Quote:
Originally Posted by O.city
I had never heard of Fermi's quesiton. Thanks for that. I checked it out. Very interesting.
I'm thinking it's more of a we don't know what we're listening for and it's too far away, plus we're still infants in universe years.
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My thinking is that life as we know it is rarer than we think. We used to think that "okay, so as long as the ball of rock is close to the same size as ours, and is far enough away from its sun, but not too far, then viola!"
The truth is it is much more complicated than that.
Here are some factors that I think most people don't consider.
1) It takes about 3-4 generations of stars to get the necessary heavy metals we need for life (iron, high enough concentration of carbon, sodium, calcium, zinc, etc) to exist in a meaningful abundance. That means that life probably wasn't possible in the universe until about 6-9 billion years ago.
2) In addition to a solar system based Goldilocks zone, there is also a galaxy wide Goldilocks zone. Too close to the center, the chances of you getting hammered with radiation from nearby stars going supernova or getting sucked into a blackhole are much higher. The probability of going the necessary hundres of millions or billions of years without a catastrophic event are next to nil. That means the best places for live to form and thrive in a galaxy are going to be along it's outer arms.
3) Earth is lucky in that it has a Jupiter. Solar systems that don't have a Jupiter-like planet on the opposite side of the sun from the earth-like planet are not going to be likely to have life. Jupiter not only shields us from asteroid impacts, but it also helps stabilize Earth's axis of rotation. Without Jupiter, our axis of rotation would eventually flop over towards the Sun. It also helped stabilize the rotations of the planets in the solar system into their stable orbits we see now.
4) Plate Tectonics. Thinking goes that plate tectonics are essential to keep a planet at equilibrium. Plate Tectonics sequester carbon, etc. Venus is a "bottle-cap" planet, in which it has no plate tectonics, and billions of years ago, Venus had a runaway greenhouse gas problem, which is why it is as hellish as it is now.
5) Earth-Gaia collision. A while back, Earth collided with a Mars sized planet, which gave us two things. First, we got an unusually large core. The molten core is what emits the magnetosphere, which protects us from the Sun's radiation. Secondly, we got a huge moon compared in respect to the size of our planet. The tidal interactions between our earth and the moon may have been essential to the formation of life.
So, in conclusion, I would say that the most common estimates for intelligent life in the galaxy (around 10,000) is way too high. I'd say its most likely that there are 100 at most. My personal guess is there are probably no more than 20 intelligent civilizations in the Milky Way.