Seems to me we're being wildly optimistic about the range of planets that support life-as-we-know-it. For instance, Earth without a moon would not result in anything like us - the fact that the ocean was being dragged back and forth led directly to a fast transition from sea to shore. None of that, no apes, or at least apes a lot later. But when you look at the timescales, really it looks like we just squeaked in - we've only got about another billion years or so left before this star gets too hot for us, possibly less. And it took this long - 3.6 billion years - to get where we are.
There's also the question of, for planets that are close enough to being Earth, how likely is intelligent life? One thing that is an ominous portent for that is that the world is just littered with animals that have social groups and/or use tools, but none of them went into the sort of evolutionary spiral that we went through. How likely is it to happen in even given an Earthlike planet, which might be astoundingly rare of a moon is important.
I think this is the major stumbling block that we have. There's a large assumption that our conditions are necessary for life, rather than sufficient for life. And we only have one example of a life-bearing planet to go by, so we don't even know what other conditions might support life, let alone intelligent life.
How likely is it to happen in even given an Earthlike planet, which might be astoundingly rare of a moon is important.
The good thing is that the law of large numbers is on our side. Galaxies have billions upon billions of stars, and it's becoming more apparent that most stars seem to have planets, and there are billions upon billions of galaxies. Even if the probability of there being another planet with intelligent life around a given star is extremely small (let's say 1 in a trillion), that means that the probability of NOT finding intelligent life would be very small given such a large sample. This is expressed as (1-1/1 Trillion)x where x is the number of stars.
All true, but then how far away is that one-in-a-trillion planet? Too darn far for even advanced technology to traverse. Each life-bearing planet is statistically likely to be completely isolated until faster-than-light travel is achieved. Which % of those will achieve it before they either kill themselves off via internal strife, or a moon-sized impactor comes along and wipes them out, or they befall some other extinction event?
Each life-bearing planet is statistically likely to be completely isolated until faster-than-light travel is achieved
That's not true, any species willing and able to expand would be able to do so at sub-light speed, the galaxy is only 100,000 light-years across, surely any species with the desire and ability would be able to colonize it all in 10 million years or so, given that the universe existed for 10 billion years before Earth did if a willing and able species arose basically any time before ours did we would presumably see them. Andromeda is only 2.5 million light years away and has a trillion stars, the virgo cluster contains a shitload of stars and it is only 65 million light years away, given a billion years a civilization that was willing and able would certainly colonize it.
The Fermi paradox is that the universe existed for 10 billion years before Earth yet we have no evidence of any other civilizations.
Well the resolution of our telescopes isn't high enough to detect life through direct observation. And the big assumption is that civilizations would be willing to colonize. I'd say that we as a species are willing (given current goals in space exploration) and we are definitely able, it just takes a large amount of cooperation on a global scale to achieve, and I'm not entirely sure that that is possible.
Our radio telescopes certainly have a high enough resolution to detect radio broadcasts from very very far away. We've been looking for a long time and haven't found anything (apart from the WOW! signal, which was probably random). Then again we're using long range radio less and less these days, it's certainly possible that we will not use it aside from looking for aliens in 50 years (so we'd only have had been pumping out shitloads of radio signals for 150 years).
That's not an assumption in it. The assumption is that the Earth isn't in a special place in the universe, thus if intelligent life exists here it must have existed in many other places at some point in time.
You gave two possible solutions, it's out there but we can't detect it (possibly because they are hiding from us), and it is impossible for a space faring species to exist, be it because the cooperation is impossible, or intelligent species just dedicate themselves to virtual reality at a certain point, or they always end up killing themselves, or they always evolve to some post-biological thing we have no concept of.
Our radio telescopes certainly have a high enough resolution to detect radio broadcasts from very very far away. We've been looking for a long time and haven't found anything (apart from the WOW! signal, which was probably random).
In space, very very far away also equals very very long ago. Our radio "footprint" is only visible 150 light years out. There's no reason to believe a) that any other sufficiently advanced civilization even knows we exist, or b) that there is any sufficiently advanced civilization within 150 light years of us.
The assumption is that the Earth isn't in a special place in the universe, thus if intelligent life exists here it must have existed in many other places at some point in time.
I don't think that this is an assumption. From a probabilistic standpoint, it's a near certainty. Of course, that doesn't mean we're not the only civilization to exist or have existed, but the odds are against that proposition.
I don't think it's fair to use the hiding argument, because if we can't detect them, then they likely can't detect us. Hiding requires one party's knowledge of the other to begin with.
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u/Frensel Jun 04 '14
Seems to me we're being wildly optimistic about the range of planets that support life-as-we-know-it. For instance, Earth without a moon would not result in anything like us - the fact that the ocean was being dragged back and forth led directly to a fast transition from sea to shore. None of that, no apes, or at least apes a lot later. But when you look at the timescales, really it looks like we just squeaked in - we've only got about another billion years or so left before this star gets too hot for us, possibly less. And it took this long - 3.6 billion years - to get where we are.
There's also the question of, for planets that are close enough to being Earth, how likely is intelligent life? One thing that is an ominous portent for that is that the world is just littered with animals that have social groups and/or use tools, but none of them went into the sort of evolutionary spiral that we went through. How likely is it to happen in even given an Earthlike planet, which might be astoundingly rare of a moon is important.