This is one of the topics that I find the most fascinating, and if I die before we learn more about life in the Universe other than on Earth, I will probably be very sad that my life span did not coincide with its discovery.
There's an entire body of knowledge that we cannot chart yet because we have no data to formulate it from. It seems likely and intuitive that if there are life forms on planets other than Earth, they are subject to evolution; but we cannot hypothesize much further than that.
Under what conditions does sentient meta-cognizant life evolve? How does it develop culture, religion, mathematics, art, philosophy, language? (has the Church-Turing thesis been formulated identically somewhere else than on Earth?) Which of those are constants amongst such species, and for the ones who aren't, what leads to their creation? How intertwined are they to biology? (e.g., death and religion) How frequently does the notion of "gender" happen in complex living structures? Do principles of cultural development such as the ones presented in "Guns, germs and steel" hold for non-Earth civilizations?
And if we find advanced sentient life that is much older than we are, that will be even more interesting. Are there events that this civilization went through/constructs that it built that are similar to ours? (various notions of democracy/freedom/government; mechanical transportation, "computers", electricity, digital communications, artificially expanding life (i.e. healthcare), etc.)
"Xenopology" is going to be one fascinating subject[1]. And on a related note, if any one is aware of serious academic work in that field (it seems pretty much impossible right now, because we just don't have the data; but you never know), I'd love to hear recommendations :)
[1] With fascinating consequences when it arises, too. We'll have to rewrite a lot of the more "meta" Wikipedia articles, for starters (Wikipedia is terribly anthropo-centered). And then, what will happen with our body of knowledge? We will merge human mathematics with xenomathematics? (if it's even possible) If they have a communications construct comparable to the internet, do we keep the two separate? Do we want them to be able to communicate at all on an individual level, much like any human on Earth can email any other human on Earth freely right now? Those are all of course very hypothetic considerations, but they're probable and fascinating to think about.
Under what conditions does sentient meta-cognizant life evolve? How does it develop culture, religion, mathematics, art, philosophy, language? (has the Church-Turing thesis been formulated identically somewhere else than on Earth?) Which of those are constants amongst such species, and for the ones who aren't, what leads to their creation? How intertwined are they to biology? (e.g., death and religion) How frequently does the notion of "gender" happen in complex living structures? Do principles of cultural development such as the ones presented in "Guns, germs and steel" hold for non-Earth civilizations?
It could well be that all advanced civilizations decide that it's easier to answer these questions with simulations than observation. More interestingly if that is true and you also believe the odds of a singularity in our future is high, then the odds of us being in a simulation now are quite high.
It is fascinating. Imagine if we did detect a radio signal from intelligent life elsewhere. What sort of reply would we send them? I imagine it would be every sort of reply imaginable, as everybody with access to a radio telescope gave it their best shot. I expect a lot of new radio telescopes would be constructed also.
If we don't receive any such signals, then finding life elsewhere is going to be a long, hard slog. It seems we don't yet have the energy/technology levels required to get a probe to another star within a reasonable amount of time (100 years travel time, would perhaps be reasonable? Could any of our equipment last that long?) Self-replicating space probes that could exponentially explore the entire galaxy seem to be right out of the question, at present.
> Do principles of cultural development such as the ones presented in "Guns, germs and steel" hold for non-Earth civilizations?
I find this particularly fascinating, because it could lead to a corollary to the Drake equation. This equation would quantify the (possibly insurmountable) barriers that a species must overcome to become a space-faring civilization: strength of the planet's gravity well, ease of access to and total planetary quantity of rare elements required to build space hardware, etc.
Basically, Guns, Germs, and Steel -- but on a planetary scale.
It seems the most likely would be that most planets are inhabited by life forms that aren't intelligent.
Out of 13Bn years, humans in any form have been around 1M years. Civilized societies only a few thousand.
We'd find many more planets with Dinosaurs on them (they lasted 200M years)....
The thought that 1 out of 7 suns has earth-like planets is still amazing though. Wouldn't it be rather likely that an advanced intelligence is watching us at that point?
It fascinates me to think about what this will mean to science fiction. There's obviously lots of sci fi that assumes lots of planets out there, but just like actually going to the moon means sci fi depictions of the moon "had to" align with what they actually found and it altered depictions of space ships and suits (and caused endless crappy attempts at trying to capture "low gravity"), it will increasingly "have" to deal with actual facts about what's out there.
One idea that fascinates me is the possibility of two planets in the same solar system evolving intelligent/technological life. How amazing would it have been to have been one of the first astronomers on such a planet, and see macro-structures like large cities on another planet.
Like many here I find the subject of finding life on other planets fascinating and consider it inevitable. What's interesting is that the estimate of planet incidence is seemingly much higher than originally postulated by the Drake Equation [1].
A factor in the development of life, especially sentient life, is metallicity [2]. Almost all of the first 100 elements naturally occur on Earth. This is pretty amazing. Nuclear fusion in stars naturally produces elements up to iron [3]. S-capture is thought to produce elements up to Bismuth (atomic number 83). Elements higher than this are thought to be produced only in supernovae or other cataclysmic events.
It's amazing to think that enough time has gone by in the Universe to take the abundant hydrogen and helium, form stars, have those stars run out of fuel and enough of them explode to scatter their elements to form heavy planets around later stars.
While heavy elements may not be required for life it seems less likely that starfaring sentience can form without them. Semiconductors for example require an odd mix of heavy elements.
It seems amazing that even we exist given that you need metals, a long-lived and stable star, likely billions of years of evolution, a sufficiently stable (and probably geologically active) planet with an atmosphere that has water in liquid form (a pretty narrow temperature band even taking into account different atmospheric pressures) and no cataclysmic events to happen in all that time (it seems to have been ~65 million years since the last big one).
It may just be that sentient life is fleeting. We've had "civilization" for X0,000 years, which is the blink of an eye. It's entirely possible we'll wipe ourselves out due to war or simply lack of (sufficiently cheap) resources in another blink. The problem isn't lack of resources. They are plentiful in space. The problem is the cost of getting them if energy is anything other than free.
Additionally interstellar distances seem almost unconquerably large that one has to wonder if we'll ever meet another sentient life form face to face (assuming they have faces).
Even if we do, one wonder what evolved elsewhere for facilitate communication. Will they see? Will the wavelengths of light they see cross over ours at all? These are questions we can only really speculate about.
It's also been suggested (by Hawking among others) that we really don't want to meet a much more advanced species as it will probably be bad for us, perhaps even an Outside Context Problem [4] and it seems unlikely given the rate of change we're experiencing that another civilization will be at the same point as us.
We could of course be "first". I mean someone has to be right? It does seem unlikely however. But I suspect there were many "firsts" (in the sense that they evolved independently and without any contact or evidence of other species).
The seeming lack of self-replicating robots, something we'll almost certainly be able to build and start filling the galaxy with within a thousand years I'm sure, is also somewhat puzzling.
Personally I just hope we find evidence of extraterrestial life sometime soon as it will settle [5] a whole bunch of issues about us being "special" (in the typically religious sense).
"What's interesting is that the estimate of planet incidence is seemingly much higher than originally postulated by the Drake Equation."
I always assumed that the estimates there were purposefully low to show "Hey, even with all these low estimates, we should still find something, right?"
If planets are abundant, that puts the kibosh on the "rare Earth" theory, as shaky as that was to begin with. The other explanations are less optimistic: Maybe they all nuke themselves or turn to grey goo before they can muster the technology and energy to build a starship. Or they are roasted by random blasts of radiation before they become space-faring.
It's either something universal about civilizations, or something is wrong with the Drake equation or the underlying cosmology.
A) The universe is very large. The nearest star is 4 and some change lightyears (ly) away. That means any message take over 8 years to get, process, and transmit to the nearest star. All other stars are further than that. Since we have been weakly radio broadcasting for about 100 years, the number of stars we have been able to speak with is at best 1600 (http://wiki.answers.com/Q/How_many_stars_within_50_light_yea...).
B)Messages get lost in noise. We assume that we are heard out in the universe. But it is very very difficult to hear a mosquito at a rock concert 100 miles from you. The reverse is true for us. Also, you have to know to look. The concert has been going on for 100 years but the venue, so to speak, is 4 billion years old. Also, you might be on the other side of the galaxy, or in another one entirely.
C)Messages aren't understood as such. Do you know the protocol for USB to serial conversion? (If so I have many questions for you) We may think an actual message is just noise. Or, that noise is a message. We cannot possibly tell. Yes hopefully the other side will start out easy on us but define 'easy' to an alien.
D)Lets assume that they have spotted us and are pre-sending signals. In what medium? We haven't even figured out the basic laws of the universe yet. Heck Dark matter is ~25% of the mass-energy of the universe. The other ~75% is some crazy stuff we just labeled Dark Energy. We have no clue what is going on there. They may already be blasting us with data, but we just haven't got the interstellar radio invented yet.
E) They simply don't give a shit. What do we have that they want? Lets assume they are about 10,000 years older in tech than we are. Geologically speaking, thats nada, thats the last ice age. People were around then. And look now we have radios and iPads and ISS's and stuff. 10,000 years is a lot of time to think and make stuff. What could we do in that much more time? Well, make a computer that'll calculate just about anything, probably. And if your civilization is all entertained, why bother looking at the stars? Why bother with a,likely, giant telescope array that beams out gibberish for a thousand years. What stuff on Earth over 1000 years old? Not all that much but piles of rocks and some windows. The engineering of a giant thingy is very hard. And all for what? Some algae that you hope turns into a little curious squid or something?
F) They dont give a shit. Not because they are hedonistic but because they live under an ice-sheet the planet wide. Or they are at the bottom of a giant cloud where pressure is just right. Or they are frozen periodically in ammonia ice for 700 years. Or they have no idea of math and science because they don't have nerves that work like that. Or because they don't have cells at all. Or because they have no photoreceptors and can't even begin to imagine light. Or because they think that thing we call matter is just a rounding error. Or because they already migrated into dark energy beings and are just waiting to see us.
It seems many people here make the implicit assumption that once there's life, there will be a technological civilization.
We do know that microbial life did appear quite soon after the formation of the Earth, so we have some evidence that life can bootstrap itself readily given a favorable environment. However, we also know that life then spent the next three billion years quite content at being unicellular, until the Cambrian Explosion made lots of things happen very quickly (at least on the astronomical timescale). We don't really have much ideas about why the CE happened, and how inevitable it was to happen at some point at least by sheer probability. I believe the shift from unicellular to multicellular life was the most fine-toothed of the Great Filters we've already passed - let us hope there won't be even stricter ones in our future. Given the number of ways it appears a technological civilization could snuff itself out of existence in an eyeblink, I'm not very optimistic.
It's been a decade since I read the book but IIRC very little of it had to do with whether lots of planets exist. In fact they assume microbial life is abundant but argue against complex multi-cellular life being very common.
It's a fascinating book ("Rare Earth") but even without their arguments, I'm curious: why would one assume that planets equal civilizations?
Or we've been going at this for way too short a time to be able to draw definite conclusions.
There are hundreds of plausible reasons why, if there is life outside, we haven't been contacted.
Maybe they know about us but we're not interesting, maybe they don't know about us, maybe they tried to contact us but we haven't been able to detect them, maybe we just don't have the right technology, or we're not looking in the right place, maybe we're all limited by these pesky laws of physics and there is no chance that we could ever meet or even know about each other, maybe they are not looking in the right place and missed us, maybe they are not yet aware of our existence since we've been emitting radio for such a short time, etc
Maybe for the same reason we're not "calling" that much anymore? For the last several decades we've been investing tons of money and engineer-hours to make radio waves stop going up, as we mostly need them on the ground, and we don't have cable or cellular subscribers in space.
They probably have, or are trying to. But even if they want to, a start system say 2000 light years away looking at us is seeing the world as it was during the time of Jesus. And we are looking at them when they were equally ancient.
And not to mention, if they tried to communicate with us we won't know until the next 2000 years. Basically you get the point. For a civilization to communicate to us, they should've started the process of sending signals out x years, based on for x light years far they are.
And that's just the first problem. The universe is so big, each galaxy has billions of stars and there are some billions of galaxies in the universe. Given the vastness and size of universe, its next to impossible to search such a large space with already existing limitations of distance and time.
Thirdly, we've hardly been listening for a few decades, we might have missed a signal if it was ever sent out or haven't received one.
Let's say someone was beaming a very strong signal at us, would we have detected it by now with all our SETI programs? Nope, not very likely we would have. We've only scratched a tiny bit of the search space with SETI, spatially and in wavelength.
Similarly, what if an Earth-twin existed in a stellar system within 20 light-years of us, would we have detected it by now? Again, also no. It would take rather a lot of luck for us to have detected it by now, our methods of detecting planets are very limited. It will likely take many more decades before we can confidently have a nearly complete survey of exoplanets near Earth, let alone at greater distances.
As far as the Fermi paradox, I never bought it as a paradox. All it says is that we probably don't understand the nature of space-faring technological civilizations, which we clearly don't, nothing more.
[+] [-] GuiA|12 years ago|reply
There's an entire body of knowledge that we cannot chart yet because we have no data to formulate it from. It seems likely and intuitive that if there are life forms on planets other than Earth, they are subject to evolution; but we cannot hypothesize much further than that.
Under what conditions does sentient meta-cognizant life evolve? How does it develop culture, religion, mathematics, art, philosophy, language? (has the Church-Turing thesis been formulated identically somewhere else than on Earth?) Which of those are constants amongst such species, and for the ones who aren't, what leads to their creation? How intertwined are they to biology? (e.g., death and religion) How frequently does the notion of "gender" happen in complex living structures? Do principles of cultural development such as the ones presented in "Guns, germs and steel" hold for non-Earth civilizations?
And if we find advanced sentient life that is much older than we are, that will be even more interesting. Are there events that this civilization went through/constructs that it built that are similar to ours? (various notions of democracy/freedom/government; mechanical transportation, "computers", electricity, digital communications, artificially expanding life (i.e. healthcare), etc.)
"Xenopology" is going to be one fascinating subject[1]. And on a related note, if any one is aware of serious academic work in that field (it seems pretty much impossible right now, because we just don't have the data; but you never know), I'd love to hear recommendations :)
[1] With fascinating consequences when it arises, too. We'll have to rewrite a lot of the more "meta" Wikipedia articles, for starters (Wikipedia is terribly anthropo-centered). And then, what will happen with our body of knowledge? We will merge human mathematics with xenomathematics? (if it's even possible) If they have a communications construct comparable to the internet, do we keep the two separate? Do we want them to be able to communicate at all on an individual level, much like any human on Earth can email any other human on Earth freely right now? Those are all of course very hypothetic considerations, but they're probable and fascinating to think about.
[+] [-] Steko|12 years ago|reply
It could well be that all advanced civilizations decide that it's easier to answer these questions with simulations than observation. More interestingly if that is true and you also believe the odds of a singularity in our future is high, then the odds of us being in a simulation now are quite high.
[+] [-] incompatible|12 years ago|reply
If we don't receive any such signals, then finding life elsewhere is going to be a long, hard slog. It seems we don't yet have the energy/technology levels required to get a probe to another star within a reasonable amount of time (100 years travel time, would perhaps be reasonable? Could any of our equipment last that long?) Self-replicating space probes that could exponentially explore the entire galaxy seem to be right out of the question, at present.
[+] [-] Wingman4l7|12 years ago|reply
I find this particularly fascinating, because it could lead to a corollary to the Drake equation. This equation would quantify the (possibly insurmountable) barriers that a species must overcome to become a space-faring civilization: strength of the planet's gravity well, ease of access to and total planetary quantity of rare elements required to build space hardware, etc.
Basically, Guns, Germs, and Steel -- but on a planetary scale.
[+] [-] nikster|12 years ago|reply
The thought that 1 out of 7 suns has earth-like planets is still amazing though. Wouldn't it be rather likely that an advanced intelligence is watching us at that point?
[+] [-] vidarh|12 years ago|reply
[+] [-] marcosscriven|12 years ago|reply
[+] [-] wikiburner|12 years ago|reply
[+] [-] dkural|12 years ago|reply
[+] [-] Zikes|12 years ago|reply
[+] [-] Wingman4l7|12 years ago|reply
[+] [-] baddox|12 years ago|reply
[+] [-] cletus|12 years ago|reply
A factor in the development of life, especially sentient life, is metallicity [2]. Almost all of the first 100 elements naturally occur on Earth. This is pretty amazing. Nuclear fusion in stars naturally produces elements up to iron [3]. S-capture is thought to produce elements up to Bismuth (atomic number 83). Elements higher than this are thought to be produced only in supernovae or other cataclysmic events.
It's amazing to think that enough time has gone by in the Universe to take the abundant hydrogen and helium, form stars, have those stars run out of fuel and enough of them explode to scatter their elements to form heavy planets around later stars.
While heavy elements may not be required for life it seems less likely that starfaring sentience can form without them. Semiconductors for example require an odd mix of heavy elements.
It seems amazing that even we exist given that you need metals, a long-lived and stable star, likely billions of years of evolution, a sufficiently stable (and probably geologically active) planet with an atmosphere that has water in liquid form (a pretty narrow temperature band even taking into account different atmospheric pressures) and no cataclysmic events to happen in all that time (it seems to have been ~65 million years since the last big one).
It may just be that sentient life is fleeting. We've had "civilization" for X0,000 years, which is the blink of an eye. It's entirely possible we'll wipe ourselves out due to war or simply lack of (sufficiently cheap) resources in another blink. The problem isn't lack of resources. They are plentiful in space. The problem is the cost of getting them if energy is anything other than free.
Additionally interstellar distances seem almost unconquerably large that one has to wonder if we'll ever meet another sentient life form face to face (assuming they have faces).
Even if we do, one wonder what evolved elsewhere for facilitate communication. Will they see? Will the wavelengths of light they see cross over ours at all? These are questions we can only really speculate about.
It's also been suggested (by Hawking among others) that we really don't want to meet a much more advanced species as it will probably be bad for us, perhaps even an Outside Context Problem [4] and it seems unlikely given the rate of change we're experiencing that another civilization will be at the same point as us.
We could of course be "first". I mean someone has to be right? It does seem unlikely however. But I suspect there were many "firsts" (in the sense that they evolved independently and without any contact or evidence of other species).
The seeming lack of self-replicating robots, something we'll almost certainly be able to build and start filling the galaxy with within a thousand years I'm sure, is also somewhat puzzling.
Personally I just hope we find evidence of extraterrestial life sometime soon as it will settle [5] a whole bunch of issues about us being "special" (in the typically religious sense).
[1]: http://en.wikipedia.org/wiki/Drake_equation
[2]: https://en.wikipedia.org/wiki/Metallicity
[3]: http://hyperphysics.phy-astr.gsu.edu/hbase/astro/nucsyn.html...
[4]: http://en.wikipedia.org/wiki/Excession#Outside_Context_Probl...
[5]: http://xkcd.com/1235/
[+] [-] prawn|12 years ago|reply
I always assumed that the estimates there were purposefully low to show "Hey, even with all these low estimates, we should still find something, right?"
[+] [-] RickyShaww|12 years ago|reply
[+] [-] vidarh|12 years ago|reply
[+] [-] grannyg00se|12 years ago|reply
"In other words, roughly 15 percent of all suns could, in principle, be hosting a place suitable for life as we know it. "
[+] [-] Zigurd|12 years ago|reply
If planets are abundant, that puts the kibosh on the "rare Earth" theory, as shaky as that was to begin with. The other explanations are less optimistic: Maybe they all nuke themselves or turn to grey goo before they can muster the technology and energy to build a starship. Or they are roasted by random blasts of radiation before they become space-faring.
It's either something universal about civilizations, or something is wrong with the Drake equation or the underlying cosmology.
[+] [-] Balgair|12 years ago|reply
A) The universe is very large. The nearest star is 4 and some change lightyears (ly) away. That means any message take over 8 years to get, process, and transmit to the nearest star. All other stars are further than that. Since we have been weakly radio broadcasting for about 100 years, the number of stars we have been able to speak with is at best 1600 (http://wiki.answers.com/Q/How_many_stars_within_50_light_yea...).
B)Messages get lost in noise. We assume that we are heard out in the universe. But it is very very difficult to hear a mosquito at a rock concert 100 miles from you. The reverse is true for us. Also, you have to know to look. The concert has been going on for 100 years but the venue, so to speak, is 4 billion years old. Also, you might be on the other side of the galaxy, or in another one entirely.
C)Messages aren't understood as such. Do you know the protocol for USB to serial conversion? (If so I have many questions for you) We may think an actual message is just noise. Or, that noise is a message. We cannot possibly tell. Yes hopefully the other side will start out easy on us but define 'easy' to an alien.
D)Lets assume that they have spotted us and are pre-sending signals. In what medium? We haven't even figured out the basic laws of the universe yet. Heck Dark matter is ~25% of the mass-energy of the universe. The other ~75% is some crazy stuff we just labeled Dark Energy. We have no clue what is going on there. They may already be blasting us with data, but we just haven't got the interstellar radio invented yet.
E) They simply don't give a shit. What do we have that they want? Lets assume they are about 10,000 years older in tech than we are. Geologically speaking, thats nada, thats the last ice age. People were around then. And look now we have radios and iPads and ISS's and stuff. 10,000 years is a lot of time to think and make stuff. What could we do in that much more time? Well, make a computer that'll calculate just about anything, probably. And if your civilization is all entertained, why bother looking at the stars? Why bother with a,likely, giant telescope array that beams out gibberish for a thousand years. What stuff on Earth over 1000 years old? Not all that much but piles of rocks and some windows. The engineering of a giant thingy is very hard. And all for what? Some algae that you hope turns into a little curious squid or something?
F) They dont give a shit. Not because they are hedonistic but because they live under an ice-sheet the planet wide. Or they are at the bottom of a giant cloud where pressure is just right. Or they are frozen periodically in ammonia ice for 700 years. Or they have no idea of math and science because they don't have nerves that work like that. Or because they don't have cells at all. Or because they have no photoreceptors and can't even begin to imagine light. Or because they think that thing we call matter is just a rounding error. Or because they already migrated into dark energy beings and are just waiting to see us.
G) We are just plain jane alone.
[+] [-] Sharlin|12 years ago|reply
We do know that microbial life did appear quite soon after the formation of the Earth, so we have some evidence that life can bootstrap itself readily given a favorable environment. However, we also know that life then spent the next three billion years quite content at being unicellular, until the Cambrian Explosion made lots of things happen very quickly (at least on the astronomical timescale). We don't really have much ideas about why the CE happened, and how inevitable it was to happen at some point at least by sheer probability. I believe the shift from unicellular to multicellular life was the most fine-toothed of the Great Filters we've already passed - let us hope there won't be even stricter ones in our future. Given the number of ways it appears a technological civilization could snuff itself out of existence in an eyeblink, I'm not very optimistic.
[+] [-] GrantS|12 years ago|reply
It's been a decade since I read the book but IIRC very little of it had to do with whether lots of planets exist. In fact they assume microbial life is abundant but argue against complex multi-cellular life being very common.
It's a fascinating book ("Rare Earth") but even without their arguments, I'm curious: why would one assume that planets equal civilizations?
[+] [-] jussij|12 years ago|reply
Here's how far our out going call has gone:
http://zidbits.com/wp-content/uploads/2011/07/how-far-in-spa...
[+] [-] Renaud|12 years ago|reply
There are hundreds of plausible reasons why, if there is life outside, we haven't been contacted. Maybe they know about us but we're not interesting, maybe they don't know about us, maybe they tried to contact us but we haven't been able to detect them, maybe we just don't have the right technology, or we're not looking in the right place, maybe we're all limited by these pesky laws of physics and there is no chance that we could ever meet or even know about each other, maybe they are not looking in the right place and missed us, maybe they are not yet aware of our existence since we've been emitting radio for such a short time, etc
[+] [-] TeMPOraL|12 years ago|reply
Maybe for the same reason we're not "calling" that much anymore? For the last several decades we've been investing tons of money and engineer-hours to make radio waves stop going up, as we mostly need them on the ground, and we don't have cable or cellular subscribers in space.
[+] [-] spc476|12 years ago|reply
[+] [-] kamaal|12 years ago|reply
They probably have, or are trying to. But even if they want to, a start system say 2000 light years away looking at us is seeing the world as it was during the time of Jesus. And we are looking at them when they were equally ancient.
And not to mention, if they tried to communicate with us we won't know until the next 2000 years. Basically you get the point. For a civilization to communicate to us, they should've started the process of sending signals out x years, based on for x light years far they are.
And that's just the first problem. The universe is so big, each galaxy has billions of stars and there are some billions of galaxies in the universe. Given the vastness and size of universe, its next to impossible to search such a large space with already existing limitations of distance and time.
Thirdly, we've hardly been listening for a few decades, we might have missed a signal if it was ever sent out or haven't received one.
[+] [-] InclinedPlane|12 years ago|reply
Let's say someone was beaming a very strong signal at us, would we have detected it by now with all our SETI programs? Nope, not very likely we would have. We've only scratched a tiny bit of the search space with SETI, spatially and in wavelength.
Similarly, what if an Earth-twin existed in a stellar system within 20 light-years of us, would we have detected it by now? Again, also no. It would take rather a lot of luck for us to have detected it by now, our methods of detecting planets are very limited. It will likely take many more decades before we can confidently have a nearly complete survey of exoplanets near Earth, let alone at greater distances.
As far as the Fermi paradox, I never bought it as a paradox. All it says is that we probably don't understand the nature of space-faring technological civilizations, which we clearly don't, nothing more.