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Fine-tuned universe

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The deepest visible-light image of the cosmos. Hubble Ultra Deep Field.

The term fine-tuned universe refers to the idea that conditions that allow life in the universe appear to be the result of the universal physical constants relating to one another exactly as they do, and that small changes in these relationships would correspond to a very different universe, not conducive to the establishment and development of matter, astronomical structures, or life as we know them.

Some arguments relating to the fine-tuned universe concept are related to the weak 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.

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[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 fine-structure constant (which can be thought of as a function of the electron charge relative to the Planck charge) were slightly different, or if the strong nuclear force were only 2% stronger, diprotons would be stable and hydrogen would fuse too easily, making stars as we know them impossible and prevent the universe from developing life as we know it.

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."<ref>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</ref> 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."<ref>Is The Universe Fine-Tuned For Us? Victor J. Stenger, University of Colorado. (PDF file)</ref>. Stenger in that paper is critical of the claims and provides his own explanations highlighting the flaws in claims of the fine-tuning advocates and concludes that "The universe is not fine-tuned for humanity. Humanity is fine-tuned to the universe." <ref>Is The Universe Fine-Tuned For Us? Victor J. Stenger, University of Colorado. page 21 (PDF file)</ref>.

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 fine-tuning does not exist 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,<ref>L. Susskind, The cosmic landscape: string theory and the illusion of intelligent design (Little, Brown, 2005).</ref> 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<ref>William Lane Craig, "The Teleological Argument and the Anthropic Principle," [1]</ref> as an evidence for the existence of God or some form of intelligence capable of manipulating (or designing) the basic physics that govern the universe.

Critics of both the fine-tuned universe assertion and the anthropic principle argue that they are essentially a tautology;<ref>See, e.g., Our place in the Multiverse Joseph Silk. Nature, Volume 443 Number 7108, September 14 2006.</ref> life as we know it may not exist if things were different, but a different sort of life might exist in its place. 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 carbon chauvinism). 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 through natural selection. 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.<ref>See, e.g., Gerald Feinberg and Robert Shapiro, "A Puddlian Fable" in Huchingson, Religion and the Natural Sciences (1993), pp. 220-221</ref>

[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: [2], [3], [4], [5], [6], [7])

  • The nuclear strong force holds together the particles in the nucleus of an atom. If the strong nuclear force were slightly weaker, by as little as 2%, multi-proton nuclei would not hold together and hydrogen would be the only element in the universe. If the strong force were slightly stronger, by as little as 1%, hydrogen would be rare in the universe and elements heavier than iron (elements resulting from fusion during the explosion of supernovae) would also be rare.
  • The nuclear weak force affects the behavior of leptons (e.g. neutrinos, electrons, and muons) that do not participate in strong nuclear reactions. If the weak force were slightly larger, neutrons would decay more readily, and therefore would be less available, and little or no helium would be produced from the big bang. Without the necessary helium, heavy elements sufficient for the constructing of life as we know it would not be made by the nuclear furnaces inside stars. If the weak force were slightly smaller, the big bang would burn most or all of the hydrogen into helium, with a subsequent over-abundance of heavy elements made by stars, and life as we know it would not be possible.
  • 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 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 1040 (10 to the 40th power) times 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 numbers 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).

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." <ref>Is The Universe Fine-Tuned For Us? Victor J. Stenger, University of Colorado.(PDF file) page 20</ref>.

[edit] Explaining fine-tuned universe

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.

  • Random chance: It could be that through sheer random circumstance, this universe is the one that was created, and that there is no further explanation. Some, like Stephen Jay Gould[citation needed], 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). 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. 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 a mechanism that has created 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.<ref name = "Michio Kaku">Parallel Worlds,2005, Michio Kaku, pp. 220-221</ref> 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 (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. By extension, these same universes are optimized for creating stable atoms, long lived stars, and lots of stable carbon atoms. This last point also happens to explain why our universe seems to be biophillic.
  • 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 biophillic.
  • Providence or Creation<ref>Following the classification scheme of Martin Rees in Just Six Numbers</ref> The universe may have been created with the special charateristics 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 may differ in detail from the ones listed above.
  • 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-religous metaphysical reasons why this has happened. The discussions by Steven Hawking of the Wave-Function of the Universe might be considered to come in this broad category.

[edit] Naturalistic fine-tuned universe arguments

As discussed, the theoretical physicist Lee Smolin is attempting to verify a theory which he calls "cosmological natural selection" in which the universe fine-tuned itself. By his reasoning, self-organizing critical systems are capable of fine-tuning all by themselves, following only a simple set of physical laws — thus making it likely that the parameters are "fine-tuned" the way we see them, but as the result of natural processes, not an intelligence.

[edit] Bayesian arguments

A Bayesian probabilistic discussion by mathematician Michael Ikeda and astronomer William H. Jefferys<ref>Jefferys</ref> (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.[8] 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".) <ref> 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.</ref>

The philosopher of science Elliott Sober makes a similar argument (2004)[citation needed]. 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.

[edit] Notes

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[edit] References

[edit] See also

[edit] External links

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