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Anthropic principle
From Wikipedia, the free encyclopedia
In astrophysics and cosmology, the anthropic principle is the philosophical
argument that observations of the physical Universe must be compatible with
the conscious life that observes it. Some proponents of the argument reason
that it explains why the Universe has the age and the fundamental physical
constants necessary to accommodate conscious life. As a result, they believe
that the fact is unremarkable that the universe's fundamental constants
happen to fall within the narrow range thought to allow life.
The strong anthropic principle (SAP) as explained by Barrow and Tipler (see
variants) states that this is all the case because the Universe is compelled
, in some sense, to have conscious life eventually emerge. Douglas Adams
used the metaphor of a living puddle examining its own shape, since, to
those living creatures, the universe may appear to fit them perfectly (while
in fact, they simply fit the universe perfectly). Critics argue in favor of
a weak anthropic principle (WAP) similar to the one defined by Brandon
Carter, which states that the universe's ostensible fine tuning is the
result of selection bias: i.e., in the long term, only survivors can observe
and report their location in time and space.
Contents
[hide] 1 Definition and basis
2 Anthropic coincidences
3 Origin
4 Variants
5 Character of anthropic reasoning
6 Observational evidence
7 Applications of the principle 7.1 The nucleosynthesis of carbon-12
7.2 Cosmic inflation
7.3 String theory
7.4 Ice density
8 The Anthropic Cosmological Principle
9 Criticism
10 See also
11 Footnotes
12 References
13 External links
[edit] Definition and basis
The principle was formulated as a response to a series of observations that
the laws of nature and parameters of the Universe take on values that are
consistent with conditions for life as we know it rather than a set of
values that would not be consistent with life on Earth. The anthropic
principle states that this is a necessity, because if life were impossible,
no one would know it. That is, it must be possible to observe some Universe,
and hence, the laws and constants of any such universe must accommodate
that possibility.
The term anthropic in "anthropic principle" has been argued [1] to be a
misnomer.[2] While singling out our kind of carbon-based life, none of the
finely tuned phenomena require human life or some kind of carbon chauvinism.
[3][4] Any form of intelligent life would do; so, specifying carbon-based
life, per se, is irrelevant.
The anthropic principle has given rise to some confusion and controversy,
partly because the phrase has been applied to several distinct ideas. All
versions of the principle have been accused of discouraging the search for a
deeper physical understanding of the universe. The anthropic principle is
often criticized for lacking falsifiability and therefore critics of the
anthropic principle may point out that the anthropic principle is a non-
scientific concept, even though the weak anthropic principle, "conditions
that are observed in the universe must allow the observer to exist",[5] is "
easy" to support in mathematics and philosophy, i.e. it is a tautology or
truism. However, building a substantive argument based on a tautological
foundation is problematic. Stronger variants of the anthropic principle are
not tautologies and thus make claims considered controversial by some and
that are contingent upon empirical verification.[6][7]
[edit] Anthropic coincidences
Main article: Fine-tuned Universe
In 1961, Robert Dicke noted that the age of the universe, as seen by living
observers, cannot be random.[8] Instead, biological factors constrain the
universe to be more or less in a "golden age," neither too young nor too old
.[9] If the universe were one tenth as old as its present age, there would
not have been sufficient time to build up appreciable levels of metallicity
(levels of elements besides hydrogen and helium) especially carbon, by
nucleosynthesis. Small rocky planets did not yet exist. If the universe were
10 times older than it actually is, most stars would be too old to remain
on the main sequence and would have turned into white dwarfs, aside from the
dimmest red dwarfs, and stable planetary systems would have already come to
an end. Thus Dicke explained away the rough coincidence between large
dimensionless numbers constructed from the constants of physics and the age
of the universe, a coincidence which had inspired Dirac's varying-G theory.
Dicke later reasoned that the density of matter in the universe must be
almost exactly the critical density needed to prevent the Big Crunch (the "
Dicke coincidences" argument). The most recent measurements may suggest that
the observed density of baryonic matter, and some theoretical predictions
of the amount of dark matter account for about 30% of this critical density,
with the rest contributed by a cosmological constant. Steven Weinberg[10]
gave an anthropic explanation for this fact: he noted that the cosmological
constant has a remarkably low value, some 120 orders of magnitude smaller
than the value particle physics predicts (this has been described as the "
worst prediction in physics").[11] However, if the cosmological constant
were more than about 10 times its observed value, the universe would suffer
catastrophic inflation, which would preclude the formation of stars, and
hence life.
The observed values of the dimensionless physical constants (such as the
fine-structure constant) governing the four fundamental interactions are
balanced as if fine-tuned to permit the formation of commonly found matter
and subsequently the emergence of life. A slight increase in the strong
nuclear force would bind the dineutron and the diproton, and nuclear fusion
would have converted all hydrogen in the early universe to helium. Water and
the long-lived stable stars essential for the emergence of life would not
exist. More generally, small changes in the relative strengths of the four
fundamental interactions can greatly affect the universe's age, structure,
and capacity for life.
[edit] Origin
The phrase "anthropic principle" first appeared in Brandon Carter's
contribution to a 1973 Kraków symposium honouring Copernicus's 500th
birthday. Carter, a theoretical astrophysicist, articulated the Anthropic
Principle in reaction to the Copernican Principle, which states that humans
do not occupy a privileged position in the Universe. As Carter said: "
Although our situation is not necessarily central, it is inevitably
privileged to some extent."[12] Specifically, Carter disagreed with using
the Copernican principle to justify the Perfect Cosmological Principle,
which states that all large regions and times in the universe must be
statistically identical. The latter principle underlay the steady-state
theory, which had recently been falsified by the 1965 discovery of the
cosmic microwave background radiation. This discovery was unequivocal
evidence that the universe has changed radically over time (for example, via
the Big Bang).
Carter defined two forms of the Anthropic Principle, a "weak" one which
referred only to anthropic selection of privileged spacetime locations in
the universe, and a more controversial "strong" form which addressed the
values of the fundamental constants of physics.
Roger Penrose explained the weak form as follows:
"The argument can be used to explain why the conditions happen to be just
right for the existence of (intelligent) life on the earth at the present
time. For if they were not just right, then we should not have found
ourselves to be here now, but somewhere else, at some other appropriate time
. This principle was used very effectively by Brandon Carter and Robert
Dicke to resolve an issue that had puzzled physicists for a good many years.
The issue concerned various striking numerical relations that are observed
to hold between the physical constants (the gravitational constant, the mass
of the proton, the age of the universe, etc.). A puzzling aspect of this
was that some of the relations hold only at the present epoch in the earth's
history, so we appear, coincidentally, to be living at a very special time
(give or take a few million years!). This was later explained, by Carter and
Dicke, by the fact that this epoch coincided with the lifetime of what are
called main-sequence stars, such as the sun. At any other epoch, so the
argument ran, there would be no intelligent life around in order to measure
the physical constants in question — so the coincidence had to hold, simply
because there would be intelligent life around only at the particular time
that the coincidence did hold!"
—The Emperor's New Mind, Chapter 10
One reason this is plausible is that there are many other places and times
in which we can imagine finding ourselves. But when applying the strong
principle, we only have one Universe, with one set of fundamental parameters
, so what exactly is the point being made? Carter offers two possibilities:
First, we can use our own existence to make "predictions" about the
parameters. But second, "as a last resort", we can convert these predictions
into explanations by assuming that there is more than one Universe, in fact
a large and possibly infinite collection of universes, something that is
now called a multiverse ("world ensemble" was Carter's term), in which the
parameters (and perhaps the laws of physics) vary across universes. The
strong principle then becomes an example of a selection effect, exactly
analogous to the weak principle. Postulating a multiverse is certainly a
radical step, but taking it could provide at least a partial answer to a
question which had seemed to be out of the reach of normal science: "why do
the fundamental laws of physics take the particular form we observe and not
another?"
Since Carter's 1973 paper, the term "Anthropic Principle" has been extended
to cover a number of ideas which differ in important ways from those he
espoused. Particular confusion was caused in 1986 by the book The Anthropic
Cosmological Principle by John D. Barrow and Frank Tipler,[13] published
that year which distinguished between "weak" and "strong" anthropic
principle in a way very different from Carter's, as discussed in the next
section.
Carter was not the first to invoke some form of the anthropic principle. In
fact, the evolutionary biologist Alfred Russel Wallace anticipated the
anthropic principle as long ago as 1904: "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."[14] In 1957,
Robert 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."[15]
[edit] Variants
Weak anthropic principle (WAP) (Carter): "we must be prepared to take
account of the fact that our location in the universe is necessarily
privileged to the extent of being compatible with our existence as observers
." Note that for Carter, "location" refers to our location in time as well
as space.
Strong anthropic principle (SAP) (Carter): "the Universe (and hence the
fundamental parameters on which it depends) must be such as to admit the
creation of observers within it at some stage. To paraphrase Descartes,
cogito ergo mundus talis est."
The Latin tag ("I think, therefore the world is such [as it is]") makes it
clear that "must" indicates a deduction from the fact of our existence; the
statement is thus a truism.
In their 1986 book, The Anthropic Cosmological Principle, John Barrow and
Frank Tipler depart from Carter and define the WAP and SAP as follows:[16][
17]
Weak anthropic principle (WAP) (Barrow and Tipler): "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."[18]
Unlike Carter they restrict the principle to carbon-based life, rather than
just "observers." A more important difference is that they apply the WAP to
the fundamental physical constants, such as the fine structure constant,
the number of spacetime dimensions, and the cosmological constant —, topics
that fall under Carter's SAP.
Strong anthropic principle (SAP) (Barrow and Tipler): "The Universe must
have those properties which allow life to develop within it at some stage in
its history."[19]
This looks very similar to Carter's SAP, but unlike the case with Carter's
SAP, the "must" is an imperative, as shown by the following three possible
elaborations of the SAP, each proposed by Barrow and Tipler:[20]
"There exists one possible Universe 'designed' with the goal of generating
and sustaining 'observers.'"
This can be seen as simply the classic design argument restated in the garb
of contemporary cosmology. It implies that the purpose of the universe is
to give rise to intelligent life, with the laws of nature and their
fundamental physical constants set to ensure that life as we know it will
emerge and evolve.
"Observers are necessary to bring the Universe into being."
Barrow and Tipler believe that this is a valid conclusion from quantum
mechanics, as John Archibald Wheeler has suggested, especially via his
participatory universe and Participatory Anthropic Principle (PAP).
"An ensemble of other different universes is necessary for the existence of
our Universe."
By contrast, Carter merely says that an ensemble of universes is necessary
for the SAP to count as an explanation.
Modified anthropic principle (MAP) (Schmidhuber): The 'problem' of existence
is only relevant to a species capable of formulating the question. Prior to
Homo sapiens' intellectual evolution to the point where the nature of the
observed universe - and humans' place within same - spawned deep inquiry
into its origins, the 'problem' simply did not exist.[21]
The philosophers John Leslie[22] and Nick Bostrom[23] reject the Barrow and
Tipler SAP as a fundamental misreading of Carter. For Bostrom, Carter's
anthropic principle just warns us to make allowance for anthropic bias, that
is, the bias created by anthropic selection effects (which Bostrom calls "
observation" selection effects) — the necessity for observers to exist in
order to get a result. He writes:
"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, though 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."
—Anthropic Bias, Introduction., [24]
Strong self-sampling assumption (SSSA) (Bostrom): "Each observer-moment
should reason as if it were randomly selected from the class of all observer
-moments in its reference class."
Analysing an observer's experience into a sequence of "observer-moments"
helps avoid certain paradoxes; but the main ambiguity is the selection of
the appropriate "reference class": for Carter's WAP this might correspond to
all real or potential observer-moments in our universe; for the SAP, to all
in the multiverse. Bostrom's mathematical development shows that choosing
either too broad or too narrow a reference class leads to counter-intuitive
results, but he is not able to prescribe an ideal choice.
According to Jürgen Schmidhuber, the anthropic principle essentially just
says that the conditional probability of finding yourself in a universe
compatible with your existence is always 1. It does not allow for any
additional nontrivial predictions such as "gravity won't change tomorrow."
To gain more predictive power, additional assumptions on the prior
distribution of alternative universes are necessary.[21][25]
Playwright and novelist Michael Frayn describes a form of the Strong
Anthropic Principle in his 2006 book The Human Touch, which explores what he
characterises as "the central oddity of the Universe":
"It's this simple paradox. The Universe is very old and very large.
Humankind, by comparison, is only a tiny disturbance in one small corner of
it - and a very recent one. Yet the universe is only very large and very old
because we are here to say it is... And yet, of course, we all know
perfectly well that it is what it is whether we are here or not."
—[26]
[edit] Character of anthropic reasoning
Carter chose to focus on a tautological aspect of his ideas, which has
resulted in much confusion. In fact, anthropic reasoning interests
scientists because of something that is only implicit in the above formal
definitions, namely that we should give serious consideration to there being
other universes with different values of the "fundamental parameters" —
that is, the dimensionless physical constants and initial conditions for the
Big Bang. Carter and others have argued that life as we know it would not
be possible in most such universes. In other words, the universe we are in
is fine tuned to permit life. Collins & Hawking (1973) characterized Carter'
s then-unpublished big idea as the postulate that "there is not one universe
but a whole infinite ensemble of universes with all possible initial
conditions".[27] If this is granted, the anthropic principle provides a
plausible explanation for the fine tuning of our universe: the "typical"
universe is not fine-tuned, but given enough universes, a small fraction
thereof will be capable of supporting intelligent life. Ours must be one of
these, and so the observed fine tuning should be no cause for wonder.
Although philosophers have discussed related concepts for centuries, in the
early 1970s the only genuine physical theory yielding a multiverse of sorts
was the many worlds interpretation of quantum mechanics. This would allow
variation in initial conditions, but not in the truly fundamental constants.
Since that time a number of mechanisms for producing a multiverse have been
suggested: see the review by Max Tegmark.[28] An important development in
the 1980s was the combination of inflation theory with the hypothesis that
some parameters are determined by symmetry breaking in the early universe,
which allows parameters previously thought of as "fundamental constants" to
vary over very large distances, thus eroding the distinction between Carter'
s weak and strong principles. At the beginning of the 21st century, the
string landscape emerged as a mechanism for varying essentially all the
constants, including the number of spatial dimensions.[29]
The anthropic idea that fundamental parameters are selected from a multitude
of different possibilities (each actual in some universe or other)
contrasts with the traditional hope of physicists for a theory of everything
having no free parameters: as Einstein said, "What really interests me is
whether God had any choice in the creation of the world." Quite recently,
proponents of the leading candidate for a "theory of everything", string
theory, proclaimed "the end of the anthropic principle"[30] since there
would be no free parameters to select. Ironically, string theory now seems
to offer no hope of predicting fundamental parameters, and now some who
advocate it invoke the anthropic principle as well (see below).
The modern form of a design argument is put forth by Intelligent design.
Proponents of intelligent design often cite the fine-tuning observations
that (in part) preceded the formulation of the anthropic principle by Carter
as a proof of an intelligent designer. Opponents of intelligent design are
not limited to those who hypothesize that other universes exist; they may
also argue, anti-anthropically, that the universe is less fine-tuned than
often claimed, or that accepting fine tuning as a brute fact is less
astonishing than the idea of an intelligent creator. Furthermore, even
accepting fine tuning, Sober (2005)[31] and Ikeda and Jefferys,[32][33]
argue that the Anthropic Principle as conventionally stated actually
undermines intelligent design; see fine-tuned universe.
Paul Davies's book The Goldilocks Enigma (2006) reviews the current state of
the fine tuning debate in detail, and concludes by enumerating the
following responses to that debate:
1.The absurd universe Our universe just happens to be the way it is.
2.The unique universe There is a deep underlying unity in physics which
necessitates the universe being the way it is. Some Theory of Everything
will explain why the various features of the Universe must have exactly the
values that we see.
3.The multiverse Multiple Universes exist, having all possible combinations
of characteristics, and we inevitably find ourselves within a Universe that
allows us to exist.
4.Creationism A creator designed the Universe with the purpose of supporting
complexity and the emergence of Intelligence.
5.The life principle There is an underlying principle that constrains the
universe to evolve towards life and mind.
6.The self-explaining universe A closed explanatory or causal loop: "perhaps
only universes with a capacity for consciousness can exist." This is
Wheeler's Participatory Anthropic Principle (PAP).
7.The fake universe We live inside a virtual reality simulation.
Omitted here is Lee Smolin's model of cosmological natural selection, also
known as "fecund universes," which proposes that universes have "offspring"
which are more plentiful if they resemble our universe. Also see Gardner (
2005).[34]
Clearly each of these hypotheses resolve some aspects of the puzzle, while
leaving others unanswered. Followers of Carter would admit only option 3 as
an anthropic explanation, whereas 3 through 6 are covered by different
versions of Barrow and Tipler's SAP (which would also include 7 if it is
considered a variant of 4, as in Tipler 1994).
The anthropic principle, at least as Carter conceived it, can be applied on
scales much smaller than the whole universe. For example, Carter (1983)[35]
inverted the usual line of reasoning and pointed out that when interpreting
the evolutionary record, one must take into account cosmological and
astrophysical considerations. With this in mind, Carter concluded that given
the best estimates of the age of the universe, the evolutionary chain
culminating in Homo sapiens probably admits only one or two low probability
links. Antonio Feoli and Salvatore Rampone dispute this conclusion, arguing
instead that the estimated size of our universe and the number of planets in
it allows for a higher bound, so that there is no need to invoke
intelligent design to explain evolution. [36]
[edit] Observational evidence
No possible observational evidence bears on Carter's WAP, as it is merely
advice to the scientist and asserts nothing debatable. The obvious test of
Barrow's SAP, which says that the Universe is "required" to support life, is
to find evidence of life in universes other than ours. Any other universe
is, by most definitions, unobservable (otherwise it would be included in our
portion of this universe), however in principle, Barrow's SAP cannot be
falsified by observing a universe in which an observer cannot exist.
Philosopher John Leslie[37] states that the Carter SAP (with multiverse)
predicts the following:
Physical theory will evolve so as to strengthen the hypothesis that early
phase transitions occur probabilistically rather than deterministically, in
which case there will be no deep physical reason for the values of
fundamental constants;
Various theories for generating multiple universes will prove robust;
Evidence that the universe is fine tuned will continue to accumulate;
No life with a non-carbon chemistry will be discovered;
Mathematical studies of galaxy formation will confirm that it is sensitive
to the rate of expansion of the universe.
Hogan[38] has emphasised that it would be very strange if all fundamental
constants were strictly determined, since this would leave us with no ready
explanation for apparent fine tuning. In fact we might have to resort to
something akin to Barrow and Tipler's SAP: there would be no option for such
a universe not to support life.
Probabilistic predictions of parameter values can be made given:
(i) a particular multiverse with a "measure", i.e. a well defined "density
of universes" (so, for parameter X, one can calculate the prior probability
P(X0) dX that X is in the range X0 < X < X0 + dX), and
(ii) an estimate of the number of observers in each universe, N(X) (e.g.,
this might be taken as proportional to the number of stars in the universe).
The probability of observing value X is then proportional to N(X) P(X). (A
more sophisticated analysis is that of Nick Bostrom.)[39] A generic feature
of an analysis of this nature is that the expected values of the fundamental
physical constants should not be "over-tuned," i.e. if there is some
perfectly tuned predicted value (e.g. zero), the observed value need be no
closer to that predicted value than what is required to make life possible.
The small but finite value of the cosmological constant can be regarded as a
successful prediction in this sense.
One thing that would not count as evidence for the Anthropic Principle is
evidence that the Earth or the solar system occupied a privileged position
in the universe, in violation of the Copernican principle (for possible
counterevidence to this principle, see Copernican principle), unless there
was some reason to think that that position was a necessary condition for
our existence as observers.
[edit] Applications of the principle
This article or section may contain previously unpublished synthesis of
published material that conveys ideas not attributable to the original
sources. See the talk page for details. (December 2010)
[edit] The nucleosynthesis of carbon-12
Fred Hoyle may have invoked anthropic reasoning to predict an astrophysical
phenomenon. He is said to have reasoned from the prevalence on earth of life
forms whose chemistry was based on carbon-12 atoms, that there must be an
undiscovered resonance in the carbon-12 nucleus facilitating its synthesis
in stellar interiors via the triple-alpha process. He then calculated the
energy of this undiscovered resonance to be 7.6 million electron-volts.[40][
41] Willie Fowler's research group soon found this resonance, and its
measured energy was close to Hoyle's prediction.
However, a recently released paper argues that Hoyle did not use anthropic
reasoning to make this prediction.[42]
[edit] Cosmic inflation
Main article: Cosmic inflation
Don Page criticized the entire theory of cosmic inflation as follows.[43] He
emphasized that initial conditions which made possible a thermodynamic
arrow of time in a universe with a Big Bang origin, must include the
assumption that at the initial singularity, the entropy of the universe was
low and therefore extremely improbable. Paul Davies rebutted this criticism
by invoking an inflationary version of the anthropic principle.[44] While
Davies accepted the premise that the initial state of the visible Universe (
which filled a microscopic amount of space before inflating) had to possess
a very low entropy value — due to random quantum fluctuations — to account
for the observed thermodynamic arrow of time, he deemed this fact an
advantage for the theory. That the tiny patch of space from which our
observable Universe grew had to be extremely orderly, to allow the post-
inflation universe to have an arrow of time, makes it unnecessary to adopt
any "ad hoc" hypotheses about the initial entropy state, hypotheses other
Big Bang theories require.
[edit] String theory
Main article: String theory landscape
String theory predicts a large number of possible universes, called the "
backgrounds" or "vacua." The set of these vacua is often called the "
multiverse" or "anthropic landscape" or "string landscape." Leonard Susskind
has argued that the existence of a large number of vacua puts anthropic
reasoning on firm ground: only universes whose properties are such as to
allow observers to exist are observed, while a possibly much larger set of
universes lacking such properties go unnoticed.
Steven Weinberg[45] believes the Anthropic Principle may be appropriated by
cosmologists committed to nontheism, and refers to that Principle as a "
turning point" in modern science because applying it to the string landscape
"...may explain how the constants of nature that we observe can take values
suitable for life without being fine-tuned by a benevolent creator." Others
, most notably David Gross but also Lubos Motl, Peter Woit, and Lee Smolin,
argue that this is not predictive. Max Tegmark,[46] Mario Livio, and Martin
Rees[47] argue that only some aspects of a physical theory need be
observable and/or testable for the theory to be accepted, and that many well
-accepted theories are far from completely testable at present.
Jürgen Schmidhuber (2000–2002) points out that Ray Solomonoff's theory of
universal inductive inference and its extensions already provide a framework
for maximizing our confidence in any theory, given a limited sequence of
physical observations, and some prior distribution on the set of possible
explanations of the universe.
[edit] Ice density
When water freezes into ice, the ice floats because ice is less dense than
liquid water. This is one possible example of the anthropic principle,
because if ice did not float, it might have been difficult or impossible for
living organisms to have existed in water; without the insulating
properties of a top ice layer, lakes and ponds would tend to freeze solid
and thaw very little during warmer periods. This principle has been
criticized as neglecting the existence of the tropical zone and other warmer
climates.
Ice is unusual in that it is approximately 9% less dense than liquid water.
Water is the only known non-metallic substance to expand when it freezes.
The density of ice is 0.9167 g/cm3 at 0°C, whereas water has a density of 0
.9998 g/cm3 at the same temperature. Liquid water is densest, essentially 1.
00 g/cm3, at 4°C and becomes less dense as the water molecules begin to
form the hexagonal crystals[48] of ice as the freezing point is reached.
This is due to hydrogen bonding dominating the intermolecular forces, which
results in a packing of molecules less compact in the solid.
[edit] The Anthropic Cosmological Principle
A thorough extant study of the anthropic principle is the book The Anthropic
Cosmological Principle by John D. Barrow, a cosmologist, and Frank J.
Tipler, a theosophist and mathematical physicist. This book sets out in
detail the many known anthropic coincidences and constraints, including many
found by its authors. While the book is primarily a work of theoretical
astrophysics, it also touches on quantum physics, chemistry, and earth
science. An entire chapter argues that Homo sapiens is, with high
probability, the only intelligent species in the Milky Way.
The book begins with an extensive review of many topics in the history of
ideas the authors deem relevant to the anthropic principle, because the
authors believe that principle has important antecedents in the notions of
teleology and intelligent design. They discuss the writings of Fichte, Hegel
, Bergson, and Alfred North Whitehead, and the Omega Point cosmology of
Teilhard de Chardin. Barrow and Tipler carefully distinguish teleological
reasoning from eutaxiological reasoning; the former asserts that order must
have a consequent purpose; the latter asserts more modestly that order must
have a planned cause. They attribute this important but nearly always
overlooked distinction to an obscure 1883 book by L. E. Hicks.[49]
Seeing little sense in a principle requiring intelligent life to emerge
while remaining indifferent to the possibility of its eventual extinction,
Barrow and Tipler propose the:
"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."
—[50]
Barrow and Tipler submit that the FAP is both a valid physical statement and
"closely connected with moral values." FAP places strong constraints on the
structure of the universe, constraints developed further in Tipler's The
Physics of Immortality.[51] One such constraint is that the universe must
end in a big crunch, which seems unlikely in view of the tentative
conclusions drawn since 1998 about dark energy, based on observations of
very distant supernovas.
In his review[52] of Barrow and Tipler, Martin Gardner ridiculed the FAP by
quoting the last two sentences of their book as defining a Completely
Ridiculous Anthropic Principle (CRAP):
"At the instant the Omega Point is reached, life will have gained control of
all matter and forces not only in a single universe, but in all universes
whose existence is logically possible; life will have spread into all
spatial regions in all universes which could logically exist, and will have
stored an infinite amount of information, including all bits of knowledge
which it is logically possible to know. And this is the end."
—[53]
[edit] Criticism
Carter himself[54] has frequently regretted his own choice of the word "
anthropic," because it conveys the misleading impression that the principle
involves humans specifically, rather than intelligent observers in general.
Others[55] have criticised the word "principle" as being too grandiose to
describe straightforward applications of selection effects.
A common criticism of Carter's SAP is that it is an easy deus ex machina
which discourages searches for physical explanations. To quote Penrose again
enough theory to explain the observed facts."[56]
Carter's SAP and Barrow and Tipler's WAP have been dismissed as truisms or
trivial tautologies, that is, statements true solely by virtue of their
logical form (the conclusion is identical to the premise) and not because a
substantive claim is made and supported by observation of reality. As such,
they are criticized as an elaborate way of saying "if things were different,
they would be different," which is a valid statement, but does not make a
claim of some factual alternative over another. The anthropic principles
implicitly posit that our ability to ponder cosmology at all is contingent
on one or more fundamental physical constants having numerical values
falling within quite a narrow range, and this is not a trivial tautology[
according to whom?]; nor is postulating a multiverse. Moreover, working out
the consequences of a change in the fundamental constants for the existence
of our species is far from trivial, and, as we have seen, can lead to quite
unexpected constraints on physical theory. This reasoning does, however,
demonstrate that carbon-based life is impossible under these altered
fundamental parameters.
Critics of the Barrow and Tipler SAP claim that it is neither testable nor
falsifiable, and thus is not a scientific statement but rather a
philosophical one. The same criticism has been leveled against the
hypothesis of a multiverse, although some argue that it does make
falsifiable predictions. A modified version of this criticism is that we
understand so little about the emergence of life, especially intelligent
life, that it is effectively impossible to calculate the number of observers
in each universe. Also, the prior distribution of universes as a function
of the fundamental constants is easily modified to get any desired result.[
57]
Many criticisms focus on versions of the Strong Anthropic Principle, such as
Barrett and Tipler's anthropic cosmological principle, which are
teleological notions that tend to describe the existence of life as a
necessary prerequisite for the observable constants of physics. In a lecture
titled "The Confusion of Cause and Effect in Bad Science," the
paleophysicist Caroline Miller said:[58]
"The Anthropic Principle is based on the underlying belief that the universe
was created for our benefit. Unfortunately for its adherents, all of the
reality-based evidence at our disposal contradicts this belief. In a
nonanthropocentric universe, there is no need for multiple universes or
supernatural entities to explain life as we know it."
Similarly, Stephen Jay Gould,[59][60] Michael Shermer[61] and others claim
that the stronger versions of the Anthropic Principle seem to reverse known
causes and effects. Gould compared the claim that the universe is fine-tuned
for the benefit of our kind of life to saying that sausages were made long
and narrow so that they could fit into modern hotdog buns, or saying that
ships had been invented to house barnacles. These critics cite the vast
physical, fossil, genetic, and other biological evidence consistent with
life having been fine-tuned through natural selection to adapt to the
physical and geophysical environment in which life exists. Life appears to
have adapted to physics, and not vice versa.
Some applications of the anthropic principle have been criticized as an
argument by lack of imagination, for tacitly assuming that carbon compounds
and water are the only possible chemistry of life (sometimes called "carbon
chauvinism", see also alternative biochemistry).[62] The range of
fundamental physical constants consistent with the evolution of carbon-based
life may also be wider than those who advocate a fine tuned universe have
argued.[63] For instance, Harnik et al.[64] propose a weakless universe in
which the weak nuclear force is eliminated. They show that this has no
significant effect on the other fundamental interactions, provided some
adjustments are made in how those interactions work. However, if some of the
fine-tuned details of our universe were violated, that would rule out
complex structures of any kind — stars, planets, galaxies, etc.
Lee Smolin has offered a theory designed to improve on the lack of
imagination that anthropic principles have been accused of. He puts forth
his fecund universes theory, which assumes universes have "offspring"
through the creation of black holes, and that these offspring universes have
values of physical constants that depend on these of the mother universe.[
65][self-published source?][unreliable source?] Some versions of the
anthropic principle are only interesting if the range of physical constants
that allow certain kinds of life are unlikely in a landscape of possible
universes. But Lee Smolin assumes that conditions for carbon based life are
similar to conditions for black hole creation, which would change the a
priori distribution of universes such that universes containing life would
be likely. In [66][self-published source?][unreliable source?] the string
theorist Leonard Susskind disagrees about some assumptions in Lee Smolin's
theory, while Smolin defends his theory.
The philosophers of cosmology John Earman,[67] Ernan McMullin [68] and Jesú
s Mosterín contend that "in its weak version, the anthropic principle is a
mere tautology, which does not allow us to explain anything or to predict
anything that we did not already know. In its strong version, it is a
gratuitous speculation".[69] A further criticism by Mosterín concerns the
flawed "anthropic" inference from the assumption of an infinity of worlds to
the existence of one like ours:
“The suggestion that an infinity of objects characterized by certain
numbers or properties implies the existence among them of objects with any
combination of those numbers or characteristics [...] is mistaken. An
infinity does not imply at all that any arrangement is present or repeated.
[...] The assumption that all possible worlds are realized in an infinite
universe is equivalent to the assertion that any infinite set of numbers
contains all numbers (or at least all Gödel numbers of the [defining]
sequences), which is obviously false.”
[edit] See also
Big Bounce
Doomsday argument
Final anthropic principle
Fine-tuned Universe
The Great Filter
Infinite monkey theorem
Inverse gambler's fallacy
Mediocrity principle
Metaphysical naturalism
Neocatastrophism
Nick Bostrom
Puddle thinking
Quark Mass and Congeniality to Life
Rare Earth hypothesis
Selection bias
Triple-alpha process
Teleology
[edit] Footnotes
1.^ Mosterín (2005) pp. 12 http://philsci-archive.pitt.edu/1658/"
2.^ "anthropic" means "of or pertaining to mankind or humans"
3.^ The Anthropic Principle, Victor J. Stenger
4.^ Anthropic Bias, Nick Bostrom, p.6
5.^ Merriam-Webster Online Dictionary
6.^ The Strong Anthropic Principle and the Final Anthropic Principle
7.^ On Knowing, Sagan from Pale Blue Dot
8.^ Dicke, R. H. (1961). "Dirac's Cosmology and Mach's Principle". Nature
192 (4801): 440–441. Bibcode 1961Natur.192..440D. doi:10.1038/192440a0.
9.^ Davies, P. (2006). The Goldilocks Enigma. Allen Lane. ISBN 0713998830.
10.^ Weinberg, S. (1987). "Anthropic bound on the cosmological constant".
Physical Review Letters 59 (22): 2607–2610. Bibcode 1987PhRvL..59.2607W.
doi:10.1103/PhysRevLett.59.2607. PMID 10035596.
11.^ http://www.newscientist.com/blog/space/2007/02/physicists-debate-nature-of-space-time.html
12.^ Carter, B. (1974). "Large Number Coincidences and the Anthropic
Principle in Cosmology". IAU Symposium 63: Confrontation of Cosmological
Theories with Observational Data. Dordrecht: Reidel. pp. 291–298.
13.^
[Edit this reference]
Barrow, John D.; Tipler, Frank J. (19 May 1988). The Anthropic Cosmological
Principle. foreword by John A. Wheeler. Oxford: Oxford University Press.
ISBN 9780192821478. LC 87-28148. Retrieved 31 December 2009.
14.^ Wallace, A. R. (1904). Man's place in the universe: a study of the
results of scientific research in relation to the unity or plurality of
worlds, 4th ed. London: George Bell & Sons. pp. 256–7.
15.^ Dicke, R. H. (1957). "Gravitation without a Principle of Equivalence".
Reviews of Modern Physics 29 (3): 363–376. Bibcode 1957RvMP...29..363D.
doi:10.1103/RevModPhys.29.363.
16.^ Barrow, John D. (1997). "Anthropic Definitions". Quarterly Journal of
the Royal Astronomical Society 24: 146–53. Bibcode 1983QJRAS..24..146B.
17.^ Barrow & Tipler's definitions are quoted verbatim at Genesis of Eden
Diversity Encyclopedia.
18.^ Barrow and Tipler 1986: 16.
19.^ Barrow and Tipler 1986: 21.
20.^ Barrow and Tipler 1986: 22.
21.^ a b Jürgen Schmidhuber, 2000, "Algorithmic theories of everything."
22.^ Leslie, J. (1986). "Probabilistic Phase Transitions and the Anthropic
Principle". Origin and Early History of the Universe: LIEGE 26. Knudsen. pp.
439–444.
23.^ Bostrom, N. (2002). Anthropic Bias: Observation Selection Effects in
Science and Philosophy. Routledge. ISBN 0-415-93858-9. 5 chapters available
online.
24.^ Bostrom, N. (2002), op. cit.
25.^ Jürgen Schmidhuber, 2002, "The Speed Prior: A New Simplicity Measure
Yielding Near-Optimal Computable Predictions." Proc. 15th Annual Conference
on Computational Learning Theory (COLT 2002), Sydney, Australia, Lecture
Notes in Artificial Intelligence. Springer: 216-28.
26.^ Michael Frayn, The Human Touch. Faber & Faber ISBN 0571232175
27.^ Collins C. B., Hawking, S. W. (1973). "Why is the universe isotropic?"
. Astrophysical Journal 180: 317–334. Bibcode 1973ApJ...180..317C. doi:10.
1086/151965.
28.^ Tegmark, M. (1998). "Is 'the theory of everything' merely the ultimate
ensemble theory?". Annals of Physics 270: 1–51. arXiv:gr-qc/9704009.
Bibcode 1998AnPhy.270....1T. doi:10.1006/aphy.1998.5855.
29.^ Strictly speaking, the number of non-compact dimensions, see String
theory.
30.^ Kane, Gordon L., Perry, Malcolm J., and Zytkow, Anna N. (2002). "The
Beginning of the End of the Anthropic Principle". New Astronomy 7: 45–53.
arXiv:astro-ph/0001197. Bibcode 2002NewA....7...45K. doi:10.1016/S1384-1076(
01)00088-4.
31.^ Sober, Elliott, 2005, "The Design Argument" in Mann, W. E., ed., The
Blackwell Guide to the Philosophy of Religion. Blackwell Publishers.
32.^ Ikeda, M. and Jefferys, W., "The Anthropic Principle Does Not Support
Supernaturalism," in The Improbability of God, Michael Martin and Ricki
Monnier, Editors, pp. 150-166. Amherst, N.Y.: Prometheus Press. ISBN 1-59102
-381-5
33.^ Ikeda, M. and Jefferys, W. (2006). Unpublished FAQ "The Anthropic
Principle Does Not Support Supernaturalism."
34.^ Gardner, James N., 2005, "The Physical Constants as Biosignature: An
anthropic retrodiction of the Selfish Biocosm Hypothesis," International
Journal of Astrobiology.
35.^ Carter, B.; McCrea, W. H. (1983). "The anthropic principle and its
implications for biological evolution". Philosophical Transactions of the
Royal Society A310 (1512): 347–363. doi:10.1098/rsta.1983.0096.
36.^ Feoli, A. and Rampone, S.; Rampone (1999). "Is the Strong Anthropic
Principle too weak?". Nuovo Cim. B114: 281–289. arXiv:gr-qc/9812093.
Bibcode 1999NCimB.114..281F.
37.^ Leslie, J. (1986) op. cit.
38.^ Hogan, Craig (2000). "Why is the universe just so?". Reviews of Modern
Physics 72 (4): 1149–1161. arXiv:astro-ph/9909295. Bibcode 2000RvMP...72.
1149H. doi:10.1103/RevModPhys.72.1149.
39.^ Bostrom (2002), op. cit.
40.^ University of Birmingham Life, Bent Chains and the Anthropic Principle
41.^ Rev. Mod. Phys. 29 (1957) 547
42.^ Kragh, Helge (2010) When is a prediction anthropic? Fred Hoyle and the
7.65 MeV carbon resonance. http://philsci-archive.pitt.edu/5332/
43.^ Page, D.N. (1983). "Inflation does not explain time asymmetry". Nature
304 (5921): 39. Bibcode 1983Natur.304...39P. doi:10.1038/304039a0.
44.^ Davies, P.C.W. (1984). "Inflation to the universe and time asymmetry".
Nature 312 (5994): 524. Bibcode 1984Natur.312..524D. doi:10.1038/312524a0.
45.^ Weinberg, S. (2007). "Living in the multiverse". In B. Carr (ed).
Universe or multiverse?. Cambridge University Press. ISBN 0521848415.
preprint
46.^ Tegmark (1998) op. cit.
47.^ Livio, M. and Rees, M. J. (2003). "Anthropic reasoning". Science 309 (
5737): 1022–3. Bibcode 2005Sci...309.1022L. doi:10.1126/science.1111446.
PMID 16099967.
48.^ The word crystal derives from Greek word for frost.
49.^ Hicks, L. E. (1883). A Critique of Design Arguments. New York:
Scribner's.
50.^ Barrow and Tipler 1986: 23
51.^ Tipler, F. J. (1994). The Physics of Immortality. DoubleDay. ISBN
0385467982.
52.^ Gardner, M., "WAP, SAP, PAP, and FAP," The New York Review of Books 23
, No. 8 (May 8, 1986): 22-25.
53.^ Barrow and Tipler 1986: 677
54.^ e.g. Carter (2004) op. cit.
55.^ e.g. message from Martin Rees presented at the Kavli-CERCA conference
(see video in External links)
56.^ Penrose, R. (1989). The Emperor's New Mind. Oxford University Press.
ISBN 0198519737. Chapter 10.
57.^ Starkman, G. D., Trotta, R. (2006). "Why Anthropic Reasoning Cannot
Predict Λ". Physical Review Letters 97 (20): 201301. arXiv:astro-ph/0607227
. Bibcode 2006PhRvL..97t1301S. doi:10.1103/PhysRevLett.97.201301. PMID
17155671. See also this news story.
58.^ Miller, Caroline (2006). "The Confusion of Cause and Effect in Bad
Science". Lecture at Piffard University.
59.^ Gould, Stephen Jay (1998). "Clear Thinking in the Sciences". Lectures
at Harvard University.
60.^ Gould, Stephen Jay (2002). Why People Believe Weird Things:
Pseudoscience, Superstition, and Other Confusions of Our Time. ISBN
0716730901.
61.^ Shermer, Michael (2007). Why Darwin Matters. ISBN 0805081216.
62.^ e.g. Carr, B. J., Rees, M. J. (1979). "The anthropic principle and the
structure of the physical world". Nature 278 (5705): 605–612. Bibcode
1979Natur.278..605C. doi:10.1038/278605a0.
63.^ Stenger, Victor J (2000). Timeless Reality: Symmetry, Simplicity, and
Multiple Universes. Prometheus Books. ISBN 1-57392-859-3.
64.^ Harnik, R., Kribs, G., Perez, G. (2006). "A Universe without Weak
interactions". Physical Review D74 (3): 035006. arXiv:hep-ph/0604027.
Bibcode 2006PhRvD..74c5006H. doi:10.1103/PhysRevD.74.035006.
65.^ Lee Smolin (2001). Tyson, Neil deGrasse and Soter, Steve. ed. Cosmic
Horizons: Astronomy at the Cutting Edge. The New Press. pp. 148–152. ISBN
978-1565846029.
66.^ Smolin vs. Susskind: The Anthropic Principle
67.^ Earman John (1987). "The SAP also rises: A critical examination of the
anthropic principle". American Philosophical Quarterly 24: 307–317.
68.^ McMullin, Ernan. (1994). "Fine-tuning the universe?" In M. Shale & G.
Shields (ed.), Science, Technology, and Religious Ideas, Lanham: University
Press of America.
69.^ Mosterín, Jesús. (2005). Op. cit.
[edit] References
[Edit this reference]
Barrow, John D.; Tipler, Frank J. (19 May 1988). The Anthropic Cosmological
Principle. foreword by John A. Wheeler. Oxford: Oxford University Press.
ISBN 9780192821478. LC 87-28148. Retrieved 31 December 2009.
Cirkovic, M. M. (2002). "On the First Anthropic Argument in Astrobiology".
Earth, Moon, and Planets 91 (4): 243–254. doi:10.1023/A:1026266630823.
Cirkovic, M. M. (2004). "The Anthropic Principle and the Duration of the
Cosmological Past". Astronomical and Astrophysical Transactions 23 (6): 567
–597. arXiv:astro-ph/0505005. Bibcode 2004A&AT...23..567C. doi:10.1080/
10556790412331335327.
Conway Morris, Simon (2003). Life's Solution: Inevitable Humans in a Lonely
Universe. Cambridge University Press.
Craig, William Lane (1987). "Critical review of The Anthropic Cosmological
Principle". International Philosophical Ouarterly 27: 437–47.
Hawking, Stephen W. (1988). A Brief History of Time. New York: Bantam Books
. pp. 174. ISBN 0-553-34614-8.
Stenger, Victor J. (1999), "Anthropic design," The Skeptical Inquirer 23 (
August 31, 1999): 40-43
Mosterín, Jesús. (2005). "Anthropic Explanations in Cosmology." In P. Há
yek, L. Valdés and D. Westerstahl (ed.), Logic, Methodology and Philosophy
of Science, Proceedings of the 12th International Congress of the LMPS.
London: King's College Publications, pp. 441–473. ISBN 1-904987-21-4.
Taylor, Stuart Ross (1998). Destiny or Chance: Our Solar System and Its
Place in the Cosmos. Cambridge University Press. ISBN 0521785219.
Tegmark, Max (1997). "On the dimensionality of spacetime". Classical and
Quantum Gravity 14 (4): L69–L75. arXiv:gr-qc/9702052. Bibcode 1997CQGra..
14L..69T. doi:10.1088/0264-9381/14/4/002. A simple anthropic argument for
why there are 3 spatial and 1 temporal dimensions.
Tipler, F. J. (2003). "Intelligent Life in Cosmology". International
Journal of Astrobiology 2 (2): 141–48. Bibcode 2003IJAsB...2..141T. doi:10.
1017/S1473550403001526.
Walker, M. A., and Cirkovic, M. M. (2006). "Anthropic Reasoning, Naturalism
and the Contemporary Design Argument". International Studies in the
Philosophy of Science 20 (3): 285–307. doi:10.1080/02698590600960945. Shows
that some of the common criticisms of AP based on its relationship with
numerology or the theological Design Argument are wrong.
Ward, P. D., and Brownlee, D. (2000). Rare Earth: Why Complex Life is
Uncommon in the Universe. Springer Verlag. ISBN 0-387-98701-0..
Vilenkin, Alex (2006). Many Worlds in One: The Search for Other Universes.
Hill and Wang. ISBN 978-0809095230.
[edit] External links
Caner, Taslaman, Anthropic Principle and Infinite Universes
Nick Bostrom: web site devoted to the Anthropic Principle.
Chown, Marcus, Anything Goes, New Scientist, 6 June 1998. On Max Tegmark's
work.
Stephen Hawking, Steven Weinberg, Alexander Vilenkin, David Gross and
Lawrence Krauss: Debate on Anthropic Reasoning Kavli-CERCA Conference Video
Archive.
Tobin, Paul N., 2000, "Is the Universe Fine-Tuned for Life?" (Archived 2009
-10-25) A critique of the Anthropic Principle from an atheist viewpoint.
"Anthropic Coincidence"—the anthropic controversy as a segue to Lee Smolin
's theory of cosmological natural selection.
Leonard Susskind and Lee Smolin debate the Anthropic Principle.
debate among scientists on arxiv.org.
Evolutionary Probability and Fine Tuning
Benevolent Design and the Anthropic Principle at MathPages
Critical review of "The Privileged Planet"
The Anthropic Principle - a review.
Berger, Daniel, 2002, "An impertinent resumé of the Anthropic Cosmological
Principle." A critique of Barrow & Tipler.
Jürgen Schmidhuber: Papers on algorithmic theories of everything and the
Anthropic Principle's lack of predictive power.
Paul Davies: Cosmic Jackpot Interview about the Anthropic Principle (starts
at 40 min), 15 May 2007. | l*s
发帖数: 6372 | 2 万事万物都有趋势，种瓜得瓜，种豆得豆。只是时机在老天爷手里。 | l**i
发帖数: 8144 | 3 你说随机是不是趋势？
【在 l*s 的大作中提到】
: 万事万物都有趋势，种瓜得瓜，种豆得豆。只是时机在老天爷手里。
| l*s
发帖数: 6372 | 4 赌盘有点厚薄，那么转盘就会有偏向，自然界总存在趋势的。因果是相随的，只是时间
问题。老毛当年种下文革的因，几十年后结果，老邓种下改开的因，也会在数十年后结
果。
【在 l**i 的大作中提到】
: 你说随机是不是趋势？
| l**i
发帖数: 8144 | 5 你说有没有真随机这种东西？
【在 l*s 的大作中提到】
: 赌盘有点厚薄，那么转盘就会有偏向，自然界总存在趋势的。因果是相随的，只是时间
: 问题。老毛当年种下文革的因，几十年后结果，老邓种下改开的因，也会在数十年后结
: 果。
| l*s
发帖数: 6372 | 6 不存在，佛家说因果，今日果乃昔日因，将来果乃今日因。所谓的缘分，也是宿缘，旧
日因罢了。
【在 l**i 的大作中提到】
: 你说有没有真随机这种东西？
|
|
