The main conclusion is that the human civilization is unique in the observable Universe only when the likelihood of intelligent life on a suitable exoplanet equal to ten to the minus 22 degree.
That is assuming that human civilization is not unique in space, and the probability of the origin of intelligent life on a suitable exoplanet is ten to the minus 12 degree, at the present time in the Universe there may exist approximately ten billion sentient worlds.
To such conclusions scientists have come, by modifying equation Francis Drake given the open to date of exoplanets. The ratio of Drake is an equality, one side of which is the product of seven multipliers, and the other is the number of extraterrestrial civilizations.
Astrophysics in the Drake equation has seven multipliers replaced by two. The first one describes the number of inhabited planets in a given volume of the Universe, the second is the likelihood of intelligent civilizations on suitable for this exoplanet. This approach does not involve the use of information about the life time of civilization.
If the scientists estimate the fair is likely in the milky Way of humanity is the only intelligent civilization: the old worlds have already died, and new ones will arise after the man is gone (or getting them would require too long of human existence).