This paper reports new, more sensitive observations of nine of the eleven extrastatistical signals in the Megachannel Extraterrestrial Assay (META). These extrastatistical signals had all of the expected characteristics of extraterrestrial transmissions, except that they did not repeat. Cordes, Lazio, & Sagan (1997) showed that this lack of repeatability could be explained by interstellar scintillation of intrinsically steady sources. We use their methodology and our observations to exclude the scintillation hypothesis at a confidence level of at least 97.8% (for the case of an intrinsically weak source) to a level in excess of 99% (if the source strengths are comparable to that favored by Cordes, Lazio, & Sagan 1997). We also demonstrate that gravitational microlensing cannot account for the initial detection of these candidates nor is microlensing likely to play a role in future SETI programs. We conclude that the META candidates do not reflect a large population of powerful beacons.

We continued our search for partial (incomplete) Dyson spheres associated with solar-type stars (spectral types F, G and K) within 25 pc of the Sun. No candidate objects were found in a total of 384 stars.

Volcanic super-eruptions that produce >1000 km3 of ejected material and ≥ 1000 Mt (1015g) of stratospheric aerosols and sub-micron dust may be capable of creating global climatic disturbances sufficient to cause a severe setback or crash of modern civilization. Eruptions of similar magnitude are estimated to occur on average about every 50000 to 100000 years, which may be considerably more frequent than impacts by asteroids and comets that could cause similar climatic disasters. Prediction, prevention, and mitigation of global volcanic climatic disasters are potentially more difficult than planetary protection from large impactors, so that volcanism might provide an ultimate limit on the longevity of technological civilizations. If the lifetime of technological civilizations were limited to less than 50 000 years by volcanism, then the number of communicative civilizations in the Galaxy might be less than 1 per 10 million stars. Thus, super-eruptions on geologically active, habitable planets may strongly affect the prospects in radio telescopic SETI.

ACETI (algorithmic communication with extraterrestrial intelligence) builds upon mathematical languages to create a general purpose programming language. While the underlying framework may be quite simple, the programs derived from even a small instruction set, when run on a sufficiently fast computing substrate, may interact with their users in real-time and may exhibit complex behavior.

Over two hundred years ago Capt. James Cook sailed up Whitsunday Passage, just a few miles from where we now sit, on a voyage of astronomical observation and discovery that remains an inspiration to us all. Since the prospects of our visiting planets beyond our solar system are slim, we will have to content ourselves with searching for life using remote sensing, not sailing ships. Fortunately, a recently completed NASA study has concluded that a Terrestrial Planet Finder could be launched within a decade to detect terrestrial planets around nearby stars. A visible light coronagraph using an 8–10 m telescope, or an infrared nulling interferometer, operated on either a ∼ 40 m structure or separated spacecraft, could survey over 150 stars, looking for habitable planets and signs of primitive life. Such a mission, complemented by projects (Kepler and Eddington) that will provide statistical information on the frequency of Earth-sized planets in the habitable zone, will determine key terms in the “Drake equation” that describes the number of intelligent civilizations in the Galaxy.

Based on the study of several long-term societal indicators we estimate the phase transition between the “Technological Adolescent Age” (TAA) and the “Technological Mature Age” (TMA). Assuming the “Principle of Mediocrity” and using the Drake Equation we estimate a lower threshold for the number of technological civilizations in the galaxy.

Not infrequently it is suggested that the luminosity function (the distribution of the space densities of objects as a function of their luminosities) of extraterrestrial transmitters can plausibly be modeled as a power law, L-α, of the luminosity L (Drake 1973; Gulkis 1985; Lampton 2002). This assertion is usually motivated by analogy to the luminosity function for stars in the solar vicinity, which can be (very) roughly modeled as such a power law Fig. 1, data from Mihalas and Binney (1981). The argument then continues that if the power law is sufficiently flat (α < 1.5), then a flux limited sample of transmitters will be dominated by the most luminous, since their relative scarcity is more than made up by the much larger volume in which they can be detected. This is an extreme example of the infamous Malmquist bias (Mihalas & Binney 1981). It is then concluded that if the distribution of ET transmitters were to have such a flat distribution, then the seemingly obvious SETI search strategy of starting with the nearest stars and working outward would be incorrect, and, since we do not know the value of α it makes sense to “hedge” our bets by performing all-sky SETI searches even if such searches are much less sensitive.

The Search for Extraterrestrial Intelligence (SETI) has been, in its modern sense, a search for signs of technology beyond the Solar System. Such a search is a natural companion to visual and radio astronomy, which searches the electromagnetic spectrum to glean information about natural cosmic events. To succeed, SETI must demonstrate the existence of signals that cannot be explained by natural events and that are not of terrestrial origin.

We describe a new search for intrinsically short (μs) dispersed pulses at 21 cm. This search uses coherent de-dispersion, implemented in a distributed computing framework. It will have a sensitivity of 10−18 W/m2 and cover the Arecibo sky ∼ 3 times.

A recurrent neural network was trained to detect the time-frequency domain signature of narrowband radio signals against a background of astronomical noise. The objective was to investigate the use of recurrent networks for signal detection in the Search for Extra-Terrestrial Intelligence, though the problem is closely analogous to the detection of some classes of Radio Frequency Interference in radio astronomy.

We speculate about possible cosmic exploration by extraterrestrial civilizations using interstellar smart probes. We call attention to some emerging technologies that may be used for interstellar exploration. We estimate that advanced civilizations may already have these technologies and may be using them to contact their galactic neighbors. We explore some observational consequences of these contacting strategies.

Implicit in the significant resources invested globally in SETI searches is the assumption that there is a small but finite probability that one such search will be successful in the next few years. The potential significance of such an event makes it essential to have contingency plans in place to deal with it. I describe the processes that are in place to deal with a SETI detection, including the SETI Post-Detection Committee and outline the challenges facing us.

Messages for ETI written in a terrestrial language admitting linear notation, should be supplied with extra-linguistic annotations – also linearized in some way – as an aid for interpretation by recipients. In several papers the first author has advocated the use at the second level of an abstract system (a new Lingua Cosmica, still under development), based on constructive logic – with a minimal set of primitives. Expressions at the meta level explain the logic contents of messages.

The interaction between any LINCOS and text may suffice for interpretation of both – provided the messages and annotations are of considerable size. Finding a measure for the sizes involved is, however, a non-trivial problem. As a result, one is interested in methods for interpreting a LINCOS without recourse to natural languages. The present paper is concerned with the problem of interpretation of the new system within itself. For that purpose, interpretation of parts of it and (complete) propositional logic in terms of each other is considered (commutativity). This leads to self-interpretation as all semantic terms reside in the closed context of the system.

As archaeology is established on Earth and we are actively exploring the Solar System and beyond, there is the potential to develop a number of forms of exo-archaeology. The archaeology of the things intelligent species do in theory could be practised anywhere, provided one can detect the evidence. Sites are being created by us elsewhere within our star's habitable zone (HZ), namely on the Moon and Mars, and at least molecular traces of human-created probes are being left beyond the HZ (Venus, Jupiter etc.). The successful detection of extrasolar planets and the possible identification of HZs round other stars raise the possibility for the development of extrasolar archaeology, at least initially by remote sensing techniques. Within the Milky Way the main region to investigate is the galactic habitable zone (GHZ), though there could be archaeological traces of technological behaviours beyond it.

The idea of communicating cultural concepts in a SETI message, suggesting that analogy may be a useful tool, is developed in this paper in a systematic way, aiming at the construction of an effective message with wide cultural content. Here, I discuss both materials and methods in relation to three questions. Firstly, which of the main concepts of our culture are likely to be communicated in this way? Secondly, is the conceptual cluster (Dutil, 2004) sufficient as a basis to apply the analogical methodology or should it be extended further? And lastly, what is the possible contribution of the different kinds of logic (i.e. classical, mathematical, fuzzy and so on) and which are their relationships (if any) with analogy?

Information theory, as first introduced by Claude Shannon (Shannon & Weaver 1949) quantitatively evaluates the organizational complexity of communication systems. At the same time George Zipf was examining linguistic structure in a way that was mathematically similar to the components of the Shannon first-order entropy (Zipf 1949). Both Shannon's and Zipf's mathematical procedures have been applied to animal communication and recently have been providing insightful results. The Zipf plot is a useful tool for a first estimate of the characterization of a communication system's complexity (which can later be examined for complex structure at deeper levels using Shannon entropic analysis). In this paper we shall discuss some of the applications and pitfalls of using the Zipf distribution as a preliminary evaluator of the communication complexity of a signaling system.

Biological contamination from space is a remote but recognized possibility. SETI signals might also contain harmful information. Some argue that a SETI signal could not contaminate a terrestrial computer because the idiosyncratic computer logic and code constitute an impenetrable firewall. Suggestions are given below on how to probe these arguments and decontaminate SETI signals.

The SETI Institute, the California Academy of Sciences, NASA Ames Research Center, and San Francisco State University have developed standards-based curriculum materials for a one-year high school integrated science course centered on the unifying theme of evolution. Scientists, teachers, curriculum writers, and media specialists are currently finalizing six modules that integrate astronomical, geological, and biological sciences as well as the history of science and technology. The sequence of lessons in each module is designed to promote students' understanding and skills as defined by the National Science Education Standards and Benchmarks for Science Literacy. The modules cover: Cosmic Evolution, Planetary Evolution, Origin of Life, Evolution of Life, Hominid Evolution, and the Evolution of Technology. The core lessons for all six modules are provided via CD-ROM, including instructional guidelines, science background information, and additional resources (print, audiovisual, software, WWW sites, and databases). These products will be published as a complete set for use as a yearlong science course and will also be available as individual modules for use in discipline-based courses. Evolutionary change is a powerful framework for studying our world and our place therein. It is a story of epic size, capable of inspiring awe and of expanding our sense of time and place. This story is the basis of Voyages Through Time.

Cosmic evolution-change, broadly construed-has become a powerful unifying factor in all of science, underlying the rise of complexity throughout Nature writ large. That complexity can be defined and quantified for a whole hierarchy of ordered structures by examining the rate at which normalized energy flows through open, non-equilibrium, thermodynamic systems, from quark to quasar, microbe to mind.

Of all the research areas of modern discovery science, few attract more attention than the search for extraterrestrial intelligence. This is partially due to the fact that SETI is accessible, since the public can readily understand the goals of the research. The man in the street also finds SETI particularly exciting, a fact reflected by the ubiquitous presence of extraterrestrials in popular culture. The media interact with SETI in three areas: (1) reporting on research efforts, (2) being the principal conduit of information in case of a SETI detection, and (3) linking the subject deliberately or otherwise to the many stories of alien visitation. In this paper we will discuss the way science meets the media, and how and whether this often dicey relationship might serve to raise the general level of science literacy.