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Different responses to Fermi Paradox


Martin
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http://arxiv.org/abs/0907.3432

 

This is a 39 page article that delves into a dozen or so different answers to the Fermi question/paradox that have been proposed over the past half century.

 

The author is a Belgrade astronomer/SETI expert/future generalist. He seems to know a lot and reason carefully, like a credible academic.

Well, that's my first impression. Maybe you can find some flaws, if so please let the rest of us know where you think he is wrong.

 

I don't think he has any preferred answer, he compares and weighs them all.

Maybe he ends up throwing out some as relatively improbable, and narrowing down to the ones he thinks are better. But on the whole it looks like a balanced survey of all the ideas.

 

If you are interested in Fermi question, have a look.

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I just read the paper now, and it seems to me that the paper is either jumping to conclusions, or not really considering all possible arguments.

 

For example, those who argue that most nearly every "habitable" planet must have been colonized seem to forget that despite our so-called technological might, more than 70% of the Earth remains uninhabited. And even though modern nation-states claim to own vast swaths of land, most of that is either uninhabited, or populated by various tribes that do not acknowledge the legitimacy of whatever government is in place (take, for example, the Amazon tribes of Brazil).

 

It is interesting that the paper does note that because most Earth-like planets out there are billions of years older than our own planet, then there is a strong possibility that any civilizations that have evolved on those planets would have gone out and colonized the galaxy long ago. Of course, one has to remember that our current biosphere has only existed for 350 million years or so, and complex life in general for only 500 million years tops. If a civilization had visited Earth prior to that time (which would seem very likely), they would have found nothing of interest. If we assume that they are also oxygen breathing, then it would be very likely that they could have perceived Earth as a hostile planet at the time, and just simply not bothered with it. This and other factors could very well lead, I think, to a scenario in which even an aggressive type II or type III civilizations leave vast areas of the galaxy just simply out of touch.

 

Also, I think it severely overestimates how easy it would be to detect extraterrestrial civilizations. Our own civilization is not visible even if we were as close as the Moon, and I read somewhere that even just past one light year our radio signals would be much too weak to detect. Certainly any alien probes standing on, say, Saturn wouldn't know that any intelligent life existed in our solar system (if you ever watched Pale Blue Dot, Sagan himself notes this). For us to be anywhere near visible on a galactic scale, our energy output would have to rival that of the sun. By contrast, we are trying to detect civilizations that are, at minimum, in the next few light years around.

 

Also, if they did engage on mega projects on an interstellar scale, how would we tell the difference? Assuming a Ringworld like structure is possible (never mind a dyson sphere), that data could just as easily be interpreted as a dense asteroid field. Any large number of orbital space stations could just as easily be dismissed as asteroids, or even small moons. Any "star mining" could just as well be just solar flares; I feel that the argument that large Type II or Type III scale civilizations should be easily detectable to be a massively flawed argument and demonstratively false.

 

Barring that, the only argument that I find to be defensible in that paper is the Rare Earth argument. While we may find loads of worlds with either simple or complex life, planetary space-faring species could be rare. Indeed, the fossil record suggests that evolution does not go in any particular direction, and there is no reason to believe that intelligence is inevitable. It certainly wasn't the case for us, and it sure as hell won't be the case for any ET biospheres we find in the universe.

Edited by Reaper
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Reaper, I was glad someone gave this paper a critical reading.

If you have some particular points of criticism, where you can give a page (and maybe even paragraph) reference and point out some statement that is wrong, that would be appreciated too. Not necessary! But it would give me something extra to chew over.

 

Did you think the author favored some one particular explanation, or reply to Fermi's Question?

 

It seemed to me that he didn't pick a favorite or favorites. He just surveyed all the different possible responses that have been made, and tried to restate each argument concisely.

 

Do you have a preferred explanation yourself?

 

I don't have one, so far. It just seems bizarre to me that we have seen no evidence of another tech civilization. But I think it is just a fact that we have not---no alien beercans, no intercepted messages---and we just have to accept this as another bizarre unexplained fact.

 

And hope that eventually we understand why.

 

But I don't claim my attitude on this is especially correct or sound or an example to be followed:D, it is just my personal reaction. So I interested by the paper because it surveyed what other people had thought about it and what their attitudes were. There was even some paranoid answers to Fermi Question which he included, as I recall;)

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I don't think there is a paradox. The Fermi Paradox is based on too many optimistic assumptions about how many intelligent space-traveling civilizations there are. Perhaps they are so very rare and far apart, that they haven't found us yet. Or they don't explore space as much as we like to think. Maybe long-distance space travel is more difficult than we think. We were brain-washed by scifi to think it is easy. They may have explored out to a few hundred light years, and called it quits.

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A couple thousand years man has been fairly intelligent, the last hundred technical, mere pinpricks of time on the grand scale. From caves to space in very little time. Consider how long the dinosaur existed and never evolved enough to explore space, build cars, or anything for that matter.

 

Us humans, a freak speck of intelligence in the vast cosmos of space??

 

I'm sure, positive even, that we will eventually find life elsewhere. But will it be intelligent??

 

We have about a hundred years of good science under our belts. Are we really that intelligent?? How much more will we know in another hundred years or a thousand??

 

If there is intelligent life out there, it is more than likely far more advanced than we are. Especially if it has the ability to discover us. We are probably the primitive species.

 

And then one has to consider this human freak of nature, in a short time from caves to space, I wonder..... did he get a little help?? Hmmmm.....

 

Humans are a fairly oddball species no doubt.

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Well I haven't read it all yet, but it seems that he is attempting to separate philosophical belief from scientific observation. That is what Copernicanism is all about, really. People who insist that there must be ETI need to find a way to prove it and not just pen into the edges of the map of the universe that "Thar be intelligent aliens!". In a more desparate sense, for some people SETI is actually a search for extraterrestrial mentors. They don't see much hope for hairless apes with nuclear arsenals or the ability to destroy the environment. Imagine nineteen terrorists had crashed five spaceliners into the Earth at 90% of the speed of light (good-bye civilization). If greater technology really means that a small group can now do incredible harm, then it would be advantageous to find someone else to tell us how to get by this point in our history (the "been there, done that" factor). The most important transmission for SETI to receive is simply that some species, somewhere made it. So the interstellar silence has a gnawing OMG factor that cannot be ignored.

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Did you think the author favored some one particular explanation, or reply to Fermi's Question?

 

It seemed to me that he didn't pick a favorite or favorites. He just surveyed all the different possible responses that have been made, and tried to restate each argument concisely.

 

Well, for one, it seems to strawman the Rare-Earth argument, on page 19 where it compares it to "special creationism", when in reality it's almost nothing like that at all.

 

And I saw one part where it tried to refute the idea that there could be large volumes of space uncolonized without really giving a convincing reason for why every habitable world in the galaxy has to be colonized in the first place.

 

Other then that, I think my feeling, now that I think of it, was directed at the theories themselves rather than the paper. The paper itself does a good job presenting the different viewpoints.

 

 

Do you have a preferred explanation yourself?

 

My personal preference is for the Rare Earth Hypothesis, even though there is scant empirical evidence for it to date. In particular, I think it is far more likely that intelligent life is much more rare than any other form of life, and that can be verified through the fossil record here on Earth.

 

Some sci-fi novels, such as Asimov's Foundation series, does touch upon this somewhat.

 

I don't have one, so far. It just seems bizarre to me that we have seen no evidence of another tech civilization. But I think it is just a fact that we have not---no alien beercans, no intercepted messages---and we just have to accept this as another bizarre unexplained fact.

 

And hope that eventually we understand why.

 

I don't find it that bizarre. I just think its a consequence of the fact that we don't really have any idea of what we are looking for. Sure, we might easily be able to find tons of ET biospheres, since the criteria for their existence is already well established. On the other hand, the criteria for what constitutes an extra-terrestrial civilization is not. The fact that there are a bunch of theories trying to answer the Fermi Paradox testifies to that. After all, we have such a hard time trying to agree on one with our own civilizations, let alone an alien one.

 

In all the arguments I've seen, they all seem to agree that Type II or Type III level civilizations are easily detectable, although they don't give any rational for it at all. If all of those kinds of civilizations are like the ones we see in Star Trek, for example, then we would have almost no hope of detecting them simply due to the fact that they don't use conventional radio waves, and their engineering feats would simply be undetectable even if they aren't trying to hide it. I would imagine that even the ones that are capable of large interstellar projects would be extraordinarily difficult to detect, since it has yet to be addressed on how they could be distinguished from ordinary natural phenomenon.

 

Also, there is the problem of trying to outguess what a Gyr civilizations would be like. We are talking about a civilization that has outlived entire geological epochs and eons, and quite possibly entire stars. It certainly has had more than enough time to survey and colonize our galaxy. The fact that there is no evidence whatsoever that they have visited Earth at anytime in the past 4.5 billion years means that either:

 

1)Faster than light travel is impossible

2)It's impossible to colonize the entire galaxy this large, even given an infinite amount of time.

3)They don't exist in our galaxy.

 

Or

 

4) All of the above.

Edited by Reaper
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Martin,

 

Read half the article and skimmed the rest. I think the solution of the riddle is to be found in a little bit of each of many of the solutions, but mostly in reframing the question. All the solutions seem to have a major flaw in that the question has an anthropic bias, and an earthly bias, in that we are wondering why we haven't been able to zoom our telescopes in to an extraterrestrial Cape Kennedy, or intercept a radio show on the Alpha Centauri interplanetary football finals. Combine the fact that the signs we are looking for, may not be the traces left by other civilizations, with the fact that we may already have already seen signs which we have ignored, misinterpreted or dismissed, and the paradox sort of dwindles away.

 

Our ideas of what life, intelligence and conciousness are, are very anthropically biased.

Do you think the sun is alive? Do you think a tree is intelligent? Do you think an ant colony is conscious? Why do we not have SETI type programs aimed at comminicating with these types of entities?

 

So my answer to the riddle is "no, we are not alone", and "yes, we have seen signs", and "probably" we will eventually be contacted by, or notice, or visit, extraterrestrials, but most likely they will not be what we expected.

 

Our evolution from the first mitochondria to our present form, was dictated by the special characteristics of Earth. The temperature, the pressure, the elements in the air, water, rock and soil. Dictated by the other life forms that evolved beside us. Our evolution as a civilization was dictated by finding ways to utilize our surroundings to ensure survival and reproduction. Each technological advance and social progress was built on the body of knowledge and philosophy that previous members of our species laid down. Our civilization would be different had it not been for Plato, Hitler, Newton, Pasteur, Mohammed, Einstein, Confucius, etc. etc..

 

That WE would be different, given a few small changes in our past, and given that WE do not recognize the life, intelligence and conciousness in the entities we HAVE run into in the universe already, I would say there is little chance we will run into US, anywhere else, but here.

 

Regards, TAR


Merged post follows:

Consecutive posts merged

By the way, I do think I saw some alien crafts when I was 18, out on a farm in PA. It was during a party in the early 1970s, so all the observers were either intoxicated like I was, or stoned, but at least a dozen people, witnessed the same thing. 5 or 6 lights were hovering over a powerline that we knew ran through the woods behind the farm. Maybe about 1 or 2 miles away. Several of us stood together talking about the lights and what they could be for 5 or 10 minutes. We heard no sound, and figured we were close enough that we would have heard them if they were heliocopters, so we figured they were probably aliens, and were considering what we should do, others came from the house and mostly we decided it would be best just to put out positive "vibes" and not be scared or involve the authorities (we did have illegal substances about), or be aggressive in anyway or find our way over there. After several more minutes, they left, one by one, starting out, and then zipping out of sight in a manner not familar to us or any technology we were aware of. We figured they just fueled up, off of the magnetic flux surrounding the high voltage AC lines, and went off about their business.

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Something to consider:

 

We assume we are the intelligent species of the universe because we have not detected any other intelligent life forms out there so far. This is a great, great big assumption. We assume this primarily because of the lack of identifiably civilized radio wave transmissions.

 

How long have we been using radio transmissions??

 

How much longer will we be??

 

Wouldn't light be a much better method of communicating for a highly intelligent species?? Our use of radio waves may be ancient technology. It may be like looking for smoke signals! LoL!

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Something to consider:

 

We assume we are the intelligent species of the universe because we have not detected any other intelligent life forms out there so far. This is a great, great big assumption. We assume this primarily because of the lack of identifiably civilized radio wave transmissions.

 

How long have we been using radio transmissions??

 

How much longer will we be??

 

Wouldn't light be a much better method of communicating for a highly intelligent species?? Our use of radio waves may be ancient technology. It may be like looking for smoke signals! LoL!

Rockman,

 

You are a man after my own heart. And add these considerations:

1. Why does intellegent life have to exist in our time scale? Their lifetime could be a minute or a million years.

2. Why does intellegent life have to exist in our size scale? They could be as big as an ant or a planet.

3. Why does intellegent life have to sense electro magnetic waves in the same way we do? They could "see" gamma rays and "feel" gravitational and magnetic fields.

4. They could be so different from us in their structure, senses, thinking, goals and needs, that they would not even recognize us as intelligent life. Much less have any requirement to look for a way to communicate with us.

 

The beings fueling up off the power lines and moving on, could be analogous to a couple of us picking some apples off a tree and not even noticing, or caring that some leaves sensed our presence.

 

Regards, TAR

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There are something like 50,000 galaxies within half a billion light years of us (approximately five quadrillion stars). If interstellar travel is possible at even a fraction of the speed of light by spaceships that are essentually enclosed microcosms, then a technologically advanced civilization that evolved over the first few billion years of the universe could have easily colonized that entire volume by now. (Galaxies were created after about 500 million years, allowing 10 billion years for one single, advanced, space-faring civilization to evolve anywhere and 3 billion years for them to colonize the 50,000 galaxies with simple, exponential growth cycles). Colonization would not mean looking for any specific type of planet. A star is a useful and practical source of energy and any material orbiting a star would be used to construct more microcosms around it (Bernal Spheres, etc.). Thus, every star would be colonized. So you wouldn't need radios or laser detectors (BTW, SETI Australia is using laser detection) to listen in to their messages, because they would/should be right here in our solar system where they would have been living on their Dyson ring for the past several million years. Further, a civilization that chose to stay only around its original star would eventually be doomed to a supernova or a GRB, so advanced civilizations must expand or die out completely. This is the reasoning behind the FP. This Type IV civilization is the subject in, "Where are they?"

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That is a breath-taking vision, Arch.

 

Gee...I dunno.

 

=======================

 

Wait. What's the motive for going outside your home galaxy? A civilization concerned about its longterm survival would have a motive to spread to other stars, and perhaps might spread to a substantial number in one galaxy. But what's the point of going beyond that? especially on a systematic routine basis?

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There are something like 50,000 galaxies within half a billion light years of us (approximately five quadrillion stars). If interstellar travel is possible at even a fraction of the speed of light by spaceships that are essentually enclosed microcosms, then a technologically advanced civilization that evolved over the first few billion years of the universe could have easily colonized that entire volume by now. (Galaxies were created after about 500 million years, allowing 10 billion years for one single, advanced, space-faring civilization to evolve anywhere and 3 billion years for them to colonize the 50,000 galaxies with simple, exponential growth cycles). Colonization would not mean looking for any specific type of planet. A star is a useful and practical source of energy and any material orbiting a star would be used to construct more microcosms around it (Bernal Spheres, etc.). Thus, every star would be colonized. So you wouldn't need radios or laser detectors (BTW, SETI Australia is using laser detection) to listen in to their messages, because they would/should be right here in our solar system where they would have been living on their Dyson ring for the past several million years. Further, a civilization that chose to stay only around its original star would eventually be doomed to a supernova or a GRB, so advanced civilizations must expand or die out completely. This is the reasoning behind the FP. This Type IV civilization is the subject in, "Where are they?"

 

Thoughts on the speed of that:

 

That's 1/6 of lightspeed, or almost that, accounting for the 3 billion years of expansion. (that's colonization speed, not just travel)

 

How much energy is required to maintain 1/6 c , never mind achieve it, with respect to the CMBR isotropy? How much hotter and intense was the CMBR back then, 3 billion years ago?

 

Wouldn't colonization generally require round trips, or at least decelerating/accelerating to/from the speeds of most planets, solar systems etc, (that are for the most part locked to the CMBR isotropy), for refueling and at least a minimal amount of hunting/gathering for maintenance, re-manufacture or refurbishing of whatever it is that will be moving on?

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Again, Copernicanism is scientific fact versus conjecture. There is no scientific reason that they could not travel at 1/6 c, or 5/6 c for that matter. This would be a pan-galactic culture that is probably a million years into the space colonization business by the time they start seeding near-by galaxies. Von Neumann probes could pave the way so that the "seed" ships would arrive with the colonists ready to move into the finished Dyson rings. What might we do in three billion years? As for round trips or two-way communication, my ancestors never went back to Europe and e-mails to Alpha Centauri would take many years for an answer. So I guess we'll just have to forget about space colonization? These would be explorers. Anything that can be organized, can be done. Why should aliens come here just to do a few anal probes and then go back home or only send us a message in cryptic galactican? Either an advanced civilization actually colonizes as much as possible in order to increase their survival chances, or they end up huddled around a single dying White Dwarf Star for eternity.

So, where are they?

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I'd like to point out that at an age of the universe of 3 billion years old, the galaxies were considerably closer together than they are now. So a civilization at this time would have less trouble crossing between galaxies.

 

So, I tend to ask as Arch does, where are they?

Edited by SH3RL0CK
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FYI my earlier post, it's actually more like five hundred thousand galaxies, not fifty thousand.

It's unlikely that we live in some kind of an experiment or a simulation, so either the universe is much more dangerous than we can imagine (SNs and GRB's) or technology is a one-way trip to extinction.

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Again, Copernicanism is scientific fact versus conjecture. There is no scientific reason that they could not travel at 1/6 c, or 5/6 c for that matter. This would be a pan-galactic culture that is probably a million years into the space colonization business by the time they start seeding near-by galaxies. Von Neumann probes could pave the way so that the "seed" ships would arrive with the colonists ready to move into the finished Dyson rings. What might we do in three billion years? As for round trips or two-way communication, my ancestors never went back to Europe and e-mails to Alpha Centauri would take many years for an answer. So I guess we'll just have to forget about space colonization? These would be explorers. Anything that can be organized, can be done. Why should aliens come here just to do a few anal probes and then go back home or only send us a message in cryptic galactican? Either an advanced civilization actually colonizes as much as possible in order to increase their survival chances, or they end up huddled around a single dying White Dwarf Star for eternity.

So, where are they?

 

Assuming they have the technology:

 

Their would be considerable resistance to maintaining 1/6 c wrt the cmbr isotropy. Trying to maintain 5/6 c would take many times that same mass and energy, What sources of mass and energy can be harvested at that velocity with any efficiency?

 

It may simply be that "they" are all still back close to home.

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Assuming they have the technology:

 

Their would be considerable resistance to maintaining 1/6 c wrt the cmbr isotropy. Trying to maintain 5/6 c would take many times that same mass and energy, What sources of mass and energy can be harvested at that velocity with any efficiency?

 

It may simply be that "they" are all still back close to home.

 

Actually, there is not. We know of at least one way of traveling at a significant fraction of the speed of light: http://en.wikipedia.org/wiki/Project_Orion_%28nuclear_propulsion%29

 

While we humans as of yet haven't worked out the political difficulties of allowing this technology to become commonplace, there is no reason to believe that other civilizations would be as restrictive. Certainly, if there are other advanced civilizations out there, sooner or later it will develop the same capabilities and technologies that are currently available to us.

Edited by Reaper
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Actually, there is not. We know of at least one way of traveling at a significant fraction of the speed of light: http://en.wikipedia.org/wiki/Project_Orion_%28nuclear_propulsion%29

 

While we humans as of yet haven't worked out the political difficulties of allowing this technology to become commonplace, there is no reason to believe that other civilizations would be as restrictive. Certainly, if there are other advanced civilizations out there, sooner or later it will develop the same capabilities and technologies that are currently available to us.

 

That theoretically gets you up to speed. How do you maintain it?

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That theoretically gets you up to speed. How do you maintain it?

 

If you can get to the speed you want, why couldn't you supply sufficient thrust to maintain? The maintenance thrust required is considerably less than that required to reach the desired speed in the first place.

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That theoretically gets you up to speed. How do you maintain it?

 

If you can get to the speed you want, why couldn't you supply sufficient thrust to maintain? The maintenance thrust required is considerably less than that required to reach the desired speed in the first place.

 

:doh:

 

You're in space! You don't need to maintain it. Don't tell me that you guys actually thought friction would be significant factor in space travel...

 

All you need is enough fuel to speed up and slow down. And maybe a little extra to change direction.

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I can't tell you how a culture a million years more advanced would travel through space. However, the physics we understand says that you cannot travel at 7/6 c, but that there is no scientific reason that you can't travel at 1/6 c. That's all that I am saying. They would have the energy of all the stars in their home galaxy at their disposal. We're talking googolplex-joules. Either there is some unknown reason that makes interstellar travel impossible, or I am quite cretain that they would figure it out.

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I can't tell you how a culture a million years more advanced would travel through space. However, the physics we understand says that you cannot travel at 7/6 c, but that there is no scientific reason that you can't travel at 1/6 c. That's all that I am saying. They would have the energy of all the stars in their home galaxy at their disposal. We're talking googolplex-joules. Either there is some unknown reason that makes interstellar travel impossible, or I am quite cretain that they would figure it out.

 

The distances between galaxies are gigantic. If they are traveling at 1/6c to go between galaxies, it would take tens of millions of years minimum. Unless you can create a craft capable of functioning that long in the vacuum of intergalactic space, I don't think it would be possible for them to spread out over the volume that you proposed earlier.

 

Besides which, I have not yet heard of one good reason for why every star in a galaxy has be colonized, should there exist a civilization capable of venturing away from their home star system. Just because they can travel between stars doesn't mean that they will colonize all of them. Indeed, humanity's current plans involve us colonizing only systems with Earth-like planets once we gain the capability.

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If you can get to the speed you want, why couldn't you supply sufficient thrust to maintain? The maintenance thrust required is considerably less than that required to reach the desired speed in the first place.

 

Considerably less but maintained for hundreds of years (for an extremely "local" trip on the scale we are discussing), not just the days or weeks required to get up to (and down to) speed.

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