ABracewell 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, as well as being able to communicate over long timespans, it can thus 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–Bracewell probe) may outlive the civilization which created and launched it.
There have been some efforts under the SETA and SETV projects[clarification needed] to detect evidence for the visitation of the Solar System by such hypothetical probes, and to signal or activate such an alleged probe that may be lying dormant in local space.[dubious – discuss][citation needed] Variations in the echo delay times of radio transmissions, known as long delayed echoes, or LDEs, have also been interpreted in Professor Bracewell's 1960 paper as evidence for such probes.[dubious – discuss][1][2]
The near-Earth object 1991 VG was initially suggested as a candidate for a Bracewell probe due to its unusual characteristics.[3] In more recent years, however, additional discoveries have accounted for the characteristics of 1991 VG, and it is no longer regarded as anomalous.[4]