Fine-tuned universe

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The term fine-tuned universe refers to 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.

Contents 1 Premise 2 Nature of the constants 3 Meaning of "universe" 4 Known physical constants and possible examples of fine tuning 5 Implications of fine tuning 5.1 Major possibilities 5.2 Bayesian arguments 6 In fiction 7 Notes 8 References 9 See also 10 External links

[edit] Premise

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.

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]

[edit] 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).

[edit] 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. A larger multiverse may exist where different parts have different parameters. Our observable universe, according to this has the parameters necessary for carbon based life. Other parts of the multiverse may be sterile or may contain different types of self-aware systems or life.

[edit] Known physical constants and possible examples of fine tuning

(Sources for this section: Walter Bradley's "Is there Scientific Evidence for the Existence of God", [2], Robin Collins's essay "Evidence of fine tuning", [3], [4])

• The nuclear strong force holds together the particles in the nucleus of an atom. If the strong nuclear force were 2% (9% according to Bradley, 50% according to Collins) weaker, multi-proton nuclei would not hold together and hydrogen would be the only stable element in the universe. If the strong force were 1% stronger, hydrogen would rapidly fuse into helium-2; it is also argued that elements heavier than iron would be rare, since they result from fusion during the explosion of supernovae. Collins disputes this on the grounds that the helium-2 would rapidly decay into deuterium which could then fuse into helium-4, but has claimed that this increase would drastically decrease the amount of oxygen (relative to carbon) in the Universe (and that a decrease would have the reverse effect).

• The nuclear weak force affects the behavior of leptons (e.g. neutrinos, electrons, and muons), which do not participate in strong nuclear reactions. Bradley has argued that if the weak force were slightly larger, neutrons would decay more readily, and therefore would be less available, and little or no helium would have been produced from the big bang. Without the necessary helium, heavy elements such as carbon could not be made by the nuclear furnaces inside stars. Conversely, he and Collins argue, if the weak force were slightly smaller, the big bang would have burned most or all of the hydrogen into helium, which would make hydrogen-containing molecules rare, and shorten the lifespan of stars, since they would be fusing helium instead of hydrogen.

• The intensity of the force binding electrons to protons in atoms depends on the electromagnetic coupling constant. The characteristics of the orbits of electrons about atoms determines to what degree atoms will bond together to form molecules. If the electromagnetic coupling constant were different atoms and molecules would be significantly different.

• The ratio of electron to proton mass also determines the characteristics of the orbits of electrons about nuclei. A proton is approximately 1836 times more massive than an electron. If the electron to proton mass ratio were different, atoms and molecules would be significantly different. Bradley has also quoted Stephen Hawking as saying that the neutron mass minus the proton mass must be roughly twice the mass of the electron, in order to ensure the approximate stability of both particles. Collins attributes a similar argument to Barrow and Tipler, although he disputes its relevance to the formation of life on the grounds that pairs of neutrons could decay into deuterons.

• The entropy level of the universe affects the condensation of massive systems. The universe contains about one billion photons for every baryon. This makes the universe extremely entropic, i.e. a very efficient radiator and a very poor engine. If the entropy level for the universe were slightly larger, no galactic systems would form (and therefore no stars). If the entropy level were slightly smaller, the galactic systems that formed would effectively trap radiation and prevent any fragmentation of the systems into stars. In either case, the universe would be devoid of stars and solar systems.

• The force of gravity affects the interaction of particles. In order for life as we know it to form, the force of gravity must be many orders of magnitude weaker than the force of electromagnetism for charged elementary particles. (Frank Wilczek has said that it is not the force of gravity that is so weak, but the mass of the particles that is so small.) The relationship of gravity to electromagnetism as it currently exists is this: The positively charged particles must equal in charge the negatively charged particles or else electromagnetism will dominate gravity, and stars, galaxies and planets will not form. The numbers of electrons must equal the numbers of protons to better than one part of 10³⁷ (10 to the 37th power), since gravity is 10³⁸ times weaker than electromagnetism. Collins cites arguments (for example by Martin Rees) that if gravity were a billion times stronger than it is, no planet could support any significant ecosystem or civilization. He considers this fine-tuning on the grounds that "to the total range of strengths of the forces in nature (which span a range of 10⁴⁰ as we saw above), this still amounts to a one-sided fine-tuning of one part in 10³¹".

• Both Bradley and Collins have argued that the cosmological constant must be fine-tuned to within one part in 10⁵⁰ for the Universe not to enter a runaway expansion phase.

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]

[edit] 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.

[edit] Major possibilities

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

• 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.^{[citation needed]}

• 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 (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.

• 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.

• Providence or Creation^[10] The universe may have been created with the special characteristics required to be biophilic. Variants on this approach include:

• Intelligent design: Proponents of Intelligent Design need not assume that only physical reasons exist for the constants of nature to be as they are. Therefore they are able to reason that the universe was purposely designed to support life by God (redesignated the "Intelligent Designer"). 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. Such proponents generally dispute some of the scientific facts about evolution or the age of the universe.

• 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.^[11] The Jewish physicist Gerald Schroeder argues that the apparent discrepency 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.

• Non-religious creation views. 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 non-religious metaphysical 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.

[edit] Bayesian arguments

A Bayesian probabilistic discussion by mathematician Michael Ikeda and astronomer William H. Jefferys^[12] (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.[5] 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".)^[13]

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

[edit] In fiction

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

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, Time 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.

The Sphere Builders of Star Trek: Enterprise 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 made said changes in order to live and conquer our universe.

[edit] Notes

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, 2001.online
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," [1]
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. ^ Following the classification scheme of Martin Rees in Just Six Numbers
11. ^ see eg his 3-volume Scientific Theology and his shorter book The Science of God
12. ^ Jefferys
13. ^ 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.

[edit] References

• 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.

[edit] See also

• Anthropic principle
• Fine-tuning
• Intelligent design
• Origin of life
• Rare Earth hypothesis
• Ultimate fate of the universe
• Teleology

[edit] External links

• Robin Collins's Fine-Tuning Website
• Does the Cosmos Show Evidence of Purpose?
• Fine-Tuning Argument links to online references, at the Secular Web
• Cosmological fine-tuning, by Robin Collins
• Design and the Anthropic Principle by Hugh Ross
• The Anthropic Principle Does Not Support Supernaturalism by Michael Ikeda and Bill Jefferys
• Overview of the Cosmological Intelligent Design argument Stephen M. Barr. July 2001. First Things, the Journal of Religion, Culture, and Public Life.
• The Design Argument by Elliott Sober (Adobe PDF format)
• Home page of Templeton Foundation project on fine-tuning
• Sharpening Ockham's razor on a Bayesian strop by William H. Jefferys and James O. Berger (Adobe PDF format)
• The cosmos is fine-tuned to permit human life at the talk.origins index to creationist claims.
• Is the Universe fine-tuned for us? (Adobe PDF format)
• Interview with Charles Townes discussing science and religion.
• Evidence For Design In The Universe