A Bracewell probe is a hypothetical concept for an autonomous interstellar space probe dispatched for the express purpose of communication with one or more alien civilizations. It was proposed by Ronald N. Bracewell in a 1960 paper, as an alternative to interstellar radio communication between widely separated civilizations.
A Bracewell probe would be constructed as an autonomous robotic interstellar space probe with a high level of artificial intelligence, and all relevant information that its home civilization might wish to communicate to another culture. It would seek out technological civilizations–or alternatively monitor worlds where there is a likelihood of technological civilizations arising–and communicate over "short" distances (compared to the interstellar distances between inhabited worlds) once it discovered a civilization that meets its contact criteria. It would make its presence known, carry out a dialogue with the contacted culture, and presumably communicate the results of its encounter to its place of origin. In essence, such probes would act as an autonomous local representative of their home civilization and would act as the point of contact between the cultures.
Since a Bracewell probe can communicate much faster, over shorter distances, and over large spans of time, it can communicate with alien cultures more efficiently than radio message exchange might. The disadvantage to this approach is that such probes cannot communicate anything not in their data storage, nor can their contact criteria or policies for communication be quickly updated by their "base of operations".
While a Bracewell probe need not be a von Neumann probe as well, the two concepts are compatible, and a self-replicating device as proposed by von Neumann would greatly speed up a Bracewell probe's search for alien civilizations.
It is also possible that such a probe (or system of probes if launched as a von Neumann probe) may outlive the civilization which created and launched it.
There have been some efforts under the SETA and SETV projects to detect evidence for the visitation of our solar system by such probes, and to signal or activate such a probe that may be lying dormant in local space. Variations in the echo delay times of radio transmissions, known as long delayed echoes, or LDEs, have also been interpreted as evidence for such probes.
The near-earth object 1991 VG was initially suggested as a candidate for a Bracewell probe due to its unusual characteristics. In more recent years, however, additional discoveries have accounted for the characteristics of 1991 VG, and it is no longer regarded as anomalous.
- In Arthur C. Clarke's novel The Fountains of Paradise the extraterrestrial Starglider probe is an example of a Bracewell probe. In Clarke's story The Sentinel, later adapted into the movie 2001: A Space Odyssey, the 'Monolith' appears to be a Bracewell probe placed on the moon to ensure that only a civilization capable of spaceflight would be able to discover it.
- Alien Planet is a 94-minute special which aired on the Discovery Channel in 2005 about two internationally-built robot probes, and their mothership, searching for alien life on the fictional planet Darwin IV.
- Bracewell probes are featured in David Brin's 2012 novel Existence.
- In the Star Trek: The Next Generation episode "The Inner Light", a Bracewell probe transmits details of an extinct civilization to Captain Picard.
- An alien probe contacts the space station Babylon 5 in the season 3 episode "A Day in the Strife". The probe is a Bracewell probe, asking a series of questions and offering new technologies, medicine and science in return for answers to said questions. However, if the probe receives correct answers — thus proving that whatever civilization the probe has come into contact with is advanced — the probe detonates with a yield of 500 megatons, removing said civilization's homeworld or facility. This makes it more of a berserker probe.
- The Snark, an alien probe that visits Earth in the novel In the Ocean of Night (1977) by Gregory Benford.
- Bracewell probes in the role-playing game Eclipse Phase infect the seed AIs created by humanity with a deadly computer virus.
- Malicious aliens create a Bracewell probe in the form of a convincingly-human android and covertly send it to Earth in order to communicate a false cover story to humans that disguises the aliens' own arrival, in the Doctor Who episode Victory of the Daleks.
- Steel, D. (1995). "SETA and 1991 VG". The Observatory 115: 78–83. Bibcode:1995Obs...115...78S.
- Eclipse Phase Core Rulebook. Catalyst Game Labs. pp. 352–353. ISBN 978-1-934857-16-8.
- Bracewell, R. N. (1960). "Communications from Superior Galactic Communities". Nature 186 (4726): 670–671. Bibcode:1960Natur.186..670B. doi:10.1038/186670a0. Reprinted in A. G. Cameron, ed. (1963). Interstellar Communication. New York: W. A. Benjamin. pp. 243–248.
- Bracewell, R. N. (1973). "The Opening Message from an Extraterrestrial Probe". Astronautics & Aeronautics 11: 58–60.
- McCollum, M. (1983). LifeProbe. New York: Ballantine Books.
- Freitas Jr., R.A.; Valdes, F. (1985). "The Search for Extraterrestrial Artifacts". Acta Astronautica 12 (12): 1027–1034. doi:10.1016/0094-5765(85)90031-1.
- Biographical entry for Ronald Bracewell at The Encyclopedia of Astrobiology, Astronomy, and Spaceflight
- Bracewell probes, also at The Encyclopedia of Astrobiology, Astronomy, and Spaceflight
- SETV projects