DESTINIES OF LIFE AND THE UNIVERSE:
THE FINAL FRONTIERS OF ASTROBIOLOGY AND COSMOLOGY (*)

JULIAN CHELA-FLORES
The Abdus Salam International Centre for Theoretical Physics
Strada Costiera 11; 34136 Trieste, Italy
and
Instituto de Estudios Avanzados,Caracas 1015A, Venezuela

_______________________________________________________________________
(*) The author wishes to dedicate his chapter to the memory of John Oro,

a friend, a colleague and a teacher.

_______________________________________________________________________

1. The intelligibility of the universe

Up to the present the intelligibility of the universe has been a topic restricted to natural theology. Amongst the various aspects of intelligibility we wish to highlight the destinies of the related phenomena of the emergence of life and the origin and evolution of the universe where life has evolved. The arguments presented in this chapter argue in favour of bringing these fundamental topics within the frontier of astrobiology (Chela-Flores, 2001). Consequently, amongst the priorities of this new science, we should consider the search for other lines of biological evolution, in order to elucidate the intelligibility of the universe. The main conclusions of such a study are likely to be relevant not only to astrobiology, but also to ethics, philosophy and especially natural theology.
Intelligible means the capability of being understood, or comprehended. Alternatively intelligible can signify to be apprehensible by the intellect alone. A third aspect of intelligible, closer to the significance of the term in the context of the present work, is related to something that is beyond perception. In this sense an "intelligible universe" can be the starting point of a prolonged and systematic analysis by astrobiologists, and other space scientists, philosophers as well as by natural theologians.
The question of the intelligibility of the universe becomes a stimulating discussion in its most general cultural context. The Belgian Nobel Laureate Christian de Duve, at the end of his recent review on the origin and evolution of life, asks himself the question "What does it all mean? (de Duve, 2002). Like many contemporary scientists, philosophers and theologians, de Duve returns to an often quoted, but less frequently debated statement (Weinberg, 1977):

"The more the universe seems comprehensible, the more it also seems pointless."

This quotation can be best understood in the context of a philosophical trend called Existentialism. Earlier doctrines (Rationalism, Empiricism and Idealism) had maintained that the cosmos is a well determined ordered system, and hence comprehensible to all observers. In that framework there is no motivation for viewing the origin and evolution of the universe and life as being absurd, or pointless. On the other hand, the existentialists went beyond Rationalism represented, amongst others, by Benedict De Spinoza the Dutch-Jewish philosopher and foremost exponent of this 17th-century doctrine. The existentialists also went beyond Empiricism that arose from the increased scientific knowledge of the 17th and 18th centuries.
Another influential philosophical view stresses the central role of the ideal, or the spiritual, in the interpretation of experience. Known as Idealism, this philosophic doctrine, unlike Rationalism and Empiricism, maintains that the world, or reality, exists essentially as spirit or consciousness, that abstractions and laws are more fundamental in reality than sensory things. Rationalists, empiricists and idealists laid down a solid bases to raise questions related to the eventual destiny of life and of the universe itself. Rationalists and empiricists had argued that we could discover all natural universal laws by reason and experimentation, largely in agreement with the emergence of modern science with Nicholas Copernicus, Galileo Galilei, Giordano Bruno, Thomas Digges, Isaac Newton and others.
A systematic idealist, Georg Wilhelm Hegel attempted to elaborate a comprehensive and systematic ontology from a logical starting point. In other words, although differing somewhat from other idealists such as Berkeley and Kant, Hegel attempted to defend faith as being logical. This movement was influenced by the growth of science since the Enlightenment. The need was felt for a harmonious development of human culture. The bases of natural theology had to be extended to accommodate so much new revolutionary scientific knowledge. Faith in a Creator had to be seen in a new light.
The Danish philosopher and religious writer Siren Kierkegaard opposed Hegel's views, particularly the concept that religious faith was logical. Kierkegaard, anticipating the still-to-come Existentialism, insisted in a thesis opposite to Hegel's: humans suffer a deep anxiety (and hence need religion) because one has no certainties. In more modern terms we can paraphrase Kierkegaard and other pioneers of Existentialism by saying that life in the universe is pointless and absurd. To put it simply, according to Kierkegaard, life in the universe is not intelligible. Consequently, the questions of our destinies could not be incorporated as reasonable frontiers between astrobiology and the humanities. The advocate of extreme Rationalism, Friedrich Nietzsche, also extended the concepts of anxiety and alienation. According to this philosopher, not only there is no logic to existence but, in addition, a positive aspect of human nature is to rise above the absurdity of life. In turn, Nietzsche was largely influenced by the pessimism of Arthur Schopenhauer, who is often called the "philosopher of pessimism". Schopenhauer's writings influenced later existential philosophy.
A third relevant aspect of Existentialism came from the implications of the philosophy of Martin Heidegger, as interpreted by his close follower Jean Paul Sartre, who formalized Existentialism on the basis of the work of Edmund Husserl, a German philosopher who had founded Phenomenology. This earlier method of enquiry was applied to the description and analysis of consciousness through which philosophy attempts to gain the character of a strict science. Husserl's method is an effort to resolve the opposition between the emphasis on observation that is maintained by Empiricism, and on reason that is stressed by Rationalism. Against this background, Sartre maintained that Existentialism is an attempt to live logically in a universe that is ultimately absurd. Another eloquent supporter of this doctrine was the French Literature Nobel Laureate Albert Camus, who in the mid-twentieth century became the spokesman of his own generation through writings addressed to the isolation of man in what Camus considered to be an alien universe. At the end of this long line of intellectuals that were under the influence of Existentialism, in the above quotation Weinberg reflects a view of the universe to which he had constrained himself by the philosophical doctrine that influenced his generation.
In the Existentialist view of the universe there still remains some hope for the concept of a meaningful universe, namely intelligibility of the universe could be approached with the hope of the eventual emergence of a future "theory of everything". In this proposed all-embracing future theory we would hopefully discover the fundamental laws of nature in terms of a set of equations (Weinberg, 1993). Then, all phenomena should follow from these equations (the hope being that chemistry and biology could also be deduced). This is an extreme form of Reductionism, not an inevitable choice, given the many insights of current progress in science as a whole. Since the Enlightenment the ever-increasing growth of science has encouraged Reductionism. The reductionist dream has been supported by preliminary sets of successful equations that have embodied general phenomena at the most disparate scales (both microscopic and macroscopic). Today we recognize such efforts by assigning the equations the surnames of their authors: Newton, Maxwell, Einstein, Schrödinger Dirac, Salam and Weinberg.
We are still at a very early stage in the comprehension of life in the universe. When the still open question of the intelligibility of the 'living universe'' is posed in a wider cultural context, including the earth and life sciences, the restricted view of Reductionism becomes more evident. This illustrates the relevance of the last frontier of astrobiology for the whole of human culture, especially under the influence of philosophical doctrines (other than Existentialism) that will tend to encourage any future constructive dialogue between science and the humanities.

2. What is the likely destiny of the universe itself?

The Big Bang model tells us that as time t increases, the universe cools down to a certain temperature, which at present is close to 3 0 K. This discovery took place in 1964 by Arno Penzias and Robert Wilson; they provided solid evidence that the part of the universe surrounding us is presently illuminated by "3 0 K." radiation, the 'cosmic microwave radiation', but since it has a typical wavelength of about 2 mm due to the enormous red shift it has suffered since the moment it was last scattered during the first moments of expansion, it is referred to as the cosmic 'microwave' background (CMB) that may be confidently considered to be a cooled remnant from the hot early phases of the universe. It has an 'isotropic' distribution, in other words, its temperature does not vary appreciably independent of the direction in which we are observing the celestial sphere (the accuracy of this statement is 10 parts per million, ppm). The isotropy is a consequence firstly of the uniformity of cosmic expansion, secondly, of its homogeneity when its age was 300,000 years and temperature of 3,000K. On the other hand, in 1992 more precise measurements of the T = 3o K" radiation, began to be made by means of the satellite called the Cosmic Background Explorer (COBE): When the accuracy of the isotropy was tested with more refined measurements, it was found that there was some degree of anisotropy after all - the temperature did vary according to the direction of observation (one part in 100,000). This fact is interpreted as evidence of variations in the primordial plasma, a first step in the evolution of galaxies. Further accuracy in understanding the deviations from isotropy of the CMB (and hence a better understanding of the early universe) can be expected in the next few years. The Microwave Anisotropy Probe (MAP) - an initiative of the National Aeronautics and Space Administration (NASA) - should extend the precise observations of the CMB to the entire sky. MAP will be in a solar orbit of some 1,5 million kilometers. The European Space Agency (ESA) will be extended this work subsequently by means of the Planck spacecraft whose launching is planned for the year 2007. Andre Linde envisions a vast cosmos in a model in which the current universal expansion is a bubble in an infinitely old 'superuniverse'.
In other words, in this model the universe we know is assumed to be a bubble amongst bubbles, which are eternally appearing and breeding new universes. Final observational confirmation is still missing. The 'radius of the universe', or scale parameter 'R' evolves as a function of time t in such a cosmology, but as in the model of Alan Guth ­ the 'inflationary universe' - the Linde model, on the other hand, differs from the Friedmann solution in the first instants of cosmic evolution. The prediction of that in an expanding universe the contribution of a field to the energy density and the pressure of the vacuum state need not have been zero in the past.
Why is the generalization of Big Bang cosmology associated with the word inflation? During the very earliest times of the Big Bang (10-43 second - 10-35 second), the lowest-energy state may have corresponded in microscopic physics (quantum mechanics) to a phenomenon called a "false vacuum," This quantum state is characterized by a combination of mass density and negative pressure that results gravitationally in a large repulsive force.
In Albert Einstein's theory of General Relativity of 1916 this repulsive force is called a 'cosmological constant'. The false vacuum may be thought of as producing a corresponding repulsive force that gave rise to the scale factor R of the universe to grow (or 'to inflate') extremely fast (mathematically 'exponentially fast'). This means that R may have doubled its size roughly once every 10-43 or 10-35 second. After several doublings, the temperature, which started out at over one thousand degrees K, would have dropped to values near the absolute zero. At these low temperatures the true vacuum state may have lower energy than the false vacuum state, in an analogous fashion to how solid ice has lower energy than liquid water. Such 'supercooling' of the universe may therefore have induced a rapid phase transition from the false vacuum state to the true vacuum state. The transition would have released energy (analogous to the "latent heat" released by water when it freezes). This, in turn, reheats the universe to high temperatures. In such high temperature (and the gravitational energy of expansion) the particles and antiparticles of the standard Big Bang cosmologies would have emerged.
We should conclude this brief overview of cosmology with a note of caution. The theoretical framework described here may have to be revised in order to take into account careful measurements of the velocities of very distant galaxies as defined by their stars in their late stage of evolution, namely, exploding stars that have exhausted their nuclear fuel. These important dying stars are normally called supernovae (Riess, A. et al, 1998). The value of these velocities may be interpreted as some evidence for an accelerating expansion of the universe, a phenomenon, which is still to be understood. We have to learn whether the constant that Einstein introduced into his equations of gravitation (the 'cosmological constant'), purely on theoretical grounds, may represent some form of gravitational repulsion, rather than attraction (Krauss, 1998; Ostriker and Steinhardt, 2001).
We should dwell on this question a little longer. Only a small fraction of the matter in the universe is in the form of the familiar chemical elements found in the Periodic Table. It is assumed that a large proportion of the cosmic matter consists of 'dark matter', whose composition consists of particles that play a role in the sub-nuclear interactions, mostly foreign to our everyday experience. The term 'dark matter' is not a misnomer, for the sub-nuclear particles that contribute to it, do not interact with light. However, a remarkable aspect of cosmic matter is emerging: the sum total of the standard chemical elements and the dark matter make up a small fraction of the matter content of the universe. The remaining fraction of cosmic matter has been referred to as dark energy with the astonishing property that its gravity is repulsive, rather than attractive.
A possibility that has to be considered seriously in the future is that the repulsive gravity may dominate the overall evolution of the universe. This could lead to ever increasing rates of expansion. If this was to be the future of our cosmos, then future of life in the universe may hold some surprises. Eschatological considerations may have to be revisited. Will our universe be biofriendly? In any case even in the simple Friedmann model there is the possibility to discuss eschatology: The geometry of space in Friedmann's closed model is similar to that of General Relativity; however, there is a curvature to time as well as one to space. Unlike Einstein's model, where time runs eternally at each spatial point on an uninterrupted horizontal line that extends infinitely into the past and future, there is a beginning and end to time in Friedmann's model of a closed universe when material expands from, or is recompressed to infinite densities. These instants are called respectively the "Big Bang" and the "Big Crunch." But this has taken us far enough into the general picture of the origin and evolution of the universe and within this framework we may begin to consider how life was inserted in the universe in the first place.
A high-flying balloon that flew over Antarctica has given experimental support to the cosmological view of the expanding universe. It has demonstrated that the universe is "flat", in other words, the usual rules of geometry are observed. A beam of light is not bent by gravity as it propagates. The path followed is straight lines, not curves. But since Einstein's theory of General Relativity was proposed, the possible paths followed by beams of light over cosmological distances has remained to be verified. Another result of the study is the prediction that the Universe will continue its steady expansion, which started at the Big Bang, and will not collapse into a "Big Crunch".
The new information is a map of the CMB. Small temperature variations in the CMB would allow a test of different models of the expanding universe. The map represents an image of the early Universe, about 300,000 years old. The current estimate of the age of the universe is over 12 thousand million years old (12 Gyr). The light that has been detected has traveled across the entire Universe The project to map the CMB was called Boomerang (Balloon Observations of Millimetric Extragalactic Radiation and Geophysics). The measurements were made using a very sensitive telescope suspended from a balloon 40,000 meters above Antarctica. The instrument flew around Antarctica towards the end of 1998. The fundamental cosmic parameters derived from the work are accurate to within just a few percent. The Boomerang result supports a flat Universe. A perfectly flat Universe will keep on expanding forever, because there is not enough matter to trigger a Big Crunch. Boomerang backs the inflation theory of the Universe. As we have seen above this approach suggests that the whole of the cosmos expanded from the Big Bang, with the scale factor expanding exponentially fast during the first instances of the Hubble expansion. Looking beyond Boomerang we have the interference of the Earth's atmosphere: It sets a limit to the precision of measurements that are of interest to astronomy and cosmology.
A new space mission to overcome such difficulties is the Wilkinson Microwave Anisotropy Probe (WMAP). This probe traveled to a point in space known as L2, about a million miles from the Earth (four times farther than the moon), in the direction opposite from the Sun. Anything placed at L2 orbits the Sun at just the speed needed to keep it at L2. With this probe it was possible to obtain a map of the inhomogenieties of CMB very accurately. The confrontation of these measurements with theoretical models has confirmed the emergence of fluctuations in the very early universe. It has demonstrated that the present structure of the cosmos consists of about 4 percent ordinary atoms, 23 percent matter of 'dark matter' that does not interact with radiation, and the remaining fraction, over 70 per cent, consists of a mysterious 'dark energy' having negative pressure. Last, but not least, it has given us an upper bound for the age of the universe to be 14 billion years. To sum up, these results suggest that the universe is flat; we are entitled to entertain the hypothesis that in principle life may also be eternal in its eternal abode.

3. What is the likely destiny of life itself?

In order to discuss the destiny of life we should return to the earlier stages of astrobiology: the origin, evolution and distribution of life in the universe. Although the origin of life is not fully understood, the general outline of the question of the chemical evolution of the precursors of the biomolecues has greatly advanced since the early days of the research of Ivanovich Oparin, Stanley Miller, Cyril Ponnamperuma, Sidney Fox, John Oro and many other organic chemists that have traced out the likely pathways that nature may have followed during the molecular evolution that preceded the Darwinian evolution of the living cell, which constitutes the second stage in the discussion of astrobiology.
Darwinian evolution is much better understood. In earlier works several authors have argued that evolution on Earth has taught us that evolutionary convergence is an important feature of the Earth biota. Hence, if Darwinian evolution were assumed to be a universal process we would expect that whenever life emerges elsewhere in the universe, life would be bound largely by the same general properties that we have found on Earth. So we can anticipate new insights in the distribution of life in the universe. Perhaps the leading approaches for searching for lives elsewhere are first of all the exploration of the solar system. Secondly, astronomers have devised an observational technique for the search for life that has separated them into a sub field of the space sciences called bioastronomy. This process has been improving for over half a century. It is called the SETI project (Search for Extra-Terrestrial Intelligence).
Bioastronomers, since the pioneering days of the early 1960s, have followed the lead of Frank Drake by probing various windows of the electromagnetic spectrum for narrow-frequencies signals (Drake and Sobel, 1992; Ekers et al, 2002). Such output would be characteristic of other civilizations instead of being the product of natural phenomena, such as supernova explosions or regular emissions from pulsars. For this reasons we devote the remainder of this paper to issues that may clarify aspects of a Second Genesis. The compatibility of a Second Genesis with religious beliefs and traditions lies within the domain of natural theology. The Anthropic Principle raises the question of whether the laws and general statements of science imply that life is inevitably distributed in the universe. Once life emerges, does it necessarily evolve towards organisms provided with a human level of intelligence? We will attempt to discuss such questions. In so doing the intimately related topic of fine-tuning in science will also be considered and we will attempt to place such questions squarely into the cultural domain in which they belong. The closely related questions of the Anthropic Principle and fine-tuning in living systems (Carr and Rees, 2003) would be simpler to understand with more than a single Genesis.
Our religious traditions go back to Jewish theology: there is a sole omnipotent God who created heaven and earth, and subsequently life on earth. This view of our origins has traditionally been referred to as a 'first' Genesis. But revelations through the scriptures never raise the question associated with Giordano Bruno: the plurality of inhabited worlds. There is no incompatibility between religious tradition and the possibility that we may not be alone in the universe. What is exciting about the emergence of the new science of astrobiology is that we can explore the possibility that the evolution of intelligent behavior is inevitable in an evolving cosmos (Chela-Flores, 2001).

4. To understand the destiny of life we should search for a Second Genesis

An aspect of these reflections should be highlighted from the beginning: Although intelligent signals from other civilizations are in principle detectable, with the help of the bioastronomers, the fact remains that our lives are short and we crave for an answer. After almost half a century of searching for life in the universe - with extraordinary technological progress in the detection equipment used in this search - sadly no intelligent signals have so far been identified. But technology not only has progressed in recent years in the field of bioastronomy, it has also progressed especially in the exploration of the solar system with missions that are in principle capable of detecting microscopic life.
The search for extraterrestrial life has been attempted for the first time on the surface of the planet Mars a quarter of a century ago - the Viking missions were capable of detecting life, although the results were not convincing to most scientists. The search continues today with Mars being the present target of several space missions. Yet given the harsh conditions for the survival of extremophilic microorganisms on the Red Planet, the best digging equipment with present technology is still unable to probe as far as the more likely sites, deep underground where we expect liquid water to be present. We have argued in favor of the inevitability of the origin and evolution of life. by assuming that Darwinian evolution is a universal process (Dawkins, 1983) and that the role of contingency has to be seen in the restricted context of parallelism and evolutionary convergence (Akindahunsi and Chela-Flores, 2004). Convergence is not restricted to biology, but it has some relevance in other realms of science.
The sharp distinction between chance (contingency) and necessity (natural selection as the main driving force in evolution) is relevant for astrobiology. Independent of historical contingency, natural selection is powerful enough for organisms living in similar environments to be shaped to similar ends. For this reason, it is important to document the phenomenon of evolutionary convergence at all levels, in the ascent from stardust to brain evolution. In particular, documenting evolutionary convergence at the molecular level is the first step in this direction. Our examples militate in favor of assuming that, to a certain extent and in certain conditions, natural selection may be stronger than chance (Conway-Morris, 1998; 2003). We raise the question of the possible universality of biochemistry, one of the sciences supporting chemical evolution.
We have assumed that natural selection seems to be powerful enough to shape terrestrial organisms to similar ends, independent of historical contingency. Besides, it can be said in stronger terms that essentially, evolutionary convergence can be viewed as a 're-run of the tape of evolution', with end results that are broadly predictable; hence, if life arises again elsewhere in the cosmos, we would expect some degree of convergence with terrestrial life.
The universality of biochemistry suggests that in solar system missions, biomarkers should be selected from standard biochemistry. Given the importance of deciding whether the evolution of intelligent behavior has followed a convergent evolutionary pathway, and given the intrinsic difficulty of testing directly (the above-mentioned SETI project), within the realm of science we can begin testing the lowest sages of the evolutionary pathway within the solar system. Indeed, we are in a position to search directly evolutionary biomarkers on Europa. We have considered that if extant microorganisms are to be encountered, the most urgent set of evolutionary biomarkers are ion channels (Chela-Flores, 2003). Given the length of time before we can test them directly, a full discussion at the present time of the feasibility of carrying out a proper test is timely.
Within the restrictions of an in-situ laboratory, tests on the ice surface for microorganisms present some challenges that seem within the possibilities of molecular biology techniques. However, the most interesting case concerns the next orbital mission. It is expected to determine specific locations where the icy surface is thin enough for a submersible penetration, or for testing directly the surface for the presence of microorganisms.
Evolution of the cosmos, and especially biological evolution right from the biochemical level, may be 'fine-tuned' for the inevitable emergence of intelligent behavior in the cosmos, provided there is preservation of steady planetary conditions over geologic time. The most attractive site for the search for life is at almost four times as far from us as planet Mars. The Galileo mission arrived in the Jovian system in 1995 and completed its work in 2003. This mission has exposed an environment that can in principle support life: Europa is the second Galilean satellite with respect to its distance from Jupiter.
In the 17th century Galileo discovered Europa together with three other satellites Io, Ganymede and Callisto, but Europa remains the leading contender for being the host of an independent evolutionary line, distinct from the one that raised methanogens and other chemosynthetic microorganisms to man and to the most intriguing of life's aspects: the intelligibility of the universe itself that gave rise to life. We have so far demonstrated that a second evolutionary line can in principle be brought to our attention in the foreseeable future. Right now the next orbital mission is being planned and has been called "The Jupiter Icy Moons Orbiter" (JIMO). This is an ambitious project for a mission that is intended to orbit three planet-sized moons of Jupiter. In fact, the Galileo Mission gave us data to make us believe that Callisto, Ganymede and Europa may harbor large oceans underneath their icy surfaces. The mission would launch in 2012, or later.
Not only is there strong evidence for the internal oceans in the Jovian system, but also Jupiter's large icy moons appear to have three ingredients essential for the origin and sustained evolution of life, namely, water, energy and the necessary chemical molecules. The evidence from Galileo suggests melted water on Europa has been in contact with the surface in geologically recent times and may still lie relatively close to the surface. Observations of Callisto and Ganymede would provide additional comparisons that would contribute towards our understanding evolution of life of all three moons.
The JIMO mission would support one of astrobiology's main objectives: to explore the solar system in a well-focused effort to obtain our first insights into firstly how life is distributed in the universe, and consequently this would help us take the first steps in our understanding of the destiny of life in the universe. Even if we allow ourselves to think beyond JIMO, the eventual construction of a lander is conceivable, although our earlier hope of including even a submersible for exploring for the first time an extraterrestrial ocean is probably too premature (Horwath et al, 1997). But for learning whether a Second Genesis has occurred, probably a lander may be sufficient, given the dynamics of the icy Europan surface. It is possible that matter from the interior may be raised to the surface itself. The Galileo mission has led to the discovery of a phenomenon called 'lenticulae' which may be surface areas, whose origin is matter from the deep interior.

5. Insights into our destinies from astrobiology, ethics, philosophy and theology

Science is not contradicted by the main monotheistic religions of the world. A conflict will not arise with the potential discovery of a Second Genesis. Instead, a real conflict could emerge with a discussion of the evolution of all the attributes of man, including those that are of prime importance for theology, namely the spirit of man that may distinguish humans from the ancestors of the Homo line.
However, if we remain within the constraints that the science of biology has imposed onto itself - namely that the life sciences remain as an experimental academic pursuit, the question of man's spirit and soul should not even enter into the biological discourse: indeed, the natural framework within which to discuss such matters may even lie in some branches of philosophy such as ethics, and clearly in natural theology as well. However, it may be argued that ethics and biology should be integrated with moral philosophy and biology (bioethics) in an effort to achieve the main objective of science in general, namely to work for the benefit of mankind.

6. References

Akindahunsi, A. A. and Chela-Flores, J. (2004). On the question of convergent evolution in biochemistry, In: J. Seckbach, J. Chela-Flores, T. Owen, T. and F. Raulin (eds.) Life in the universe: from the Miller experiment to the search for life on other worlds. Springer, Dordrecht, The Netherlands. (In press.)
Carr, B. J. and Rees, M. J. (2003). Fine-Tuning in Living Systems. International Journal of Astrobiology 2: 1-8.
Chela-Flores, J. (2001). The New Science of Astrobiology From Genesis of the Living Cell to Evolution of Intelligent Behavior in the Universe, Kluwer Academic Publishers, Dordrecht, The Netherlands.
Chela-Flores, J. (2003). Testing Evolutionary Convergence on Europa. International Journal of Astrobiology 2: 307-312. http://www.ictp.trieste.it/~chelaf/ss13.html
Chela-Flores, J. (2004). Astrobiology's Last Frontiers Distribution and destiny of Life in the Universe, In:J. Seckbach (ed.) Origins: Genesis, Evolution and the Biodiversity of Life. Springer, Dordrecht, The Netherlands, pp. 667-679.
Conway Morris, S. (1998). The Crucible of Creation. The Burgess Shale and the Rise of Animals. London, Oxford University Press, p. 202.
Conway Morris, S. (2003). Life's Solution: Inevitable Humans in a Lonely Universe. Cambridge, CambridgeUniversity Press.
Coyne S. J., G. (1996). Cosmology: The Universe in Evolution, In J. Chela-Flores and F. Raulin (eds.) Chemical Evolution: Physics of the Origin and Evolution of Life. Kluwer Academic Publishers, Dordrecht, pp. 35-49.
Dawkins, R. (1983). Universal Darwinism, In: D.S. Bendall, (ed.), Evolution from molecules to men. London, Cambridge University Press, pp. 403-425.
de Duve, C. (1995). Vital Dust Life as a Cosmic Imperative. New York, HarperCollins Publishers, pp. 296-297.
de Duve, C. (2002). Life Evolving Molecules Mind and Meaning. New York, Oxford University Press.
Drake, F. and Sobel, D. (1992). Is there anyone out there? The scientific search for Extraterrestrial Intelligence. Delacorte Press: New York.
Ekers, R. D., Kent Cullers, D., Billingham, J. and Scheffer, L. K. (eds.) (2002). SETI 2020. SETI Press, Mountain View CA.
Horvath, J., Carsey, F., Cutts, J. Jones, J. Johnson, E., Landry, B., Lane, L., Lynch, G., Chela-Flores, J., Jeng, T-W. and Bradley, A. (1997). Searching for ice and ocean biogenic activity on Europa and Earth, In: R.B.Hoover (ed.) Instruments, Methods and Missions for Investigation of Extraterrestrial Microorganisms, The International Society for Optical Engineering, Bellingham, Washington USA. Proc. SPIE, 3111: pp. 490-500. http://www.ictp.trieste.it/~chelaf/searching_for_ice.html
Krauss, L. M. (1998). The end of the age problem and the case for a cosmological constant revisited. Astrophysical Journal 501: 461-466.
Ostriker, J. and Steinhardt, P. (2001). The Quintessential Universe. Scientific American, January, pp. 37-43.
Riess, A. G., Filippenko, A. V., Challis, P. (1998). Observational evidence from supernovae for an accelerating universe and a cosmological constant. Astronomical Journal 116: 1009-1038.
Weinberg, S. (1977). The first three minutes. London, Fontana/Collins.
Weinberg, S. (1993). Dreams of a final theory. London, Vintage.