We have been slightly technical for 100 years or so. It is just a sliver of time. To have been hit upon by another civilization in that slice of time would be fortunate. Our planet has been a silent rock in space for 4.5 million years. We have sent radio waves only in the last century.
I’m not really a fan of these ‘science fiction’ explanations. They assume far too much. When there are perfectly good mundane explanations for why we aren’t hearing/seeing other species, we don’t need to invoke Galactic Codes of Silence or Berserker races to explain it. Occam’s razor, and all.
For instance, consider the rare earth hypothesis. Basically, it says that when you drill into the Drake equation, you find lots of potentially limiting factors. For instance:
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A planet that could have intelligent life must be in just the right region of the galaxy - too close in, and there’s too much radiation and too much bad stuff going on (nearby supernovae, etc). Too far out, and the stars don’t have enough metal for rocky planets to form. So there’s a ‘galactic habitable zone’ that excludes the majority of stars.
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A host star must be in an orbit that doesn’t take it through the spiral arms. Therefore it must be clear of a spiral arm and in a very circular orbit like our sun. That eliminates a majority of the remaining stars.
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A host star must be in a region that has not had a major supernovae or gamma ray burst close enough to it to wipe out life. It has to have stayed clear of these events for billions of years.
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The star must be of exactly the right spectral type and not too variable.
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The planet might need to have a moon to provide tides. It needs to have a rotational period fast enough that the temperature difference between night and day is not too great. It can’t be tidally locked with its host star.
Anyway, there could be far more conditions required that we’re just beginning to understand, and combined they could reduce the odds of a planetary environment staying stable for the billions of years required for evolution to take place to a vanishingly small number.
If this hypothesis is correct, there could be billions of planets with rudimentary ecologies. Millions with planetary ecologies of plants and simple animals. Maybe hundreds of thousands somewhere on the evolutionary chain between the emergence of complex life and us, but only a handful with intelligent species.
I find that type of analysis far more likely than the existence of interstellar cops or berserker races forcing everyone to keep their heads down.
Goldilocks Principle. Fair enough. Tell that to algae. That shit grows everywhere it can, and it don’t need no damn Goldilocks to do it. Life isn’t that precious and fragile. It’s tenacious and unrelenting. It’s not a delicate flower you have to nurture, it’s a Terminator robot you can’t stop.
At least, life now is tenacious and unrelenting. It’s possible, though, that some just-barely-alive proto-organism might be much more fragile, and require a very forgiving environment to give it enough time to evolve into something more robust.
We’re not talking about the likelihood of life - we’re talking about conditions so that an ecosystem can exist, thrive, and evolve for billions of years without the conditions around changing enough to wipe it out. That’s a very different thing.
We’re also talking about the likelihood of evolution of a truly intelligent species capable of making radios and spaceships. Again, we have a sample size of one, so we don’t really know how likely that is. We do know that of the billions of species that have existed on the planet, there’s only one evolutionary chain that led to us. If the early hominids had been wiped out, would another intelligent species have taken its place? Or would we have a world today with nothing smarter in it than dolphins and lesser primates?
Uuuum, no. Let me put my “this is friendly face on.” 
Neanderthals evolved too. Please don’t say “only one species made it.” Only one species made it here. Lots of species could have, and still might, “make it.” Humans weren’t the only ones who evolved intelligence.
Where then are the Neanderthals?
Nice strawman–really, really firm and well-packed. But, that’s not what he said. He said only one evolutionary chain led to us; and that’s absolutely correct. We are currently the only technologically-capable species on the planet. Arguing about species which could have made it or might one day make it is irrelevant.
No, but we’re the only ones who made it to a technological civilization. Notice I said if “early hominids” were wiped out, not Homo Sapiens. We don’t know if Neanderthal would have evolved into a technological race. We don’t know what limitations they had that allowed Homo Sapiens to out-compete them. We also don’t really understand the conditions that led to us evolving the way we did - maybe it was a one-in-a billion confluence of factors.
A lot of people make the mistake of thinking that evolution is a progression from simple animals to highly intelligent animals. That we are ‘more evolved’ than others. There’s nothing inevitable about intelligence increasing until you’re flying spaceships. Dolphins don’t seem to be getting smarter. There are still primates around that have been largely unchanged for millions of years. For that matter, if an outside observer was looking at our planet without our biases, he might conclude that the most successful species on the planet is the cockroach. Or maybe the squid - there is a larger mass of squid flesh on the planet than there is human flesh.
Evolution is largely a random walk. Crocodiles have been around for a long, long time. Maybe that random path that leads to flying spaceships is a one-in-trillion possibility, and only then if your planet is already one of of the one-in-a-billion lucky ones that happens to be a good long-term nursery for life.
To me, this is a good reason to fund SETI. Even negative results are good science - for example, SETI’s failure so far means we can discount the notion that most star systems evolve intelligent life, or that the universe is teeming with civilizations beaming around high-powered radio signals. That helps us narrow down some of the unknowns. But until we can find life elsewhere, much of this is guesswork.
Okay, okay! Don’t beat me up. You guys are bigger than me!
All I’m saying is that there is the argument that intelligence is very rare. All I’m saying is it’s not that rare. It happened more than once on earth. Not everything in the universe lead up to humans. It all lead up to Neanderthals too. More than one intelligence, on one planet.
But only one really intelligent chain that felt the need to use technology. We dont’ have intelligent spiders, and intelligent crocodiles, and intelligent fish. Cetaceans are somewhat intelligent, but their intelligence didn’t lead to dolphin spaceships. On the other hand, some lowly that aren’t intelligent at all use tools - trap-door spiders, birds that drop shells on rocks and build complex nests, etc. Some birds appear to be highly intelligent. But they don’t build spaceships.
We’re just starting to understand why we evolved the way we did - to have art, and science, and the kinds of social organization we have. For example, it may be that we were lucky to have an ice age hit at exactly the right time to force us to protect ourselves artificially from the environment, which selected out those smart enough to do so. It may also be that our evolutionary line got whittled down to a very, very small number that happened to have just the right combination of intelligence and willingness to band together in social units, and that changed the species forever. Maybe we evolved the way we did because we were hit with just the right stresses, at just the right times, to direct our evolution down the path that led to where we are today.
And even with our high intelligence, we might not have developed technological cultures if conditions had been different. If there had been fewer of us and the environment was more hospitable, maybe we would have had no need to progress beyond the hunter-gatherer stage, or we would have started evolving in a direction that sacrificed intelligence for stronger jaws and smaller heads. Who knows?
That’s not quite right. Neanderthals didn’t evolve intelligence separately from modern humans, we both inherited it from a common ancestor. This is like saying intelligence evolved 6 billion times on earth because there are 6 billion intelligent humans.
If some species of bird or whale evolved human-like intelligence, that would be a different story.
Though not really, since it’s still the same evolutionary path that led to animal life, which has the distinct advantage of already possessing a nervous system. Of all the variety of life on earth, the brain has still only evolved once. Maybe if some plant evolved intelligence, or some bacteria worked its way up from scratch, that would be more akin to alien intelligence. There’s no reason to believe “animal” or “plant” or anything like those two categories would even evolve anywhere else from a fresh-start abiogenesis event, let alone an animal-like nervous system. All this speculation about ‘intelligence’ seems to be using an extremely anthropomorphic (or even zoomorphic?) definition of the term.
We don’t have to wonder if the Neanderthals would have become a technological race, because we know from the fossil record that they did. They didn’t have radios, true, but they had pretty much the same tools as the H. sapiens that were their contemporaries. And we’re not any more intelligent now than we were in our stone-tools days.
Maybe, if by “brain” you’re referring to the network of nerves you’d find in a jellyfish. But vertibrates and cephalopods both have brains much more complicated than anything their last common ancestor had.
We are the only ones who developed a technology so far. In a few hundred thousand years there may be lots of them. We will kill ourselves off. But dolphins may waddle out onto land and start the process over again. Perhaps octopi or squids will be handier than we think.
I’m quite curious about this. Is it really quite impossible that the bacteria made its way up there somehow from the ground? Thermal drafts or somesuch, perhaps??
You seem to be under the impression that we know just about everything there is to know about physics and that there is just a little clearing up to do and then we have it all.
Physics as far as we’re concerned is mostly guesswork and ignorance,there is just so much that we DONT know about the laws of the universe(s).
Extrapolating future interstellar travel on the science we already have is like someone in the middle ages predicting future world travel on guessed at improvements in the design of sails and their materials,hull shapes etc.without having any idea of Jumbo jets and so on.
Thinking that we know it all now is nothing more then intellectual arrogance/complacency.
Most of my theories have been listed above, but I’ll recap anyway.
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They have been transmitting all along and we just haven’t developed the tech to build a receiver. I’ve got the schematics right here, I’m just waiting for Radio Shack to stock Higgs Bosuns rods in 10’ lengths for the antenna. Or. We have been recieving signals, we just can’t tell the difference between their digitally encoded signals and random noise.
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Light speed is indeed insurmountable and signals just haven’t gotten here or if they have, they’re attenuated to the point of being indetectable at our current level of development. And if FTL is not possible, we’re just another decimal behind the number designating our sun. No reason to come here rather than anywhere else.
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We are under some sort of prime directive isolation. They won’t talk to us until we find them.
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Gleaned from this thread. The span of time where a species is capable and interested in travel is so short on the cosmic scale that we just don’t get there at the same time, or if we do, we’re so far apart that we never encounter each other. The ant colony in Texas will never be aware of the hill in Georgia. Mankind has gazed at the stars for thousands of years, but only put a satellite up 50 years ago. We may get out there and find evidence that a race died out or disappeared ten million years ago. In ten million years it may be found that we have long since gone missing from this galactic coil.
It depends on how high up I suppose. I’m no atmospheric scientist, but I believe that the troposphere doesn’t really mix with anything higher up.
Then why is there, so far as we know after much probing, no life in the Solar System except on Earth?
Okay, the Terminator robot analogy isn’t quite right. Life isn’t that tenacious, but we haven’t much probed the oceans of Europa, for instance. We really haven’t done that much probing, really. What can I say? If there were an Earth II in our solar system, I’d be astonished it didn’t have life on it.