Scientists have argued that if we ever find a sign of an advanced alien civilization, it is likely that these aliens are already dead.

It is believed that there are 20 to 40 billion terrestrial worlds in the Milky Way with habitable conditions. However, we cannot yet estimate how many of these could have spawned life, nor whether they were long enough to retain liquid water and evolve.


Humankind only covered 0.001% of the Milky Way with signs in 80 years. Even at the upper limit of life for our civilization, we will not have covered the entire galaxy.

But if some civilization sent a signal and lasted less than 100,000 years - the width of the galaxy in light years - then the chances of finding a living civilization are unbelievably small.

"If the civilization emanating from the other side of the galaxy, when the signal comes here, civilization is probably over," said Claudio Grimaldi of the Swiss Federal Polytechnic School in Lausanne, the study's lead author.

They note that when a civilization stops issuing, its signals will continue to travel through space, in a kind of echo of dead civilization. And it may be possible to detect these, but the odds are not necessarily good to find someone alive.

"Broadcasts arriving on Earth can come from extinct civilizations, while civilizations are still alive are sending signals to arrive," they write. Still, the big factor here is that we just do not know the probability of life reaching the planet. There are plenty of potentially habitable worlds within 80 light-years of Earth, close enough to have received a signal from our planet

Is intelligent life on our planet a coincidence, or is it generalized? Until we answer that question, it is still difficult to draw conclusions. [ IFLS ]