Fine tuning of the natural constants

from Wikipedia, the free encyclopedia

In cosmology, fine-tuning of the universe is the precise adjustment of the size of natural constants in current physical theories, which is necessary to explain the physical state of the observable universe with them. Whether this fine-tuning is necessary for the explanation of nature or just a consequence of inadequate, incomplete theories is also discussed, as is the possibility that this fine-tuning basically does not exist, since there could also be a multitude of other combinations of natural constants which also include a habitable universe. In the English-language literature, the term “anthropic coincidence” is often used instead of “fine-tuning”.

Constants Affected

A possible fine-tuning is being discussed for the following physical constants:

Expansion rate

The expansion of the universe must on the one hand not be so weak that the universe collapses again after a few million years , on the other hand not so strong or the distribution of matter not so thin that the formation of suns and galaxies is prevented. In the original cosmological standard model, which did not yet include today's inflation theory , the expansion rate is determined solely by the mass density, which must therefore have exactly matched the so-called critical density at the beginning of the universe to the extremely small factor of 1:10 57 enable the formation of solar systems and galaxies. The inflation theory would make this fine-tuning unnecessary, but here again a fine-tuning of the cosmological constant would be necessary.

Cosmological constant

The cosmological constant was originally introduced by Albert Einstein into his general theory of relativity, as this was the only way to explain the universe - according to the opinion that was common at the time - stable. With Edwin Hubble's discovery that the universe is not stable, but rather expands, the need for a cosmological constant was eliminated and Einstein is said to have described it as "the greatest ass of a life".

The inflation theory developed in the 1980s and the observation made in 1998 that the universe is expanding at an accelerated rate led to explanatory models that make the cosmological constant necessary again. The inflation theory and the theory to explain the accelerated expansion require a so-called dark energy , which can be interpreted as vacuum energy - caused by a cosmological constant other than zero. However, in this case the cosmological constant at the beginning of the universe directly after the "inflationary phase" would have to have been different from zero, but at the same time 10 120 times smaller than its current value. This corresponds to an extremely tiny vacuum energy density. According to these explanatory models, even the smallest deviations from this value would lead to space-time in our present-day universe being strongly curved and stars and planets not being possible.

It is doubtful whether fine-tuning is necessary. Theories have been developed in which dark energy is no longer associated with a curved space-time, but is caused by a scalar field - also called quintessence . No cosmological constant is needed in these theories.

Mass from proton to electron

Max Born was of the opinion that with approximately the same proton and neutron mass, the properties of all atomic and molecular systems are essentially determined by two parameters: the mass ratio of electron to proton and the fine structure constant , which indicates the strength of the electromagnetic interaction . If the ratio of electron mass to proton mass is plotted in a diagram over the fine structure constant, then, according to Max Tegmark, one can specify a local area outside which no life like ours is possible. For example, if the mass ratio is too high, stable molecular systems would not be able to exist because of too great core fluctuations; if the fine structure constant is too large, no stars could exist. However, Tegmark does not rule out that there can be many local areas in parameter space in which life of a different kind is possible.

Electromagnetic and strong nuclear power

William H. Press and Alan Lightman extended Max Born's model in 1983 and showed that the essential properties of macrophysical phenomena are determined by four quantities: the electron mass, the proton mass, the strength of the electromagnetic force and the strength of the strong force. Victor J. Stenger came through analyzes and computer simulations in which he - in contrast to Tegmark - allowed all four of the constants named by Press and Lightman to be varied at the same time, to the conclusion that much larger fluctuations in the constants were allowed. Analyzes of a hundred universes, in which he randomly allowed the constants to fluctuate in a range of ten orders of magnitude (10 10 ), resulted in stars with a lifespan of more than a billion years in more than half of the cases. According to Stenger, this could hardly be called fine-tuning.

Production of carbon

The nuclear energy levels of beryllium-8 are considered to be essential for the extent and the speed of the nucleosynthesis of carbon-12 in the stars and thus for the formation of carbon-based life (see also three-alpha process ). In 1954, Fred Hoyle had theoretically predicted the exact location of the nuclear energy levels of beryllium, which was later confirmed experimentally. Often the location of this level is said to be fine-tuned.

The positions of the energy levels are not fundamental constants of nature, but depend on them. A change in these levels can only be accompanied by either a change in the natural constants or a change in the underlying physical theories. A change in the natural constants, as well as the theories, changes not only the position of the nuclear energy levels of beryllium, but also many other properties of all elements; this could possibly lead to other branches of development towards carbon. Heinz Oberhummer , together with Attila Csótó and Helmut Schlattl, succeeded in deriving quantifiable statements for this by examining the cosmological fine-tuning of the fundamental forces in the universe during the formation of carbon and oxygen in the three-alpha process in red giants .

'Fine-tune' the dimensions

Mathematically, a universe could have any number of dimensions. However, complex structures only seem possible in more than two dimensions. In a universe with more than three spatial dimensions, both atoms and planetary orbits are unstable. However, if one assumes that other natural laws would also apply in a different universe, then stable atoms or stable planetary orbits due to other laws of motion could also be possible in higher-dimensional universes. In principle, the dimensions do not have to be limited to a natural number . Mathematically, fractal dimensions of universes could also be represented; the assumption that life is only possible in the - for us observable - four-dimensional space-time continuum could also be the result of the anthropic principle .

doubt

It is widely disputed that fine-tuning even exists. If this does not exist, then there would logically not be any need for explanation. If they exist, it is unclear to what extent this could be proven at all.

The considerations for possible universes concentrate largely on how nature must be constituted in order to generate the requirements for carbon-based life - as it could develop in our planetary system ( carbon chauvinism ). Changes in the natural constants might not produce stars long enough to allow the evolution of carbon-based life. Or perhaps no or too little carbon would be formed; possibly not even atomic or stable structures could arise. However, even for the given natural constants, not all stable structures and environments are known that are possible alternatives for carbon and a life-friendly planetary environment. For example, it is debated whether silicon-based life is possible, although silicon cannot form as many compounds as carbon. If the natural constants are changed, the properties of silicon and all other elements may also change, which could lead to silicon or another element acquiring properties that are equivalent to those of carbon. It can also not be ruled out that when the constants are changed, completely different non-atomic (or non-molecular) stable structures become possible, which can form connections in a variety of ways and thus come into question as the basis for life. New stable environments could also become possible, which can offer space for the development of life as an alternative to a planetary environment.

It is therefore questionable to what extent there is evidence of a fine-tuning, since it may not be possible to name all possible universes in which - under other conditions - life could arise. Therefore, instead of naming some special requirements for carbon-based life, an attempt is made to formulate general assumptions that are necessary for all forms of life. For example, the presence of entropy gradients is often seen as such a fundamental requirement for all forms of life. If it could be shown for certain constants that even with small variations no entropy gradients can exist in the universe - for example if only homogeneous, dilute hydrogen gas could exist - that would be a strong argument for an actual fine-tuning within the framework of current standard theories. So far, however, this has not been successful.

If the fine-tuning of current physical theories existed and generally accepted evidence were presented, only a stronger rationale for the existence of our universe would be satisfactory; a statement that precludes the need for chance. All potential explanations can currently be divided into three categories, the transitions of which are fluid and which are not necessarily mutually exclusive:

Theory without fine-tuned constants

One view assumes that current physical theories are incomplete. If it were possible in the future to develop more comprehensive theories, then the apparent fine-tuning might only be an artifact of the imperfection of the currently available body of theories. Today's theories would therefore be incomplete and must therefore be fine-tuned in order to describe the universe. The high number of constants in current theories can then be seen as a kind of adjusting screw.

With this reasoning, one should expect these artifacts to disappear once physical theories have been established that no longer require fine-tuning. In the case of a theory without fine-tuning, then perhaps all or at least a large proportion of all possible universes would have the necessary complexity for life and not just a vanishingly small proportion as in the case of an existing fine-tuning. The superstring theory , among other things, is traded as a candidate for such a fundamental theory ( world formula ) .

Ensemble hypothesis and anthropic principle

Random fine-tuning is usually considered to be highly improbable. In contrast, the anthropic principle argues that only those universes or parts of them can be observed in which we can exist; that is, there is no statistical independence between our existence and the observation of fine tuning as a prerequisite for statistical argumentation. Statements about the probability or the improbability of fine-tuning can therefore not be made or only with additional assumptions. An additional assumption that is often made and which, together with the anthropic principle, could offer an explanation is the hypothesis of a multiverse : Instead of a single universe, there are very many or even an infinite number of parallel universes with different physical properties. Our universe would then be just one of many - one in which the right conditions make life possible. It is discussed whether a multiverse itself should also have finely tuned natural constants, so that this would only mean a shift in the question; the philosopher Nick Bostrom, however, denies this.

A similar explanation would be the postulate of a sufficiently large single universe in which unobservable parts have different physical properties.

Teleological and theological explanation with criticism

Proponents of this hypothesis assume that the universe is created either by a teleological principle or by a conscious, intelligent being, e.g. B. a god in the theological sense, directed towards a certain goal and that the universe therefore has life-friendly conditions. There is a purposeful meaning that may not be accessible to the human mind due to its limitations. This hypothesis is represented e.g. B. by the religious philosopher Richard Swinburne .

The term "fine tuning" is criticized: It is not a scientific term, but comes from the engineering sciences and is misleading because of its teleological connotation . In addition to objections that generally concern the validity of teleological hypotheses within scientific explanations, there are objections that reverse the argumentation of the teleology proponents. Exemplary:

  • In the opinion of E. Sober, as well as M. Ikeda and B. Jefferys, the assumption of an otherwise unspecified Creator does not explain the fine-tuning, since this Creator, who is powerful enough to create universes, could create life in a universe that is not finely tuned . Even if none of the finely tuned constants in a universe had the right size, it would certainly also be possible for him to provide conditions in this otherwise hostile universe in a local place that would make life possible. If z. For example, if the interaction constants of the forces were not of the correct size, so that carbon-12 could not arise naturally, an omnipotent Creator could nevertheless create the carbon-12 necessary for life through supernatural intervention. According to this view, if the universe had been created by a Creator, there would be no reason to expect a finely tuned universe, and thus the teleological hypothesis does not provide an explanation for a finely tuned universe.
  • For M. Ikeda and B. Jefferys, this reasoning is a powerful affirmation of naturalism ; H. the assumption that everything in our universe is “right”, that is, in accordance with the law and without supernatural interference. They argue that the very hypothetical observation that the universe is not only not fine-tuned, but even downright unsuitable for life, would point to a Creator. Because only under the prerequisite that our universe behaves strictly according to the law, there is a need for fine tuning and the need for divine-creative interventions and impulses is eliminated. However, the thesis is also put forward that a possible creative force created the laws of nature from the beginning in such a way that they make life possible. The rational comprehensibility of the universe is consequently interpreted as an indication of the existence of a creative force. Representatives of this view are, for example, the mathematician and philosopher John Lennox or the human geneticist Francis Collins .
  • Both Richard Swinburnes' argument and the argument of M. Ikeda and B. Jefferys use Bayesian statistics for their proof , which is not generally accepted and, for example, is rejected by representatives of an objective concept of probability. Even among adherents of Bayesian statistics, there is no consensus on what kind of hypotheses Bayesian statistics can be applied to. One of the best-known representatives of Bayesian statistics, B. de Finetti , limits the applicability of Bayesian statistics e.g. B. on such statistical hypotheses, which are ultimately empirically decidable.

literature

  • SG Karshenboim, E. Peik: Astrophysics, Clocks and Fundamental Constants. Springer 2007, ISBN 3-540-21967-6
  • Matthias Schleiff: Creation, coincidence or many universes? A teleological argument from the fine-tuning of the fundamental constants, Mohr Siebeck, Tübingen 2020, ISBN 978-3-16-156418-5

Web links

Individual evidence

  1. ↑ John Leslie: Universes. Routledge London.
  2. ^ Anthony Aguirre: The Cold Big-Bang Cosmology as a Counter-example to Several Anthropic Arguments. Physics preprint archive astro-ph / 0106143.
  3. ↑ AG Riess et al .: Observational Evidence from Supernovae for an Accelerating Universe and a Cosmologial Constant. In: The Astronomical Journal. 116: 1009-1038, September 1998.
  4. ^ VJ Stenger: Is the Universe fine-tuned for us? Chapter 12 of “Why Intelligent Design Fails” (Editors: M. Young, T. Edis) Rutgers University Press, 2004, ISBN 0-8135-3872-6 .
  5. ↑ Ulrich Walter: Civilizations in space - we are alone in the universe. Spectrum Akademischer Verlag GmbH, Heidelberg Berlin 1999.
  6. ^ AB Kaganovich: Quintessence without the fine tuning problem of the potential. In: Nuclear Physics B - Proceedings Supplements. Volume 87, Number 1, June 2000, pp. 496-497.
  7. ↑ Yungui Gong, Anzhong Wang, Yuan-Zhong Zhang: On curvature coupling and quintessence fine-tuning. In: Europhys. Lett. 74 (5), 2006, pp. 930-936.
  8. ^ A b Max Tegmark: Is “the theory of everything” merely the ultimate ensemble theory? (PDF; 511 kB) In: Annals of Physics. 270, 1998, 1-51.
  9. ^ WH Press, A. Lightman: Dependence of Macrophysical Phenomena on the Values ​​of the Fundamental Constants. In: Philosophical Transactions of the Royal Society of London. Series A, 1983, 310, pp. 323-336.
  10. ↑ a b V. J. Stenger: Natural Explanation For The Anthropic Coincidences. (PDF; 64 kB) Philo 3, 50.
  11. ↑ H ,. Oberhummer, A. Csótó, H. Schlattl: Stellar production rates of carbon and its abundance in the Universe (PDF; 93 kB), Science 289, 2000, 88, doi : 10.1126 / science.289.5476.88 .
  12. ↑ Stephen Hawking: Public Lectures - Space and Time Warps. ( Memento from July 30, 2007 in the Internet Archive )
  13. ↑ Paul Ehrenfest: In that way does it become manifest in the fundamental laws of physics that space has three dimensions? In: KNAW, Proceedings 20 I, 1918, Amsterdam, 1918, pp. 200-209.
  14. ^ Frank R. Tangherlini: Einstein's Pseudo-Tensor in n Spatial Dimensions for Static Systems with Spherical Symmetry. In: Journal of Modern Physics. 04, 2013, p. 1200, doi : 10.4236 / jmp.2013.49163 .
  15. ↑ The problem here, besides the problem of defining the entropy for a total universe, is z. B. whether there is any stable thermodynamic equilibrium for a universe. SW Hawkins ( Commun. Math. Phys Vol. 43, 199, 1975) and later JD Barrow and FJ Tipler ("Eternity is unstable." Nature Vol. 276, 453-459, 1978) have shown that the final state of a open or shallow universe is unstable. This changes the picture that research has painted of the heat death of the universe. Until then it was assumed that no new structures can form after heat death, that there are no entropy gradients and that a state of eternal calm has returned to the universe, now a completely new picture of heat death emerges. Accordingly, even there, new structures are constantly being created in the form of space-time vortices, which are increasingly destroying the isotropy of the universe.
  16. ^ GL Kane: The Beginning of the End of the Anthropic Principle. Physics preprint archive astro-ph / 0001197.
  17. ↑ "The multiverse itself need not be finetuned." N. Bostrom: Anthropic Bias. Page 13.
  18. ↑ Nick Bostrom: Anthropic Bias, Observation Selection Effects in Science and Philosophy. Routledge, 2002.
  19. ^ Richard Swinburn: Argument from the fine-tuning of the universe. In Physical Cosmology and Philosophy. J. Leslie, New York, Macmillan, 154-173.
  20. ↑ Mark Isaak: What Design Looks Like.
  21. ^ E. Sober: The design argument. ( Memento of the original from November 6, 2012 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. In: NA Manson (Ed.): God and Design: The Teleological Argument and Modern Science. Routledge, New York 2003, pp. 27-54. @1@ 2Template: Webachiv / IABot / philosophy.wisc.edu
  22. ↑ M. Ikeda, B. Jefferys: Anthropic Principle Does Not Support Supernaturalism.
  23. ↑ John Lennox, "Has Science Buried God?" Brockhaus, Witten; Edition: 7th edition (October 31, 2007)
  24. ^ Salon.com: The believer , Aug. 7, 2006.
  25. ^ W. Stegmüller: Problems and results of the philosophy of science and analytical philosophy. Volume IV, Personal and Statistical Probability, 1973.