Problem of Aliens: The Fermi Paradox

[Mr. Mask]

I was considering running a an early space faring game, and was considering how to implement aliens in a reasonable way. In particular, I'm concerned with the Fermi Paradox.

The short version is: If there are aliens, Earth should have found their radio signals, or they should have found Earth's, assuming alien civilizations are spreading out at all. Extra Credits goes into a few explanations for why they mightn't be found which could be elaborated upon for a setting. Namely: 1) They're staying home and not colonizing other planets. 2) They don't exist. 3) They're hiding their presence. Or 4) The government is hiding their presence.


Since the idea is to include aliens, 2 can be ignored. To get into some other ideas of why aliens haven't been discovered...

The universe, or intelligent life, is young. If either hasn't been around for long, that can justify alien life hasn't spread out enough to be noticed.
Similar is if alien sentience was figured to develop at a similar rate to humans. That would deny very advanced aliens.

There are no aliens in our galaxy. By the time any aliens were advanced enough to reach our galaxy, they're likely to develop technology that doesn't announce their presence from light years away on even extremely primitive sensors like Earth has, explaining why they haven't been sighted. Also, it leaves the possibility that while they are advanced, they're not at a level yet where they're willing to colonize a second galaxy, where communications would likely be so poor between the two galaxies that their colonies would form a separate, possibly competing space empire. With that theory, exploration of this galaxy and the chances of finding humans seems low.

Mass Effect's Version. There were aliens, but they all got wiped out. Allows for alien ruins to be discovered, which is fun.


Those are the ideas which spring to mind. A combination of factors is probably the best idea. What ideas have you used for your settings, or in the stories or rulebooks you've read?

[The Oni]

I guess the question is how much do you want the species to interact?

For example, you could have a situation wherein the aliens have incredibly slow space travel. But, they could have comparatively fast communication. So the aliens can't pop over to Earth in a week or so, but they can send a message that gets here in about a day, leading to a very weird sort of pen pal relationship.

Which could be interesting if there are other, less-friendly aliens who can travel much faster...

[Esprit15]

We haven't looked long enough/in the right places. Maybe they use frequencies/wavelengths that we don't normally look at.

[Mr. Mask]

Smeagle: I like the idea of diverse aliens. Some might be like pen-pals, others might be like a threat that's zooming over to stomp Earth into space dust. Of course, to make for an interesting game, you need the mix to result in having a fighting chance, and a logical reason for why you're discovering them recently. Of course, a plot-twist where humanity is destroyed by an unstoppable alien menace as soon as they were noticed could be interesting, particularly if there are some human survivors who take shelter with friendlier aliens.

For the early parts of the game of an early space faring setting, you probably want to focus on human conflict, with elements of mystery as to alien life, building up to an encounter near the end.


Espirit: As mentioned, alien life may well be operating at a level human sensors aren't able to detect. I mean, with current Earth tech, space war would be as stealthy as sending your enemy big neon signs elaborating your plan a week in advance of enacting it, which is to say that space war is a pretty lousy prospect at this time. Aliens will want to change that, if they want to have any decent war capability whatsoever.

If the aliens were in another galaxy, I don't think there are any signals they could send powerful enough for Earth to detect them.

[Mr Beer]

If the aliens were in another galaxy, I don't think there are any signals they could send powerful enough for Earth to detect them.

Depending on their tech, sure there are. It just seems extravagant to communicate via gamma ray bursts.

[Storm_Of_Snow]

IIRC, it's theorised that there's a relatively short period of time that a civilisation would be detectable via picking up transmissions, as they eventually become either more guarded, or simply more efficient (narrower beam radio communications that use less power, don't interfere with other signals and are less able to be intercepted, non-broadcast methods like fibre optics and so on), and so less signal leaks out that can be detected.

I think we ourselves are actually getting to that point at the moment.

There's also signal attenuation - even if they're effectively shouting as loud as they can, by the time it arrives at your receiver, there simply might not be enough of a signal left to pick out against background radiation.

[Mr. Mask]

Beer: Communicating like that, you're either the big fish in the galaxy, or terminally insane.


Snow: I asked someone about how far Earth's radio traffic can be seen from. They reckoned it would be hard to sport outside of the solar system... which is basically no communication distance at all, compared to distances within the galaxy.

[Millennium]

We haven't looked long enough/in the right places. Maybe they use frequencies/wavelengths that we don't normally look at.

We haven't looked long enough/in the right places. Maybe they use frequencies/wavelengths that we don't normally look at.

Organizations like SETI tend to use the concept of a civilization's radiosphere: when a civilization begins to use radio above a certain level of power, the signals start to expand outward from that world in a roughly spherical shape, and can in theory be detected by other civilizations in the order they were sent, if only the signal comes in at the right time.

But there's a hole in this theory: its assumption that once a civilization develops radio, that technology is never replaced. It's held so far on Earth, but the earliest documented discoveries and/or predictions of radio are only about 130 years old: in a historic sense, we haven't actually been using it all that long. Already our scientists are starting to look at possible ways to overcome radio's most serious limitations, and our artists were imagining possibilities well before science caught up to them. It could be that civilizations to not have radiospheres so much as "radio bubbles": a shell of radio signals that starts when radio starts to be used, but tapers off and eventualy vanishes as radio is replaced.

This is important for organizations like SETI, because it means that each civilization can only be detected for a limited window of time using radio. In order for that to happen, the searchers must also be using radio at just the right time. For example, let's imagine an alien civilization that lives 200 light-years away from us. It would take that civilization's radio signals 200 years to reach us, so if they started using radio 200 years ago, we would only be just starting to receive the very first signals they had ever sent. If they'd started 400 years ago, then we'd receive signals from 200 years ago, because that's how long it takes radio to travel 200 light-years.

But let's imagine something slightly different. The alien civilization started using radio about 1000 years ago -a time we'd have called 1000 CE- and used it for about 300 years before replacing it with some other technology (ansibles, perhaps). The first signals from this civilization would have started to reach us around the year 1200, when humanity was in no condition to listen. Radio might still have been at its peak in the alien civilization at this time, and they continued sending signals for another hundred years, but then -in what we'd call the year 1300- they invented the ansible and stopped using radio. Signals continued to come to us for another 200 years, as the old signals continued to arrive.

But around 1500 they stopped, and this was still long before we ever invented radio. That civilization could still be out there, but our radio detectors will never notice. They just weren't there when they needed to be.

[Mr. Mask]

And that's assuming you can make them out against all the background noise.

[Eldan]

And then, of course, there's the problem that SETI et al simply:

a) Can't watch the entire sky all the time so might miss a transmission
b) Can't analyze all the data they produce properly, so might not even realize they found something

[Elderand]

Other problems, space is ridiculously big, our own radio transmission haven't spread all that far even on a galactic scale. Anything farther than 110 light years away isn't being reached yet. Our galaxy alone is 1200 000 light years accross.

[Storm_Of_Snow]

Snow: I asked someone about how far Earth's radio traffic can be seen from. They reckoned it would be hard to sport outside of the solar system... which is basically no communication distance at all, compared to distances within the galaxy.

And even then, what would you actually pick up? Would it be intelligible fragments, or just garbage mixed with a lot of static?

And that's assuming you can make them out against all the background noise.

Plus our detection gear is basically a small series of dots under an atmosphere that can absorb and scatter electromagnetic signals, on a spinning sphere with it's own electromagnetic fields (the Van Allen belts) that's orbiting a massive electromagnetic radiation emitter (the sun) at a relatively close proximity, with other spinning spheres scattered at various points inside and outside that orbit, trying to pick up electromagnetic signals across x light years emitted by pin point emitters from civilisations that are themselves on spinning spheres closely orbiting massive electromagnetic radiation emitters, with other massive EMR emitters of various size and activity scattered around, and the whole lot's orbiting the centre of the galaxy.

And we're kind of guessing at what we're looking for, based on our understanding of physics and a bit of "well, it's what we'd do if we were trying it...".

Here's a large number of fields full of haystacks, there may or may not be a needle in one of them.

[Eldan]

Here's a large number of fields full of haystacks, there may or may not be a needle in one of them.

Also, some of it probably isn't hay, but made of needle-like objects and you aren't allowed ot search the stack, only to make three photographs, then take them home for analysis.

[Segev]

I'm a fan of the idea that, given the age of the universe and the probabilities of sentient life occurring, we actually beat the odds. We're early. So there aren't other sentient beings out there, most likely.

Why do I like this idea? Because it ties in nicely to the "aliens had a big advanced civilization, but it's gone now, and their relics are all that's left behind" idea: we are the antecedent race. We are the "ancients," in our own infancy today.

If you wanted to use this in conjunction with an "early space exploration" setting, perhaps you could have a large colony group head out at ludicrously relativistic speeds to set up in some distant part of the galaxy. In the time that passes on Earth during the time-dialated transit of these explorers, mankind actually arises to a great height and expands across the stars by technologies as much beyond the ken of the colonists as they will be of the aliens that will come about in the billions of years of the colonists' relativistic travel.

The world and system they colonize was preserved by the ancient human civilization, who honored and revered the colonists exploratory spirit but knew that simply hopping aboard to say "hi" and hand off tech millenia beyond them would be a disservice. So they arranged for their exploring ancestors to find their destination an ideal place to set up, and protected it from all outside comers. Some of the only deliberate relic sites, with primers and automated systems designed to recognize the exporing colonists, exist in that system, intended for them to find and unlock as they grow and expand. Highly primitive compared to the troves other aliens find in teh unintentional relic sites (since those were just abandoned or the like, not deliberatley set up), but still advanced compared to "early space" tech, and useful to defend themselves and help them ratchet up.

When the colony world, using "early space exploration" tech, extends beyond the system that was preserved and reserved for them by the machinations of their descendent humanity that achieved such great heights, they find the more traditional sci-fi galaxy full of advanced races. Being "early space faring" in tech, the colonists are a bit behind, at first.

However, it was human culture and human language - even with the many generations of drift - that was behind the "ancient relics" of the "lost, hyperadvanced civilization." Thus, through a combination deliberate primers left behind for these revered explorers from the ancient civilization, and a simple cultural familiarity that is best served by a study of how it evolved from what our explorers remember of their own cultures they left behind, our "backwards" human colonists discover not only that these advanced alien races are younger than they are, objectively, but that they have an advantage when it comes to deciphering and controlling and even identifying and finding the "ancient relic" devices that are still far more advanced than anything anybody else has.

[Jacob.Tyr]

Organizations like SETI tend to use the concept of a civilization's radiosphere: when a civilization begins to use radio above a certain level of power, the signals start to expand outward from that world in a roughly spherical shape, and can in theory be detected by other civilizations in the order they were sent, if only the signal comes in at the right time.

But there's a hole in this theory: its assumption that once a civilization develops radio, that technology is never replaced. It's held so far on Earth, but the earliest documented discoveries and/or predictions of radio are only about 130 years old: in a historic sense, we haven't actually been using it all that long. Already our scientists are starting to look at possible ways to overcome radio's most serious limitations, and our artists were imagining possibilities well before science caught up to them. It could be that civilizations to not have radiospheres so much as "radio bubbles": a shell of radio signals that starts when radio starts to be used, but tapers off and eventualy vanishes as radio is replaced.

This is important for organizations like SETI, because it means that each civilization can only be detected for a limited window of time using radio. In order for that to happen, the searchers must also be using radio at just the right time. For example, let's imagine an alien civilization that lives 200 light-years away from us. It would take that civilization's radio signals 200 years to reach us, so if they started using radio 200 years ago, we would only be just starting to receive the very first signals they had ever sent. If they'd started 400 years ago, then we'd receive signals from 200 years ago, because that's how long it takes radio to travel 200 light-years.

But let's imagine something slightly different. The alien civilization started using radio about 1000 years ago -a time we'd have called 1000 CE- and used it for about 300 years before replacing it with some other technology (ansibles, perhaps). The first signals from this civilization would have started to reach us around the year 1200, when humanity was in no condition to listen. Radio might still have been at its peak in the alien civilization at this time, and they continued sending signals for another hundred years, but then -in what we'd call the year 1300- they invented the ansible and stopped using radio. Signals continued to come to us for another 200 years, as the old signals continued to arrive.

But around 1500 they stopped, and this was still long before we ever invented radio. That civilization could still be out there, but our radio detectors will never notice. They just weren't there when they needed to be.

This, seriously. If they're only a few hundred years ahead of us, then we wouldn't have overlapped enough to notice. Between advancing beyond using radio, civilization dying out, signal degradation, and minimal monitoring you can easily work around this "paradox".

I'm debating the validity of this for space horror, now. Echoes of dead civilizations, mysterious communication blips picked up now and then by travelers and colonists, etc. Throw in some sci-fi space time anomalies that obscure the time/location of sending for added mind-f!@#, and this could be a great thing for some first time colonists in a new system to encounter.

[Spore]

Sooo.....*adjusts tinfoil hat*

I'd go for the needle in a haystack approach. They may have noticed you but this doesn't mean they can notify you or even reach you before their civilization ends. Cellular life is around for some millions of years. Humankind is around for several tenthousands of years and we have the technology for travel to the moon for about 50 years now. We send "items" to several celestial bodies in our solar system and yovagers out of there. So my guess is that the average highly intelligent civilization not only is rare, depend on specific constant planetary situations (we nearly got killed by an ice age, and those things pop up every so often) but also have to develop efficient interplanetary travel (by what is effectively teleport, all this warp stuff) to reach us in a life-time. So you'd introduce a quick way to travel (Warp Drive for Star Trek, Mass Effect Engines for Mass Effect, Lightspeed for Star Wars). Your advanced aliens monitor earth until we're "ready" which is basically the development of our own hyper drive and what not.

So the typical development goes:
- survive cellular phase
- have sufficient ecosystem to support multicellular life
- have CONSTANT ecosystem to support life
- develop quickly enough to create the technology for that
- not have your homeplanet destroyed/inhabitable by celestial events
- find a way to get to Earth within one life cycle
- not screw up this mission as normal signals could take millenia to reach back to home planet
- not have a society like ours that heavily believes that every investition towards discovering new species is wasted resources (read: money)

Those are A LOT of variables.

[Jeff the Green]

I'm a biologist, so my answer leans towards 2) but isn't quite there. Intelligent life is incredibly rare. For that matter, multicellular life is incredibly rare. Evolution is historically constrained and dominated by chance events with natural selection only filtering what gets produced by mutations. And really, natural selection isn't going to favor intelligence anyway because it's metabolically expensive and not particularly useful for propagating genes (compare our population size to that of gnats, or worse, bacteria). So the most complex organisms you're likely to see are comparable to earth invertebrates.

Of course, this does mean that your players' interactions with alien life will mostly consist of getting it on their boots, but that's the sacrifice we make for biological plausibility.

[Elderand]

I'm a biologist, so my answer leans towards 2) but isn't quite there. Intelligent life is incredibly rare. For that matter, multicellular life is incredibly rare. Evolution is historically constrained and dominated by chance events with natural selection only filtering what gets produced by mutations. And really, natural selection isn't going to favor intelligence anyway because it's metabolically expensive and not particularly useful for propagating genes (compare our population size to that of gnats, or worse, bacteria). So the most complex organisms you're likely to see are comparable to earth invertebrates.

Of course, this does mean that your players' interactions with alien life will mostly consist of getting it on their boots, but that's the sacrifice we make for biological plausibility.

You have a data sample of 1 here, you can't make any sort of claim about what is rare or not in the universe.

[Larkas]

I'm a fan of the idea that, given the age of the universe and the probabilities of sentient life occurring, we actually beat the odds. We're early. So there aren't other sentient beings out there, most likely.

Why do I like this idea? Because it ties in nicely to the "aliens had a big advanced civilization, but it's gone now, and their relics are all that's left behind" idea: we are the antecedent race. We are the "ancients," in our own infancy today.

If you wanted to use this in conjunction with an "early space exploration" setting, perhaps you could have a large colony group head out at ludicrously relativistic speeds to set up in some distant part of the galaxy. In the time that passes on Earth during the time-dialated transit of these explorers, mankind actually arises to a great height and expands across the stars by technologies as much beyond the ken of the colonists as they will be of the aliens that will come about in the billions of years of the colonists' relativistic travel.

The world and system they colonize was preserved by the ancient human civilization, who honored and revered the colonists exploratory spirit but knew that simply hopping aboard to say "hi" and hand off tech millenia beyond them would be a disservice. So they arranged for their exploring ancestors to find their destination an ideal place to set up, and protected it from all outside comers. Some of the only deliberate relic sites, with primers and automated systems designed to recognize the exporing colonists, exist in that system, intended for them to find and unlock as they grow and expand. Highly primitive compared to the troves other aliens find in teh unintentional relic sites (since those were just abandoned or the like, not deliberatley set up), but still advanced compared to "early space" tech, and useful to defend themselves and help them ratchet up.

When the colony world, using "early space exploration" tech, extends beyond the system that was preserved and reserved for them by the machinations of their descendent humanity that achieved such great heights, they find the more traditional sci-fi galaxy full of advanced races. Being "early space faring" in tech, the colonists are a bit behind, at first.

However, it was human culture and human language - even with the many generations of drift - that was behind the "ancient relics" of the "lost, hyperadvanced civilization." Thus, through a combination deliberate primers left behind for these revered explorers from the ancient civilization, and a simple cultural familiarity that is best served by a study of how it evolved from what our explorers remember of their own cultures they left behind, our "backwards" human colonists discover not only that these advanced alien races are younger than they are, objectively, but that they have an advantage when it comes to deciphering and controlling and even identifying and finding the "ancient relic" devices that are still far more advanced than anything anybody else has.

Wow, I REALLY like this!

[HighWater]

And really, natural selection isn't going to favor intelligence anyway because it's metabolically expensive and not particularly useful for propagating genes (compare our population size to that of gnats, or worse, bacteria).

Hold on, that's an argument against large lifeforms, not necessarely an argument against intelligence. Intelligence of the human form is very beneficial: human population is several orders of magnitude larger than it should be when compared to organisms of similar size. By cellular count, large organisms do alright, though the microbial masses are teeming everywhere (and necessarely so, or the rest of life would die). Calling large organisms "more adapted" than single celled life would, of course, be an error, but they certainly fill a rich niche. High intelligence is indeed metabolically expensive, so it only works if you can use it to your advantage. Basically, if you can make it worth the costs.

I reject the use of intelligence in this context anyway, as lots of animals score at least reasonably well in the intelligence department. It is not completely unthinkable that one of these would've served as the progenitor of another civilisation-building species. The thing that sets humans apart, and the thing we need alien civilisations to have, is sufficiently advanced technology. Intelligence may be a prerequisite, but it's not enough.

More on topic:
The Great Filter is a possible explanation for the Fermi Paradox (either somewhere in our past, or somewhere in our future lies hurdle that eliminates (almost) 100% of contenders, which is why the universe seems so empty of civilisation). Another is that other civilisations stop transmitting (like we are reducing transmission) and just happen to not have colonised our solar system yet (as far as we know). Another one is that some other civilisation never started transmitting, because they are so fundamentally different from us that their preferred method of communication has nothing to do with long-range signals we could pick up...

[Thrudd]

I was considering running a an early space faring game, and was considering how to implement aliens in a reasonable way. In particular, I'm concerned with the Fermi Paradox.

The short version is: If there are aliens, Earth should have found their radio signals, or they should have found Earth's, assuming alien civilizations are spreading out at all. Extra Credits goes into a few explanations for why they mightn't be found which could be elaborated upon for a setting. Namely: 1) They're staying home and not colonizing other planets. 2) They don't exist. 3) They're hiding their presence. Or 4) The government is hiding their presence.


Since the idea is to include aliens, 2 can be ignored. To get into some other ideas of why aliens haven't been discovered...

The universe, or intelligent life, is young. If either hasn't been around for long, that can justify alien life hasn't spread out enough to be noticed.
Similar is if alien sentience was figured to develop at a similar rate to humans. That would deny very advanced aliens.

There are no aliens in our galaxy. By the time any aliens were advanced enough to reach our galaxy, they're likely to develop technology that doesn't announce their presence from light years away on even extremely primitive sensors like Earth has, explaining why they haven't been sighted. Also, it leaves the possibility that while they are advanced, they're not at a level yet where they're willing to colonize a second galaxy, where communications would likely be so poor between the two galaxies that their colonies would form a separate, possibly competing space empire. With that theory, exploration of this galaxy and the chances of finding humans seems low.

Mass Effect's Version. There were aliens, but they all got wiped out. Allows for alien ruins to be discovered, which is fun.


Those are the ideas which spring to mind. A combination of factors is probably the best idea. What ideas have you used for your settings, or in the stories or rulebooks you've read?

Post-physical evolution is the norm in the universe, at a certain point most intelligent species evolve beyond the restriction of physical form. The chances of two species that are evolving at roughly the same time and are in close enough proximity to one another to detect and interact with each other is very low. If there is even as little as a million years (possibly less) between the rise of one species and another, they likely will have no chance or desire to interact. The younger species may barely be able to perceive the existence of the older, if at all, and the older be so far advanced that communicating with the younger would be akin to our interactions with invertibrates.

That said, even within a single galaxy the number of planets capable of supporting life is so great that there must be hundreds or thousands of intelligent species evolving at roughly the same time. Most of those species, however, will plateau at certain technological levels due to the vagaries of their particular biology and environment, or will go extinct for one reason or another. There will still remain many that continue evolving and develop space travel. The problem is, the interstellar distances are so great that radio signals and technology working only on the Newtonian-level (propelling physical vessels through space at less than c) will never be a viable option for meaningful contact or interaction.

At some point, however, those signals will come flooding in, and this will be a significant event in human history. The technology of the species who originated the earliest radio signals, including ourselves, will at that point be significantly advanced enough to overcome the c-barrier with probably some meaningful advancements toward post-physical ascension (teleportation, true AI, manipulation of quantum effects) and will initiate contact. Travel and communication will likely be more along the lines of stargates/wormholes, or vessels which use this sort of effect. Each civilization will likely have colonized or at least fully explored and exploited their own solar systems for resources by that point.
Also, by this point, these civilizations will start becoming aware of the existence of post-physical species. Most such species will likely not engage in much contact, but even awareness of them could inspire research and accelerated advancement.

[Slipperychicken]

Maybe the aliens were largely avoiding Earth because it doesn't support life as they know it.

[LimSindull]

Since it hasn't been brought up, the government hiding the alien activity would be a very good option.

First, what type of government would be in control during this Expansion Era? Would there be a United Solar Empire where the ruler(s) of Earth decide the best course of action for all of humanity? If so, then, having the government not only hide, but make it illegal to look for alien vessels/technology would be an option.

Or you could go old Sci-Fi and make the aliens communicate telepathically and already be here hiding themselves.

If the government is a loose coalition of planets and colonies, they may not get along very well. This could allow one or two planets to know of and even have tried to communicate with alien presence, while the group could be from a planet or group of civilizations that have not had any communication from the aliens.

Last, an alien force could be jamming any signals coming into our solar system (or galactic civilization) for whatever reason. (They may view our destructive nature of a danger to all life or they may want to cripple and enslave/eat us.)

I hope you find this helpful.

[Grinner]

Those are the ideas which spring to mind. A combination of factors is probably the best idea. What ideas have you used for your settings, or in the stories or rulebooks you've read?

You should read this.

[Jeff the Green]

You have a data sample of 1 here, you can't make any sort of claim about what is rare or not in the universe.

Millions, actually. Every species whose lineage has been around since the beginning of life on earth (i.e. all of them) and that isn't capable of building advanced technology (i.e. all of them - 1) is a data point. (And before you mention it, no, it wasn't necessary for 4 billion years of evolution to pass before sapience evolved.)

Seriously, if you want to know about the likelihood of extraterrestrial life, ignore astronomers. Read biologists.

Hold on, that's an argument against large lifeforms, not necessarely an argument against intelligence. Intelligence of the human form is very beneficial: human population is several orders of magnitude larger than it should be when compared to organisms of similar size. By cellular count, large organisms do alright, though the microbial masses are teeming everywhere (and necessarely so, or the rest of life would die). Calling large organisms "more adapted" than single celled life would, of course, be an error, but they certainly fill a rich niche. High intelligence is indeed metabolically expensive, so it only works if you can use it to your advantage. Basically, if you can make it worth the costs.

First, cell count is irrelevant. In the context of ecology and evolution you use either biomass (unicellular organisms have 10 times the mass) or effective population size (unicellular organisms not only dwarf multicellular organisms, they make them negligible). Second, yes, we have a much larger population size than expected for our size now. For most of our evolutionary history, our population size was less than 1 million, at points dropping below 10,000. It's only by chance that we survived; one plague or natural disaster at the wrong time would have entirely extinguished our line. Finally, the issue isn't whether multicellularity or large brains can be beneficial, it's whether the intermediate steps can survive. Which is rarely true, and, as I mentioned before, it's currently believed that the only reason multicellularity evolved in the first place is a ridiculously small population size that resulted in a whole bunch of detrimental mutations that, when the population survived by chance, were repurposed to form the backbone of the eukaryotic genome.

[Storm_Of_Snow]

Millions, actually. Every species whose lineage has been around since the beginning of life on earth (i.e. all of them) and that isn't capable of building advanced technology (i.e. all of them - 1) is a data point. (And before you mention it, no, it wasn't necessary for 4 billion years of evolution to pass before sapience evolved.)

Seriously, if you want to know about the likelihood of extraterrestrial life, ignore astronomers. Read biologists.

Define "advanced technology".

For instance, some of the corvids can use tools and solve problems. Or spider web silk, which is stronger than steel wire of the same thickness, and is used by some species of spider to fly from one place to another (and would probably be the equivalent of us extruding a 100 foot pole and using it to fly across the atlantic). Do they count?

As for ignoring astronomers in favour of biologists, whilst I'm a biologist at heart too, I'd rather hear what all sides have to say on the matter.

[Mastikator]

You have a data sample of 1 here, you can't make any sort of claim about what is rare or not in the universe.

Sure you can, we orbit an average star and live on an average planet and are made of average elements. By all accounts we're normal and average and it's not unreasonable to assume others will be like us.

If we take a peek at the timeline of life, it took a billion years for life to emerge on the planet, for the first billion years there was no photosynthesis, so no oxygen in the atmosphere, then over one and a half billion years passed after photosynthesis started before multicellular life emerged, then within the last 500 million years animals emerged, then maybe a million years ago highly intelligent life forms emerged.

So if we look at a random earth like planet then it's: (rounding HEAVILY here)
20% chance no life, just a lifeless rock
20% chance life, but not breathable atmosphere
35% chance life with breathable atmosphere
15% chance life with plant like life is most complex life form
9% chance life with animal like life as most complex life form
0.9% chance life with intelligent animals as the most complex life form, probably civilization and somewhere between stone age and spacefaring
0.1% chance life with animals so intelligent we can't even guess what they are like OR post apocalyptic planet

[Thrudd]

We can resolve the biological improbability problem with intelligent design/progenitor species. Yes, the odds of biological life surviving through all the stages to attain interstellar civilization are shockingly low, but it only needed to happen once in the life of the galaxy, possibly only once in the whole universe.

One single intelligent species evolved and survived early in the life of the galaxy, billions of years before earth had even formed. They have since made it their mission to ensure life spreads and survives throughout the galaxy, seeding life based on their own DNA tailored to all manner of environments. Perhaps they eventually went extinct, or ascended to post-physical existence. They may still check in and assist their many experiments and offspring, or they may simply spread life and allow nature to take its course. But once intelligence reaches a certain point, its spread and continued existence are assured, barring total galactic annihilation.

Intelligent life may be seeded and evolve on every planet capable of supporting it, or its locations may be carefully selected so that no two species can interact with each other too early in their development. The reason we have not yet encountered any extra-terrestrial intelligence is by design.

Read Arthur C Clarke for stories on this theme, the Space Odyssey series and Rama series with Gentry Lee both present version of this.

[NichG]

First, cell count is irrelevant. In the context of ecology and evolution you use either biomass (unicellular organisms have 10 times the mass) or effective population size (unicellular organisms not only dwarf multicellular organisms, they make them negligible). Second, yes, we have a much larger population size than expected for our size now. For most of our evolutionary history, our population size was less than 1 million, at points dropping below 10,000. It's only by chance that we survived; one plague or natural disaster at the wrong time would have entirely extinguished our line. Finally, the issue isn't whether multicellularity or large brains can be beneficial, it's whether the intermediate steps can survive. Which is rarely true, and, as I mentioned before, it's currently believed that the only reason multicellularity evolved in the first place is a ridiculously small population size that resulted in a whole bunch of detrimental mutations that, when the population survived by chance, were repurposed to form the backbone of the eukaryotic genome.

I'm surprised you'd say this. Biofilms, for example, are incredibly common and pretty much span the gap between unicellular and multicellular modalities. Often they can toggle that as a response to environment. You can get anything from genetically heterogeneous films where the composition is semi-faithfully reproduced to monoclonal films with internal structures, spore-based replication, and 'altruistic' cellular behavior (e.g. some of the film-scale function is managed by cell suicide, such as the necking-off behavior in the aforementioned sporulation.

So it seems rather that multicellularity is (perhaps surprisingly) easy to find.

As far as large brains, I don't think that's any stranger than e.g. evolving transcriptional regulation of genes. Both are a form of biologically-mediated computation that allows the organism to respond to changes in its immediate environment on scales shorter than its lifespan, and also to adapt more smoothly to longer-term changes (e.g. ~20-30 generations) without requiring an overly high mutation rate that would otherwise be generally harmful.

[Storm_Of_Snow]

Any alien advanced enough to be starfaring probably thinks of us in the same way that Columbus thought of New World monkeys. An interesting evolutionary path (if you're a botanist), but hardly something you'd want to stop and talk with.

Or if you're studying animal behaviour, someone you might want to work out how to talk with, same as we do with chimps and dolphins.

Alternatively, maybe an advanced alien species can't do something we can (maybe they're from a planet around a hotter star, so can see more in the blue-ultraviolet range, but can't see green to red like we can), and aren't rude enough to just grab a few of us and chop them up to find out how we do it.

Or maybe their starfaring technologies are way more advanced than ours because, for whatever reason, they focussed on them, but another technology is a lot less advanced - say, their medical sciences are roughly equivalent to what we had in the early roman empire, or they stuck with valves and never developed the transistor, meaning their computers are massive machines that take 99% of the volume of the ship, but have less processing capability than a laptop.