The other "unknown" is under what conditions can intelligent life evolve? Once you know that window, the Drake equation gets even more interesting.
The notion that we are the only intelligent species in the galaxy seems more and more unlikely.
Von Neumann: 1) They arrived too early for us to have a chance of detecting them and they left little trace 2) One or more have arrived recently but they are discrete e.g. no active propulsion, passive sensors, tight beam communication, they only harvest a small amount of material for self-replication etc. 3) We just aren't looking hard enough, space is big and we have limited resources devoted to this pursuit 4) We've observed the activity of a probe but we mistook it for an anomaly or a natural occurrence
Bracewell: 1) Non-self replicating and arrived and left too early 2) Present but not fully autonomous and awaiting confirmation to begin contact (could be a long time waiting depending on distance from home) 3) Present, fully autonomous but we haven't met the criteria to begin contact 4) Present, fully autonomous, has attempted to contact us but we lack the ability to detect and understand their method of communication 5) Present, fully autonomous, has successfully contacted us but whoever was in contact has successfully convinced the probe to not make itself more widely known and has managed to keep their own communication with it a secret (probably the most unlikely scenario but still possible if the probe has protocols for dealing with local geopolitics)
If we're talking about colonization by the alien species itself there are still further explanations for silence:
1) All civilizations capable of reaching us have some equivalent of the "Prime Directive" where they do not forcibly colonize or contact primitive civilizations 2) No civilizations attempt to colonize the entire galaxy, perhaps they all focus on fully utilizing each solar system as they need it, maybe they eventually run out of needs that require expansion. The human population is trending towards replacement level birthrate within the next 100 years, if that is a common trend for all intelligent life then their population may simply stop expanding at some point and after a limited number of systems are colonized they may not have enough population to support further expansion. Maybe birthrates actually trend to 0 and lifespan approaches immortality. 3) Maybe colonizing planets is a dumb idea. Gravity wells are hard to get out of so once your civilization moves to space maybe it just stays in space. We are proposing generation ships as a main method of colonization but if the ship is good enough to live on for generations then why disembark? Why not just continue to live in space habitats and travel the galaxy continuously? Planets are dangerous and unpredictable with uncontrolled weather, volcanism, asteroid impacts, solar flares, etc. If you build a synthetic world you don't need to worry about that. 4) There might be other alternatives, upload to VR, conversion to another form of matter, time travel, alternate universes. These are pretty unlikely but so is the probability that we are the only life to have emerged in such a vast galaxy.
And what would such sings look like? The only conceivable sign that we could observe with our current technology is Dyson spheres. It's however entirely reasonable that intelligent civilizations can advance to quite highly technological levels and not develop Dyson spheres.
If a civilization like ours were to inhabit the nearest star system, Proxima Centauri, and zip happily in rockets from one planet to another (of which there are at least 2 confirmed), and beam radio messages back and forth among themselves, would we be able to tell?
I'll start listening to people telling me about missing signs after we have a unified theory of physics that includes an interpretation of QM, quantum gravity with proper explanations for galactic rotation and inflation among other things.
One I find interesting is that we are like a chick pecking away at our egg shell. As we get closer to being multi-planetary do we get to be more or less warlike? Do we settle on one ruling class and everyone else in bonds, or do we settle on a shared bounty? Do we destroy the world that birthed us, or do we come to grips with our own needs and develop what we need to live in perpetuity on the world we started on?
On a much larger scale it doesn't seem all that much different than the growth of a person from child, to teen, to young adult, and adult. And in those stages of growth the perception of the world and one's place in it changes. Some learn self restraint, others do not, Etc. Even before young people start to drive they get to point where doing stupid things can kill them.
The theory I find interesting is that civilizations are out there watching and the history is that some civilizations "grow up" and survive, and others don't. Some do something stupid in their "teen years" and kill themselves off, some develop a personality that results in them doing something that kills them. Some make it through that and become adults with a reasonable understanding and nominal "acceptance" of the things one has to do to stay alive and be civil.
Maybe when we're "old enough" as a civilization, and we certainly will have enough science to understand that other civilizations could exist and how. They will introduce themselves.
I think that if we were truly the only ones out here that would be the best evidence for God..
I mean, we don’t need to look outside our own planet to find traits of what I consider intelligent behavior in other species.
I have a feeling that if we find an alien species it wont be intelligent, simply because we won’t define it as such. They might even have technology we couldn’t even begin to understand, but at the same time they will probably fail at exhibiting something we consider basic. And worse, they will have no way of being taught.
Aside: I suggest in the future—if you want to avoid pedantic comment like these—that you reword your last sentence to include intelligent life on earth, e.g. “The notion that earth is the only planet to harbor intelligent life...”
In casual conversation however, per Gretchen McCulloch's book "Because Internet"[1], I tend to stick with phrases that are most accessible rather than those that are most precise.
My experience is that being overly precise in my speech can be off-putting to people. Enough so, that when I have encouraged feedback, both positive and negative, on my communication skills it came up more than once as "making you seem like you are showing off how much you know about something and making others feel dumb."
[1] Really a great read, my daughter got it for me for my birthday and I thoroughly enjoyed it.
I wish we could get past this (finding intelligence offensive while finding physical strength appealing) as a species. But until then it's good advice.
It's also a bit of a double bind: if you're not precise enough, someone will be offended by your ambiguity. If you're too precise, someone will be offended by your precision. It limits the rate at which experts can convey knowledge, which can be problematic at work as teams are limited to the pace of whoever is most offended.
If you want to go all mathematical, that's similar to just sticking a checksum on tcp packets and resending vs the lengths that CD-ROMs go to correct errors.
Or to bring another analogy, compare an interactive proof (https://en.wikipedia.org/wiki/Interactive_proof_system) with a more conventional formal proof.
As an aside, people do admire intelligence in real life perhaps more so than physical strength, but a minimum of social acumen goes a long way.
File this under 'know your audience'. On HN (and other nerdy and text-based communication) precision is often much more welcome than in oral communication in real life. Even with the same sort of people.
That said, if we are ever able to establish communication with a species other then our own that evolved elsewhere in the galaxy, intelligence might at that point become an outdated concept.
If we do come across extra-terrestrial life (more likely through our telescopes, rather then by paying a visit) it will be even more alien to us then our mushroom cousins. It will have evolved in a planet vastly different from us, it might communicate in a way we can’t even think of. Our technology will have more in common with the ant colonies then with the alien technology.
If we do come across extra-terrestrial life and are able to marvel at their intelligence, then I think it will have more to do with our ability to understand things out of our scope, rather then some absolute and arbitrary metric of intelligence.
Actually, ants are frequently deemed smart and intelligent. Such suppositions are common.
The question that arises though, when we find more and more examples of intelligent behavior across the tree of of life, is intelligence actually that useful of a concept?
Humans have been roughly at their current biological level of intelligence for at least thousands of years. But our ability to detect aliens has increased dramatically. Similar, a slightly more intelligence alien species that's lagging us by a few million years would have a hard time detecting us anytime.
Or, conceivably dolphins and wales might be more intelligent than us. Or you could conceive of a highly intelligent squid like species on another world. Problem is, if their whole world is an ocean, they are going to have a harder time with metallurgy or electricity.
(It's probably not impossible to build up technology under water, but it's probably harder and requires more cleverness and time. And even if it doesn't, because there's an easy way that humans just don't see; there are probably some circumstances that make it much harder. Eg assume a world that's all ice or desert, so it can only sustain a million people instead of billions.)
― Douglas Adams, The Hitchhiker's Guide to the Galaxy
Pedantic note on "I suggest in the future": you didn't suggest it in the future. If you want to avoid pedantic comments like these, I suggest you assume good faith and stop being an ass, or, take an English class. Also, Earth, in your usage, is capitalized.
Also can people please stop attacking each others english ability, it is a really bad abelist thing to do. We don’t all come from an educated background, we don’t all have english as our native language. Please try to empathize with those of us that have a harder time using english then you.
In a kind of allergic reaction to this sort of thing, there was a movement in SF that aliens would be likely to be so different from us that we would be unlikely to even recognise them as intelligent. Stanislaw Lem's Solaris is a well known example, and the Pandora sequence by Frank Herbert was interesting. I never quite bought it though, and Nemesis by Isaac Asimov seemed to me to be a particularly lazy example that pretty much put me off the whole idea. (I'm a fan of Asimov, but this one didn't work for me).
On the one had we can look at life on earth to see the huge variety of biological forms that are possible even just on our own planet, with fundamentally the same core biology throughout. On the other hand, any life in our universe is going to be constrained by the same basic principles of chemistry, physics and emergent constraints such as thermodynamics, information theory and natural selection. The problem with most of the efforts at 'truly alien' aliens is they emphasise their alien-ness by showing them violate such principles to show how 'we don't know as much as we think we do'.
I don't buy it. Thermodynamics, natural selection, information theory, etc - we know these things. They're real constraints that any life, anywhere must contend with and they constrain what can or can't work within comprehensible limits. I'm not at all saying that genuine alien life can't be surprising, that we won't learn anything new from it. We learn new stuff form like here on earth all the time. I'm just saying we actually know a pretty decent amount about how the universe works at a basic level and this will give us a decent chance at figuring this stuff out.
That's where I am this this now, but it's a complex issue. I really need to watch Arrival though.
Thanks!