Constraints on a Chance Universe & The Anthropic Principle

1. Constraints on a Chance Universe & The Anthropic Principle Physical Science 410 James Mackey

2. ASSUMPTIONS In all of the following discussion, it is assumed that life is carbon based. While silicon based life has been discussed by a few individuals, the length of amino acid chains based on silicon are no more than a few hundred at the most - insufficient for the complexity required for life as we know it.

3. Additionally, boron has been advocated as an alternate basis for life; however, boron is relatively rare in the universe compared to carbon or silicon, which would make life even less probable than it is.

4. Boron 7.0 X 10-7 2 x 10-9

5. It is also assumed that physical laws, as best as we understand them, operate the same at all places and times in the evolution of the universe. No unknown physical laws can be postulated to explain currently unexplainable phenomena.

6. It is possible for something to be so improbable that even in the possible time span of the universe, 13.6 Billion years or about 4.3x1017 seconds, it will never happen. Any argument from design is usually faith strengthening not faith producing!

7. The Anthropic Principle The Universe possesses narrowly defined characteristics that permit the possibility of a suitable habitat for humanity

8. This principle has been recognized by numerous scientists in recent years, and has been increasingly publicly stated. Physicist Paul Davies “[There] is for me powerful evidence that there is something going on behind it all…It seems as though somebody has fine-tuned nature’s numbers to make the Universe…The impression of design is overwhelming.” The Cosmic Blueprint (New York, Simon & Schuster, 1988) p203

9. Theoretical Physicist Tony Rothman in a popular article wrote: “The medieval theologian who gazed at the night sky through the eyes of Aristotle and saw angels moving the spheres in harmony has become the modern cosmologist who gazes at the same sky through the eyes of Einstein and sees the hand of God not in angels but in the constants of nature.......

10. ....When confronted with the order and beauty of the universe and the strange coincidences of nature, it’s very tempting to take the leap of faith from science into religion. I am sure many physicists want to. I only wish they would admit it.” "A ‘What You See is What You Beget ‘ Theory," Discover (May 1987) p99

11. Studied relativity and cosmology under Stephen Hawking at the Institute of Astronomy in Cambridgeand at Caltech. Prof. of Math & Astronomy at Queen Mary College Cosmologist Bernard Carr “One would have to conclude either that the features of the universe invoked in support of the Anthropic Principle are only coincidences or that the universe was indeed tailor made for life. I will leave it to the theologians to ascertain the identity of the tailor!” "The Anthropic Principle and the Structure of the Physical World," Nature 278 (1979) p53

12. Physicist Vera Kistiakowlsky, past president of Association of Women in Science “The exquisite order displayed by our scientific understanding of the physical world calls for the divine” Cosmos, Bios, and Theos, Margenau & Varghese, ed. (LaSalle Il,Open Court,1992) p52

13. George Ellis, a colleague of Stephen Hawking and Roger Penrose “Amazing fine-tuning occurs in the laws that make this [complexity] possible. Realization of the complexity of what is accomplished makes it very difficult not to use the word ‘miraculous’ without taking a stand as to the ontological status of that word” ”The Anthropic Principle : Laws and Environments,” in The Anthropic Principle, Bertola & Curi, ed. (New York, Cambridge University Press,1986) p30

14. Cosmologist Edward Harrison • “Here is the cosmological proof of the existence of God – the design argument of Paley – updated and refurbished. • The fine tuning of the universe provides prima facie evidence of deistic design. • Take your choice: blind chance that requires a multitude of universes or design that requires only one… • Many scientists, when they admit their views, incline toward the theological or design argument.” • Masks of the Universe (New York, Collier Books,1985) pp252,263 (emphasis mine)

15. Mathematical Physicist Robert Griffiths “If we need an atheist for a debate, I go to the philosophy department. The physics department isn’t much use.” ”Cease Fire in the Laboratory,” Christianity Today, 3 April 1987, p18

16. Planet hunters Geoff Marcy and Paul Butler In discussing the 33 (at that time) known planets discovered orbiting other star systems, the authors observe that most such systems are dominated by highly elliptically orbit giant planets. • "The predominance of elliptical orbits implies that planetary systems with circular orbits may be the exception rather than the norm. • Apparently our nine planets were just far enough apart and low enough in mass to avoid this chaos [referring to the tendency of giant planets to slingshot neighbors out of their systems]. • The nine planets do perturb one another, but not enough to cause close passages.

17. The planetary house of cards that we call our solar system may be one of the rare systems that remains just barely stable. • If our solar system is unusual in its circular orbits, we humans would seem to be extraordinarily lucky to be here. • After all, the circular orbit of earth keeps solar heating nearly constant, minimizing temperature fluctuations. • Perhaps biological evolution would not have proceeded to intelligence if Earth's temperature were fluctuating widely.

18. It may be that Darwinian evolution towards complex organisms is enhanced by circular orbits. If so, we owe our existence to Earth's stable orbit." Despite the fact there are currently 1079 extrasolar planets, these conclusions are still perfectly applicable Astronomy, March 2000, "Planets Beyond" by Geoff Marcy and Paul Butler, page 45

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20. In an article, “Exploring Our Universe and Others”, in Scientific American’s The Once and Future Cosmos, Martin Rees observed.. “Our universe could not have become structured if it were not expanding at a special rate.If the big bang had produced fewer density fluctuations, the universe would have remained dark, with no galaxies or stars… ..If our universe had more than three spatial dimensions, planets could not stay in orbits around stars.”

21. continuing “If gravity were much stronger, it would crush living organisms of human size and stars would be small and short-lived. If nuclear forces were a few percent weaker, only hydrogen would be stable: there would be no periodic table, no chemistry and no life. Some would argue that this fine-tuning of the universe, which seems so providential, is nothing to be surprised about, because we could not exist otherwise.”

22. Always keep in mind, the opposite side of this viewpoint.. “The more the universe is comprehensible, the more it also seems pointless.” Steven Weinberg, The First Three Minutes “The usual approach of science of constructing a mathematical model cannot answer the questions of why there should be a universe for the model to describe.Why does the universe go to all the bother of existing?” Stephen W Hawking

23. To serve as an introduction to the problem of the probability of intelligent life having arisen by purely chance means, we will look at a famous equation, The Drake Equation, and its implications for the existence of intelligent “communicating” life in our galaxy. A highly recommended resource is Rare Earth, by Peter Ward and Donald Brownlee (Copernicus Books, Springer, Feb. 2000)

24. The Drake Equation Originally postulated by astronomer Frank Drake in the 1950s to predict how many civilizations might exist in our galaxy in order to estimate the likelihood of our detecting radio signals from other technologically advanced civilizations. N = N*  fs fp ne fi fc fl L

25. where N* = stars in the Milky Way galaxy (or often R* = avg. rate of star formation in galaxy) fs = fraction of sun-like stars fp = fraction of stars with planets ne = number of planets in a star’s habitable zone fi = fraction of habitable planets where life does arise fc = fraction of planets inhabited by intelligent beings fl = % of lifetime of a planets with a civilization capable of communication L = length of time civilization survives

26. The initial assumptions made for the terms in this equation (whose values, except for N*, were very poorly known) were exceedingly optimistic. For example, Carl Sagan assumed that ALL stars had 10 planets. The results of these assumptions were an estimate of perhaps one million civilizations of creatures in our galaxy capable of interstellar communication at this time! Without doubt this is a totally unrealistic estimate!

27. Fairly common assumptions made by SETI supporters are listed as follows: N* - the number of stars in the Milky Way galaxy is probably fairly well known at 200 to 300 billion. This is normally based on measures of the mass of the galaxy, and the mass of an average star (assumed ~ 1 M0). The actual average size star in the Milky Way is an M class star about 50% of Sun’s mass

28. fp - the fraction of stars that have planets around them - Current estimates range from 20% to 100%. ne - number of planets per star that are capable of sustaining life For each star that has a planetary system, how many planets are capable of sustaining life? Estimates range from 1 to 2.

29. fl - the fraction of planets in ne where life evolves: On what percentage of the planets that are capable of sustaining life does life actually evolve? Current estimates are 100% (where life can evolve it will) . fi - the fraction of fl where intelligent life evolves On the planets where life does evolve, what percentage evolves intelligent life? Estimates are 50 – 100 %

30. fc - the fraction of fi that communicate What percentage of intelligent life forms have the means and the desire to communicate? Estimates are 10% to 20% L - fraction of a planet's life during which - communicating civilizations may survive For each civilization that does communicate, for what fraction of the planet's life does the civilization survive? This is the most vague question.

31. Using the Earth as our model, the expected lifetime of our Solar System is approximately 10 billion years. Already communication by radio has been for less than 100 years. How long can our civilization survive without destroying ourselves as some predict or will we beat our problems and survive indefinitely? If doomsday came today this figure would be 10-9. If we survive for 10,000 more years this figure would be 10-6.

32. N = N*  fs fp ne  fi fc L N = 200 billion (1/4) 2 (1/2) (1/10) (1/10) (1/100 million) N ~ 50 technological civilizations in just the Milky Way Galaxy! Since there are billions of galaxies, the assumption is then that there are billions of technological civilizations capable of radio communication in the universe!

33. The Delimma! Where are they? (Known as the Fermi paradox) If there are/have been highly technological and long-lived civilizations in our Galaxy, why haven’t we seen them or their effects?

34. Considering some of the terms in this equation, let’s try to arrive at a reasonable estimate based on current discoveries and understanding. If we rewrite the equation in more modern terms, and rename the modified Drake Equation as the: RARE EARTH EQUATION N = N* fpm fp ne ng fi fc fl fm fj fme

35. where N* = stars in the Milky Way fp= fraction of stars which have planets similar to earth fpm = fraction of metal-rich planets ne= planets in a star’s AHZ ng = stars in a Galactic HZ fi = fraction of planets where life (of any kind) arises fc = fraction of planets where complex metazoans arise

36. fl = % of planet’s lifetime that is marked by Complex metazoans fm= fraction of planets with a single large moon fj = fraction of solar systems with Jupiter- sized planets fme = fraction of planets with a critically low number of mass extinction events.

37. Some Definitions Habitable Zones (HZ) - regions about a parent star where conditions are conducive to the development & survival life of any form: i.e. temps that allow liquid water Animal Habitable Zones (AHZ) - regions about the parent star where complex life can arise. This is more restrictive than the simple HZ.

38. Located at an optimal distance from the Sun for liquid water to exist. What makes a planet habitable?

39. Large enough for geological activity to release & retain water and atmosphere.

40. Galactic Habitable Zones (GHZ) regions in the galaxy where solar systems and planets can safely form without appreciable danger from catastrophic events in the galaxy.

41. N* - the number of planets in the Milky Way galaxy is probable fairly well known at about 400 billion. This is normally based on measures of the mass of the galaxy, and the mass of an average star.

42. fp - the fraction of stars that have planets similar to Earth Based on the most recent successes in finding extrasolar planets orbiting distant stars, it would seem that the value of the first ½ of this factor would be rather high. Optimists placing its value at 1.0 and pessimists at 0.1 (about 10% of surveyed stars reveal the presence of planets). A reasonable value for this alone would be 0.5. However the “similar to Earth” is vastly more restrictive, of 1771 planets (3/14/2014) ~ 15 are similar IN SIZE to Earth… prob ~ 0.008

43. Exoplanet mass as function of semi-major axis Red lines locate the Earth at 1 AU and mass 0.00314 MJ

44. Not one of the Earth size planets has an orbit even close to 1 AU The most common stars in our galaxy are M stars, which are fainter than the sun and probably about 100 times more numerous. These can be ruled out because their HZ (habitable zones - where surface temperatures would be conducive to life) are uninhabitable for other reasons… increased radiation exposures increased tidal effects likelihood of no moon

45. To be in its HZ, a planet must be so close to these small stars that tidal effects would lock these stars into synchronous rotation with one side always facing the star and the other side always permanently dark. A real life example would be the planet Mercury. If the stars are much more massive than the sun, their stable lifetimes are only a few billion years - inadequate time for the development of advanced life and the evolution of an ideal atmosphere.

46. fpm - the fraction of metal-rich planets The evidence for the importance of metal-rich stars comes indirectly from the planet search program. Spectroscopic studies of the stars about which we have been able to identify planets shows that they, like our own sun, are rich in metals. Yet general surveys of stars in our neighborhood show that the metal content of our sun is abnormally large.

47. Based on Extrasolar planets as of 3/14/2014 Sun’s metallicity is 0

48. It would seem to be impossible for complex life to develop on a planet formed in the nebula of a metal-poor star. The elements so important to life as we know it are exceedingly rare in the universe – in a sense human beings are trace elements in the universe. A very conservative estimate of the fraction of stars that are sufficiently metal-rich like the sun would be ~ 0.5

49. ne - the fraction of planets in a star’s AHZ The fraction of planets in a star’s habitable zone can be reasonably estimated from our own solar system. If we take the sun’s HZ to be 1.0 AU  0.3 AU in a solar system ranging out to more than 40 AU, we can estimate the fraction as 1.3/40 or ~ 0.027. However, as we will see our solar system is not common, so a smaller value is likely

50. Of the 1771 planets discovered about other stars, only 3 are close to Earth’s mass (smallest is PSR-1257 12b ~ME /50) with KOI-52c at 2/3 ME and Kepler 42 c ~ ME though none of these few orbit within 20% of 1 AU