I thoroughly enjoyed this video on the fundamental question of extra terrestrial life. And he goes even more in depth here, where he talks about the Great Filter. First, read this whole section on the Fermi paradox.
The critical feature of the Fermi paradox is that in terms of TIME & SCALE, we should already see e-t life. Because, "there are an estimated 200–400 billion stars in the Milky Way and 70 sextillion in the visible universe." and the universe is 13.7 billion years old.
I like how they wrote this. It boils down to essentially this...
The Fermi paradox can be asked in two ways. The first is, "Why are no aliens or their artifacts physically here?" If interstellar travel is possible, even the "slow" kind nearly within the reach of Earth technology, then it would only take from 5 million to 50 million years to colonize the galaxy.[11] This is a relatively small amount of time on a geological scale, let alone a cosmological one. Since there are many stars older than the Sun, or since intelligent life might have evolved earlier elsewhere, the question then becomes why the galaxy has not been colonized already. Even if colonization is impractical or undesirable to all alien civilizations, large-scale exploration of the galaxy is still possible; the means of exploration and theoretical probes involved are discussed extensively below. However, no signs of either colonization or exploration have been generally acknowledged.
The argument above may not hold for the universe as a whole, since travel times may well explain the lack of physical presence on Earth of alien inhabitants of far away galaxies. However, the question then becomes "Why do we see no signs of intelligent life?" since a sufficiently advanced civilization[Note 1] could potentially be observable over a significant fraction of the size of the observable universe.[12] Even if such civilizations are rare, the scale argument indicates they should exist somewhere at some point during the history of the universe, and since they could be detected from far away over a considerable period of time, many more potential sites for their origin are within range of our observation. However, no incontrovertible signs of such civilizations have been detected.
It is unclear which version of the paradox is stronger
Now the Great Filter from what I understand, is some hypothesis that there is a most critical test, that should we not pass, we cannot be labelled at "expanding lasting life". This is a very odd hypothesis to me, because all things begin and end, so I'm not sure why they assume there is some final obstacle we must cross to see if we are really viable in this universe. But either way, from one perspective, it appears there are obstacles - for a single celled organism to turn into a multi celled one, we assume that it has reached the next level, and is a higher, more intelligent being as a result of it.
I like how he ends the Great Filter video though, noting that "it's entirely possible no one really knows we're here." When he said that, it took loneliness to a whole other level. What if there is a community of extra-terrestrial beings out there... who are completely focused on another section of the sky. They forgot to check here, or they find it improbable that we would exist? But if they knew, they would be able to contact us right away. Wow, what a strange thing to think of.
With that... good night :)
