Fine-tuned universe

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Deep-space structures such as the Eta Carinae Nebula would not form in a universe with different physical constants. Photo: HST / NASA / ESA.
The fine-tuned Universe is the idea that conditions that allow life in the Universe can only occur with the tightly restricted values of the universal physical constants, and that small changes in these constants would correspond to a very different universe, not likely conducive to the establishment and development of matter, astronomical structures, or life as it is presently known.

The arguments relating to the fine-tuned universe concept are related to the anthropic principle, which states that any valid theory of the universe must be consistent with our existence as human beings at this particular time and place in the universe. In other words, even though the actual probability of a universe to be one which supports intelligent life is very low, the conditional probability given our existence in it is 1 - and even if there are other universes devoid of life, there will be no one to observe them.


The premise of the fine-tuned universe assertion is that any small change in the approximately 26 dimensionless fundamental physical constants would make the universe radically different: if, for example, the strong nuclear force were 2% stronger than it is (i.e. if the constant representing its strength were 2% larger), diprotons would be stable and hydrogen would fuse into them instead of deuterium and helium. This would drastically alter the physics of stars, and presumably prevent the universe from developing life as it is currently observed on the earth. However, many of the 26 constants describe the properties of the unstable strange, charmed, bottom and top quarks and mu and tau leptons which seem to play little part in the universe or the structure of matter. It seems unlikely that the precise values of these constants are important for life; at any rate they are not included in the usual discussion of fine-tuning.

Larry Abbott describes the issue thus: "the small value of the cosmological constant is telling us that a remarkably precise and totally unexpected relation exists among all the parameters of the Standard Model of particle physics, the bare cosmological constant and unknown physics."[1] Victor Stenger characterizes the fine-tuned universe concept as capable of being interpreted as a "claim of evidence for divine cosmic plan": "As the argument goes, the chance that any initially random set of constants would correspond to the set of values that we find in our universe is very small and the universe is exceedingly unlikely to be the result of mindless chance. Rather, an intelligent, purposeful Creator must have arranged the constants to support life".[2] Stenger in that paper is critical of the claims of the fine-tuning advocates and provides his own explanations highlighting the flaws in those claims, concluding that "The universe is not fine-tuned for humanity. Humanity is fine-tuned to the universe".[3]

As modern cosmology developed, various hypotheses have been proposed (including an oscillatory universe or a multiverse) where physical constants are postulated to resolve themselves to random values in different iterations of reality, resulting in separate parts of reality with wildly different characteristics. In such scenarios the issue of fine-tuning does not arise at all, as only those "universes" with constants hospitable to life (such as what we observe) would develop life capable of pondering the question.

Though there are fine tuning arguments that are naturalistic,[4] the assertion that the universe was designed to be fine-tuned is largely promoted by advocates of intelligent design and other forms of creationism. This apparent fine-tuning of the universe is cited[5] as an evidence for the existence of God or some form of intelligence capable of manipulating (or designing) the basic physics that governs the universe.

Critics of both the fine-tuned universe assertion and the anthropic principle argue that they are essentially a tautology.[6] The claim of a fine-tuned universe has also been criticized as an argument by lack of imagination for assuming no other forms of life are possible (see also alternative biochemistry). In addition, critics see it as an example of backwards reasoning since it asserts that the universe is adapted to humans instead of that humans are adapted to the universe through the process of evolution. Critics also see it as an example of the logical flaw of hubris or anthropocentrism in its assertion that humans are the purpose of the universe.[7]

Nature of the constants

Modern science as practiced since René Descartes is reductionist, meaning that it attempts to discover the most fundamental objects and rules governing the observable behavior of the universe. In descriptions of the physical universe, fundamental rules take the form of laws (usually equations relating physical quantities and properties) involving physical constants, while the fundamental objects are elementary particles with constant mass, charge, and other physical properties. This reductionism is a pragmatic approach that obtains results and is not a philosophical position on ontology. The nature of these constants is a much debated topic in physics and metaphysics (see string theory).

Meaning of "universe"

Both popular and professional research articles in cosmology often use the term "universe" to refer to the observable universe. The reason for this usage is that only observable phenomena are scientifically relevant. Since unobservable phenomena have no perceptible effects, physicists argue that they "causally do not exist". Since unobservable parts of the universe cannot be measured, hypotheses about them are not testable, and thus inappropriate for a scientific theory.

In metaphysics, "universe" refers to everything that exists. This encompasses both observable and unobservable phenomena. Metaphysics seeks to describe everything that is knowable about existence.

All the arguments that refer to the observable universe would not necessarily apply to the unobservable parts of reality sometimes called "other universes", if such there be. Although our observable universe has the parameters necessary for carbon based life, other parts of a larger multiverse may be sterile, or may have physical parameters conducive to different types of life or other, possibly self-aware, systems.

Possible fine-tuning

There are many cases where the Known physical constants suggest fine tuning These and other examples are often given as evidence of the universe being fine-tuned. Whether they actually are proof of fine-tuning is a matter debated between proponents of the fine-tuning argument and critics who feel that such reasoning is a subjective anthropomorphism of natural physical constants or, in the words of Victor Stenger, that "...The fine-tuning argument and other recent intelligent design arguments are modern versions of God-of-the-gaps reasoning, where a God is deemed necessary whenever science has not fully explained some phenomenon.". Victor Stenger furthers his critical view that "...a wide variation of constants of physics leads to universes that are long-lived enough for life to evolve, although human life need not exist in such universes".[8]

Implications of fine tuning

Fine-Tuning comes with caveats. The fact that a universe with different physical constants might be inhospitable to life as we know it does not necessarily mean that it is inhospitable to any form of life. Currently, there is no way of experimentally determining if a universe allows for life or not. Further, most of this universe, especially the interstellar vacuum, appears to be devoid of life; other physical constants may exist that allow a much greater density of life than in this universe.

Naturalistic possibilities

If it is accepted that the universe is fine-tuned, there are a number of possibilities to account for it.

Random chance

  • Random chance: It could be that through sheer random circumstance, this universe is the one that was formed, and that there is no further explanation. Some believe that fine-tuning does not need any more explanation than that a particular roll of dice would result in a double six (i.e. an extremely lucky event). They argue that our universe had to have physical constants, and they just happen to be the ones that permit our existence, as opposed to no living creatures, or different ones, and suggest that, had there been other sapient and sentient beings in a totally different universe living in totally different bodies they would have asked the exact same apparently meaningless question.


  • Multiverse: This assumes the existence of many universes with different physical constants, some of which are hospitable to intelligent life. Because we are intelligent beings, we are by definition in a hospitable one. This approach has led to considerable research into the anthropic principle and has been of particular interest to particle physicists because theories of everything do apparently generate large numbers of universes in which the physical constants vary widely. As of yet, there is no evidence for the existence of a multiverse, but some versions of the theory do make predictions which some researchers studying M-theory and gravity leaks hope to see some evidence of soon.[9] Multiverses are not necessarily falsifiable, and thus some are reluctant to call multiverses a "scientific" idea. Variants on this approach include:

Cosmological natural selection

  • Cosmological natural selection (CNS), was created by physicist Lee Smolin as a testable alternative to string theory predictions of an enormous landscape of possible universes. CNS holds that the creation of a black hole often (perhaps always) entails the creation of baby universes, and that through a process of selection that in some ways mimics evolutionary natural selection, universes are created that are optimized for creating black holes. In other words, these universes are optimized for creating stable atoms, long lived stars, and in particular lots of stable carbon atoms — a point that also happens to explain why our universe seems to be biophilic. These "self-organizing critical systems" are capable of fine-tuning themselves by a simple mechanism, following a simple set of physical laws — thus making it likely that the parameters we observe are indeed "fine-tuned", but as the result of natural processes rather than intelligence. Louis Crane has proposed a meduso-anthropic principle suggesting that universes could be fine-tuned for life by intelligent beings themselves manufacturing new universes. He argues that the destiny of highly evolved intelligence is to infuse the entire universe with life.

Ekpyrotic universe

  • The Ekpyrotic universe. Brane cosmology assumes that the visible universe lies on a three-dimensional brane which moves in higher dimensional space. Our brane may be one of innumerable others moving through these extra dimensions. The ekpyrotic scenario was proposed by Khoury, Ovrut, Steinhardt and Turok in 2001. It suggests that the visible universe was empty and contracting in the distant past. At some time, our brane collided with another, parallel "hidden" brane, which caused the contracting universe to reverse and begin expanding. Hot matter and radiation was created in the collision, which started the hot big bang from which the present-day universe originated. The brane collision, from the four-dimensional perspective of the visible brane, looks like a big crunch followed by a big bang. Over a long enough period of time it might not be surprising that some of these universes would be biophilic. Detractors of the original ekpyrotic scenario point out that it requires fine-tuned, nearly supersymmetric initial conditions, and thus replaces the problems solved by cosmic inflation with a new set of problems.

Speculative physics

  • Speculative physics. Following the classification scheme of Martin Rees in Just Six Numbers the universe may have emerged with the special characteristics required to be biophilic. Some scientists (of which Paul Davies and Fred Hoyle might stand as examples) argue that, although the fine-tuning of the universe is too implausible to have occurred by chance, there may be physical reasons why this has happened. The discussions by Stephen Hawking of the Wave-Function of the Universe might be considered to come in this broad category.

Quantum uncertainy of fundamental constants

  • Quantum uncertainty. The theory argues that fundamental constants and other conditions of the universe may be subjects of quantum-mechanical uncertainty. With the emergence of observer with his first observation the wavefunction of the universe collapses to the state compatible with obsrver's existence. This theory explained in the form based on Many-Worlds interpretation of quantum mechanics and related quantum suicide principle states that probability of any observation that leads to destruction of the observer is zero. This principle extended into the past makes the Universe which is not compatible with eventual existence of the observer impossible.

Alien design

  • The Universe may have been designed by an alien or by aliens. This would solve the problem of how a designer or design team capable of fine-tuning the Universe could come to exist. Possibly the extraterrestrial designer/designers evolved in a universe, which can sustain life despite being less finely tuned than ours. If any designer or design team are members of a species which evolved then there is or was a breeding population of the designer species. A designer is not one single supreme being. Note, one single designer would need to be very much more capable than any individual member of a design team cooperating together. Therefore Occam's razor may favour a design team.

Religious opinions

Certain religious groups have seized on the idea that providence or creation are responsible for fine-tuning. Variants on this approach include:

Intelligent design

  • Intelligent design: Proponents of Intelligent Design argue that certain features of the universe and of living things are best explained by an intelligent cause, not an undirected process such as natural selection. The fine-tuned universe argument is a central premise or presented as a given in many of the published works of prominent Intelligent Design proponents, such as William A. Dembski and Michael Behe.

Other religious creation views

  • Other religious creation views. Most religions have some kind of account of the creation of the universe, although they generally differ in detail from the ones listed above. Some of these may be fully compatible with known scientific facts (notwithstanding their use of metaphysical ideas which are beyond the domain of science). For example scientist-theologians such as John Polkinghorne emphasise the implications of Anthropic Fine-Tuning within an orthodox Christian framework whilst fully accepting the scientific findings about Evolution and the age of the Universe. This is also the position of the Roman Catholic Church and of most Anglican theologians, of whom Alister McGrath is probably the most prolific in this area.[10] The Jewish physicist Gerald Schroeder argues that the apparent discrepancy between the "days" in Genesis and the billions of years in a scientific understanding are due to the differences in frames of reference. Many other religious creation views are either incompatible with, or indifferent to, scientific understandings.

Bayesian arguments

A Bayesian probabilistic discussion by mathematician Michael Ikeda and astronomer William H. Jefferys[11] (2006) argues that the traditional reasoning about intelligent design from the presence of fine-tuning does not properly condition on the existence of life and is also based on an incorrect reversal of conditional probabilities.[1] They argue that it is an example of the prosecutor's fallacy, which in this form erroneously claims that if fine-tuning is rare in naturalistic universes, then a fine-tuned universe is unlikely to be naturalistic. (In this context, "naturalistic" is taken to be synonymous with "not intelligently designed".)[12]

The philosopher of science Elliott Sober makes a similar argument (2004). Richard Swinburne reaches the opposite conclusion using Bayesian probability (Swinburne 1990).

In fiction & poetry

Isaac Asimov

The second part of The Gods Themselves by Isaac Asimov deals with a parallel universe with a different Strong nuclear force.

Stephen Baxter

Stephen Baxter has written several novels and short stories in which the setting is an alternative universe with different physical laws. The most obvious example is Raft in which the force of gravity is a billion times stronger than in our universe. The novel, of the Manifold sequence includes the interesting concept that the universe itself is not perfectly tuned for life to exist and is still in the process of evolution itself. The climax of the book involves the destruction of the universe so that a new version, better suited to life, may replace it.

Star Trek

The Sphere Builders of created the Delphic Expanse in an attempt to alter the physical laws of our universe to match those of their own parallel universe. Their form of life was not compatible with the current physical laws of our universe (as evidenced by their quickly decaying bodies), and thus needed to make said changes in order to conquer and live in our universe.

Neal Stephenson

Author Neal Stephenson discussed the issue of fine-tuning in the conclusion to his essay In The Beginning Was The Command Line, speculating on what might happen if an all-powerful entity had access to a computer program that could generate universes with any desired set of properties.
The demiurge sits at his teletype, pounding out one command line after another, specifying the values of fundamental constants of physics:
:universe -G 6.672e-11 -e 1.602e-19 -h 6.626e-34 -protonmass 1.673e-27....
and when he's finished typing out the command line, his right pinky hesitates above the ENTER key for an aeon or two, wondering what's going to happen; then down it comes--and the WHACK you hear is another Big Bang.[13]


1. ^ Larry Abbott, "The Mystery of the Cosmological Constant," Scientific American, vol. 3, no. 1 (1991): 78; quoted in Michael A Corey, The God Hypothesis: Discovering Divine Design in Our Goldilocks Universe Rowman and Littlefield,
2. ^ Is The Universe Fine-Tuned For Us? Victor J. Stenger, University of Colorado. (PDF file)
3. ^ Is The Universe Fine-Tuned For Us? Victor J. Stenger, University of Colorado. page 21 (PDF file)
4. ^ L. Susskind, The cosmic landscape: string theory and the illusion of intelligent design (Little, Brown, 2005).
5. ^ William Lane Craig, "The Teleological Argument and the Anthropic Principle," [2]
6. ^ See, e.g., Our place in the Multiverse Joseph Silk. Nature, Volume 443 Number 7108, September 14 2006.
7. ^ See, e.g., Gerald Feinberg and Robert Shapiro, "A Puddlian Fable" in Huchingson, Religion and the Natural Sciences (1993), pp. 220-221
8. ^ Is The Universe Fine-Tuned For Us? Victor J. Stenger, University of Colorado.(PDF file) page 20
9. ^ Parallel Worlds,2005, Michio Kaku, pp. 220-221
10. ^ see eg his 3-volume Scientific Theology and his shorter book The Science of God
11. ^ Jefferys
12. ^ The Ikeda and Jefferys paper, which has not been published in any peer-reviewed journal, offers a proof which, they argue, indicates one should in fact draw a conclusion opposite to the traditional reasoning: instead of implying intelligent design, the presence of fine-tuning actually argues against such design. Their argument hinges on the assumptions that
  1. our universe exists and contains life (L),
  2. our universe is "life friendly" (F), in that its conditions are compatible with life existing naturalistically, and
  3. life can exist in a "naturalistic" (N) universe only if that universe is "life-friendly" (N&L ⇒ F: the weak anthropic principle).

The Ikeda-Jefferys fine-tuning proposition states that, under these assumptions, the probability that our universe is naturalistic, given it contains life, is less than, or equal to, the probability that our universe is naturalistic, given that it contains life and is also life-friendly — in probabilistic notation, P(N|L) ≤ P(N|L&F). In other words, the fact that the universe is life-friendly increases (or rather, cannot decrease) the probability that our universe is naturalistic, given that we already know it contains life, regardless of how low P(F|N) might be. Thus, Ikeda and Jefferys argue ironically, supporters of intelligent design should try to prove that our universe is not fine-tuned.

The Ikeda-Jefferys argument arrives at a different conclusion from that of standard Cosmological Intelligent Design due to a differing assumption held by the two arguments concerning the nature of omnipotence. Cosmological Intelligent Design arguments assume that an intelligent designer has chosen to work through "natural" laws (which he can modify) while the Ikeda-Jefferys argument does not make this assumption. Thus the conclusion most Cosmological Intelligent Design arguments draws is that one should look for a low probability of randomness producing life-friendly conditions, and the Ikeda-Jefferys conclusion is that one should look for life that is not supported by natural law. If the Ikeda-Jefferys argument holds the same assumptions as Cosmological Intelligent Design, fine-tuning provides no new information about the likelihood or unlikelihood of design; using the variables above, we would obtain P(N|L) = P(N|L&F), because we would have L -> F: life could exist only in a life-friendly universe, regardless of how that universe came to be, or whether it was subject to continued divine intervention.
13. ^ "In The Beginning Was The Command Line" available online


  • John D. Barrow and Frank J. Tipler, 1986. The Anthropic Cosmological Principle. Oxford Univ. Press. ISBN 0-19-282147-4
  • John D. Barrow, 2003. The Constants of Nature, Pantheon Books, ISBN 0-375-42221-8
  • Nick Bostrom, 2002. Anthropic Bias: Observation Selection Effects in Science and Philosophy, Routledge, New York, ISBN 0-415-93858-9
  • Paul Davies, 1982. The Accidental Universe, Cambridge University Press, ISBN 0-521-24212-6
  • Michael Ikeda and William H. Jefferys, "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
  • Simon Conway Morris, 2003. Life's Solution: Inevitable Humans in a Lonely Universe. Cambridge Univ. Press.
  • Martin Rees, 1999. Just Six Numbers, HarperCollins Publishers, ISBN 0-465-03672-4
  • Elliott Sober, 2004. The Design Argument, in The Blackwell Guide to the Philosophy of Religion, W. E. Mann, Editor. Blackwell Publishing, ISBN 0-631-22129-8
  • Richard Swinburne, 1990. Argument from the fine-tuning of the universe, in Physical cosmology and philosophy, J. Leslie, Editor. Collier Macmillan: New York. pp. 154-73.
  • Ward, P. D., and Brownlee, D., 2000. Rare Earth: Why Complex Life is Uncommon in the Universe. Springer Verlag.

See also

External links

Life (Biota)

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In physics, a physical constant is a physical quantity that is generally believed to be both universal in nature and constant in time. It can be contrasted with a mathematical constant, which is a fixed numerical value but does not directly involve any physical measurement.
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In physics and cosmology, the anthropic principle states that we should take into account the constraints that our existence as observers imposes on the sort of universe that we could observe.
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In dimensional analysis, a dimensionless quantity (or more precisely, a quantity with the dimensions of 1) is a quantity without any physical units and thus a pure number.
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dimensionless or fundamental physical constants are, in the strictest sense, universal physical constants that are independent of systems of units and hence are dimensionless quantities.
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Victor J. Stenger (born January 291935) is emeritus professor of physics and astronomy at the University of Hawaii and adjunct professor of philosophy at the University of Colorado.
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The oscillatory universe is a cosmological model, originally derived by Alexander Friedman in 1922, investigated briefly by Einstein in 1930 and critiqued by Richard Tolman from 1934, in which the universe undergoes a series of oscillations, each beginning with a big bang and
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A multiverse (or meta-universe) is the hypothetical set of multiple possible universes (including our universe) that together comprise all of physical reality. The different universes within a multiverse are sometimes called parallel universes.
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random is used to express lack of order, purpose, cause, or predictability in non-scientific parlance. A random process is a repeating process whose outcomes follow no describable deterministic pattern, but follow a probability distribution.
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Intelligent design is the assertion that "certain features of the universe and of living things are best explained by an intelligent cause, not an undirected process such as natural selection.
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Creationism is a religious belief that humanity, life, the Earth, and the universe were created in their original form by a deity or deities (often the Abrahamic God of Judaism, Christianity and Islam), whose existence is presupposed.
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A teleological argument, or argument from design, is an argument for the existence of God or a creator based on perceived evidence of order, purpose, design and/or direction in nature.
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An intelligent designer, also referred to as an intelligent agent, is the willed and self-conscious entity that the intelligent design movement argues had some role in the origin and/or development of life and who supposedly has left scientific evidence of this
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Physics is the science of matter[1] and its motion[2][3], as well as space and time[4][5] —the science that deals with concepts such as force, energy, mass, and charge.
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