It has been almost 40 years since the raging of the Sagan-Tipler debate on SETI – Carl Sagan adopted the Copernican principle as an advocate in favour of the existence of extraterrestrial intelligence while Frank Tipler adopted the Occam’s razor principle against the existence of extraterrestrial intelligence on lack of evidence. The crux of the argument was the concept of von Neumann (self-replicating) probes that Tipler proposed as a medium to colonise the Galaxy quickly and efficiently.

Since then, certain features are now apparent primarily due to new technologies for interrogating the world around us:

(i) extrasolar accretion disks and planetary systems have been discovered and exhibit bewildering variety compared with our solar system;
(ii) surging astrobiological studies have revealed that terrestrial biology exhibits a much wider variety of ecological niches than previously expected;
(iii) our knowledge of genetics has expanded enormously including novel genetic innovations in eukaryotes within “junk” DNA;
(iv) our knowledge of neural and brain processes as the engine of intelligence has expanded dramatically;
(v) Hart’s Fact A still stands despite 40 years of searching the skies for extraterrestrial radio and optical signals with ever-increasing sophistication;
(vi) shift away from radio signals to other technosignatures of intelligent extraterrestrial activity; (vii) developments in interstellar travel technology;
(viii) developments in self-replicating machine technology.

All of these issues inform the original arguments deployed by both Tipler and Sagan but it is the last two which are particularly poignant. We would invite papers on all relevant issues to the Sagan-Tipler debate in the light of new knowledge and new perspectives.

Submission deadline: December 31, 2021

Guest Editor:

Alex Ellery, Canada Research Professor, Carleton University, Ottawa, Canada aellery@mae.carleton.ca