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Comment by Ostrogodsky | Hacker News Reader

For me intelligent life should be from somewhat to very common across the universe.

Simplistically you would need:

A source of energy, aka a star, at the very least there are 10^22 of them

A rocky planet situated in the habitability zone of the star (and this is lacking the imagination for life in other kind of environments).These guys are common.

The creation of chemical self-replication with a stable set of compounds (The hardest part for me, but far from impossible)

The appearance of intelligence as an evolutionary trait (nature loves that explore/exploit game)

Time

We modern humans lived 99.7% of our 200k year history entirely unaware there were other people and land a mere "earth radius" away, we may as well repeat that story in a cosmic scale.

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You should read the article. They are making the same kind of argument as you, but more carefully.

In particular, the key logic is: either intelligent life takes much longer to evolve than stars’ lifetimes, or about the same, or much less. We evolved at about 80% of Earth’s habitable lifespan. That would be very unlikely, if on average intelligence took less time to evolve than star lifetimes. Taking the same time on average is a knife edge case (I think this depends on the multiplicative nature of the probability distributions involved). So probably it is more. In which case, life is very rare.

The problem is really that we spent 99.7% of our history extremely close to the surface of an extremely large sphere. Space is somewhat less lacking in, like, physical obstacles. I mean really, a priori, if there were loads and loads of intelligent species in our galaxy, wouldn't you expect to see them? Why bother positing a brand new set of technologies that just by chance happens to thread whatever needles are necessary to avoid detection, and just figure "oh, guess for some reason there are fewer technological civilizations than I expected"? Obviously we aren't alone in the universe, but it takes some real gymnastics to justify nearby neighbors.

> I mean really, a priori, if there were loads and loads of intelligent species in our galaxy, wouldn't you expect to see them?

Not according to the Dark Forest theory. There are either quiet civilizations or dead civilizations due to realpolitik. This video summarizes the details[1]

1. https://www.youtube.com/watch?v=xAUJYP8tnRE

We can't see Planet Nine right under our nose, why would we see anything beyond that?

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