthly intelligent life and the anthropic principle. B. Carter concluded in 1983 that when interpreting evolutionary history, astrophysical limitations of the process must also be taken into account. Carter assumes that earthly life arose according to the theory of evolution, and continues from the remarkable coincidence that the duration from the emergence of life to the development of earthly intelligent life (≈ 4 billion years) is in the same order of magnitude as the lifespan of the sun-like stars. According to Carter, this would be a very big coincidence if the typical development time of intelligent life were much shorter than the lifespan of the sun (≈ 10 billion years). However, it could be easily explained using the weak anthropic principle (self-selection principle) if the typical development time of intelligent life were (much) longer than the solar lifespan. To explain the long development period, there must be at least one improbable evolutionary step in the development of intelligent life. Carter further points out that although the development time of earthly intelligent life is in the same order of magnitude as the lifespan of the sun, it also shows a difference. From this difference, Carter estimates an upper limit of at most about two unlikely evolutionary steps. This result is often used to estimate the possibility of extraterrestrial intelligence in the visible universe. Antonio Feoli and Salvatore Rampone argued that if the estimated size of our visible universe and the number of planets in it are taken into account, there is a higher possibility of extraterrestrial intelligence developing in this visible universe than the Carter's finding implies.

Fine tuning of the natural constants

The more extensive question of why the laws of nature and the natural constants of the observable universe even have the necessary properties and values ​​to allow life is often answered with the anthropic principle. However, strong anthropic principles and multi-world theories are used, so that the arguments are predominantly more speculative in character. Here, too, the question arises to what extent the possibility of life does not have to be given from the outset in most logically possible universes. So it is not clear whether there is ultimately a need for explanation and therefore a reason for applying the anthropic principle.

Barrow and Tipler write about fine-tuning; This means that the natural constants in the universe seem to be precisely coordinated to make life possible:

Not just that humans fit into the universe. The universe also suits people. Imagine a universe in which any of the basic dimensionless physical constants would change a few percent in one direction or another? Man could never have come into existence in such a universe. That is the linchpin of the anthropic principle. According to this principle, the entire mechanism and structure of the world is based on a factor which enables the existence of life.
(John Barrow and Frank Tipler, The Anthropic Cosmological Principle , p. 7).

The anthropic principle, together with many-world theories (multiverses), is able to explain the fine-tuning of the universe claimed by some cosmologists - which therefore makes life possible. The anthropic principle thus contradicts the need for intelligent, planning-based creation to explain this fine-tuning, as proposed, for example, by proponents of the intelligent design hypothesis, such as the religious philosopher Richard Swinburne . On the other hand, the existence of virtually infinite parallel universes is suggested for other reasons, and the anthropic principle gives additional support to this theory. Assuming that some possible universes would be capable of producing intelligent life, there must be actual universes that do, and ours obviously is one of them.

The alleged fine-tuning has been criticized as a " lack of imagination argument " for assuming that no other forms of life are possible. It could be possible that the range of natural constants that allows the evolution of carbon-based life is subject to far fewer restrictions than has been claimed (cf. Stenger, "Timeless Reality").

But universes would also be conceivable that are so dissimilar to the known universe that they not only have slightly different constants from our universe, but even completely different particles (and thus also interactions between these particles), which nevertheless form complex structures, who are capable of self-reference. These structures would hardly have any similarities with life as we know it, but they would represent self-referential systems just like the ( self-confident ) human being.

Anthropic Principle and Infinite Universes

If the universe is infinite, or if there is an infinite number of universes, perhaps also with other natural constants or even other natural laws, then every physically possible process must occur infinitely often , no matter how small its probability in relation to the visible universe. For example, the emergence of (intelligent) life would be inevitable, no matter how unlikely some stages of development would have been.

It is criticized that this line of argument is speculative; From a radical positivist standpoint, it does not make sense to draw inferences from an unverifiable property of the universe such as “infinity”, since such properties are rejected as metaphysical and transcendent. In today's analytical philosophy, on the other hand, such transcendent quantities are entirely permissible as long as they play a role in an empirical theory that provides testable (falsifiable) predictions as a whole. Theistic attempts to explain the world, which contain indissolubly speculative-transcendent ideas, cannot reject the above argument anyway for this reason without being inconsistent.

Anthropic principle and string theory

The string theory states that there could be a large number of possible universes with different conditions: multiverse hypothesis. Some physicists see this knowledge as confirming the anthropic principle, since several universes are possible in which no intelligent life can exist and therefore conscious observers will never ask questions about their properties. Other physicists see the multiverse hypothesis as an alternative to the teleological interpretation of the anthropic principle, from which religious fundamentalists derive the necessity of a creator being. This thesis is currently still being discussed controversially in science.

See also

literature

Web links

Wiktionary: Anthropic  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. ↑ However , it was used earlier. B. 1957 Robert Henry Dicke : “The 'current' age of the universe is not random, but is determined by biological factors ... [changes in the values ​​of fundamental physical constants] would preclude the existence of people who could think about the problem . «(RH Dicke, Principle of Equivalence and Weak Interactions , Rev. Mod. Phys. 29, p. 355, 1957.) Lawrence J. Henderson and his books The Fitness of the are considered to be one of the most important masterminds of the teleologically interpreted anthropic principle Environment (1913) (German title Die Umwelt des Lebens , 1914) and The Order of Nature (1917). The agnostic Henderson, who generally rejected religious considerations, concluded from his biochemical analysis in 1913 that the universe is essentially biocentric . In his opinion, the laws of nature are such that the universe is practically oriented towards the development of life. Even earlier representations of the principle can be found in Alfred Russel Wallace's book Man's Place in the Universe , which was first published in 1903. For example: “A universe as vast and complex as the one we know exists around us might be absolutely necessary ... to produce a world that is precisely adapted to every detail for the orderly development of culminating life in man should. ”(pp. 256-257 in the 1912 edition).
  2. ^ From B. Carter: “Large Number Coincidences and the Anthropic Principle in Cosmology” IAUS 63 (1974) 291 translated
  3. ↑ a b Richard J. Gott: Implications of the Copernican principle for our future prospects , Nature, vol. 363, p. 315 (1993), online ( Memento from April 18, 2013 in the Internet Archive ) (PDF; 668 kB)
  4. ↑ J. Wheeler in The nature of scientific discovery. Owen Gingerich (editor) Washington Smithsonian Press, 1975; J. Wheeler in Foundational Problems in Special Sciences RE Butts, J. Hintikka (editors) Dordrecht, Reidel
  5. ↑ J. Earman: The SAP also rises: a critical examination of the anthropic principle , Philosophical Quarterly 24 (4), 307 (1987)
  6. ↑ Rüdiger Vaas: in Bild der Wissenschaft , issue 5/2013, p. 54.
  7. ↑ George FR Ellis , Geoffrey Brian Brundrit: Life in the infinite universe. Royal Astronomical Society, Quarterly Journal, 20, 37-41 (1979), bibcode : 1979QJRAS..20 ... 37E .
  8. ↑ B. Carter: The anthropic principle and its implications for biological evolution. Phil. Trans. R. Soc. Lond. A 310, 347-363 (1983)
  9. ^ A. Feoli, S. Rampone: Is the Strong Anthropic Principle Too Weak , 1999