The Search for Extraterrestrial Intelligence (SETI) has thus far failed to provide a convincing detection of intelligent life. In the wake of this null signal, many ‘contact-pessimistic’ hypotheses have been formulated, the most famous of which is the Rare Earth Hypothesis. It postulates that although terrestrial planets may be common, the exact environmental conditions that Earth enjoys are rare, perhaps unique. As a result, simple microbial life may be common, but complex metazoans (and, hence, intelligence) will be rare. In this paper we use Monte Carlo realization techniques to investigate the Rare Earth Hypothesis, in particular the environmental criteria considered imperative to the existence of intelligence on Earth. By comparing with a less restrictive, more optimistic hypothesis, the data indicate that if the Rare Earth hypothesis is correct, intelligent civilization will indeed be relatively rare. Studying the separations of pairs of civilizations shows that most intelligent civilization pairs (ICPs) are unconnected: that is, they will not be able to exchange signals at lightspeed in the limited time that both are extant. However, the few ICPs that are connected are strongly connected, being able to participate in numerous exchanges of signals. This may provide encouragement for SETI researchers: although the Rare Earth Hypothesis is in general a contact-pessimistic hypothesis, it may be a ‘soft’ or ‘exclusive’ hypothesis, i.e. it may contain facets that are latently contact-optimistic.

The number of habitable planets in the Milky Way and its temporal variation are major unknowns in the nascent fields of astrobiology and Search for ExtraTerrestrial Intelligence studies. All numerical models developed thus far have suffered from large uncertainties in the input data, in addition to our lack of understanding of the processes of astrobiological dynamics. Here, we argue that at least the input data can now be specified with more confidence, and use a simple Monte Carlo model of the Galactic Habitable Zone (GHZ) as a flexible platform for their elucidation. Previous papers have described some of the major results of this class of models; in this paper we present its mechanics and input parameters, notably the number of the habitable planets in the GHZ and their temporal distribution, based on the results of Lineweaver et al. (Lineweaver, C.H., Fenner, Y. & Gibson, B.K. (2004). Science303, 59–62.) Regulation mechanisms (such as gamma-ray bursts or supernovae) and their temporal evolution, assumed to be main agents responsible for large-scale correlation effects, are modelled as type α (which can sterilize part of or the entire GHZ) and type β (which are of local importance) events with decreasing mean temporal frequency over the cosmological timescale. The considered global risk function implies as an upper limit that about one out of a hundred habitable sites will achieve high astrobiological complexity. The preliminary results of numerical modelling presented here and elsewhere imply that the lack of a sudden change from an essentially dead Galaxy to a Galaxy filled with complex life – the astrobiological phase transition – in our past (a version of Fermi's paradox) may be understood as a consequence of global astrobiological disequilibrium, strongly indicating such a transitional epoch in our future.

The search for Dyson Spheres has been propelled not only by the hope of discovering intelligent alien life, but by humanity's ever-increasing need for energy. However, the Dyson Sphere is not a practical design, requiring too much matter to build and too much energy to stabilize. Here we discuss the various designs of a Dyson Sphere and propose the Solar Wind Power (SWP) Satellite, a simplistic, self-sustaining system that draws power from the solar wind and uses a laser to fire energy to collectors (on space stations, bases, etc.) positioned anywhere in the Solar System. While a small SWP Satellite can provide an estimated 2 MW of power, larger (or networks of) satellites could provide terawatts of power or more. The cost of the SWP Satellite would be relatively cheap – it primarily consists of shaped copper, with only a few complex systems onboard. Detection of such a satellite would be difficult using current technology, because at this time we can only detect solar wind deviations of up to 10−13 MS yr−1, while a 2 MW satellite would only divert 10−34 MS yr−1. Thus, only very large SWP Satellites could possibly be detected.

The extensive evidence of an ocean over a silicate nucleus makes Europa a candidate for the emergence of a second evolutionary pathway of autochthonous life. We argue that the most urgent question in astrobiology is the origin of habitable ecosystems (a question in geochemistry), rather than the alternative search for the origin of life itself (a question in chemical evolution). Since certain Solar System bodies may share a similar geophysical past with Earth, our more modest approach forces upon us the question: Can available instrumentation be the ‘pioneer’ in the discovery of habitable ecosystems in geophysical environments similar to the early Earth? It will be shown that a central piece in this dilemma is the chemical element sulphur (S). The Europan non-ice surficial elements that distort the water–ice absorption bands were found to be widespread, patchy and, most likely, endogenous. The Galileo Mission discovered these patches, which were subsequently confirmed by the 2007 flyby of New Horizons. We argue that penetrators should be inserted into orbital probes in the future exploration of Jupiter's System. Penetrators provide what could be a key instrument in the exploration of Europa, given the adverse space weather in its environment due to the Jovian magnetosphere and radiation. Indeed, there are alternative views on the radiation-induced S-cycles produced on the surficial molecules that are present on the icy surface; however, S is common to both interpretations. Hence, mass spectrometry should be an essential part of any future payload. The largest S-fractionations are due to microbial reduction and not to thermochemical processes, allowing a test of the hypothesis for the origin of habitable ecosystems. The microbial fractionation of stable S-isotopes argue in favour of penetrators for the survey of the surfaces of both Europa and Ganymede.

This paper reports the results of a questionnaire administered to university students, about several questions involving the origin of the Universe and life and biological evolution, as well as questions related to more common scientific themes. As few as between 2.4% (philosophy students) and 14% (geography students) did not accept the theory of evolution, because they believed in creation as described in the Bible. However, between 41.5% (philosophy students) and 71.3% (biology students) did not see any conflict between religion and evolution. About 80% of the students believed that the relationship between lung cancer and smoking is well established by science, but this number falls to 65% for biological evolution and 28.9% for the big bang theory. It should be pointed out that for 24.5% and 7.4% of the students the big bang theory and biological evolution, respectively, are poorly established by science. The students who self-reported being Christian but not Roman Catholic are more conservative in the acceptance of biological evolution and the old age of Earth and the Universe than are other groups of students. Other factors, such as family income and the level of education of parents, appear to influence the students' acceptance of themes related to the origin of the Universe and biological evolution.

With steadily mounting evidence that points to a cosmic origin of terrestrial life, a cultural barrier prevails against admitting that such a connection exists. Astronomy continues to reveal the presence of organic molecules and organic dust on a huge cosmic scale, amounting to a third of interstellar carbon tied up in this form. Just as the overwhelming bulk of organics on Earth stored over geological timescales are derived from the degradation of living cells, so it seems likely that interstellar organics in large measure also derive from biology. As we enter a new decade – the year 2010 – a clear pronouncement of our likely alien ancestry and of the existence of extraterrestrial life on a cosmic scale would seem to be overdue.

We have found that the principles of dialetheism, which state that some contradictions (typically at the limits of a system) may be true, and which amply demonstrate the limits of thought and conception, can be valuable in sorting out and clarifying some astrobiological problems that impede our ability to define life. The examples include the classification of viruses as alive or not alive, and the description of the transition zone for the abiotic-to-biotic transition. Dialetheism gives us the philosophical tool to state that the viruses may be both alive and not alive, and that chemical systems may exist that are both abiotic and biotic.

We have extracted some philosophical principles of the identity and have applied them to the identity of living organisms and their life forms. The first and most important idea is that we should define an individual organism via its numerical identity. For each organism its identity will be in relation to itself. As the organism undergoes various changes during its development, and as it transitions from one to the next of its life forms, one can observe numerous qualitative differences between these life forms. Although the life forms change and the organism is in a flux, what remains constant is the numerical identity of the organism. If the organism reproduces, for example by a fission mode, then the daughter cells will have their own numerical identity. We can state that the life of an organism is a sum of all its life forms over the period of time of the existence of the organism. Reproduction, particularly by fission, represents an identity dilemma, but it can be resolved by Gallois' occasional identities theory.