29 research outputs found
The Fermi Paradox revisited: Technosignatures and the Contact Era
A new solution to the Fermi Paradox is presented: probes or visits from
putative alien civilizations have a very low probability until a civilization
reaches a certain age (called the Contact Era) after the onset of radio
communications. If biotic planets are common, putative advanced civilizations
may preferentially send probes to planets with technosignatures, such as radio
broadcastings. The contact probability is defined as the chance to find a
nearby civilization located close enough so that it could have detected the
earliest radio emissions (the radiosphere) and sent a probe that would reach
the Solar System at present. It is found that the current contact probability
for Earth is very low unless civilizations are extremely abundant. Since the
radiosphere expands with time, so does the contact probability. The Contact Era
is defined as the time (since the onset of radio transmissions) at which the
contact probability becomes of order unity. At that time alien probes (or
messages) become more likely. Unless civilizations are highly abundant, the
Contact Era is shown to be of the order of a few hundred to a few thousand
years and may be applied not only to physical probes but also to transmissions
(i.e. SETI). Consequently, it is shown that civilizations are unlikely to be
able to inter-communicate unless their communicative lifetime is at least a few
thousand years.Comment: 12 pages, 5 figures, accepted for publication in the Astrophysical
Journa