Mediocrity and its Complex Relationship to ETI

Arguments for or against SETI rarely invoke the theological and philosophical evolution behind such reasoning. Tipler, in his 1981 article, presents an historical approach to the concepts of extraterrestrial intelligence (ETI). The debates and arguments for or against ETI periodically reappear throughout history, albeit slightly refashioned to reflect the principles of any contemporaneous philosophical movement. Tipler introduces two related philosophies: the principle of plenitude and the plurality of worlds. The principle of plenitude surmises that what can exist must exist, such that the Universe contains all forms of existence and intelligent life must exist in elsewhere. The plurality of worlds describes the Universe as infinite, producing an indefinite number of worlds which may harbor life. Tipler then provides the historical evolution of these ideas discussing the Greco-Roman debates, the Copernican revolution, the scholasticism of the Medieval period, the Enlightened support for the plurality of worlds, and finally the scientific view of these philosophies.

Of particular interest was to see the evolution of the concept of the plurality of worlds. Prior to the Copernican revolution, the Ptolemaic Universe reigned supreme and the plurality of worlds meant an infinite number of self-contained Universes with a central Earth. Tipler mentions that despite having the physics wrong, this particular thought is akin to the modern support of ETI by the principle of mediocrity. The principle of mediocrity states that we are not special in the Universe such that, given the existence of life on Earth, life exists in other Earth-like planets in the Universe. The Christian argument against ETI was also intriguing. St. Augustine wrote that the uniqueness of Christ meant there was no other intelligent life, else they would have a separate Christ for such a world. St. Thomas Aquinas argued that God was perfect; which was inconsistent with the plurality of worlds as this would be an act in vain if similar worlds existed and an act of imperfection if dissimilar worlds existed. It was not until the nineteenth century that the plurality of worlds was used to argue for ETI and against Christianity, as seen by the excerpt from Thomas Paine’s Age of Reason.

The post-nineteenth century pervasiveness of the plurality of worlds should be viewed through a critical scientific lens. It was through the scientific understanding of the geological, biological, and chemical evolution of the Earth that the principle of plenitude was rejected. Tipler repeats the arguments of William Whewell and Alfred Wallace, which were aligned with that of evolutionary biologists in that they argued the Earth was uninhabited for most of its history and, to our knowledge, the conditions for life and natural selection are incompatible with harsh environments elsewhere. Tipler, unfortunately, does not muse over the fact that a post-Enlightened society would use the plurality of worlds to fuel the imagination and foment the idea that humans are not alone in the Universe (i.e. It Came From Outer Space or the spoof, It Came From Planet Earth). Most surprising to this blogger was that modern evolutionists argued against ETI while physicists and theologists appeared to have no issues with it. While the scientific community, with achievements such as the development of radio communication and the Miller experiment, may have cemented the belief in the plurality of worlds and the search for ETI, the larger biological and chemical considerations appeared to be ignored during the late twentieth century. Despite the support the principle of mediocrity provides ETI, it is imperative to address all scientific concerns regarding ETI. Perhaps it is no surprise that astrobiology has recently developed to as a response to the complex scientific nature of the search for ETI.

Bracewell’s Probes: Fiction Masquerading as Science

Bracewell, 1960 contemplates the methods to detect a signal from an advanced civilization. The paper can be considered a critique and response to Cocconi & Morrison’s seminal 1959 paper on interstellar communication. Bracewell argues that using narrow-band radio signals on Earth is a flawed approach to detect “superior communities” as these are not abundant. Bracewell posits that the inherent paucity of advanced lifeforms complicates their detection as such a society would need to search and select a correct target star potentially hundreds of light years away. Given the geological timescale for the formation of an Earth-like planet, monitoring various radio telescopes would require operating these facilities for millions of years. Furthermore, the distances would result in large time-delays for information exchange between civilizations.

Bracewell instead provides a novel solution for detection of intelligent life by considering the search from the perspective of an advanced society (arguably, much more advanced than humanity). A society with comparably primitive scientific capabilities, such as ours, would be most focused on exploring their respective planetary neighborhood for life. An advanced society could exploit this by sending durable solar-powered probes equipped with radio transmitters to candidate systems (i.e. solar-like stars) as a means to garner the attention of the primitive society. The use of probes would provide an expansive radio-relay network capable of informing the advanced society while removing the need to select the correct star to observe, as is required by Cocconi & Morrison’s proposal. Bracewell also suggests the probes would potentially house artificial intelligence and a cache of pictorial information capable of communicating with the primitive society. The probe would actively listen for signals around the system and repeat these signals to the society to make itself known.

One of the largest limitations to Bracewell’s probes are the technological requirements. To this blogger, the technological descriptions can only be relegated to the realm of science fiction. This was perhaps most apparent in Bracewell’s comment that the probe could televise an image of a constellation. The flaw in Bracewell’s arguments are the various assumptions made including that (i) life should be around sun-like stars, (ii) intelligent life can create devices capable of analyzing and using electromagnetic radiation, (iii) a primitive society will readily decipher a signal from a probe, and (iv) an advanced society has fundamentally reached a point of quasi-permanence, allowing it to persist through the millions of years of development for a primitive society. It is difficult to argue for or against the use of probes when they rely on factors outside the scope of humanity’s scientific understanding (i.e. see Figure 1). There is also the issue that Bracewell’s probe should reach out to the civilization once it detects some radio emission. As of this writing, there is no evidence of contact by such a probe.

It should be noted there have been searches for Bracewell probes (i.e. Spaewatch at KPNO; Lunan & Gatland 1973, Spaceflight, 15, 122; SETA as described in Freitas Jr. & Valdes 1985, Acta Astronautica, 12, 12, 1027). The popularity of Bracewell’s idea is also emphasized by Wikipedia, which provides examples of how these probes have permeated science fiction. The search for such probes are ongoing but, to this blogger, the search for extraterrestrial artifacts may be the wrong approach in the search for life. A probe does not necessarily need to make contact to detect life. With the growing field of astrobiology and the quest for biomarkers of life, the need for a probe to transmit and directly communicate with a primitive society appears unnecessarily complex. Logic dictates that the absence of evidence is not evidence of absence such that the search for Bracewell probes will persist until we find an advanced civilization.

Figure 1: A Bracewell ProbeOne of the many images a quick Google search provides. The configuration of such a probe is limited by one’s imagination. Above is a self-replicating Bracewell probe that could theoretically propagate and populate an entire region of the galaxy. Source: David Daring, http://www.daviddarling.info/encyclopedia/B/Bracewellprobes.html