For those less familiar with this term, this paradox is the apparent contradiction between our expectation of intelligent life throughout our universe and the lack of communication or contact from said intelligent life. That is, if we are not the only intelligent life in the universe, then why haven’t we received distinguishable radio signals from these other intelligent beings? In addressing this question, most of the ideas I will be discussing in this post are well-known to those familiar with the topic, but I hope this post will encourage the onset of new ideas from those that haven’t given the topic as much consideration.
Expectation of Extra-Terrestrial Intelligence
Many scientists estimate that our solar system may be but one of many billions in the galaxy, let alone the entire observable universe, let alone the entire unobservable universe. The estimated number of stars in the observable universe is around 300 sextillion (3 × 1023) which as you may notice is on the same order as Avogadro’s number. So with all of those solar systems out there, it seems reasonable that a fraction of them may be suitable for supporting life. The number of civilizations capable of communicating with us can be calculated by what is known as the Drake equation. While we don’t know which numbers to plug in to this equation, it at least gives us a mathematical view of the variables involved to accomplish such a calculation.
Another factor to look at is the age of our Sun relative to other stars in the universe. The Sun is relatively young as it was formed a mere 4.6 billion years ago whereas most stars are between 1 and 10 billion years old clocking the average star at around 5.5 billion years old. Either way, we can see that there are presumably a lot of stars out there that are older than the sun and this means that in many cases, intelligent life could have more time to evolve (and potentially much more time than we’ve had on Earth). So this means that not only are there a large number of solar systems, but many of them are likely to be a billion or more years older than our own. If any of those solar systems have supported intelligent life with radio technology, then we may expect to detect some radio signals which have already been traveling toward us for a billion or more years. This would mean that if a radio transmission had enough energy behind it (enormous amounts of energy at that), it may have already traveled billions of light-years in which case we could detect those signals now — even if they are detected long after the originators have become extinct. It would support the idea of intelligent life existing (or having once existed) elsewhere.
These reasons basically summarize our expectations for receiving communication from extra-terrestrial intelligent life. Next, I will discuss several factors compatible with two ideas: intelligent life existing elsewhere in the universe, and the lack of evidence for receiving any communication from said intelligent life. In other words, I will discuss several ways to resolve the Fermi paradox.
Resolving the Paradox
It seems to me that the paradox can be resolved by examining a number of factors including: the statistically small concentration of intelligent life in the universe, self-destruction by technologically-advanced species, the assumption of extra-terrestrial intelligent life behaving in certain ways based on anthropocentric views (including the assumption of extra-terrestrial life desiring contact with outsiders), human’s relatively short time span with post-radio technology, problems with radio signal propagation, the Hubble constant, and other various reasons.
Small Concentration of Intelligent life in the Universe
Life requires a very narrow range of conditions, and so we’d only expect it to exist if there was a planet at the appropriate distance from a star, and for that planet to contain the correct elemental starting materials (e.g. carbon, hydrogen, oxygen, nitrogen, phosphorous, etc.). If these conditions are within some range of acceptability, Brownian motion, favorable chemical bonds, and an input of energy from a neighboring star could lead to amino acids, proto-cells, DNA, etc. Basically, we need particular planetary conditions necessary for abiogenesis (whatever that range of conditions may be). What this means is that we have at least two variables with opposite effects on the outcome: a large number of prospective solar systems, and a narrow range of conditions suitable for life. Thus, one would expect that there are a large number of solar systems that are inhabited by life, but this would constitute a tiny percentage relative to the entire population of solar systems.
On top of this, the conditions needed to support intelligent life are even scarcer, especially after we consider that out of the 3.7 billion years of life on this planet, only in the last several thousand years have we had a form of life capable of developing advanced technology (namely radio technology). Several factors contributed to intelligent life evolving from simple living systems in order to produce advanced technology. Among them are: a habitable terrestrial environment, a moon with consequential tidal forces that catalyzed ocean-life’s migration onto land, writing systems & language, opposable thumbs, etc. If we lacked any of these factors, it’s easy to see how the evolution of intelligent life capable of manipulating its environment in order to develop advanced technologies would be extremely unlikely.
So it is difficult to say how likely it is to have conditions suitable for life, let alone intelligent life. However, I think it is safe to say that the concentration of intelligent life would be rather small, that is, out of the minute concentration of life-supporting solar systems, we’d have an even smaller concentration of intelligent life-supporting solar systems. In the next section, I’ll discuss why this minute concentration of intelligent life is also compounded with a limited window of time for the species potentially able to send radio communication (due to the eventual extinction of these intelligent species).
Self-Destruction by Technologically-Advanced Species
If there are indeed many regions in the universe that are presently supporting or have previously supported life, then we must ask ourselves another question: How long do we expect those species to thrive before they self-destruct? In other words, if all or most technologically-advanced species inevitably get to a certain point in their evolution whereby they either exhaust all of their resources, succumb to nuclear or biological warfare, lose ecological sustainability (some may call this a Malthusian check/catastrophe), etc. — is it very likely that they will be in existence long enough to design and transmit interstellar radio communication? Or to ask another follow-up question, if those species are alive long enough to design and transmit interstellar radio communication, how long do they have before they become extinct and their radio communication comes to a screeching halt? The reason why this is important is because intelligent life able to communicate with us in theory may only have a relatively small window of time before the species becomes extinct. If this happens after just a few hundred or a few thousand years of developing radio technology, then any radio transmission heading our way would only last for this same time duration. If we are not in existence to receive it (whether it reached Earth before we evolved into intelligent beings or if it reaches us after we’ve become extinct) then we would have no record of it, even if radio transmission has occurred or will occur one day when we are long gone. In other words, not only are extra-terrestrials with radio technology a necessary prerequisite for receiving a signal on Earth, but we also have to be alive and able to receive it during a particular relatively narrow window of time. If the average star is older than ours, than only those solar systems at the appropriate distance would have a window of radio communication capable of reaching us.
Time Span of Radio Technology
In 1879, David Edward Hughes discovered that sparks would generate a radio signal, thus leading to the spark-gap transmitter. Shortly thereafter in 1888, Heinrich Hertz, utilizing a more rigorous scientific approach than Hughes, was the first person to prove and demonstrate that radio waves could be transmitted (and detected) through free space. This paved a large path for Marconi, and after conducting various experiments in the 1890’s, he finally produced a technically and commercially viable form of radio technology.
So we can see that radio technology ultimately surfaced in the last 150 years. Human civilization as we define it today (e.g. the utilization of agriculture, writing, weapons and other advanced technologies) has been around for about 10,000 years. This means that only in the latter 1.5% of our time as civilized human beings, did we possess radio technology. Relative to the 50-100,000 years of Homo sapiens’ existence, this is but the latter 0.1%. Relative still to the 3.7 billion years of having any form of life on this planet, it is a mere blink of an eye.
So in short, we can see that radio technology wasn’t available to us until very, very recently. What does this say about the Fermi Paradox? Well it tells me that once intelligent life has evolved, it can take many tens of thousands of years (or longer) for advanced communicative technologies to exist. Moreover, it tells me that intelligent life may exist elsewhere in the universe, even if extra-terrestrials have yet to discover radio technology (e.g. electromagnetic wave transmission). After all, intelligent life seems to require many special conditions in order to develop radio technology, including: writing systems, opposable thumbs (not necessary but it makes it much easier), a terrestrial environment (it’s difficult to fathom how our level of technological progress could be attained in an aqueous environment), etc. It’s easy enough to see that humans may have never discovered radio technology, as many special conditions were needed in order to do so. Only very recently were all of those conditions met.
Radio Wave Propagation in Space
Due to the inverse square law (of electromagnetic radiation passing through free space), radio waves tend to become indistinguishable around several light years. They may be clearly transmitted as far as a few hundred light years (if the signal is amplified and aimed in a specific direction), but radio waves require extremely large amounts of power (on the order of gigawatts) for transmission over distances as short as several light-years. What this means is that many terawatts of power are most likely needed to send a clear signal over the distances required to reach intelligent life elsewhere in the universe. So not only must we assume that this extra-terrestrial intelligent life has discovered radio wave technology, but also that it has the energy resources available to propagate radio wave signals over vast interstellar distances of many thousands or even millions of light-years. The key thing to note here is that the radio wave signal has to be strong enough to overcome the average background noise that we’re already receiving constantly.
Radio waves can also be reflected, refracted, diffracted, absorbed, polarized, scattered, etc., by various materials in between its trajectory and our planet. So in addition to the energy needed to propagate these radio waves, we must also assume that the waves have a free path so there is little or no information lost during its propagation to Earth. Now we mustn’t forget that the mean free path of outer space, that is, the average distance a photon can travel without being affected (by matter), is around 10 billion light years. So I’m willing to admit that the idea of radio waves being absorbed or affected by matter in any significant way is unlikely. However, there is still bound to be constructive and destructive interference between any radio waves sent and any other electromagnetic radiation it crosses paths with. If there are radio signals being sent from all over the universe and some were heading in our direction, how many of them have interacted with other waves with varying frequencies, amplitudes, etc.? I think it is safe to say that regardless of the mean free path in space, the true mean free path, that is, the average distance a photon can travel without being affected (by matter OR electro-magnetic radiation) is probably closer to zero. The universe is full of radiation moving in every (or just about every) direction. This ultimately means that any radio transmissions sent from afar would most likely be distorted and changed dramatically. If this was the case, we may end up receiving radio signals that are comparable to the microwave background radiation we detect now, that is, we may detect signals that don’t appear to carry much (if any) information at all. So we may just have trouble separating “noise” from potential “information”. For all we know, any and all radio signals sent in our direction may partially constitute the cosmic microwave background radiation. If this is the case, then there is little or no hope of receiving any true information.
The Hubble Constant
As it turns out, cosmologists have determined that the observable universe is expanding. Not only is it expanding, but it is also accelerating. This rate of expansion is represented by the Hubble constant. One important thing to realize is that space-time itself is expanding, not just the distance between galaxies within that space-time. This is important to realize because space-time is actually believed to be expanding faster than the speed of light. While many may think that this would violate Einstein’s Special Theory of Relativity, it is actually completely compatible. According to Special Relativity, one consequence is that nothing can travel faster than the speed of light within space-time. Within the field of cosmology, the general consensus is that space-time itself is expanding faster than the speed of light, thus not violating any physical laws. Since this cosmic expansion does not allow information to travel faster than light, we are further assured that it adheres to all known physical laws. This expansion is creating a light cone which incidentally puts a boundary on the observable universe from any point of reference. That is, due to space-time expanding faster than the speed of light, there is a maximum observable distance from any point in the universe. Past this distance, electro-magnetic radiation that is being transmitted toward the observer is never able to “outrun” the expansion rate of space-time, and thus it is never able to actually reach that observer. What this ultimately means is that any potential radio waves that are being transmitted beyond this “observable universe” (i.e. the light cone) will never be able to reach that point of reference (e.g. an observer in the center of that light cone). It does not matter how much power is used for transmission, it is physically impossible for information to reach us if it is transmitted beyond this point.
If we account for the Hubble constant, it turns out that our observable universe has a radius of approximately 46 billion light-years. Past this point we can’t see anything (including radio signals). If we take into account various theories of inflation, it is believed that the true universe (that which our “observable universe” is a constituent of) is many orders of magnitude larger. So even if the universe had intelligent life distributed at a concentration of only 1 planet per “observable universe”, we would still have billions upon billions of intelligent civilizations in existence and yet there would be no possible way to know about their existence.
Summary
So it appears that there are numerous factors that can account for and resolve the Fermi paradox. Does this mean that there is undoubtedly intelligent life elsewhere in the universe? Of course not. It seems clear to me however that the vast size of the universe (especially the unobservable universe) and the degree of homogenization we’ve observed thus far indicates that the probability of extra-terrestrial life is extremely high, regardless of whether or not we have received a radio transmission from them. So in my opinion, the “Fermi paradox” doesn’t appear to be much of a paradox at all.
The Open Mind 
I agree with that.
The earth has been potentially visible to aliens for less than 100 years (due to short wave radio and television transmissions). However, we are moving in the direction of low power radio signals (cell phones, etc), and the use of cable or fiber optics for general broadcast media. So, before long, we shall again be undetectable by alien civilizations. That’s 100 years of detectability out of around 100,000 years of the existence of our species. That shows a low probability of being detecable. And it is a lot lower for other reasons, such as the ones that you mentioned.
That is a very good point — at least in terms of radio wave transmissions used for global intercommunication. We shall be undetectable in terms of the medium we use to distribute information across the globe, but it’s also likely that some people will continue to transmit higher-powered radio signals towards outer space as they do now (in hopes of extra-terrestrial contact). So we may remain detectable for a long time, but it won’t be the unintentional electro-magnetic “leakage” you’re referring to.
Right, and if we humans never had any interest in sending signals into outer space, its easy to see how we’d only have a century or two of low level detectability at best.
I personally like the idea that the reason we haven’t found any signs of life yet are because the most advanced forms of life within our observable universe, or even just in the local “neighbourhood” (such that we might have a good chance of being able to detect them) are all around about the same level of advancement (relatively speaking).
The theory goes that the early universe was far too chaotic/hostile for life to form (fairly inarguable point really) – and as time has gone by the frequency and probability of major extinction events has dwindled for any given planetary body – such that the likelihood of some life evolving to an industrial society (and thus potentially being detectable) has been increasing over time as major events like gamma ray bursts, asteroid collisions, proto-planetary collisions, major geological activity (the younger a planet the more frequent and violent things like volcanic eruptions are) and so on become more and more infrequent (due to increasing distances and scales, older planets cooling down and becoming less geologically active, a solar system “running out” of collision-able objects (e.g. object on a trajectory capable of interacting with other objects)).
On that basis it has been hypothesised that the probability of extinction up until this point has been so high that it has precluded the advancement of a species to our level, and it is only now (or around about now) that things have “stabilised” enough to allow a species to reach our level of advancement.
The really cool thing about this, perfectly plausible theory, is that in our region of space it makes it quite likely that all intelligent life is approximately at the same level of advancement as we are – and it is therefore possible, perhaps even likely, that we are on the cusp of making contact with such intelligent life in the (relatively) very near future.
The drawback of this theory is that it also makes it quite likely that the local neighbourhood is still relatively dangerous and could obliterate us at any point – which, unfortunately, is also probably somewhat true.
:o)
As I mentioned, we only discovered radio transmission relatively recently (only in the past 150 years out of the 100,000 years or so of homo-sapien’s existence). So even if we have other forms of extra-terrestrial life that were comparable to us in terms of intelligence (or even had greater intelligence), it would be reasonable to suppose that they may never in fact have discovered radio due to the unique circumstances required for the discovery (e.g. opposable thumbs, a terrestrial environment, the Scientific Revolution and all other relevant experimentation that led up to it, etc.). It’s also difficult to say what the density of intelligent life in the universe really is. How many radio-transmitting species are out there? If it’s only a tiny fraction of the already minuscule fraction of intelligent life, then we may only have one radio-transmitting species per observable universe. This would mean that we could never hope to receive communication, and yet would not negate the inevitably large probability for the existence of that radio-transmitting intelligence.
I agree with you on this point to a certain degree. After stabilizing to the energy levels required for a biotic environment, the probability certainly increased for intelligent life to evolve. On the other hand, the fact that many stars in the universe are dying over time counteracts this probability since there is increasingly no more energy input (Second Law of Thermodynamics) which is necessary for life, and even more necessary for life to evolve into larger and more complex structures. So time elapsing has created sort of a bell curve where in the beginning the universe was inhospitable for life, then at some point these ideal conditions peak, and finally the conditions start a downward trend as the primary sources of energy are slowly dying.
Yes, this is the case if our observable universe is representative of the whole. More importantly, it is the luck of the draw for which solar systems have stars that are the proper age and an orbiting planet with the right elemental composition, etc.
If by “same level of advancement”, you mean “possessing radio technology”, then I disagree that it is likely. I disagree mainly because of the reasons I gave earlier regarding how we only very recently stumbled upon radio technology relative to the much larger age of our civilized species, let alone the even larger age of our species in general. Also, I’m not sure what you mean by “our region of space”. Are you talking about our solar system, our galaxy, or our entire observable universe?
Yes, there are certainly a number of things that could take us out at any moment. It could be another asteroid; a large solar fluctuation; a polar shift; global warming or other environmental factors that destroy the vegetation, etc. Over time as the moon recedes from us, the earth’s rotation is slowing down due to the conservation of momentum. After a long enough time, this can certainly destroy us too simply by changing the rotation speed. The Earth’s biosphere has been very effective at compensating for these environmental changes by altering its solar reflectivity (with snow coverage), altering the oxygen to carbon dioxide to water ratios to control temperature and alter ecosystem inhabitants, evolution, etc. Even so, at some point the Earth’s “thermostat” will not be able to keep up with these climate changes, and before that point occurs, some source of physical obliteration may destroy us first. It would be interesting to know where we currently lie on the “cosmic living conditions” curve.
Are you taking into consideration the ongoing formation of new stars and planets that is still occurring?
In the first instance I believe/would like to think that radio technology and other communications technology is somewhat ubiquitous in that eventually an intelligent tool-using species would develop it. There are many different appendages that could evolve that could be used to help a species become a technological species, while I don’t discount the possibility of highly intelligent life that does not ever become a technological species, I would like to think that some percentage would, and in this scenario radio waves and other physics phenomena would eventually be studied and taken advantage of. In realistic/relative terms the time-scale it took Homo Sapiens to develop from basic stone tools to radio-wave emitting industrial society is extremely short – only tens of thousands of years – and many species have existed over geological time and still not achieved this. Despite that, I still think it likely that inevitably, in the fullness of time, if a planet supports life for long enough, one (or more) species will advance to an industrial society.
Obviously any proposal, theory, hunch, belief, or imagination on this topic is completely hypothetical at this time, as we simply do not have enough data (yet) – but for some reason I feel uncharacteristically optimistic about this particular subject – and I am not the only one – there are many well respected scientists that believe (to some degree or other) that we have some chance of contacting, or at least confirming extra-solar life within their lifetimes.
By our region of space I mean relatively nearby solar systems in this section of our galaxy. Let’s say, just for the sake of this debate, within 50 light years of our sun.
On a slight tangent what are your thoughts/beliefs on the likelihood of some form of extra-terrestrial life being found to exist within our solar system (perhaps on Europa, Titan, or Enceladus)? If such a discovery were made, how would this affect the Drake equation and Fermi’s Paradox? One thing to consider when thinking about this is that none of those moons exist within the theorised habitable zone – and any evidence for life, or even life-supporting conditions would have to increase the likelihood of life being more common – as it vastly increases the zone in which life might potentially exist. How would such a discovery affect your own personal belief in this area?
Lastly, if we found evidence of past microbial life on Mars, current microbial life on Titan, and current complex life on Europe – how would this affect these same issues and beliefs, in your opinion?
Yes, I have taken that into consideration. Various astronomers have estimated that half of the stars that have ever existed in the universe were born between 9 and 11 billion years ago, with the remaining half born between then and today. This implies that the rate of new star formation has been and still is dropping dramatically. Some estimate that if this trend continues as-is, we can assume that about 95% of all stars that will ever exist, have already been born. It should be noted that the star birth rate is currently not far off from the star death rate, so we won’t expect to see a net loss of stars (based on the current estimate) for a while, but the previous statistic implies that the star birth rate peaked a long time ago and it’s pretty much downhill from here.
Also, regardless of new star formation, there will still be a point in time where the habitable conditions peak, and after that point, an inevitable downward spiral for life will ensue due to the finite life of a star and the Second Law of Thermodynamics. Even now, as new stars are being born, the energy density is decreasing as the number of stars (at least # of solar masses) per cubic light year decreases due to the cosmological constant, among other reasons. Then we also have a large number of massive stars that are large enough to turn into black holes, and once they do so, they will suck up all of those neighboring stars, planets, etc., which reside within a close enough distance. As soon as the source of matter feeding the black hole is gone, the black holes will likely evaporate into Hawking radiation, again further reinforcing the Second Law of Thermodynamics and creating smaller and smaller energy densities. These two mechanisms alone, cosmological expansion and black hole mechanics, will greatly reduce the suitable living conditions in the universe over time. As I said earlier however, we simply don’t know where we lie in terms of the ideal time frame for life in the universe. We could be at the peak, before it, or well past it. I wish we knew.
In my opinion, there are so many special requirements for interstellar radio technology (e.g. electricity, massive amounts of energy, and the unique scientific experimentation that led to the invention of radio in the first place), it seems to me that the probability (or density) of radio-transmitting intelligence is going to be relatively small compared to the number of intelligent species in general. Certainly a large number of extra-terrestrial intelligent species could invent a number of different tools (and thus be a technological species), but this doesn’t mean that they would inevitably stumble across all of the inventions that led to radio. Some would say that the invention of the printing press (seemingly unrelated to radio) was a catalyst for the Scientific Revolution, and had this invention never occurred, we may never have had the level of scientific collaboration required to discover and experiment with radio or its prerequisites (e.g. electricity; electro-magnetic spectrum; the precursors: telegraph, telephone, etc.). I agree with you that some percentage of intelligent life is likely to discover radio transmission, but I don’t think it would be a large percentage.
Yes, while the time scales for our technological progress are small in comparison to the time scales of having life on our planet, we only recently stumbled across radio transmission in the last 150 years. We could have never discovered it, or have gone another several thousand years before coming across it. I do like your thought that if a planet supports life for long enough, one or more species will advance to an industrial society. It will certainly increase their chances of doing so by having more time to occur. However, we also have to realize that the brains that we possess evolved through natural selection and it was only because of certain environmental pressures and circumstances that we had a need for such a brain. Many other intelligent species out there may have some kind of intellect, reasoning, or problem solving ability, but it may be markedly different from our own. There may be intelligent species out there that solve problems or think in a way so foreign to us, that they may be likely to invent things we have never even thought of or may never hope to understand, and likewise they may never invent particular things that we might think of as obvious, primitive, or inevitable. Dolphins for example, may be more intelligent than Homo-sapiens (in at least some ways), but if they aren’t “tool-oriented” or have the physical structure to manipulate their environment or create tools, then there may be no favorable advantage for a tool-oriented brain to evolve in those species, and any random mutations able to produce such a brain may not have the feedback loop reinforcement required to adopt it via natural selection. Sometimes its tempting to look at our inventions and think that they were inevitable or obvious in some way, however, not only did a truly unique set of circumstances surround these inventions, but they also were produced by a particular type of intelligent species that thinks in a unique way within certain boundaries. At the very least, I am in line with your train of thought that longer gestation times for life to evolve on a planet increases the chances for a radio-transmitting species to evolve.
I completely agree that there is a large degree of speculation within this topic. The purpose of this post was to point out that there can certainly be intelligent life out there (even those species that are radio-transmitting), and yet we may not see that data transmission for a number of reasons. I feel almost certain that extra-terrestrial intelligent life exists simply because the size of the universe is so large, it seems inevitable that a number of other solar systems have similar conditions and planetary elemental composition. It would be spectacular if we received a message one day!
My thoughts are that in a region as small as 50 light years, where there are only 400 or so “normal stars” (i.e. those that are not red dwarfs and lie between 0.5 and 1.5 solar masses — the most hospitable for life to form), the probability of finding life at all, let alone intelligent life is small. As for assuming that this extra-terrestrial life would be at the same level of “advancement” as us, I assume you are equating our level with that of any intelligent technological species? If so, I don’t think it is likely that these extra-terrestrial species (in this 50 light year radius) would be at the same level. We have only become a technological species in the last few thousand years, out of the millions of years that this planet has supported large, brained organisms. What level of chance was involved with this shift? Could the mass extinction of the dinosaurs have led to the emergence of intelligent primates/mammals? Perhaps. If so, then had that last asteroid missed us, we may have never evolved. We must ask ourselves if the planet Earth is representative of typical life-bearing planets, and how unique the circumstances were that led to our emergence.
I think that there is a reasonable chance that some kind of bacteria could be found due to the possibility that some other planets and their moons may have been in the habitable zone of the Sun at some point in the past and have some trace elements to support life.
I think it would have little impact on the Drake equation, simply because even if we doubled or tripled “Ne”, that is, the average number of planets that can potentially support life per star that has planets, we would be doubling or tripling a relatively small number. So if it was previously thought that we had 100 civilizations in our galaxy within our light cone, the estimate may increase to 200 or 300 if our solar system represented the average (which it does not). While this may double or triple our chance of extra-terrestrial communication, if our previous chance was only one in one trillion, and it jumps up to a two or even three in one trillion chance, it would be fairly insignificant. Finding another planet or moon that supports life in our solar system wouldn’t tell us anything about the other factors in the Drake equation specifically pertaining to “intelligent” life. As for Fermi’s paradox, I don’t think that this finding would have much impact on it, unless the life found was intelligent life. If this was the case, then we’d have to wonder “Why haven’t they tried to contact us if they are so close?” If we found out that they simply never discovered radio, then we’d see just one of many possible resolutions to this apparent paradox.
I agree with you here. Since we haven’t been able to reproduce the supposed abiogenesis that occurred on Earth 3.5 billion years ago, it seems to have involved a fragile set of conditions, which causes us to reduce our expectations of finding life elsewhere. However, for all we know there are different forms of life that we know nothing about (e.g. silicon-based, those not requiring water, etc.), and there may be a wider range or combination of suitable conditions that we have never considered even for our own carbon-based life forms. This is most likely the case in my opinion.
I think that it would illustrate a number of different possibilities. A solar system’s habitable zone may fluctuate over time causing the surrounding planets to enter or exit over time. This may allow enough time for life to evolve in some areas (perhaps even intelligent life), but perhaps not long enough (or with the right conditions) to share the solar system with another intelligent life-bearing planet in the same time frame. It may just illustrate that some planets are capable of sustaining simple life forms, while others are capable of sustaining multiple levels of life form complexity. This would not affect my views pertaining to Fermi’s Paradox, but it would definitely add to my curiosity of abiogenesis.