We know now that there are planets out there.
Lots and lots of planets.
We are still pinning down the exact incidence over all stellar populations, and we are barely at the point where we can directly confirm the presence of terrestrial planets, but if parameter space is smooth and the universe does not conspire against us, then terrestrial planets must be quite common.
10% incidence would not be a bad conservative guess, but I would not be surprised if the incidence is 30-50%.
We will know for sure soon.
We don't know how life starts.
We have some well founded suspicions, and every year the gap in the evidence shrinks as we tighten our knowledge of the transition from complex self-catalytic chemical systems to minimal living systems.
It is, still, conceivable that life is a near unique contingent event, but that is looking unlikely.
It would not be unreasonable to infer that life will appear, and quite rapidly, wherever suitable mild and stable conditions persist.
We do understand quite well know how evolution progresses, and I use that word with some deliberation.
Evolution is an emergent property of self-replicating systems, and will emerge in any such system where information is duplicated and transmitted.
Selection also occurs, and there is, in a broad range of circumstances, selection that favours the ability to efficiently process information, lots of information and fast.
So, there ought to be in many circumstances selection pressure to evolve intelligence on suitably long time scales.
We don't know the characteristic time scale for the evolution of intelligence comparable to ours, the one data point we have is inadequate, though one may infer that there was independent evolution of not insignificant progress towards intelligence in multi-cellular animals on Earth.
Some steps in the progress to get to that point may be low probability choke points, though less so as we learn more.
eg. multi-cellular life could, in principle, be a major hurdle, but current research suggests it comes about relatively easily.
There is still a lot of contingency in the emergence of intelligent life - both astronomical, geological and internal fail points.
The Earth could have been sterilized repeatedly: slightly larger asteroidal impactors; deeper snowball phases; self-pollution.
We also don't know if our particular implementation of life is uniquely possible, or if there are many systems which could implement life. The latter is looking more likely as we understand more.
So, where are they?
The Fermi Paradox has been hashed out many times, and we need data, the speculation is probably mostly complete.
Even if intelligent life is rare, there are a lot of stellar systems out there; some 100 billion or so in our galaxy, and there are trillions of galaxies.
It seems unlikely life on Earth is unique, and it seems plausible that somewhere life achieved intelligence, and technology, and that technological capabilities can expand to physical limits.
We are at the technological point where we ought to be able to see sufficiently advanced civilizations. Say anything at Kardashev level 1.7 or higher.
If they are reasonably abundant.
At roughly incidence of 10-4 we ought to be able to see our neighbours.
Now.
Unless they are very good at hiding, and have a reason to hide.
I don't know how we will see them, but it will probably not be the way we now think we will, but we are pretty good at looking.
As we get better at looking, we can squeeze both the incidence rate of arbitrarily advanced civilizations, and their level of advancement, crudely measured in terms of level of power under their control.
If they are not there, we need to seriously think about why that might be.
If they are there, we have a whole lot of new thinking to do.
Interesting times.
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Good post. I've thinking along similar lines for a while:
- Intelligence (as we know it) is not necessarily the end point of the evolution. Just another solution.
- Intelligence may also take other ways of thinking the world. Not sure if we can always recognize it. There is a need to check some interesting life species on Earth.
- Not all intelligent species are interested in developing technologies
- Suitable technology may depend a lot on the environment. Marine species, for instance, may have it harder.
- It is unknown how long a civilization lasts. We may come back to stone age at any time.
- Space travel is damn expensive in energetic terms, under our current understanding.
My own guess is that intelligence isn't particularly common.
It isn't really just intelligence; it is specifically technology we are interested in. The only example we to have available to consider is Earth.
Life has been around on Earth for some 4 billion years. This is evidence that life is comparatively straightforward, since it arose so quickly in Earth's history.
Then there's "complex" (multicellular) life. This appears to have taken some 3 billion years or more. This is evidence (I propose) that it's not a particularly natural thing to happen. It quite possibly something that's pretty uncommon. Single celled life remains dominant on Earth by most measures (variety, biomass, species count, etc).
We only have a sample space of 1 for life bearing planets to examine; and since we are multicellular, we're kind of bound to observe it no matter how common or uncommon. The fact it took so long to arise suggest to me that it could well be a most unusual evolutionary oddity for the universe.
Likewise for technological intelligence. Once complex life showed up, if intelligence was a normal outcome I'd expect it to show up comparatively quickly. But it didn't. DInosaurs were plenty big enough to go in the direction of technological ability, should it be a common thing. They didn't; and neither did any of the other species around, until some 600 million years after the multi-cellular oddity occurred.
So again, on balance, I'd suspect technological ability is a quite unusual evolutionary oddity, even given complex multicellular life.
As for how long technological life persists once it arises; no data is available. We've been around what amounts for a single spot on the lineline of life.
So my guess is... technological ability is really unusual. Not impossible, obviously. But we've no reason to think it common and good reason to suspect its very unusual.
So, technology and intelligence are in these cases defined narrowly. There is some thinking going on about just how different both could be from our canonical example, which has been somewhat explored in fiction but until recently not well in science. Over the last year or two I have started seeing some hints of progress in scientific consideration of the broader nature of intelligence.
The Big Question is lifetime of civilization, in the sense of intense reprocessing of free energy on large scales.
The problem with that question is that it really only requires one Útrás per galaxy!
Either Space Vikings are extremely rare, or we are missing something fundamental in our considerations.
Shucks. Chris Ho-Stuart beat me to it, so I'll merely second his remarks.
Let's turn the question around: Assuming that someone were out there looking, how would he know that there is intelligent life on Earth? AM radio doesn't work (our ionosphere is not transparent at those frequencies), nor does shortwave (ditto). At stellar distances you are going to need a big telescope to capture TV or FM signals to enough of an extent that you can analyze them, and I suspect those signals are on their way out as more people switch to cable or broadband. There is satellite-to-ground and vice versa, but the former has similar signal level issues and the latter depends on your being in the right direction to see the beam. So aside from the issue of how common they are, I think they are going to be harder to detect than we think. Short of catching them in the act of constructing a Dyson sphere, I'm not sure how we do it.
the notion we should have seen them by now defies logic and reason.
There are endless # of things in this world that are literally under our noses that we have yet to see.
To think that somehow we should have picked up evidence somehow, some way out of the vastness of intergalactic space of civilization somewhere is incomprehensible hubris.
Why should we have "found any" considering we've only spotted a fraction of the objects in the kuiper belt, fewer in the ort cloud.
While detecting signs of technological activity might seem to be a totally different task, when you consider the scales is it really?
Any sort of advanced life is likely to be light years away, and thus many times more difficult to spot than local solar system objects using technology of today that is some of the most advanced we have. Yet we've only been able to locate a handful of these things.
Any civilization that we should be able to spot would likely be on a similar level of technological development.
However the time a civilization stays at any level of technological development rapidly dwindles the more advanced they become.
The time it took to build the first telegraph networks is many times greater than the time it took to go from there to build the first supercomputer.
That means the "easy window of observation" is extremely small and extremely transient. We'd have to have had extremely good luck to have found one by now.
Just as the past modern tech of the telegraph area would have had a hard time detecting, analyzing Etc. the activities of our day, so too is it likely that we are unable to detect evidence of interstellar life, because our tech is simply too primitive, even if they are only 100 yrs more advanced then us.
The pace geometric nature technological advancement means the time it takes for a technology to become "invisible" using means restricted to the abilities of a past technology becomes shorter and shorter as technology advances.
Great post, and great comments overall especially by C. Ho-Stuart because it reflects my current thinking as well on this topic.
We are actually getting pretty good at looking.
Modern astronomical sensors are approaching quantum limits in many wavebands and we're not mostly limited by collecting area and cadence. Oh, and ability to process and analyse the data.
What we can see are, essentially, energy flows - any civilization that is not actively stealthed, and which is utilizing large energy flows - something like Kardashev scale 2 or higher - we ought to be able to detect those if they are close enough or there are lots of them.
We have no idea how long civilization spend in such a phase, but any civ that was speed of light limited, expansionary and utilized significant fraction of stellar energy flow for each star colonized ought to be detectable and persistent.
I found an interesting article that may be of interest to fellow science lovers. It talks about how two new, circumbinary planets have been discovered by an international team of researchers. This helps to confirm and establish a whole new class of planets that orbit two stars.
If you guys want to read the whole story, check it out on:
http://www.science-fare.com/article/tatooine-planets-may-be-more-common…