Solution to the Fermi paradox?

[Silver Jedi]

From here

Fermi’s paradox solved?
February 2nd, 2009 | by KFC |

We have little to guide us on the question of the existence intelligent life elsewhere in the universe. But the physicist Enrico Fermi came up with the most obvious question: if the universe is teeming with advanced civilizations, where are they?

The so-called Fermi Paradox has haunted SETI researchers ever since. Not least because the famous Drake equation, which attempts put a figure on the number intelligent civilisations out there now, implies that if the number of intelligent civilisations capable of communication in our galaxy is greater than 1, then we should eventually hear from them.

That overlooks one small factor, says Reginald Smith from the Bouchet-Franklin Institute in Rochester, New York state. He says that there is a limit to how far a signal from ET can travel before it becomes too faint to hear. And when you factor that in, everything changes.

Smith uses this idea to derive a minimum density of civilizations below which contact is improbable within a given volume of space. The calculation depends on factors such as the lifetime of a civilization and the distance that it might be possible to communicate over and it produces some interesting scenarios:

“Assuming the average communicating civilization has a lifetime of 1,000 years, ten times longer than Earth has been broadcasting, and has a signal horizon of 1,000 light-years, you need a minimum of over 300 communicating civilization in the galactic neighborhood to reach a minimum density.”

So if there are only 200 advanced civilizations in our galaxy, the chances are that they’ll never notice each other.

Of course, we’ve no way of knowing how many advanced civilizations are out there. But this kind of thinking could, for the first time, put a limit on the number that could be out there: less than 200 perhaps?

It also has significant implications for Fermi’s line of thinking.

Would it be too early to say the paradox has been solved?

Ref: arxiv.org/abs/0901.3863: Broadcasting But Not Receiving: Density Dependence Considerations for SETI Signals

The link at the bottom is the actual paper.

I've got ta say, this is nice to hear. On the one had, this means there's still hope that we're not alone out here. On the other hand, it does mean that SETI may be as pointless as some have always feared

[NetKnight]

The author's conclusion is perfectly reasonable, given the assumptions. However, I don't think the assumption on civilization lifetimes is necessarily warranted. It's both too high, and too low.

Let's take a civilization that has just discovered radio. Assuming they are fairly human-like (that they don't naturally see and communicate in the radio spectra, say, which is an assumption of my own, I'll admit), this implies they are a technological civilization, with the surplus production to have the luxury of tinkering with practical aspects of electromagnetism, if not the theory, and with enough electronics industry to produce radios capable of penetrating the local ionosphere. In short, a civilization like ours, with exponentially advancing growth of scientific knowledge and technological capability.

If this is so, then in all but a few fluke special cases (a society akin to Ancient Egypt with radios, say), if exponential growth continues, they should be getting off-world sometime relatively soon after the invention of radio. A mass societal collapse before then could disrupt this, but a sufficiently large collapse should also most likely disrupt radio communication powerful enough to be detected 100s of light years away.

In this way, the broadcasting civilization would have a short lifespan. However, if their development was on the same order of magnitude as ours, this lifespan would be on the order of 10^2, not 10^3 years, for it to occur pre-space. This is of course a nitpick, but an order of magnitude seems pertinent.

Assuming that even a few civilizations do, in fact, establish a space presence, however, a 10^3 year lifetime seems unreasonable. Basically, once a civilization has expanded in to space, and baring the occasional fluke (example: a near supernova or gamma ray burst. We cannot rely on these calamities to consistently kill off all, or even all but a few, burgeoning civilizations), what universal mechanism is going to kill them off? Scarcity of resources doesn't really apply any more: once a ~Type 2 civilization is starting to strain their local resources, they can simply move to another star system. Perhaps it is a failure of imagination on my part, but if even a tiny fraction of nascent technological civilizations get off their planet, I find it hard to conceive them failing to survive far longer then a millennium- and in doing so, expanding beyond their home star system. If this is the case, of course, one wonders why we haven't detected their farthest-flung colonies' radio emmisions, c-fractional starships, and indeed, their presence in the Sol system, getting us right back the the Fermi Paradox.

I'd argue that a rarity of habitable planet formation, abiogenesis, or of intelligent life evolving in the first place is more reasonable for making the Drake equation spit out a low number then a low civilization lifetime for intelligent, technological life. (My money's personally on the latter). Of course, like all speculation concerning extraterrestrial life, working as we are from one data point, this 'reasonable speculation' is really nothing more then philosophy tempered with a spot of physics.

Hmm... verbose post, full of a large train of assumptions, and not advancing an argument that those interested in the Fermi Paradox probably haven't already heard? Check. Oh well, this post might get some some responses tearing it apart, which would be quite enlightening. My apologies to everyone who waded through all that rambling.

[Glass Pearl Player]

On top of all that, the original Fermi paradox is even more blatant: If aliens do exist, they should have visited us by now.
Even with pure STL travel, it would theoretically be possible for an alien species to colonize the entire galaxy within a large but reasonable - given the scale of the project - timespan. All it takes is - in the original argument - one expansionist species. One intriguing counterargument using (iirc) perculation theory says this already did happen - but we are in a region of space where all adjancent colonies decided not to send another generation of colony ships. An amusing counterargument claims that they are already there, and declared earth a wildlife refuge for our primitive species.

An interesting counterargument claims that we live in a region of space labeled "Here be berserkers".

[NomAnor15]

The Fermi "paradox" strikes me as pretty stupid. Why should aliens have necessarily visited us by now? It took four billion years for a form of life to appear on Earth that is capable of even rudimentary space travel, and we've only been here to visit as a civilization (for lack of a better word) for approximately 10,000 years. That's a pretty damn small window given the timescale the universe operates on. So what makes people think that aliens must have visited by now? Or hell, what if they did, but 500,000 years ago? Or 5,000,000? Or their ship is on the way but won't be for another 100,000 years? This doesn't look like a "paradox" to me at all.

[Stark]

Probably because of the whole star-generation heavy-metals thing, methinks. Pointing out it took the solar system 4.5B years to produce vague spacefaring is irrelevant because it's not going to take anywhere near that time for space travel to improve (barring extinction events anyway). And the Fermi paradox isn't about 'visiting', it's about evidence of any kind, and I believe it was aimed at optimistic numbers from the past, where people imagined the galaxy teeming with spacefaring or starfaring civilisations.

[NomAnor15]

Ah, well then. That makes significantly more sense. I stand corrected.

[Guardsman Bass]

I always figured that the reasons behind the Fermi Paradox were

1. Few intelligent, sapient species develop advanced tool-making, or grow up in an environment where that is very difficult (like a water-based sapient life form). Think about if you implanted human-level intelligence into, say, a dolphin. You've got no manipulable arms, no fire, and so forth.

2. Few intelligent species pursue technology in a direction that leads them to radio communication and space travel.

Meaning that while there could be numerous alien civilizations of sort, the vast majority of them never send out a radio signal or send a spaceship into orbit. Those that do are perhaps pretty spread out and very, very very, very rarely come into contact with each other, although obviously this is all just an educated guess. Perhaps the nearest such civilization to ours is over in Andromeda.

[Mayabird]

I never could figure out why it's a paradox. I just always figured that space is MINDBOGGLINGLY ENORMOUS and the whole speed of light deal means that we can't see what's going on everywhere except in the distant past. There could be galaxies where a billion year old civilization was turning them into Dyson megaspheres (Dyson sphere over an entire fucking galaxy, this being about the biggest thing I could think of) and we wouldn't know because the galaxies are four billion light years away. In another three billion years (would it be three billion years? Or would it be more with the whole expansion of space thing?) any astronomers looking in the right direction would be freaking out at the blatantly obvious signs of alien life. There could be happy little STL interstellar civilizations flying around the Andromeda galaxy (which is still really close in the grandest scheme of things) and unless they start blowing up stars for shits and giggles we're probably not going to notice them.

[Sky Captain]

There can be a lot of reasons why we have not detected signs of aliens.

Perhaps we are the first technological civilization that developed in this corner of galaxy/in this galaxy.

It could be an intelligent life forms capable of radio communications are very very rare perhaps on average 1 per 10 galaxies.

Perhaps our solar system in unusually clean of asteroids and comets and that allowed life to get past the level of bacteria. On other star systems suitable for life there could be too much bombardment from space.

Perhaps other intelligent radio capable civilizations are lot more paranoid and avoid broadcasting in space fearing to attract unwanted attention.

Maybe we are really lucky to be away from nasty neutron stars, gamma ray bursters, black holes capable of irradiating our planet with deadly levels of radiation, other systems capable supporting complex life might not be so lucky.

At the end of all that we don`t have any hard data regarding alien life so the whole Fermi paradox thing is more or less an educated guessing.

[TheLostVikings]

Maybe we are really lucky to be away from nasty neutron stars, gamma ray bursters, black holes capable of irradiating our planet with deadly levels of radiation, other systems capable supporting complex life might not be so lucky.

Afaik, our neighborhood is called the "local bubble," named so because the interstellar medium is much less dense than average in our galaxy. I don't remember exactly offhand, but I think it had something to do with a supernova discharge (or something like that) blasting it away.

So I guess one might say we live in a relatively quiet part of town.

[Sarevok]

Would it really be bad if humans were the only or first species to develop sentience ? Methinks not having to put up with kind of godlike entities speculated on the Kardashev scale is an good thing.

[18-Till-I-Die]

Perhaps other intelligent radio capable civilizations are lot more paranoid and avoid broadcasting in space fearing to attract unwanted attention.

Well...actually yeah this was what i always assumed.

This isn't exactly scientific but one idea i always had, kind of an answer to both the Fermi Paradox and the Drake Equation, and i used this in a story before, goes as such.

Life, including intelligent life, is fairly common. In this instance life would not probably be anywhere near Earth, but abundant enough that it is effectively a certainty it would exist and thrive. However...one of these races is rather "hostile". They're extraordinarily xenophobic, or even worse, like White Europeans in our own history just have a belief they're literally BETTER than everyone else. Manifest Destiny in Space. We're talking about something like a Type-II civilization here. So they go from one system to the next--FTL, STL, it doesn't matter how--and then just annihilate or conquer every race they find. Lets just say they're the Inhibitors, for ease of discussion. So, every intelligent races either:

A--figures out that they're out there, and goes completely silent, or tries to hide away (a la the Backgrounders of Orion's Arm) to escape these Inhibitors.

Or

B--they're obliterated or conquered outright by people who believe themselves to be their "betters", just like White Europeans did on Earth to dozens of other civilizations. Aztecs, Africans, Indians (both kinds) the list goes on.

Now this is of course pure conjecture, but it's actually a thought i hit upon while reading about the storied history of Western Civilization. "Big" powerful civilizations obliterate smaller ones, and unlike what many people who write sci-fi think, it wasn't because the Europeans needed or wanted any resources. It was because they honestly, truly thought they were doing these other races a favor by conquering them. Or "Civilizing" them, as our spanish friend Mr. Cortes would put it.

[Samuel]

We do NOT live in The Forge of Gods 18! Defense is superior with STL- you can see you opponent coming and have an entire system to oppose them.

You guys don't seem to get the paradox. The Milky Way has 200 to 400 billion stars. Where is everyone?

[GrandMasterTerwynn]

Probably because of the whole star-generation heavy-metals thing, methinks.

It's not as much a factor as one might think. The median age for stars with sufficient heavy-metals to have formed from something that might support rocky planets ought to be something like a billion or two years older than the Sun. Which is to say even if we assume Earth to be typical, the Galaxy ought to have started producing civilizations back when the most sophisticated form of life on Earth was blue-green algae.

Pointing out it took the solar system 4.5B years to produce vague spacefaring is irrelevant because it's not going to take anywhere near that time for space travel to improve (barring extinction events anyway).

Indeed. Once you develop space travel, it shouldn't take you more than a couple of centuries to get to the point where you're colonizing your local solar system. And once you settle your local solar system and begin converting it into a Dyson swarm, the only thing that can kill you is your sun becoming a red giant, staring down the bore of a gamma-ray burst, a really close supernova, or an unholy combination of superintelligent AI and grey goo gone horribly, horribly wrong.

A Dyson swarm building civilization ought to also be able to eventually afford the energy expenditure for the type of slow interstellar travel that the laws of physics would seem to permit. And once one establishes their first interstellar colonies, the odds against the species going completely extinct drop dramatically.

Perhaps we are the first technological civilization that developed in this corner of galaxy/in this galaxy.

Given the median age of habitable systems in the Galaxy, this is highly unlikely. Not to mention anthropocentrically arrogant to the first degree.

Perhaps our solar system in unusually clean of asteroids and comets and that allowed life to get past the level of bacteria. On other star systems suitable for life there could be too much bombardment from space.

There's no real reason to assume that our solar system is in any way special. Yes, in our search for extrasolar planets, most of the systems we've discovered are nothing like ours, but that's just selection bias . . . our detection methods lend themselves to discovering systems with those characteristics.

Perhaps other intelligent radio capable civilizations are lot more paranoid and avoid broadcasting in space fearing to attract unwanted attention.

Discussed before. You'd have to be unusually determined to wipe out another civilization. And really, the best time to do it is before they invent radio and industry, since, typically by the time you discover they have radio emissions strong enough for you to detect, they've shed their infantile planet-dependency, and are well on their way to being able to withstand anything short of Singularity Gone Horribly Wrong.

Life, including intelligent life, is fairly common. In this instance life would not probably be anywhere near Earth, but abundant enough that it is effectively a certainty it would exist and thrive. However...one of these races is rather "hostile". They're extraordinarily xenophobic, or even worse, like White Europeans in our own history just have a belief they're literally BETTER than everyone else. Manifest Destiny in Space. We're talking about something like a Type-II civilization here. So they go from one system to the next--FTL, STL, it doesn't matter how--and then just annihilate or conquer every race they find.

For a hostile homogenizing swarm species to enjoy any sort of success, they would have to have been among the first species to achieve sapience and space travel in the Galaxy. And they should only target non-spacefaring civilizations (or, even better, planets which have only developed macroscopic, multicellular life,) as interplanetary civilizations are incredibly hard to kill, and the energy expended in doing so would eventually attract the attention of someone bigger than them. In other words, the fact that we exist is probably evidence that there aren't any homogenizing swarms out there, or at least, none which have arisen in the last 600 million years.

A--figures out that they're out there, and goes completely silent, or tries to hide away (a la the Backgrounders of Orion's Arm) to escape these Inhibitors.

You can't hide a whole civilization. An industrial civilization ought to be detectable by someone with a sufficiently large telescope to a distance of several light-years. The only ways to hide a the fact that you've got a sapient species resident in a system is to destroy all traces of civilization more sophisticated than rudimentary agriculture, or to become so advanced that you can transform your solar system into a vast network of supercomputers operating on ambient energy sources and spend the rest of the history of the universe in a really slow-running reality simulation.

[Solauren]

You guys don't seem to get the paradox. The Milky Way has 200 to 400 billion stars. Where is everyone?

And how of those 400 billion stars...

#1 - How many of planets?
#2 - How many have planets that can support life?
#3 - How many of those planets have developed life?
#4 - How many of those planets have developed sentient life?

Using what we know of the galaxy, that's what, roughly 60 stars with planets (out of how many surveyed), 1 known to support life (ours), with 1 /2 of the planets believed to be capable actually doing it. And at that, only one sentient, tool using, communication capable species out of dozens of potiental sentients.

As we know things right now, that's an infinitely small percentage of stars supporting life.


Unless we see a massive upswing in planetary populations capable of supporting life (i.e water, carbon monoxide) being detected, the Fermi Paradox is just intellectual air blowing, based on the currently unsupported assumption that the galaxy is teeming with life.

[GrandMasterTerwynn]

You guys don't seem to get the paradox. The Milky Way has 200 to 400 billion stars. Where is everyone?

And how of those 400 billion stars...

#1 - How many of planets?

From our understanding of the physics involved, the galaxy should be absolutely overflowing with planets.

#2 - How many have planets that can support life?
#3 - How many of those planets have developed life?

Taking our solar system as an example, there are no fewer than seven worlds which could've supported life somewhere in or on them at one point or another in the history of the Solar System (Venus, Earth, Mars, Europa, Ganymede, Titan, and Enceladus.) And given that the ingredients of life are plentiful, and the chemistry fairly straightforward, life ought to be pretty much everywhere.

#4 - How many of those planets have developed sentient life?

Now that's the interesting question. If you've got multicellular life, evolutionary pressure would eventually drive it to get smarter . . . to a point. Big, sophisticated brains are a huge drain on an animal's metabolic resources. For most species, there's a point where you encounter diminishing marginal returns on investing in more intelligence.

Using what we know of the galaxy, that's what, roughly 60 stars with planets (out of how many surveyed),

Beware selection bias. First, the number is closer to 300. Second, our search methods are biased towards turning up large gas giants in oddball orbits. We've only recently started discovering Neptune-mass worlds (barring the occasional Earth-mass world turned up through one-off gravitational lensing events.)

[Furlong]

Whenever people start talking about life on other worlds, and why haave we yet to see evidance of this, I like to bring up a few theories.

1) Of the extra-solar planets we have discovered, most of them are gas giants of some kind. Some seem to take this to mean that our system is unique. I take it to mean we have yet to have the capability to detect rocky planets that are relatively closer to the star they orbit.

2) The Human race has been transmitting radio signals for only about 100 years, and we have been listening to radio waves from other worlds for about half that. As was mentioned in the OP, these signals deteriorate into worthless background noise eventually, but who's so say that even if we detected a signal, we would be able to distinguish it from any other background noise.

3) Simple Psychology. Some cultures here are isolationist by their nature, Ancient China comes to mind. Why do we assume that aliens would even want to make contact with us?

4) Related to #3, perhaps, like in Star Trek, their is a sort of Prime Directive that prevents contact with alien species that have yet to mature to a specific level. Keep in mind, it wasn't too long ago that the USA and the USSR could have obliterated most life on Earth. If you were in charge of monitoring life on earth, would you recommend contact be made with these warlike savages?

[Sky Captain]

Regarding our civilization there is some crucial natural resources which was/is irreplaceable to our civilization`s development especially easily accessible fossil fuels and metal ores. If this is rare combination (I have heard claims that our big moon is somehow responsible for Earth to have metal rich crust) then on other planets intelligent beings simply may can`t develop advanced technology because of the lack of necessary resources. Inability to extract resources also can happen if planet is mostly covered by water with only few percent of total surface being land.

[Solauren]

On the other end of the spectrum from my earlier post;

What about sentient spieces that never had the need to bother to develop technology? Or the biological capacity to do so? (i.e no useable appendiges).

After all, nessicity is the mother of invention. If you don't have a need to develop cloths, you're not going to. The same with anything else.

I mean, why develop long range communication technology if your entire population lives in a small area?

[starslayer]

(I have heard claims that our big moon is somehow responsible for Earth to have metal rich crust)

This is not true. Plate tectonics is responsible for the abundance of heavy elements found in the upper layers of Earth's crust. Without plate tectonics, all the metals sink towards the center of the planet relatively quickly, and are not brought back to the surface.

One thing that intelligent life needs in order to develop is a planet like Jupiter. In its present position, Jupiter prevents most asteroids and comets from actually hitting us, either by deflecting them away from us or simply swallowing them (as it did to Comet Shoemaker-Levy 9). If Jupiter weren't there, complex life may never have gotten very far, because our planet would be bombarded by asteroids far more often than it actually is.

[Samuel]

3) Simple Psychology. Some cultures here are isolationist by their nature, Ancient China comes to mind. Why do we assume that aliens would even want to make contact with us?

Non-isolationist cultures tend to be the technologically advanced ones and seize control over the planet. Plus, aliens make good propaganda for societies that desire an "outside".

4) Related to #3, perhaps, like in Star Trek, their is a sort of Prime Directive that prevents contact with alien species that have yet to mature to a specific level. Keep in mind, it wasn't too long ago that the USA and the USSR could have obliterated most life on Earth. If you were in charge of monitoring life on earth, would you recommend contact be made with these warlike savages?

Sure- it isn't like we could hurt them. Stand off at the Moon with PDs and nothing we have could touch our xeno friends.

What about sentient spieces that never had the need to bother to develop technology? Or the biological capacity to do so? (i.e no useable appendiges).

You mean dolphins?

One thing that intelligent life needs in order to develop is a planet like Jupiter. In its present position, Jupiter prevents most asteroids and comets from actually hitting us, either by deflecting them away from us or simply swallowing them (as it did to Comet Shoemaker-Levy 9). If Jupiter weren't there, complex life may never have gotten very far, because our planet would be bombarded by asteroids far more often than it actually is.

Aren't gas giants rather common? So far, they are almost all we have found with our planet searching and they tend to be very big.

[starslayer]

Aren't gas giants rather common? So far, they are almost all we have found with our planet searching and they tend to be very big.

Yes, gas giants themselves seem to be quite common, even Jupiter mass and above ones. However, we do not have enough data to say whether or not gas giants of Jupiter's size and position in the outer solar system are. After all, Jupiter's year is about 12 times that of ours, and if the friendly neighborhood gas giant is near where Saturn is in our solar system, its year will be about 30 times ours. We haven't even been looking for exoplanets for that long, much less the time required for the multiple orbits necessary to definitively conclude that there's a planet out there.

Besides which, there may even be situations where the gas giants eject the potentially complex life bearing worlds from the system. For his senior thesis, an astrophysics major here helped run simulations of the Solar System for several billion years into the future. In a couple permutations, Mercury was ejected by Jupiter 1-2 billion years from now (or is sent crashing into the Sun or even Venus). Of course, the uncertainty for that far into the future is quite large, but it could happen. Likewise, potential terrestrial planets are unlikely to be ejected from a system like ours, but if the Jupiter is closer, or there are a couple of them, it could actually happen before complex life develops. Gravity's a funny thing...

[Junghalli]

The Fermi Paradox, as others have already pointed out, goes beyond signals.

Now, the Milky Way has had enough heavy elements to form large terrestrial planets since ~9.3 billion years (reference). Our sun is ~4.6 billion years old. That means that there are (or should be) large terrestrial planets over 4 billion years older than Earth. Put it another way, if there are aliens out there, the oldest ones should logically have had a head-start on us of over 4 billion years.

Now let's say one of those aliens started colonizing the galaxy. Assuming they expand at an average speed of, say, .01 c, they could colonize every star in the galaxy within 10 million years. It's a simple matter of exponential growth.

Now you might say that civilizations would be unlikely to do that for various reasons, but the problem is if intelligent alien life is common, logically, somebody should have done it by now. It doesn't matter if a thousand matches fail to start a fire - all that is necessary is for one to succeed. Billions of years has already passed in which this might happen, if the timeframes of human evolution are any guide. All it takes is one successful expansionistic civilizations and we're back to the Paradox. Even if they died out long ago for some reason, they would probably have left detectable artifacts.

Personally, my money is on intelligent life being relatively rare, combined with other factors like very few of the civilizations that do arise survive long enough to colonize more than a small fraction of the galaxy's disk.

[Junghalli]

Now that's the interesting question. If you've got multicellular life, evolutionary pressure would eventually drive it to get smarter . . . to a point. Big, sophisticated brains are a huge drain on an animal's metabolic resources. For most species, there's a point where you encounter diminishing marginal returns on investing in more intelligence.

Personally I have the suspicion that our intelligence is sort of like a peacock's tail: an evolutionary trend that "went out of control" and produced a species with a ridiculously extreme feature. Which if true probably means it wouldn't be too common. How many species on how planets will have a tail like a peacock?

Unless we see a massive upswing in planetary populations capable of supporting life (i.e water, carbon monoxide) being detected, the Fermi Paradox is just intellectual air blowing, based on the currently unsupported assumption that the galaxy is teeming with life.

While the assumption that the galaxy is teeming with life is indeed unsupported, drawing conclusions from the sample of planets we've detected so far would be just stupid. Our observational methods are massively skewed toward big planets in short orbits and have a lot of trouble detecting Earthlike planets. Put quite simply: at this point we don't know shit about the occurrence of Earthlike planets in the galaxy, maybe when Kepler has been running a couple of years we'll be able to make meaningful conclusions.

[Serafina]

The fermi paradox simply points out that there are questions we have to ask.
There is simplynot enough data to answer it.

As for solutions, there are only two:

-We are the only lifeform in our galaxy intelligent enough to send signals/do the other stuff descrived.

-There is something preventing those signals/other stuff

The first is arrogant, but it IS a viable solution - whether there are not enough planets, intelligence is rare for some reason or there is something wiping out civilisations - we simply do not know.

The second would require either great distances (like: life bearing planets are VERY rare) or some kind of unknown mechanism (dark matter) preventing those signals/other stuff (unlikely).