According to the calculation of Harvard astronomers Amir Siraj and Abraham Loeb, if an alien technological civilization heard any transmission from Earth, it would take more than 2,000 years to get an answer .
The researchers refer to the extraterrestrial intelligences that would be motivated to send messages to Earth in response to the detection of technological activity on our planet.
It is important to estimate the response time of extraterrestrial response intelligences (ETRI), as such an estimate informs the nature of effective SETI searches, as well as the implications of a confirmed signal if we ever receive one. The question we try to answer in our article is: when can we expect our first cosmic conversation to take place?
The Copernican principle states that it is unlikely that we are living in a privileged time and therefore the probability that another habitable planet like Earth is going through an analog of our first century of radio communications right now, given a few thousand of million years of its history, it is below one part in ten million .
The first long-range radio transmission took place in 1901. This means that if there is a civilization within a hundred light-years of Earth with sensitive radio telescopes, they have detected us. Humans would only have to wait until the 22nd century to receive a transmission from a civilization located a hundred light-years away.
Assuming that our galaxy is relatively homogeneous in terms of the distribution of stars in its disk, this results in a volume of 1 billion cubic light years or 1,000 light years in any direction. This, in turn, implies a round trip time of more than 2,000 years .