Fine-tuned universe

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Image:Universe.jpg The term fine-tuned universe refers to a collection of ideas that state the existence of life in the Universe is the result of the universe's physical constants relating to one another in exactly the fashion that is required in order for the universe to be hospitable for life. The fine-tuned universe argument is 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.

Though the concept of the precise interplay of physical constants being necessary for known life is widely accepted within mainstream science, the argument that they imply that the universe was purposely fine-tuned to support life is not. Though there are fine tuning arguments that are naturalistic, the assertion that the universe was designed to be fine-tuned is largely promoted by advocates of intelligent design and other forms of creationism. The fine-tuning of the universe apparent to some is cited as evidence for the existence of God or some form of intelligence capable of manipulating the basic physics that govern the universe, or even evidence that the universe is a simulated reality.

The premise of the fine-tuned universe assertion is that any small change in the twenty or so physical constants would make the universe radically different: if, for example, the electron's 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.

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.

Critics of both the fine-tuned universe assertion and the anthropic principle argue that they are essentially a tautology; 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).

Nature of the constants

Science as it is currently practiced is reductionist (meaning our group behavior is due to individual behavior which is due to the parts of the individual which are made of atoms which are made of particles whose behavior is specified by laws of physics that contain within them a few fundamental constants that can be measured to varying degrees of precision). 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" when they really mean "observable universe". The reason for this is that unobservable physical phenomena are scientifically irrelevant; that is, they cannot affect any events that we can perceive, and therefore, it is argued, effectively do not exist (physicists say "causally do not exist"). They also cannot be measured, and therefore hypotheses about parts of the universe that are not observable, are not measurable.

Science uses the word "universe" to mean "observable universe", while metaphysics explores what might be beyond our ability to scientifically know that nonetheless appeals to our desire to "understand".

All arguments that refer to evidence refer to the observable universe but may not apply to the unobservable parts of reality sometimes called "other universes". 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.

Known physical constants and possible examples of fine tuning

(Sources for this section: [1], [2], [3], [4], [5], [6])

• 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 electromagnetic coupling constant binds electrons to protons in atoms. 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 different; maybe not even exist.

• The ratio of electron to proton mass also determines the characteristics of the orbits of electrons about nuclei. A proton is 1836 times more massive than an electron. If the electron to proton mass ratio were different, atoms and molecules would be different — or maybe not even exist.

• 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. 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).

• A more probable explanations of Multiverse models themselves require 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 anthropomorphization of natural physical constants and even if it is improbable that they occurred by chance, that by itself, improbability is insufficient reason to conclude that they occurred by design.

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.

If it is accepted that the universe is fine-tuned, there are three major explanations for the occurrence.

• 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, 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.

• 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. Multiverses are not necessarily falsifiable, and thus some are relunctant to call multiverses a "scientific" idea.

• Intelligent design: It could be that the universe was purposely designed to support life. 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.

Naturalism and the fine tuning argument

That life as we know it would not be possible if the physical constants of the universe were even slightly different from what they are and may appear to be "fine-tuned" is an uncontroversial position within the mainstream scientific community. But conclusions drawn from that observation or appeals to the improbability of life that some intelligence intentionally "fine-tuned" the universe for life are not widely accepted. There is controversy over whether such conclusions can even be considered within natural science or whether they are better considered as matters of metaphysics or religion.

Some conjectures of fine-tuning may not by necessity violate the naturalistic underpinnings of natural science, but that any specific argument does not has not yet been established. Those that leave the question of agent or first cause unaddressed are as equally appealing to those who posit a theistic or deistic first cause as it is to those who are to strict materialists.

Cosmologist Sir Martin Rees expresses a point of view common in the scientific community: "People used to wonder: why is the earth in this rather special orbit around this rather special star, which allows water to exist or allows life to evolve? It looks somehow fine-tuned. We now perceive nothing remarkable in this, because we know that there are millions of stars with retinues of planets around them: among that huge number there are bound to be some that have the conditions right for life. We just happen to live on one of that small subset. So there's no mystery about the fine-tuned nature of the earth's orbit; it's just that life evolved on one of millions of planets where things were right." [7] Rees states a personal preference for a multiverse: "We seem to have three choices'... We can dismiss it as happenstance, we can acclaim it as the workings of providence, or (my preference) we can conjecture that our universe is a specially favoured domain in a still vaster multiverse.’ If this multiverse contained every possible set of laws and conditions, then the existence of our own world with its particular characteristics would be inevitable." [8].

Naturalistic fine-tuned universe arguments

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. This is similar to the self-regulating system proposed in Gaia theory, but on a cosmological scale.

Ikeda-Jefferys argument

A Bayesian probabilistic discussion by mathematician Michael Ikeda and astronomer William H. Jefferys 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: 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".)

Ikeda and Jefferys offer 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 proof 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 theorem 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 fine-tuned — in probabilistic notation, P(N|L) ≤ P(N|L&F). In other words, the existence of fine tuning increases (or rather, cannot decrease) the probability that our universe is naturalistic, given that we already know it contains life. Thus, Ikeda and Jefferys argue ironically, supporters of intelligent design should try to prove that our universe is not fine-tuned. The philosopher of science Elliott Sober makes a similar argument.

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.

In fiction

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

References

• John D. Barrow and Frank J. Tipler, 1986. The Anthropic Cosmological Principle. Oxford Univ. Press. ISBN 0192821474
• John D. Barrow, 2003. The Constants of Nature, Pantheon Books, ISBN 0375422218
• Nick Bostrom, 2002. Anthropic Bias: Observation Selection Effects in Science and Philosophy, Routledge, New York, ISBN 0415938589
• Paul Davies, 1982. The Accidental Universe, Cambridge University Press, ISBN 0521242126
• 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 0465036724
• Ward, P. D., and Brownlee, D., 2000. Rare Earth: Why Complex Life is Uncommon in the Universe. Springer Verlag.

See also

• Origin of life
• Fine-tuning
• Anthropic principle
• Intelligent design
• Ultimate fate of the universe

External links

• Does the Cosmos Show Evidence of Purpose?
• Fine-Tuning Argument links to online references, at the Secular Web
• Cosmological fine-tuning
• 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.de:Feinabstimmung