1. Origins and Nature of Life

In these last years a large amount of experimental information on the nature and physiology of living cells has become available. The genomes of many species have been sequenced, the structures of many cellular biomolecules have been analyzed using advanced physical methods, and the networks of interactions between biomolecules in the living cell have been identified. There is now an abundance of data which indicates that the emergence of the living phase of the matter in the cell is related to the onset of a particular phase of condensed matter. Integral to life, of course, is energy. It is energy which gives matter the dynamic qualities we associate with life.

The unity of the fundamental aspects of the living phase of matter in spite of the large biodiversity is becoming increasingly clear. Living matter is comprised of and formed by 23 of 92 atomic elements. These selected elements are assembled in a finite set of selected essential biological macromolecules and what can be described as nano-machines. The onset of a macroscopic dynamical phase of coherent biochemical reactions and the interaction with the surroundings leads from the non-living to living phase transition (Ho 2008; Jaeken 2006; Ling 2001; Rasmussen et al. 2004). Thus we know that the simplest form of life has a genome, genes, and requires substantial energy to perform the functions associated with the genome and the requirements of life.

The cell is viewed as a system of a few essential biological networks (Alm and Arkin 2008; Alon 2007; Barabási and Oltvai 2004) such as the gene-transcription, protein-protein, and metabolic network with a low network entropy (Bianconi 2008). None of these networks are however independent. Instead they form a network of networks that is responsible of the behaviour of the cell. The cell of mycoplasma genitalium shows the smallest genome and is the simplest living cell made of the essential functional networks (Gibson 2008). This is of relevance since the simplest living system should display the intrinsic features of the living phase of matter (Luisi 2008).

The classical physical laws are clearly insufficient for understanding the living state of condensed matter made of many competing phases with characteristic multiscale phase separation and coherent dynamics over a wide time scale. Several authors have proposed that quantum effects should play a key role for the emergence of life (Abbott 2008; Davies 2004; González-Díaz 2010; Poccia 2009). If all possibilities are probable, with the least likely canceling each other out, then the probability of life, such as in the framework of the "many worlds" hypothesis and the multiverse, would necessarily lead to life (González-Díaz 2010). Others, in rejecting a Big Bang origin of the universe, have proposed that in an infinite universe and given an infinite amount of time with an infinite number of possible chance combinations, that all the essential elements necessary for the creation of the first self-replicating organism would eventually combine giving rise to life (Joseph 2010).

However, what were those conditions which gave rise to life?

2. The Big Bang and Dark Energy: Life Requires Energy

Related to the concept of life is energy. Energy is required for the cell to function, to repair itself, to replicate, and to pass on information. In this work we would like to propose that dark energy (Frieman et al 2008) could be of relevance in an unknown way for the emergence of life in our universe. In fact some of the recent estimates for the emergence of life in the universe is correlated with the onset of the dominance of dark energy.

In Figure 1 we plot the hypothetical emergence of life in the actual time scale of the Universe, with temperature versus time, elapsing after the Big Bang. The quantitative measure of the time elapsed from Big Bang to today has been an object of scientific debate for years. There is now a growing scientific consensus that the age of the Universe is around 13.69 ± 0.13 Gyr (from 13.82 to 13.56 billion years ago), and this is based on Cepheids as the fundamental principal of extragalactic distances, and with distance believed to be directly related to time.

In the standard Big Bang model of our Universe, which has been accepted by general consensus, following the creation the Universe underwent an accelerated stage of expansion: the inflationary era in a short stage (10^-34 sec). Two successive stages of deccelerated expansion followed inflation: the radiation dominated, followed by the matter dominated eras (Partridge 1995; Roos 2008; Tammann 2001). The consensus of opinion is that 74% of the universe consists of dark energy, 22% dark matter, and 0.005% radiation.

The onset of the dominance dark energy began around 4-5 Gyr after the creation of the Universe. Possibly, the measured cosmic acceleration could arise from the repulsive gravity of dark energy related with the quantum energy of the vacuum.

The cosmic microwave background radiation provides a further indication about the temperature of the Universe as it is today versus what it must have been following the Big Bang. Therefore it is possible to make scientific estimates as to the evolution of the temperature of the Universe (Lineweaver 2004). In Figure 1 we have plotted the temperature as a function of time in order to show the temperature changes of the Universe after the Big Bang.

It is thought that as matter cooled, it underwent phase transitions, which triggered or allowed the condensed matter in the Universe to undergo and form multiple complex phases. The non-living to living matter transition is related to these transitions that occur in a temperature range from a maximum of about 390 K, and a minimum temperature of about 240 K.

3. Stars, Supernova and the Elements of Life

It is recognized that not all extraterrestrial life in the universe may be like the life of Earth. It may have different genetic codes, no genes at all, or be comprised of silicon, ammonia, sulfuric acid and so on (Goertzel 2010; José et al., 2010; Naganuma and Sekine 2010; Rampelotto 2010; Schulze-Makuch 2010; Sharov 2010). However, we know for a fact that living matter on Earth depends upon and requires the synthesis of 23 different elements; and most of these elements are produced during stellar nucleosynthesis or may be produced and then dispersed at the end of the life time of a star, in a supernova explosion. Thus, all the stuff of life is found in stars.

It is unknown when the first stars were formed in the Big Bang model. Based on computer simulations, the first protostars may have been created between 200 million to 400 million years after the Big Bang. These are believed to have undergone supernova after a few million years.

According to various models, these first stars were the seeds for later stars such that by 10 to 12 billion years ago, the universe was bright with stars many of which also underwent supernova, spreading the seeds not just for additional stars, but for life.

In fact, there is now a growing body of evidence suggesting that the first proto-genes and the first forms of proto-life may have been fashioned around 10 billion years ago, or within a few billion years thereafter (Jose et al., 2010; Sharov, 2010). Many scientists also believed that these first proto-life forms or actual living cells were spread from star system to star system and from planet to planet via mechanisms of panspermia (Arrhenius 2009; Burchell 2010; Jose et al., 2010; Rampelotto 2009). It has been proposed life on Earth may have been encased in meteors, asteroids, and broken planets ejected from a "parent" solar system during the red giant phase of the central star's death, which was then followed by supernova (Joseph 2009). This life containing debris fell to Earth and became part of this planet.

In fact, we find on Earth 92 stable elements which were a product of a supernova explosion that was trapped by the sun about 9 Gyrs after the Big Bang. However, this finding does not support what has been described as "hard panspermia", that is, the transfer of fully formed life to this planet, but the possibility that life on Earth originated on Earth; perhaps following the delivery of proto-cellular material (via "soft panspermia") which led to an RNA world and then complex cellular life (Jose et al., 2010).

This leads then to the question: what unique conditions on Earth would have triggered the formation of fully formed life?

4. Dark Energy and Life

The emergence of complex cellular life in the Earth could have been produced early in the history of this planet when the water temperature on Earth was around 320 K and the Universe age was 9.8 ± 0.43 Gyrs.

It is now well established that a variety of complex single celled microbes, including archae and thermophile bacteria, can thrive and reproduce at extremely high temperatures, dying (or forming spores) only as temperatures approach 394 K. Does this mean that hyperthermophiles were created during these high temperatures? Not necessarily. However, what it tells us is that similar forms of life could have also been fashioned, perhaps from proto-cells during the early phases of this universe, such as during phase transitions involving rapid temperature changes. Thus it is possible that life has had multiple genesis events.

What has life to do with extreme heat? Heat is a source of energy. Energy not only can be transformed into matter, but living matter requires energy. A primary source of energy is the sun. In the history of the universe innumerable stars have lived and died, undergoing supernova and spreading the necessary life-sustaining and life-creating elements, including carbon, throughout the cosmos.

However, another source of energy which permeates the universe is "dark energy." Dark energy is a hypothetical form of energy which is believed to permeate the entire universe and to contribute to its expansion. Dark energy is believed therefore, to contribute to the dynamic nature of this universe, preventing matter from clumping together, and filling all of empty space. The existence of a dark and unclustered energy component responsible for more than 70 % of the overall density of our universe is supported by the latest cosmological data (Perlmutter 2003, Caldwell 2009).

The consensus of opinion is that the onset of the dark energy phase took place around 4.4 ± 0.2 Gyrs and this has been accompanied by an epoch of universe acceleration starting at 6.9 ± 0.2 Gyrs after the Big Bang (Melchiorri et al 2007). Again, this is well within the range of time that many are now estimating that life or proto-life may have first began to form in this universe, i.e. around 10 billion years ago (Jose et al., 2010; Joseph 2009; Sharov 2010).

This association raises the question of whether an increase of dark energy in the universe at that time could have an influence on the emergence of life. Dark energy is related to the whole universe and can affect multiscale phenomena ranging from microscale to nanoscale, so why not life?

Dark energy permeates the vacuum of space. Therefore it is possible that the quantum vacuum energy of scalar particles could imply a novel interaction like for the Casimir effect (Hertlein 2008).

Similar to the energy involved in a Casimir effect experiments, the order of magnitude of dark energy has been estimated to be of few meV. The biological interactions in the cell, biomembrane potentials, protein-protein interactions and many other biological relevant processes have reaction energies in the 20 meV energy range.

5. Conclusion

Certainly correlation or association, is not causation. Nevertheless, there is a growing consensus that life did not begin on Earth, that life may be widespread throughout the cosmos, and that life, or at least proto-life, may have had its onset billions of years before the formation of this planet (Arrhenius 2009; Burchell 2010; Crick 1981; Jose et al., 2010; Joseph 2009; Rampelotto 2009, 2010; Sharov 2010), and possibly 4 billion or more years after the Big Bang. Therefore, it is imperative that we ask what unique conditions may have prevailed during this time and how might these conditions have contributed to the origin or multiple origins of life?

The answers include: Star formation, supernova, and dark energy.

In conclusion, first, the proximity between the time onset of the emergence of life and the time onset of the dominance of dark energy in our Universe and the rapid phase of star formation and supernova, and second, the similar interaction energy scale supports the hypothesis that dark energy, coupled with the nuclear synthesis of all the necessary elements for life, may have played an unknown but significant role in the origin and stability of living biological systems and may have contributed to the origins of life.

Acknowledgments: The author thanks Alessandro Melchiorri for helpful discussion.