Extraterrestrials

[polymath257]

First, if I were inclined to *bet*, I would bet that there at least has been other life in our galaxy. Given the number of galaxies, I would *bet* that there is other intelligent life out there.

But that is very much NOT the same as saying we have been visited by other intelligences. I find that to be rather unlikely.

Here's why.

Our species has been able to send radio signals for about 100 years. We have had agriculture for about 10,000 years. How much longer do you think we have as a species? Given how intent we ar at destroying ourselves, I'd say another 10,000 years is optimistic at best. That mens we have 20,000 years of being technological enough to have agriculture.

If that is typical, how likely is it that the 20,000 years for humans overlaps with the 20,000 years for another intelligent species in our galaxy? Remember that things like galactic rotation take 100 million years and star evolution takes billions of years. The sun is about 5 billion years old and it is only in the last 10,000 years we have had agriculture in our solar system.

So, my guess is that life (bacterial life, that is) is fairly common. But multi-cellular life, and intelligent life are, almost certainly, much less common and the likelihood of overlap and actual contact is low.

There were a number of factors involved in allowing complex life to evolve on earth: or distance from the sun, abundance of water on the planet, luck regarding planet-destroying asteroids. In addition to that, only one kind of mammalian primate (us) seems to have lucked out enough to get opposable thumbs AND higher brain functioning. It was a fluke for it to have happened on our planet (we are the only intelligent/technologically capable species here) which suggests that intelligent life would be similarly anomalous on other planets.

Exactly. Although, the big obstacle seems to be multicellularity. There has been life on Earth for around 3.8 billion years. Oxygen generation killed off many of the obligate anaerobes about 2.5 billion years ago. Multicellularity is within the last 1 billion years. So there was 2.8 billion years of only single celled life on Earth.

Once that happens, it was another half a billion before hard structures (bones, shells) became common. Then another half billion years before humans showed up. We have been around about 100,000 years, but have had agriculture for only 10,000 of those and radio for just over 100 years. I don'tknow of many who are optimistic about our prospects for another 10,000 years.

if this is a common progression, the chance that we are around at the same time as another intelligent, technological species in our galaxy is very, very low. Not impossible, but I wouldn't bet on it.