Basically time + the vastness of space = an insanely low probability that any two intelligent civilizations would overlap within a detectible sphere, especially with our current level of technology.
If we assume 1,000,000,000,000,000,000,000,000 planets exist in 100 billion galaxies and that 1 in 100 of those host single cellular life, that 1 in 1000 of those host multi-cellular life, that 1 in 1000 of those have animal life, that 1 in 10 of those has sentient tool-building species you then have 10 trillion planets with tool-building species.
If we assume an even distribution that's 100 tool-building species per galaxy spread out over 12-13 billion years.
Oof.
Even if you make far more generous assumptions, and that 1 in 2 planets has single cellular life and that 1 in 2 of those have tool-building life. That gives you an average of 25,000 tool-building worlds per galaxy, something like a 1 in 20 million change any star in our galaxy has a tool-building civilization.
If you remove the first billion years of the galaxy you get 12.21-12.51 billion years.
Again if we assume an even distribution and assume 140,000 light-years in diameter for a galaxy, that gives you something like 1 tool building civilization per 600,000 square light-years spread out over 12 billion years.
There's a big problem though, I've written about it here https://www.ryanmercer.com/ryansthoughts/2014/11/30/this-jus...
Basically time + the vastness of space = an insanely low probability that any two intelligent civilizations would overlap within a detectible sphere, especially with our current level of technology.
If we assume 1,000,000,000,000,000,000,000,000 planets exist in 100 billion galaxies and that 1 in 100 of those host single cellular life, that 1 in 1000 of those host multi-cellular life, that 1 in 1000 of those have animal life, that 1 in 10 of those has sentient tool-building species you then have 10 trillion planets with tool-building species.
If we assume an even distribution that's 100 tool-building species per galaxy spread out over 12-13 billion years.
Oof.
Even if you make far more generous assumptions, and that 1 in 2 planets has single cellular life and that 1 in 2 of those have tool-building life. That gives you an average of 25,000 tool-building worlds per galaxy, something like a 1 in 20 million change any star in our galaxy has a tool-building civilization.
If you remove the first billion years of the galaxy you get 12.21-12.51 billion years.
Again if we assume an even distribution and assume 140,000 light-years in diameter for a galaxy, that gives you something like 1 tool building civilization per 600,000 square light-years spread out over 12 billion years.
:( :( :(