We are definitely not alone. The great filter, in my opinion, does not exist. It's only the vastness of space and the relatively short time a civilization produces radio signals that makes it appear this way.
Any civilization that realizes that they are not alone quickly stops bleeding RF signals to outer space, or at least learns to mask them as natural.
Chances that two civilizations, if they detect each other, would be on the same level of development are slim. And once a less technologically advanced civilization meets a more technologically advanced one, game is over soon. Ask Aztecs, or Sioux, or pick any other historical example.
You're anthropomorphizing a hypothetical alien civilization. You can only speculate at what ideologies and motivations drive them, and those drives might (for example) involve maintaining military and technological superiority relative to other civilizations so they can make peaceful contact without risk. Imagine a Borg that seeks out and adapts technology and accumulates knowledge quietly while leaving civilizations to continue developing to a point where they're worth talking to.
There's a long history leading up to those events. I find it unlikely another planet will share it.
There need not be any nefarious intent. Just being around a civilization which is much more advanced is risky: if they operate nearby, they can hit you by mistake or negligence, and whatever consequences are tiny for them may be significant for you. They can just see you as a nuisance and want you to stay sufficiently away, no matter what your opinion is. Think about an anthill near a human settlement. (Don't think about a wasp nest near a human settlement; may be too depressing.)
>> "There are things in the universe billions of years older than either of our races. They are vast, timeless. And if they are aware of us at all, it is as little more than ants…and we have as much chance of communicating with them as an ant has with us. We know. We've tried. And we've learned we can either stay out from underfoot, or be stepped on."
I think my favorite variation on why we seem alone was how Earth exists in a space version of the Bermuda Triangle, called the Veil of Madness, that all spacefaring civilizations avoid: https://creepypasta.fandom.com/wiki/Mankind
We can’t even go as far to assume that an alien species has anything resembling an ideology! even a brief glimpse of an alien intelligence could be completely incomprehensible to us… we could spend a thousand years trying to decipher a single signal and get nowhere.
People get all worked up about dyson spheres and radio signals, but these are so deeply rooted in the human understanding of things in our tiny tiny slice of the universe.
Also even if we got lucky and found AM signal of some alien speech. Would we have any idea how to translate that? My understanding is that we already have human text which we cannot translate. And that has some ties to existing concepts we know of. With truly alien speech we would have zero context or share concepts.
Artificial Intelligence is modeled after human intelligence. It's pretty much useless against a true alien mind, unless we imagine aliens as being human-like with a different shaped body.
The beauty of the film Arrival was showing the challenge of interacting with a truly alien language.
It's obviously true that convergent evolution, that produces similar traits across distantly related species, occurs. So your assertion makes no sense to me.
The masking is just a natural result of technological development. We can pick up recognizable signals only from civilizations that have worked out electromagnetic theory but have not yet developed information theory.
50-100 years is probably par for that particular course. A very narrow timespan in the grand scheme of things.
Even now we've adopted encryption, which appears sufficiently random. How long til all signals are just encrypted by default. Anyone picking up those signals would have a hard time proving they're not noise.
Plus our receivers have gotten more sensitive allowing us to reduce transmit power and a lot of systems use much higher frequencies, which are attenuated more strongly in atmosphere. With another 100-200 years of progress it would probably be pretty hard to pick up a radio signal (that isn't intentionally broadcast) at all from the nearest stars.
Radio signals sent to space unintentionally are waste - so over time you’d expect them to be reduced or eliminated just because you want to use lower power.
Yep, and that's another layer of noise on top of the noise that results from efficient spectrum utilization. Only n00bs transmit carriers or intelligible sidebands.
Even now we've adopted encryption, which appears sufficiently random.
When you pick up an encrypted signal, it's still obvious there's a signal there. Radio telescopes will pick up cell phone signals, for example; that's why there is a radio quiet zone near the Green Bank telescope. You just can't decode the message itself without the encryption keys and algorithm.
As long as it's over the thermal floor within its own bandwidth, yes, it will be obvious that there's still a signal there.
When it comes to interplanetary reception, though, any intelligently-constructed signals will likely be below the noise floor unless deliberately broadcast for our benefit. No coherent carrier or sidebands? No spreading sequence? No chance of detection, whether encrypted or not.
Only if it's strong enough to be obvious there's a signal there to begin with. The idea behind SS is to use more bandwidth than necessary, often much more, so that a much-worse SNR can be tolerated.
Many spread-spectrum applications such as GPS use signals that are well below the thermal noise floor by the time they're received. Those signals generally can't be detected without a known sequence to correlate them against.
We can pick up recognizable signals only from civilizations that have worked out electromagnetic theory but have not yet developed information theory.
Really we are more likely to pick up recognizable signals from civilizations that are intentionally trying to contact us. It's possible we could pick up radio leakage, but the signal would be a lot weaker. So there are orders of magnitude more stars that could be intentionally contacting us, vs accidentally leaking a signal. (At least assuming the ratio of the strength of their intentional vs accidental radio emissions is similar to ours.)
And once a less technologically advanced civilization meets a more technologically advanced one, game is over soon.
That is true historically, but historically we weren't at a distance of light years. Given the vastness of the universe, it seems quite possible that by the time we detect another alien civilization via their emissions in the radio spectrum, that civilization has already gone extinct.
More controversially I would pick India and China's encounters with Europe. I think it's possible to argue that both India and China were substantially more technologically advanced than the Europeans when significant links were established. India had maths and spinning (also probably better guns), China had silk, porcelain, paper, printing and the compass; also bigger better ships.
Europeans reached India around 330 BC, in the form of the armies of Alexander the Great. I won't say that India folded in the result; it's rather the Alexander's makeshift empire folded.
There were several meetings of civilizations of comparable level of advancement and strength on Earth. I posit that in space it's significantly less probable, unless we consider these civilizations to also be sisters, all humanoids coming from a common source, like these of Earth.
It doesn’t seem likely to me that a civilization with the ability to travel interstellar distances would have any use at all for our planet or resources. I mean, the amount of matter in “empty” space between them and us would be enormous. What would they need our little rock for?
Not to mention the impracticality of communicating with your home planet across several light years.
If you’re basing this off of what’s happened in the past on this planet, without a good explanation as to why that would apply to an alien civilization, I’d suggest that you’re not using a good model. Bayesian epistemology is not a good way to decide what’s true, because new knowledge is created which makes the old models not work anymore.
I think that making the signal look natural does not need an intent to hide.
It is simply a result of Shannon's entropy. To be detectable, signals have to be broadcasted and low entropy, the opposite of what we need for efficient communication. A signal that makes best use of its bandwidth would be indistinguishable from noise for someone who doesn't know the protocol, it is also likely to be precisely targeted at the recipient and unwanted emissions kept to a minimum in order to limit interference.
It is already happening on earth as we are replacing loud analog TV emissions with more subtle and better targeted cell phone signals.
Any civilization that cares to travel to you to make contact is very likely expansionist. Or at least may have some plans on the space where you happen to dwell.
It doesn't even have to be likely for it to be a worry.
Imagine there are 1% chances that an encounter with an alien civilization spells the end of humanity.
Or 0.1%, or 0.01%
Now roll that dice for millions and millions of years. It's probably a good idea to switch to communication technologies that don't broadcast your location (and your technological unsophistication). Just in case.
You're assuming the probability for life, or at least intelligent life forming, is a lot greater than the amount of habitable places in the observable universe, such that there would be many civilizations. But we don't know what the probability is. It could be rather low, approaching the number of habitable worlds, such that we're alone or very rare, spread apart by vast distances of space and time.
I'd bet that the types of life that may exist in the universe far outclass our narrow definition of life. I get why we only look for life like ours, and I'm quite sure we're excluding the vast majority of life by narrowing the scope so much.
I'm saying that there are absolutely many more habitable planets around than we believe there to be, even among the planets we've observed. We just don't know what to look for, because we don't know what's possible.
There are multiple problems with the claim that a lack of evidence for intelligent life makes it more likely that it doesn't exist.
First, the further out we look, the less recent our data. Every event we observe that's more than 200 light-years away happened before slavery was abolished in the U.S., and well before Earth's first radio emission.
I'm not saying we shouldn't base conclusions on evidence, but I will say that our ability to gather _current_ data about our surroundings is limited to an infinitesimal fraction of the universe. Worse, it degrades with distance. Bacteria were there, but we couldn't see them for a long time. (They were theorized, though, their existence reasoned out and later proved with evidence)
Second, unlike bacteria intelligent life is...well, you know. Suppose we're the last ones to the interstellar party, or at least not the first. We come in, blasting radio waves like a toddler, BEEP BEEP BEEP BEEP. No signal hygiene whatsoever. Our neighbors on the other hand likely learned a long time ago to hide their presence from all but those they trust, and certainly from those on a lower technological playing field.
If the intelligence we're trying to prove can consciously avoid us finding out about them, then taking absence of evidence as evidence of anything becomes suspect.
Of all the intelligences that could exist - not just those we could detect, mind you - what percentage of those do you think are more advanced than us?
If you asked scientists 30 years ago about some of the extremophile life that we now know to exist, they'd have thought you were insane. They've recently found microbes loving in an asphalt lake in Trinidad. It doesn't have to be an with x% oxygen and x% CO2 and whatever else to support life. It doesn't have to be between -30 and 90 degrees C for things to survive. There's organisms out there that use sulfur compounds for respiration in the way we do oxygen.
So either whatever caused life on Earth was completely unique and couldn't have happened anywhere else, or there's a very good chance there's other life out there. The universe is huge and it's hard for me to believe that earth is the only place where the parameters were met to cause life. From there, it's hard for me to believe that those life forms couldn't adapt to circumstances that are beyond our wildest imagination.
Why is it a fallacy to believe life is elsewhere in the universe? It seems the most likely possibility to me. Of course we have no proof either way - because we've not really looked anywhere (we're not able to, yet), apart from the moon, and a few tens of square metres of Mars (both of which we knew, a priori were barren rocks - but at least they're not too far away). That doesn't make the idea of other life in the universe "wishful thinking", surely?
Why though? Surely you did not do a statistical analysis, because there are too many unknowns:
What is the likelihood of life (as we know it) forming on a given planet? What is the likelihood it will become multicellular? Life on earth was prokaryotic for billions of years and the Cambrian explosion is not yet entirely understood. How likely will it become intelligent? Remember, we don't have any reason to believe that intelligence is in any way a "goal" of evolution. Even if it does, will they have the resources necessary for becoming a technological species? Maybe dolphins are super intelligent, but living in the water and not having opposable thumbs sucks if you want to make tools and perhaps harness the power of fire to build even better tools and machines.
That does not even take into account the various catastrophic events that can happen in the universe where we do not have a good idea of how likely they are. What if a meteor hits at the wrong time? What about gamma ray bursts? What if a Carrington-type event wipes out all electronics? For all we know, these could happen with an average frequency of 100-200 years. Do we have an idea of how likely it is that the climate on a planet stays somewhat stable for a few hundred million years so it doesn't spontaneously become a planet like venus? We just don't have enough data points to assign probabilities there.
Ok, we don't know how likely life is to evolve in the universe. It could range from impossibly hard (though it cant actually be that, because we exist) to easy enough that it has occurred many times. Of all those possibilities, what difficulty range would result in it occurring once (on earth), but never again - despite the billions and billions of planets that exist. A very, very fine tuned difficulty - or to put it another way, the earth would need to be super,super unique, to be the only place capable of life in the entire universe. That strikes me as less likely that it occurring multiple times.
We don't know all forms that life can take. We simply do not know what is possible outside our own tiny realm, and our understanding is limited because of that.
In 1000 years, do you think we won't have discovered forms of life that we would say are impossible today? We've discovered things we thought were impossible just 20 years ago!
Maybe so, but what chance do have of detecting those life forms outside of our solar system? At least for now, a technosignature is our best bet, and as interesting as discovering an extremophile on some moon around a planet circling a brown dwarf would be, finding out we're not alone as a communicating civilization is what people really want to know.
While I can't fathom anything else I still believe it's hubris to believe we understand what forms of life may exist in the universe. Maybe we exist right along something else and will never notice each other.
The Great Filter can be a myriad of things. From how improbable life is to the hostility of the Universe. A magnetar has a hiccup and it sterilizes everything in a fifty light year radius. There are a shit ton of things out there that could eradicate life.
And the closest Neutron star is 200 ly away moving our way, thankfully in a safe distance in some 300.000 years. Had this thing flung in a short distance it could disturb planetary trajectories.
Supernovas can have the same effect as magnetars, as also black holes. There could even be a tiny one lurking in the outskirts of our solar system (the so-called planet 9). What I wanted to point out is that the Universe is a very hostile place. There could have been myriads of civilization that were eradicated because of a cosmic event every now and then.
Black holes do not emit gamma rays... black holes emit nothing (aside from potentially hawking radiation). Matter around supermassive black holes can give off gamma rays but planet massed black holes are just as likely to cause gamma as planets themselves are.
Right now I rather believe in the Great Filter. If you look at e.g. Climate Change and the current war mongering including unprecedented nuclear threats, it's hard to imagine the current technical civilization is long-term survivable. During the next 500 years we will get delayed genetic weapons that can eradicate all of mankind, intelligent killer robots, probably even weapons that can destroy a whole solar system, in combination with exhausting all of Earth's natural resources. I used to be more positive but looking at our own behavior and judging that most intelligent life might evolve from former predators and technology involves heavy resource exploitation, the Great Filter seems quite credible.
It's also worth noting that long-term space survivability seems to be extremely hard to achieve, we haven't even managed to create long-term sustainable fully closed biospheres yet.
One possible solution to the great filter is that we're 'first.' It usually gets dismissed out of hand as both improbable and egotistical (or whatever the whole species level equivalent is). But it's also not impossible, and whatever species was 'first' would always think it improbable that they were first, but there has to be a first (if there are eventually more). Since there are so many unknown unknowns in discussing the great filter or the Drake equation, I'd even argue that being 'first' has as much merit as any other explanation for why we don't see other advanced life out there (even if it's statistically unlikely itself).
Even climate scientists don't argue it'll be extinction level, it'll just be really bad for some regions, great if you live in Siberia and suddenly Canada and Russia have shipping lanes in the arctic and are growing tomatoes. Calm down.
The Great Filter doesn't refer only to extinctions. Anything that makes it highly improbably for a civilization to advance from our current level of technology to significant space colonization would be a Great Filter.
Climate change itself perhaps not. I'd argue there's quite a bit of precedence to believe that the way humans will react to these changes could lead us down that path.
The same as its always been. A handful of people on top of some arbitrary social hierarchy in charge of the lions share of available resources. I believe this type of social organization is in our innate behavior like how insects form colonies and fish school.
The great filter is something with odds around 10^-30 of surviving.
It's hard to find any convincing argument that climate change will destroy our civilization with anything near 1/2 odds. It's a completely different ballpark.
I think it’s a definitional thing: “a great filter” assumes that life is basically everywhere and yet one specific something (or perhaps as many as “a few”) almost always prevents it from taking over a significant fraction of its future light cone.
If there are 10^30 stars in ours, the lower bound on the odds of surpassing it have to be close to that.
Personally I expect there to be many smaller filters rather than a few great filters — 30 things each with a factor of 10 has the same effect, after all.
Personally, abiogenesis by itself looks like something on the 10^-60 to 10^-140 range, so it fully explains everything.
Anyway, there are indeed a few things in our past that look like a 10^-10 odds filter, like each time our genetic encoding changed to increase our codons and the oxygen catastrophe. There are more that look like merely "almost impossible to survive" (I'd guess some ~10^-4 filter) like large asteroid impacts, but not nearly enough to make a difference.
Some will survive but many will die as well. Our modern society has increased the carrying capacity of our planet. As we see climate change disturb food production we will see this carrying capacity fall. If this leads to the collapse of stability in regions the carrying capacity will fall further.
Climate change is a natural fact of our planet, it's been happening since its inception and will continue. Is this current push towards renewables our first forey into terraforming?
Your implicit assumption is that not a single other intelligent species decided to harness the universe by, for example, consuming stars for their raw matter, or building Dyson spheres to black out entire sections of the sky.
It is imo on you to explain why there's a hard cap on the exponential growth of intelligent life that prevents it from EVER reorganizing the universe in its own image. Not 99% of the time — that's not enough for these purposes.
The truth might be than physics are harsh mistress and there is no way to cheat. Thus actually working extra system space colonization is just not something that we or anyone else can do. Maybe even technology to do stellar engineering is out of reach.
This has always seemed like a hopeless star-eyed and wildly impractical idea.
So your robot ship turns up and what happens then?
If it's going to self-replicate it needs to recreate most of the features of an entire industrial civilisation. In our terms that would be metal refinement, chip manufacture, chemical life support and more - all done by bug-free software running on hardware which is perfectly error-free and reliable and lasts indefinitely.
If it's going to seed biological (or equivalent) colonists it needs to be clever enough to find candidate planets with an ideal biosphere and no biological threats. Then it needs to teach the colonists how to survive and colonise.
A lot of SETI and colonisation seems to be based a naive idea that all you have to do is get from A to B and you've solved your expansion problem.
In reality propulsion is just the loading screen. Winning the game is a much harder challenge. So many things that can break, fail, be destroyed by chance, or go wrong because of design flaws that it's an insanely difficult problem without very much more advanced tech.
It all depends on the goals behind leaving ones star system. If the goal is biological colonization, sending genetic material (or even better a gene database) across large spans of distance and time is far more practical than a generation ship or suspended animation. If the goal is to let your sentient machines explore then you don't even have to be burdened with recreating biological life.
To establish supply lines. If Alpha Centauri has something of value you could send out a self replicating robotic AI entity. It establishes its footing then start sending deliveries to Earth. If each one way trip takes 50 years, after say 120 years you could have a steady supply of resources.
Would Alpha Centauri have resources we lack in our solar system? Mars, Venus, The asteroid belt, various moons and gas giants should be ample for anything we need.
We have no evidence that we will ever be able to build sufficiently adaptable systems to engage with unfamiliar environments without constant direct human intervention, which is not possible at light-year (or even light-second) ranges.
You can only get so much power before something vaporizes. Some sort of ship emitting enough power to be detected at a non-trivial distance from Earth (see inverse square law) would vaporize itself.
Just because stealth in space doesn't work doesn't automatically mean you can see everything in space at all times. We need to build giant telescopes to see stars thanks to the inverse square law. The bigger our telescopes with better light collection the narrower their field of view. An antimatter spaceship could fly past Pluto tomorrow and we could easily miss it since we can't monitor all 4πr^2 of the sky at once with powerful telescopes.
> Some sort of ship emitting enough power to be detected at a non-trivial distance from Earth (see inverse square law) would vaporize itself.
Then you can say goodbye to those robotic spaceships. Note that I'm not claiming that they're possible -- I'm just saying that if they do exist, they're very detectable.
> An antimatter spaceship could fly past Pluto tomorrow and we could easily miss it
We can detect Voyager from way past Pluto, even though it emits only several dozen watts. I'm not sure how you'd miss an antimatter-powered spaceship at a comparable distance.
The concept of the Great Filter is a shallow view on evolution.
Humans are likely at the end of our biological evolution. The next steps of human artificial evolution will accelerate which means extra terrestrial intelligence is unrecognizable to us currently.
We look for modern human-like civilizations, and those obviously won't exist much.
Chances that two civilizations, if they detect each other, would be on the same level of development are slim. And once a less technologically advanced civilization meets a more technologically advanced one, game is over soon. Ask Aztecs, or Sioux, or pick any other historical example.