Deistic evolution is a position in the origins debate which involves accepting the scientific evidence for evolution and age of the universe whilst advocating the view that a deisticGod created the universe but has not interfered since. The position is a counterpoint to theistic evolution and is endorsed by those who believe in both deism and the veracity of science.
Various views on deistic evolution
In Christian Theology,
by Millard J. Erickson, 2013, is written: “deistic evolution is perhaps
the best way to describe one variety of what is generally called
theistic evolution.” He describes it as the belief that God “began the
process of evolution, producing the first matter and implanting within
the creation the laws its development has followed.” Following the
establishment of this process, this Creator then “withdrew from active
involvement with the world, becoming, so to speak, Creator Emeritus.”
God is the Creator, the ultimate
cause, but evolution is the means, the proximate cause. Thus, except for
its view of the very beginning of matter, deistic evolution is
identical to naturalistic evolution, for it denies that there is any
direct activity by a personal God during the ongoing creative process.
Deistic evolution has little difficulty with the scientific data.
There is a definite conflict, however, between deism's view of an
absentee God and the biblical picture of a God who has been involved in a
whole series of creative acts. In particular, both Genesis accounts of
the origin of human beings indicate that God definitely and distinctly
willed and acted to bring them into existence. In addition, deistic
evolution conflicts with the scriptural doctrine of providence,
according to which God is personally and intimately concerned with and
involved in what is going on in the specific events within his entire
creation.
The psychologist Steve Stewart-Williams in his book Darwin, God and the Meaning of Life (2010) states:
“
Deistic
evolutionists hold that God created the universe and the laws of
nature... but that once the ball was rolling, he ceased to intervene in
the day-today running of the world or in the course of natural law. God
was like the ether after Einstein: he no longer had any role to play in
the universe.
”
Stewart-Williams further writes that deistic evolution strips God of what most religious believers consider central. Any deistic God is not around for prayers, miracles or to intervene in people's lives and that because of this it is unpopular with monotheistic religions.
Deistic Evolution adheres to the concept of some form of God, but
denies any personal God. A recent defender of deistic evolution was Michael Anthony Corey, author of the book Back to Darwin: The Scientific Case for Deistic Evolution (1994).
Some scholars have written that Charles Darwin was an advocate of deistic evolution.
Deistic evolution is similarly the operative idea in Pandeism, which has been counted amongst the handful of spiritual beliefs which "are compatible with modern science." and specifically wherein it is noted that "pandeistic
belief systems .... [present] the inclusion of God as the ever
unfolding expression of a complex universe with an identifiable
beginning but no teleological direction necessarily present."
Theistic predeterminism
Deistic evolution is not the same as theistic evolution,
yet they are sometimes confused. The difference rests on the difference
between a theistic god that is interested in, if not actively involved
in, the outcome of his creation and humanity specifically and a deistic god
that is either disinterested in the outcome, and holds no special place
for humanity, or will not intervene. Often, there is no discernible
difference between the two positions—the choice of terminology has more
to do with the believer and her or his need for a god, than fitting into
a mostly arbitrary dictionary or academic definition.
Criticism from Christian Creationists
Deistic evolution has been criticised by Christian creationists as being incompatible with Christianity since it contradicts a literal reading of the Bible and more importantly, leaves no role for the "Christian personal God".
M. J. Erickson wrote that deistic evolution is in conflict with
the scriptural doctrine of providence according to which "God is
personally and intimately concerned with and involved in what is going
on in the specific events within his entire creation."
Charles P. Grannan wrote in 1894, "Another baseless assumption of
negative critics is that the general principles of Atheistic and
Deistic evolution, admitted by many scientists to account for the origin
of the various species of plants and animals, should also be applied to
explain the origin of the Christian religion."
Charles Wesley Rishell criticized the concept in 1899, comparing it to the notion (false, in his view), that gravity was a property of matter instead of a continued action of God:
If evolution is God's method of
creating he is still at work. Theistic Deism and evolution is possible,
but deistic evolution is a contradiction in terms. Again, it is all a
mere supposition that God created the world and endowed it with forces
which will of necessity work out his will. It is impossible for us to
say that God put forth energy in the beginning and then ceased. It is,
to say the least, as probable that gravitation is a divine force
constantly exerted on matter in a certain way as that it is a divine
force deposited in matter once for all.
The Roman Catholic Church disagrees with the doctrine of deistic evolution. In November 2005, Pope Benedict addressed a general audience of 25,000 in St. Peter's Square:
When the Pontiff finished his address, he put his papers to one
side and commented on the thought of St. Basil the Great, a Doctor of
the Church, who said that some, "deceived by the atheism they bear
within them, imagined the universe deprived of a guide and order, at the
mercy of chance. I believe the words of this fourth-century Father are
of amazing timeliness," said Benedict XVI. "How many are these 'some'
today? Deceived by atheism, they believe and try to demonstrate that it
is scientific to think that everything lacks a guide and order."
Science
Deistic evolution does not oppose or contradict evolution or come into conflict with science as it says that a God started the process and then left it to natural processes. However deism is still a religious philosophy.
Stewart-Williams wrote regarding deistic evolution and science:
“
Deistic
evolution eliminates any immediate conflict between science and belief
in God. Anyone who believes that God's role was merely to create the
laws of nature can accept the scientific worldview in its totality; they
simply add the proviso that 'God did it' - i.e., that God is
responsible for the world that science describes.
”
There is considerable room for this "god of the gaps" view, since scientific observation is entirely unable to shed any light on what happened during the Planck epoch, the earliest 10−43
seconds in the history of the universe. All development since this
initial creative act merely follows laws and principles which He
created:
God created the universe, perhaps using the "big bang" about
15,000 million years ago as his method. He set up basic laws to govern
the running of the universe, and then left the scene entirely. God has
not been seen since. The earth coalesced about 4 or 5 thousand million
years ago without any input from God. Later, elementary life forms
formed, which evolved into the animals and plant life that we see today
through purely natural forces. It is essentially identical to
naturalistic evolution, excepts that it reserves one action for God:
that of initially creating the matter of the universe. This belief is
common among Deists.
Although the term is rarely heard, deistic evolution is perhaps the
best way to describe one variety of what is generally called theistic
evolution. This is the view that God began the process of evolution,
producing the first matter and implanting within the creation the laws
which its devel- opment has followed. Thus, he programmed the process.
Then he withdrew from active involvement with the world, becoming, so to
speak, Creator emeritus. The progress of the created order is free of
direct influence by God. He is the Creator of everything, but only the
first living form was directly created. All the rest of God's creating
has been done indirectly. God is the Creator, the ultimate cause, but
evolution is the means, the proximate cause. Thus, except for its view
of the very beginning of matter, deistic evolution is identical to
naturalistic evolution for it denies that there is any direct activity
by a personal God during the ongoing creative process.
The anthropic principle is a philosophical consideration that observations of the universe must be compatible with the conscious and sapient life that observes it. Proponents of the anthropic principle reason that it explains why this universe has the age and the fundamental physical constants
necessary to accommodate conscious life. As a result, they believe it
is unremarkable that this universe has fundamental constants that happen
to fall within the narrow range thought to be compatible with life.
The strong anthropic principle (SAP), as explained by John D. Barrow and Frank Tipler,
states that this is all the case because the universe is in some sense
compelled to eventually have conscious and sapient life emerge within it. Some critics of the SAP 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 (specifically survivor bias):
i.e., only in a universe capable of eventually supporting life will
there be living beings capable of observing and reflecting on the
matter. Most often such arguments draw upon some notion of the multiverse for there to be a statistical population of universes to select from and from which selection bias (our observance of only this universe, compatible with our life) could occur.
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 living entity would be there to
observe it, and thus would not be known. 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 to be a misnomer. While singling out our kind of carbon-based life, none of the finely tuned phenomena require human life or some kind of carbon chauvinism.
Any form of life or any form of heavy atom, stone, star or galaxy would
do; nothing specifically human or anthropic is involved.
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", 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.
Anthropic 'coincidences'
In 1961, Robert Dicke noted that the age of the universe, as seen by living observers, cannot be random. Instead, biological factors constrain the universe to be more or less in a "golden age", neither too young nor too old.
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 the 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 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").
However, if the cosmological constant were only several orders of
magnitude larger than 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 interaction would bind the dineutron and the diproton and convert all hydrogen in the early universe to helium; likewise, an increase in the weak interaction
also would convert all hydrogen to helium. Water, as well as
sufficiently long-lived stable stars, both essential for the emergence
of life as we know it, 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.
Origin
The phrase "anthropic principle" first appeared in Brandon Carter's contribution to a 1973 Krakówsymposium 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." 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.
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, the argument ran, there
would be no intelligent life around 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!
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 the 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,
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 biologistAlfred 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." 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."
Variants
Weak anthropic principle (WAP) (Carter): "[W]e 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): "[T]he 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:
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."
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."
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:
"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."
"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.
The philosophersJohn Leslie and Nick Bostrom
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.
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.
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.
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".
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. 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.
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." In 2002, proponents of the leading candidate for
a "theory of everything", string theory, proclaimed "the end of the anthropic principle"
since there would be no free parameters to select. String theory now
seems to offer no hope of predicting fundamental parameters, and now
some who advocate it invoke the anthropic principle as well.
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) and Ikeda and Jefferys, argue that the Anthropic Principle as conventionally stated actually undermines intelligent design.
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:
The absurd universe: Our universe just happens to be the way it is.
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.
The multiverse: Multiple universes exist, having all possible
combinations of characteristics, and we inevitably find ourselves within
a universe that allows us to exist.
Intelligent design: A creator designed the Universe with the purpose of supporting complexity and the emergence of intelligence.
The life principle: There is an underlying principle that constrains the Universe to evolve towards life and mind.
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).
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).
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)
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.
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). Thus, in principle Barrow's SAP cannot be falsified by observing a universe in which an observer cannot exist.
Philosopher John Leslie 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;
Hogan
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:
a particular multiverse with a "measure", i.e. a well defined "density of universes" (so, for parameter X, one can calculate the prior probabilityP(X0) dX that X is in the range X0 < X < X0 + dX), and
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 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.
Applications of the principle
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-12atoms, 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 electronvolts. Willie Fowler's research group soon found this resonance, and its measured energy was close to Hoyle's prediction.
However, in 2010 Helge Kragh
argued that Hoyle did not use anthropic reasoning in making his
prediction, since he made his prediction in 1953 and anthropic reasoning
did not come into prominence until 1980. He called this an "anthropic
myth," saying that Hoyle and others made an after-the-fact connection
between carbon and life decades after the discovery of the resonance.
An investigation of the historical
circumstances of the prediction and its subsequent experimental
confirmation shows that Hoyle and his contemporaries did not associate
the level in the carbon nucleus with life at all.
Cosmic inflation
Don Page criticized the entire theory of cosmic inflation as follows. 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.
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.
String theory
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 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, Mario Livio, and Martin Rees
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.
There are two kinds of dimensions, spatial (bidirectional) and temporal (unidirectional). Let the number of spatial dimensions be N and the number of temporal dimensions be T. That N = 3 and T = 1, setting aside the compactified dimensions invoked by string theory and undetectable to date, can be explained by appealing to the physical consequences of letting N differ from 3 and T
differ from 1. The argument is often of an anthropic character and
possibly the first of its kind, albeit before the complete concept came
into vogue.
In 1920, Paul Ehrenfest showed that if there is only one time dimension and greater than three spatial dimensions, the orbit of a planet about its Sun cannot remain stable. The same is true of a star's orbit around the center of its galaxy. Ehrenfest also showed that if there are an even number of spatial dimensions, then the different parts of a wave impulse will travel at different speeds. If there are spatial dimensions, where k is a positive whole number, then wave impulses become distorted. In 1922, Hermann Weyl showed that Maxwell's theory of electromagnetism works only with three dimensions of space and one of time. Finally, Tangherlini showed in 1963 that when there are more than three spatial dimensions, electron orbitals around nuclei cannot be stable; electrons would either fall into the nucleus or disperse.
Max Tegmark expands on the preceding argument in the following anthropic manner. If T differs from 1, the behavior of physical systems could not be predicted reliably from knowledge of the relevant partial differential equations. In such a universe, intelligent life capable of manipulating technology could not emerge. Moreover, if T > 1, Tegmark maintains that protons and electrons
would be unstable and could decay into particles having greater mass
than themselves. (This is not a problem if the particles have a
sufficiently low temperature.) If N < 3, gravitation of any
kind becomes problematic, and the universe is probably too simple to
contain observers. For example, when N < 3, nerves cannot cross without intersecting.
In general, it is not clear how physical law could function if T differed from 1. If T > 1, subatomic particles which decay after a fixed period would not behave predictably, because time-like geodesics would not be necessarily maximal. N = 1 and T = 3 has the peculiar property that the speed of light in a vacuum is a lower bound on the velocity of matter; all matter consists of tachyons.
Hence anthropic and other arguments rule out all cases except N = 3 and T = 1, which happens to describe the world around us.
Metaphysical interpretations
Some of the metaphysical disputes and speculations include, for example, attempts to back Pierre Teilhard de Chardin's earlier interpretation of the universe as being Christ centered (compare Omega Point), expressing a creatio evolutiva instead the elder notion of creatio continua.
From a strictly secular, humanist perspective, it allows as well to put
human beings back in the center, an anthropogenic shift in cosmology. Karl W. Giberson has been sort of laconic in stating that
What emerges is the suggestion that cosmology may at last be in possession of some raw material for a postmodern creation myth.
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.
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.
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. 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 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.
Reception and controversies
Carter
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 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: "[I]t tends to be invoked by theorists whenever they do not have a
good enough theory to explain the observed facts."
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.
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.
Many criticisms focus on versions of the strong anthropic principle, such as Barrow 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. Similarly, Stephen Jay Gould, Michael Shermer,
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 the universe, 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). 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. For instance, Harnik et al. 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 whose offspring universes have values of physical constants that depend on those of the mother universe.
The philosophers of cosmology John Earman, Ernan McMullin, and Jesús 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".
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.
Dante shown holding a copy of the Divine Comedy,
next to the entrance to Hell, the seven terraces of Mount Purgatory and
the city of Florence, with the spheres of Heaven above, in Michelino's fresco
The work was originally simply titled Comedìa (pronounced [komeˈdiːa]; so also in the first printed edition, published in 1472), Tuscan for "Comedy", later adjusted to the modern Italian Commedia. The adjective Divina was added by Giovanni Boccaccio, and the first edition to name the poem Divina Comedia in the title was that of the Venetian humanistLodovico Dolce, published in 1555 by Gabriele Giolito de' Ferrari.
Structure and story
The Divine Comedy is composed of 14,233 lines that are divided into three cantiche (singular cantica) – Inferno (Hell), Purgatorio (Purgatory), and Paradiso (Paradise) – each consisting of 33 cantos (Italian plural canti). An initial canto, serving as an introduction to the poem and generally considered to be part of the first cantica,
brings the total number of cantos to 100. It is generally accepted,
however, that the first two cantos serve as a unitary prologue to the
entire epic, and that the opening two cantos of each cantica serve as prologues to each of the three cantiche.
The number three is prominent in the work (alluding to the Trinity), represented in part by the number of cantiche and their lengths. Additionally, the verse scheme used, terza rima, is hendecasyllabic (lines of eleven syllables), with the lines composing tercets according to the rhyme schemeaba, bcb, cdc, ded, ...
Written in the first person, the poem tells of Dante's journey through the three realms of the dead, lasting from the night beforeGood Friday to the Wednesday after Easter in the spring of 1300. The Roman poet Virgil guides him through Hell and Purgatory; Beatrice,
Dante's ideal woman, guides him through Heaven. Beatrice was a
Florentine woman he had met in childhood and admired from afar in the
mode of the then-fashionable courtly love tradition, which is highlighted in Dante's earlier work La Vita Nuova.
The structure of the three realms follows a common numerical pattern
of 9 plus 1, for a total of 10: 9 circles of the Inferno, followed by
Lucifer contained at its bottom; 9 rings of Mount Purgatory, followed by
the Garden of Eden crowning its summit; and the 9 celestial bodies of Paradiso, followed by the Empyrean
containing the very essence of God. Within each group of 9, 7 elements
correspond to a specific moral scheme, subdivided into three
subcategories, while 2 others of greater particularity are added to
total nine. For example, the seven deadly sins of the Catholic Church that are cleansed in Purgatory are joined by special realms for the late repentant and the excommunicated
by the church. The core seven sins within Purgatory correspond to a
moral scheme of love perverted, subdivided into three groups
corresponding to excessive love (Lust, Gluttony, Greed), deficient love (Sloth), and malicious love (Wrath, Envy, Pride).
In central Italy's political struggle between Guelphs and Ghibellines, Dante was part of the Guelphs, who in general favored the Papacy over the Holy Roman Emperor.
Florence's Guelphs split into factions around 1300 – the White Guelphs
and the Black Guelphs. Dante was among the White Guelphs who were exiled
in 1302 by the Lord-Mayor Cante de' Gabrielli di Gubbio, after troops under Charles of Valois entered the city, at the request of Pope Boniface VIII, who supported the Black Guelphs. This exile, which lasted the rest of Dante's life, shows its influence in many parts of the Comedy, from prophecies of Dante's exile to Dante's views of politics, to the eternal damnation of some of his opponents.
The last word in each of the three cantiche is stelle ("stars").
Inferno
Gustave Doré's engravings illustrated the Divine Comedy (1861–1868); here Charon comes to ferry souls across the river Acheron to Hell.
The poem begins on the night before Good Friday in the year 1300, "halfway along our life's path" (Nel mezzo del cammin di nostra vita). Dante is thirty-five years old, half of the biblical lifespan of 70 (Psalms 89:10, Vulgate), lost in a dark wood (understood as sin), assailed by beasts (a lion, a leopard, and a she-wolf) he cannot evade and unable to find the "straight way" (diritta via) –
also translatable as "right way" – to salvation (symbolized by the sun
behind the mountain). Conscious that he is ruining himself and that he
is falling into a "low place" (basso loco) where the sun is silent ('l sol tace), Dante is at last rescued by Virgil, and the two of them begin their journey to the underworld. Each sin's punishment in Inferno is a contrapasso, a symbolic instance of poetic justice; for example, in Canto XX, fortune-tellers and soothsayers must walk with their heads on backwards, unable to see what is ahead, because that was what they had tried to do in life:
they had their faces twisted toward their haunches
and found it necessary to walk backward,
because they could not see ahead of them.
... and since he wanted so to see ahead,
he looks behind and walks a backward path.
Allegorically, the Inferno represents the Christian soul
seeing sin for what it really is, and the three beasts represent three
types of sin: the self-indulgent, the violent, and the malicious.
These three types of sin also provide the three main divisions of
Dante's Hell: Upper Hell, outside the city of Dis, for the four sins of
indulgence (lust, gluttony, avarice, anger);
Circle 7 for the sins of violence; and Circles 8 and 9 for the sins of
fraud and treachery. Added to these are two unlike categories that are
specifically spiritual: Limbo, in Circle 1, contains the virtuous pagans
who were not sinful but were ignorant of Christ, and Circle 6 contains
the heretics who contradicted the doctrine and confused the spirit of
Christ. The circles number 9, with the addition of Satan completing the
structure of 9 + 1 = 10.
Purgatorio
Dante gazes at Mount Purgatory in an allegorical portrait by Agnolo Bronzino, painted c. 1530
Having survived the depths of Hell, Dante and Virgil ascend out of the undergloom to the Mountain of Purgatory on the far side of the world. The Mountain is on an island, the only land in the Southern Hemisphere, created by the displacement of rock which resulted when Satan's fall created Hell (which Dante portrays as existing underneath Jerusalem). The mountain has seven terraces, corresponding to the seven deadly sins or "seven roots of sinfulness." The classification of sin here is more psychological than that of the Inferno,
being based on motives, rather than actions. It is also drawn primarily
from Christian theology, rather than from classical sources.
However, Dante's illustrative examples of sin and virtue draw on
classical sources as well as on the Bible and on contemporary events.
Love, a theme throughout the Divine Comedy, is
particularly important for the framing of sin on the Mountain of
Purgatory. While the love that flows from God is pure, it can become
sinful as it flows through humanity. Humans can sin by using love
towards improper or malicious ends (Wrath, Envy, Pride), or using it to proper ends but with love that is either not strong enough (Sloth) or love that is too strong (Lust, Gluttony, Greed).
Below the seven purges of the soul is the Ante-Purgatory, containing
the Excommunicated from the church and the Late repentant who died,
often violently, before receiving rites. Thus the total comes to nine,
with the addition of the Garden of Eden at the summit, equaling ten.
Allegorically, the Purgatorio represents the Christian life. Christian souls arrive escorted by an angel, singing In exitu Israel de Aegypto. In his Letter to Cangrande, Dante explains that this reference to Israel leaving Egypt refers both to the redemption of Christ and to "the conversion of the soul from the sorrow and misery of sin to the state of grace." Appropriately, therefore, it is Easter Sunday when Dante and Virgil arrive.
The Purgatorio is notable for demonstrating the medieval knowledge of a spherical Earth. During the poem, Dante discusses the different stars visible in the southern hemisphere, the altered position of the sun, and the various timezones of the Earth. At this stage it is, Dante says, sunset at Jerusalem, midnight on the River Ganges, and sunrise in Purgatory.
After an initial ascension, Beatrice guides Dante through the nine celestial spheres of Heaven. These are concentric and spherical, as in Aristotelian and Ptolemaic cosmology. While the structures of the Inferno and Purgatorio were based on different classifications of sin, the structure of the Paradiso is based on the four cardinal virtues and the three theological virtues.
The seven lowest spheres of Heaven deal solely with the cardinal virtues of Prudence, Fortitude, Justice and Temperance. The first three spheres involve a deficiency of one of the cardinal virtues – the Moon, containing the inconstant, whose vows to God waned as the moon and thus lack fortitude; Mercury,
containing the ambitious, who were virtuous for glory and thus lacked
justice; and Venus, containing the lovers, whose love was directed
towards another than God and thus lacked Temperance. The final four
incidentally are positive examples of the cardinal virtues, all led on
by the Sun,
containing the prudent, whose wisdom lighted the way for the other
virtues, to which the others are bound (constituting a category on its
own). Mars contains the men of fortitude who died in the cause of Christianity; Jupiter contains the kings of Justice; and Saturn
contains the temperate, the monks who abided by the contemplative
lifestyle. The seven subdivided into three are raised further by two
more categories: the eighth sphere of the fixed stars that contain those
who achieved the theological virtues of faith, hope and love, and represent the Church Triumphant – the total perfection of humanity, cleansed of all the sins and carrying all the virtues of heaven; and the ninth circle, or Primum Mobile
(corresponding to the Geocentricism of Medieval astronomy), which
contains the angels, creatures never poisoned by original sin. Topping
them all is the Empyrean, which contains the essence of God, completing the 9-fold division to 10.
Dante meets and converses with several great saints of the Church, including Thomas Aquinas, Bonaventure, Saint Peter, and St. John. The Paradiso is consequently more theological in nature than the Inferno and the Purgatorio.
However, Dante admits that the vision of heaven he receives is merely
the one his human eyes permit him to see, and thus the vision of heaven
found in the Cantos is Dante's personal vision.
The Divine Comedy finishes with Dante seeing the Triune God. In a flash of understanding that he cannot express, Dante finally understands the mystery of Christ's divinity and humanity, and his soul becomes aligned with God's love:
But already my desire and my will
were being turned like a wheel, all at one speed,
by the Love which moves the sun and the other stars.
History
Manuscripts
According to the Italian Dante Society, no original manuscript
written by Dante has survived, although there are many manuscript
copies from the 14th and 15th centuries – some 800 are listed on their
site.
First edition to name the poem Divina Comedia, 1555
Illustration of Lucifer in the first fully illustrated print edition. Woodcut for Inferno, canto 33. Pietro di Piasi, Venice, 1491.
The first printed edition was published in Foligno, Italy, by Johann Numeister and Evangelista Angelini da Trevi on 11 April 1472. Of the 300 copies printed, fourteen still survive. The original printing press is on display in the Oratorio della Nunziatella in Foligno.
Early printed editions
Date
Title
Place
Publisher
Notes
1472
La Comedia di Dante Alleghieri
Foligno
Johann Numeister and Evangelista Angelini da Trevi
Commedia di Dante insieme con uno diagolo circa el sito forma et misure dello inferno
Florence
Philippo di Giunta
1555
La Divina Comedia di Dante
Venice
Gabriel Giolito
First use of "Divine" in title
Thematic concerns
The Divine Comedy can be described simply as an allegory:
each canto, and the episodes therein, can contain many alternative
meanings. Dante's allegory, however, is more complex, and, in explaining
how to read the poem – see the Letter to Cangrande – he outlines other levels of meaning besides the allegory: the historical, the moral, the literal, and the anagogical.
The structure of the poem is also quite complex, with
mathematical and numerological patterns distributed throughout the work,
particularly threes and nines, which are related to the Holy Trinity.
The poem is often lauded for its particularly human qualities: Dante's
skillful delineation of the characters he encounters in Hell, Purgatory,
and Paradise; his bitter denunciations of Florentine and Italian politics; and his powerful poetic imagination. Dante's use of real characters, according to Dorothy Sayers in her introduction to her translation of the Inferno,
allows Dante the freedom of not having to involve the reader in
description, and allows him to "[make] room in his poem for the
discussion of a great many subjects of the utmost importance, thus
widening its range and increasing its variety."
Dante called the poem "Comedy" (the adjective "Divine" was added
later, in the 16th century) because poems in the ancient world were
classified as High ("Tragedy") or Low ("Comedy").
Low poems had happy endings and were written in everyday language,
whereas High poems treated more serious matters and were written in an
elevated style. Dante was one of the first in the Middle Ages to write
of a serious subject, the Redemption of humanity, in the low and
"vulgar" Italian language and not the Latin one might expect for such a
serious topic. Boccaccio's account that an early version of the poem was begun by Dante in Latin is still controversial.
Scientific themes
Although the Divine Comedy is primarily a religious poem, discussing sin, virtue, and theology, Dante also discusses several elements of the science of his day (this mixture of science with poetry has received both praise and blame over the centuries). The Purgatorio repeatedly refers to the implications of a spherical Earth, such as the different stars visible in the southern hemisphere, the altered position of the sun, and the various timezones of the Earth. For example, at sunset in Purgatory it is midnight at the Ebro, dawn in Jerusalem, and noon on the River Ganges:
Just as, there where its Maker shed His blood,
the sun shed its first rays, and Ebro lay
beneath high Libra, and the ninth hour's rays
were scorching Ganges' waves; so here, the sun
stood at the point of day's departure when
God's angel – happy – showed himself to us.
Dante travels through the centre of the Earth in the Inferno, and comments on the resulting change in the direction of gravity
in Canto XXXIV (lines 76–120). A little earlier (XXXIII, 102–105), he
queries the existence of wind in the frozen inner circle of hell, since
it has no temperature differentials.
Inevitably, given its setting, the Paradiso discusses astronomy extensively, but in the Ptolemaic sense. The Paradiso also discusses the importance of the experimental method in science, with a detailed example in lines 94–105 of Canto II:
Yet an experiment, were you to try it,
could free you from your cavil and the source
of your arts' course springs from experiment.
Taking three mirrors, place a pair of them
at equal distance from you; set the third
midway between those two, but farther back.
Then, turning toward them, at your back have placed
a light that kindles those three mirrors and
returns to you, reflected by them all.
Although the image in the farthest glass
will be of lesser size, there you will see
that it must match the brightness of the rest.
A briefer example occurs in Canto XV of the Purgatorio (lines 16–21), where Dante points out that both theory and experiment confirm that the angle of incidence is equal to the angle of reflection. Other references to science in the Paradiso include descriptions of clockwork in Canto XXIV (lines 13–18), and Thales' theorem about triangles in Canto XIII (lines 101–102).
Galileo Galilei is known to have lectured on the Inferno, and it has been suggested that the poem may have influenced some of Galileo's own ideas regarding mechanics.
Theories of influence from Islamic philosophy
In 1919, Miguel Asín Palacios, a Spanish scholar and a Catholic priest, published La Escatología musulmana en la Divina Comedia (Islamic Eschatology in the Divine Comedy), an account of parallels between early Islamic philosophy and the Divine Comedy. Palacios argued that Dante derived many features of and episodes about the hereafter from the spiritual writings of Ibn Arabi and from the Isra and Mi'raj or night journey of Muhammad to heaven. The latter is described in the ahadith and the Kitab al Miraj (translated into Latin in 1264 or shortly before as Liber Scalae Machometi, "The Book of Muhammad's Ladder"), and has significant similarities to the Paradiso, such as a sevenfold division of Paradise, although this is not unique to the Kitab al Miraj or Islamic cosmology.
Some "superficial similarities" of the Divine Comedy to the Resalat Al-Ghufran or Epistle of Forgiveness of Al-Ma'arri have also been mentioned in this debate. The Resalat Al-Ghufran
describes the journey of the poet in the realms of the afterlife and
includes dialogue with people in Heaven and Hell, although, unlike the Kitab al Miraj, there is little description of these locations, and it is unlikely that Dante borrowed from this work.
Dante did, however, live in a Europe of substantial literary and
philosophical contact with the Muslim world, encouraged by such factors
as Averroism
("Averrois, che'l gran comento feo" Commedia, Inferno, IV, 144, meaning
"Averrois, who wrote the great comment") and the patronage of Alfonso X of Castile. Of the twelve wise men Dante meets in Canto X of the Paradiso, Thomas Aquinas and, even more so, Siger of Brabant were strongly influenced by Arabic commentators on Aristotle. Medieval Christian mysticism also shared the Neoplatonic influence of Sufis such as Ibn Arabi. Philosopher Frederick Copleston argued in 1950 that Dante's respectful treatment of Averroes, Avicenna, and Siger of Brabant indicates his acknowledgement of a "considerable debt" to Islamic philosophy.
Although this philosophical influence is generally acknowledged,
many scholars have not been satisfied that Dante was influenced by the Kitab al Miraj. The 20th century Orientalist Francesco Gabrieli
expressed skepticism regarding the claimed similarities, and the lack
of evidence of a vehicle through which it could have been transmitted to
Dante. Even so, while dismissing the probability of some influences
posited in Palacios' work, Gabrieli conceded that it was "at least possible, if not probable, that Dante may have known the Liber Scalae and have taken from it certain images and concepts of Muslim eschatology". Shortly before her death, the Italian philologist Maria Corti pointed out that, during his stay at the court of Alfonso X, Dante's mentor Brunetto Latini met Bonaventura de Siena, a Tuscan who had translated the Kitab al Miraj from Arabic into Latin. Corti speculates that Brunetto may have provided a copy of that work to Dante. René Guénon, a Sufi convert and scholar of Ibn Arabi, rejected in The Esoterism of Dante the theory of his influence (direct or indirect) on Dante. Palacios' theory that Dante was influenced by Ibn Arabi was satirized by the Turkish academic Orhan Pamuk in his novel The Black Book.
Literary influence in the English-speaking world and beyond
A detail from one of Sandro Botticelli's illustrations for Inferno, Canto XVIII, 1480s. Silverpoint on parchment, completed in pen and ink.
The Divine Comedy was not always as well-regarded as it is today. Although recognized as a masterpiece in the centuries immediately following its publication, the work was largely ignored during the Enlightenment, with some notable exceptions such as Vittorio Alfieri; Antoine de Rivarol, who translated the Inferno into French; and Giambattista Vico, who in the Scienza nuova and in the Giudizio su Dante inaugurated what would later become the romantic reappraisal of Dante, juxtaposing him to Homer. The Comedy was "rediscovered" in the English-speaking world by William Blake – who illustrated several passages of the epic – and the Romantic writers of the 19th century. Later authors such as T. S. Eliot, Ezra Pound, Samuel Beckett, C. S. Lewis and James Joyce have drawn on it for inspiration. The poet Henry Wadsworth Longfellow was its first American translator, and modern poets, including Seamus Heaney, Robert Pinsky, John Ciardi, W. S. Merwin, and Stanley Lombardo, have also produced translations of all or parts of the book. In Russia, beyond Pushkin's translation of a few tercets, Osip Mandelstam's late poetry has been said to bear the mark of a "tormented meditation" on the Comedy. In 1934, Mandelstam gave a modern reading of the poem in his labyrinthine "Conversation on Dante". In T. S. Eliot's estimation, "Dante and Shakespeare divide the world between them. There is no third." For Jorge Luis Borges the Divine Comedy was "the best book literature has achieved".
English translations
New English translations of the Divine Comedy continue to be published regularly. Notable English translations of the complete poem include the following.
The Divine Comedy has been a source of inspiration for
countless artists for almost seven centuries. There are many references
to Dante's work in literature. In music, Franz Liszt was one of many composers to write works based on the Divine Comedy. In sculpture, the work of Auguste Rodin includes themes from Dante, and many visual artists have illustrated Dante's work, as shown by the examples above. There have also been many references to the Divine Comedy in cinema, television, digital arts, comics and video games.
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