Where is everyone ? The mystery remains ...

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posted on May, 11 2010 @ 07:06 PM
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THE FERMI PARADOX




The Fermi Paradox was first stated by Enrico Fermi in 1950, allegedly during a lunch time conversation. Fermi used some straightforward math to show that if technological civilizations were common in our galaxy and moderately long-lived, then the galaxy ought to be fully inhabited. The vast distances of interstellar space should not be a significant barrier to any such civilization if based on the assumptions of exponential population growth and plausible technology.

The fact that no convincing evidence had been found of extraterrestrial activity in or near the solar system suggested to him that there were no intelligent extraterrestrial societies in the Galaxy. "If they existed," he said, "they would be here." ... hence, the paradox.

So, one can quite legitimately ask ... why the "Great Silence" out there ? ... where are the aliens?






In a universe with billions of galaxies, those galaxies having billions of stars, it is implausible that this planet is the only abode of intelligent life, that there aren't a veritable plethora of other planets around with intelligent life forms on them. Given the potential of a multitude of intelligent aliens, it is highly unlikely that we lead the pack as far as technology and science are concerned. In fact, if one thinks of the billions of years involved, there should be alien races that are millions of years ahead of us technologically. When we think of what our own race has managed to achieve in the past few hundred years of technological development, it's almost unimaginable as to what could be achieved in millions of years by these hypothetical aliens civilizations. To paraphrase Arthur C. Clarke, surely their technology must be like magic to us, as far beyond our comprehension as a plasma tv, cell phones and computers are beyond the comprehension of a caveman.

Sixty years have now passed since Fermi first posited his famous paradox, and we are still no closer to an explanation as to why we seem to be surrounded on all sides by a deathly silence. And so the paradox and one of the most elusive questions in modern cosmology yet remains to be answered ...

Where are they ?





For those ATS members who had not yet come across Fermi's paradox, hopefully in the above, I've succinctly summarized the problem as modern cosmology currently see it. In the remainder of this thread, I intend to present discussion attempting to come to terms with this paradox and in the process, offering up various explanations that may shed some light on it. However, it needs to be kept in mind that these explanations are ONLY possibilities and at the conclusion of the OP, any ATS members with interest can then jump in with their own hypothesis and thoughts.
At the conclusion of this OP, I have included a large reference resource used in the generation of this thread.



Following Fermi's observation, and a number of decades later, a similar argument was subsequently raised in articles by Freeman Dyson (US), Michael Hart (US) and David Viewing (Britain), and also by a number of others. It was shown in quite straightforward calculations that given the existence of a technological race capable of interstellar travel at (a modest) one tenth the speed of light, that that race should be able to colonize the entire Galaxy within a period of one to 10 million years. Therefore, if such civilizations existed, why has no evidence of alien visitation to the solar system plainly and unequivocally become evident ? Admittedly, to advocates of the extraterrestrial hypothesis of unidentified flying objects, or the paleocontact (ancient astronaut) hypothesis, the answer was simple: intelligent beings from the stars had arrived. Yet the continuing lack of hard evidence to support these claims, together with the availability, in most cases, of more mundane explanations, inevitably led the scientific community to consider other possibilities. Out of these possibilities, two camps have emerged. In one were those who accepted Fermi's conclusion that the absence of observable extraterrestrial artifacts in the solar system implied an absence of extraterrestrial intelligence throughout the Galaxy. Therefore according to this view, SETI (Search for Extra Terrestrial Intelligence) was essentially a pointless exercise and as Hart was to put it, a "waste of time and money". In the opposing camp, were those who favoured the existence of advanced civilizations elsewhere in the Galaxy and who sought, therefore, to find ways to explain the Fermi Paradox.


Over the ensuing decades, many and varied explanations have been put forward in an attempt to explain this mystery. I've selected a number of them that I consider have high potential and listed below:

(1) We are the first on the scene or at least we are so early that there is nobody around to visit us or to try to communicate with us.
(2) We are unique. Either planetary systems are very rare or life is very rare or intelligent life is very rare.

Note: The difference between (1) and (2) is that in (1) we are the first of many; in (2) there is nobody else at all.

(3) Interested in us but do not want us (yet) to be aware of their presence
(4) Not interested in us because they are by nature xenophobic or simply not curious
(5) Not interested in us because they are sociologically and/or technologically much further ahead of us
(6) Prone to annihilation before they achieve a significant level of interstellar colonization, because:

  1. They self-destruct.
  2. They are destroyed by external effects, such as:

    1. The collision of an asteroid or comet with their home world
    2. A galaxy-wide sterilization phenomenon, e.g. a gamma-ray burster or supernova
    3. Cultural or technological stagnation


(7) Interstellar travel is impossible.
(8) Interstellar travel is possible but is not very economical. We have not been visited because the cost is much higher than any potential return.
(9) Interstellar communication is impractical or there is a preferred mode of communication which we don't know about yet.
(10) We are a protected species. Either developing species in general are protected or ours in particular is.
(11) The first technological civilization to have developed subsequently eliminates all potential developing rival civilizations.


Continued next post ...


[edit on 11/5/10 by tauristercus]



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posted on May, 11 2010 @ 07:07 PM
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Continued from previous post ...


So based on the above possibilities, it's going to be worthwhile taking a look at some of them.



1 - We are the first on the scene or at least we are so early that there is nobody around to visit us or to try to communicate with us
Even though possible, one has to regard this particular scnario as being statistically highly unlikely. Scientific evidence indicates that life arose on this planet as early as conditions would permit, most likely within a 1.2 billion years of condensation out of the solar nebula and within 200 million years of the cessation of major bombardment of Earth by planetoids. Our star system is a Population I stellar system, i.e. it is made up elements heavier than Lithium. Population I stars are necessary for the existence of life as we know it. Without these heavier elements, it would be impossible for terrestrial type planets to form, let alone the complex organic molecules that life is constructed of. Population I stars are formed from the remnants of nova and more importantly supernova. They are necessary processes to create and disperse the heavier elements that we are made up of. It's been estimated that the amount of time required for a star to form out of an interstellar nebula is less than a million years. Given that the age of our galaxy is estimated to be 12 to 15 billion years, it is unreasonable to assume that terrestrial type planets capable of supporting life would not have formed within first several billion years of the birth of the galaxy. This would give a span of time of 10 to 13 BILLION years that no intelligent life capable of sustaining an advanced civilization occurred in our galaxy. As already mentioned, this seems a highly unlikely scenario.



2 - We are unique. Either planetary systems are very rare or life is very rare or intelligent life is very rare
One argument used against the existence, or at least for a low probability for life elsewhere is one of shear number of random events that lead to life on Earth. The implication here is that this long sequence of events leading to life is delicately balanced and any significant variation would be sufficient to break it. This is misleading in that it implies that the sequence of events leading to life, and more particularly to intelligent tool using life, is sparse and narrowly defined. A similar argument about the chain of events leading to a specific human individual can be made, yet there are billions of us on earth. Like the events leading to each unique human, the events leading to an advanced culture are not sparse but most likely many and varied.

A number of methods have been devised to give rough approximations for the expectation of intelligent life appearing in the galaxy. Even though many factors have to be taken into account, we are still left with the inescapable conclusion that there should be literally thousands, if not millions, of advanced extra terrestrial civilizations out there.
Baugher has produced estimates of approximately 200 million civilizations in our galaxy, assuming they all reached this point at the same time. Baugher has also estimated that approximately 1 advanced civilization comes into existance approximately every 100 years.
Sagan, on the other hand, has derived estimates of between 50 thousand and 1 million advanced civilizations currently in the galaxy.
Irrespective of the actual numbers of advanced civilizations in the galaxy, all estimates point to a significant number and the conclusion that the galaxy is essentially teeming with advanced life.



3 - Interested in us but do not want us (yet) to be aware of their presence
This explanation is based on the suggestion that if advanced alien civilizations do exist, that they may choose to deliberately remain "invisible" to us but continue to monitor us by employing a strategy of remotely placing automated and intelligent monitoring devices on or near the worlds of other evolving species to track their progress. Such a monitoring device might eventually establish contact with a developing race once that race had reached a certain technological threshold, such as large-scale radio communication or interplanetary flight.

Already, scientists are steadily coming to understand the basic conditions necessary for carbon-based life to develop. They can identify those stars in the solar neighborhood most like our own Sun, and can delineate approximately the habitable zone around any given star in which complex biochemistry might be expected to flourish. In the last decade or two, scientists have steadily been improving their techniques and ability to detect such extra-solar planets. If we are slowly gaining such a capability, the presumably, more advanced species would be able to stake out with reasonable accuracy those stars and their associated worlds upon which intelligent life had a good chance of eventually developing. Such promising locations might then be expected to come under increasingly intense scrutiny by the use of such automated sentinels. In fact, this very idea was used by Arthur C. Clarke in his short story "The Sentinel" which was subsequently used by MGM as the basis for the movie 2001: A Space Odyssey.

In 1960, Ronald Bracewell, an Australian physicist and electrical engineer discussed the possibility of an advanced extraterrestrial civilization making use of just such a strategy of monitoring star systems for developing technological civilizations. These hypothetical automated robotic observers became known as "Bracewell probes".
According to Bracewell, this scenario would consist of such automated spacecraft sent out by advanced technological races with the object of making contact and exchanging information with other intelligent beings in the Galaxy. Bracewell argued that interstellar "messenger probes", as he called them, offered an attractive alternative to the conventional SETI approach of listening for extraterrestrial signals and, if successful, engaging in an excruciatingly slow dialogue across many light-years.

As originally conceived, Bracewell probes, powered by high-speed propulsion units for interstellar travel, and autonomously controlled by computers with a high degree of artificial intelligence, would be dispatched toward star systems that had been earmarked as biologically interesting. Upon arrival at a target star, a Bracewell probe would enter a near-circular orbit in the middle of the star's habitable zone and in the same plane as its planetary system. This would ideally place it to make contact with any intelligent, technological residents. Having powered up its instruments and drawing power from the host star, it would scan for narrow-band radio transmissions indicative of an artificial origin. If any were found, it would record them, identify their source, and broadcast their contents back unaltered in order to draw attention to itself. This would allow the existence and location of the probe to be established, and a subsequent dialogue to be conducted.


Continued next post...



posted on May, 11 2010 @ 07:07 PM
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Continued from previous post...


Bracewell pointed out that the use of messenger probes, offers a number of advantages over the conventional strategy of searching for interstellar signals and should any be found, subsequently trying to carry out a remote conversation. A probe stationed within a solar system could deliver a far more powerful signal to target worlds than could a transmitter positioned many light-years away in a neighbouring star system, so that its chance of being noticed would be that much greater. It would also not have to rely on potential recipients continuously monitoring a large number of stars. If necessary, it could bide its time while a species evolved to roughly the stage we are at now. If its ploy of echoing local radio transmissions were not immediately successful, it could try beaming a message of its own across a wider frequency range. Once it had established contact, its other great strength would come into play; that is, the conversation with the contact race could be carried out virtually in real-time. Using its on-board intelligence and memory store, the probe could pass on a vast amount of information about its origins and the civilization which had sent it, without the need to wait many years for an exchange of greetings across the interstellar void.

With this scenario in mind, some preliminary telescopic searches for Bracewell probes were carried out at Kitt Peak National Observatory and Leuschner Observatory. Among the sites regarded as most promising for scrutiny are the Earth-Moon Lagrangian points and other similar stable orbital regions in the Solar System. However, these preliminary searches were unsuccessful.

Civilizations like ours which have learned how to carry out interplanetary missions may quickly go on to acquire the ability to launch artificially intelligent robot spacecraft to nearby stars at reasonable speeds. Indeed, since Bracewell first suggested the idea of messenger probes, rapid progress has been made in a number of relevant technological fields, including robotics, information storage, and spacecraft propulsion. These developments are bringing closer the time when we may be able to send out Bracewell probes of our own.



4 - Not interested in us because they are by nature xenophobic or simply not curious
Based on existing calculations indicating that there should be a minimum of thousands of technological civilizations currently in the galaxy, it's difficult to comprehend that every single one of those advanced civilizations have decided not to attempt to colonize the galaxy. All that is required is for just one of those civilizations to have embarked on a von Neumann colonization wave in the last four billion years for Earth to have been colonized.



5 - Not interested in us because they are sociologically and/or technologically much further ahead of us
Assuming that extraterrestrial civilizations in fact do exist, there is a high degree of probability that some of them will prove to be much more scientifically and technologically advanced than we are ourselves. One only has to look at the astonishingly rapid progress that we humans have made, for instance, in the development of computers over the past few decades shows what dramatic strides can be achieved by a technologically ambitious and capable race in a very relatively short period of time. Looking forward just another century or so, we may even have acquired capabilities in genetic engineering, nanotechnology, life prolongation, artificial intelligence, space propulsion, and other fields that, at present, we can barely imagine.
Indeed, it was Arthur C. Clarke who once wrote


"Any sufficiently advanced technology is indistinguishable from magic."


So, extrapolating such technological development and capabilities to an extraterrestrial civilization that was a thousand, or a million years, ahead of us, could they have the potential to evolve technologically in ways we couldn't even imagine or comprehend and thereby making us completely unaware of their presence ?
In fact, one of the consistent and prevalent arguments put forward against the existence of advanced extraterrestrials is that if they were present surely we would have picked up signals from them by now ? However, advanced civilzations that are technologically significantly ahead of us might lie beyond our communications horizon; that is, we may simply not have the means to tap into their conversations and consequently from our point of view, such civilizations may as well be totally invisible to us. According to Drake, a communications horizon of only 1,000 years might render us oblivious to 99.9 percent of the intelligent technological races in the Galaxy. Yet another argument follows the line of reasoning that advanced extraterrestrial civilizations would leave clear and undisputable visible signs of their existence – for example, large-scale engineering projects in the Galaxy which would be the equivalent of bridges, highways, and skyscrapers on Earth. But this argument again, assumes too much and for all we know, very advanced stellar and galactic engineering projects have the appearance of natural celestial objects, so that we may be looking straight at them without realizing their true nature. Or perhaps, more likely, the devices of highly evolved species are not dramatic and obvious, but are subtle and discrete so that they are simply undetectable from a distance.

Could there be any other events that might also result in all technological civilizations everywhere to lose interest in colonizing the universe ? Such a process would have to be inescapable and one that ultimately affects every developing technological civilization once it reaches a certain critical point in it's development. Vinge and others have postulated that this inescapable event is something they've referred to as the "Singularity". This Singularity therefore must naturally arises as a direct consequence of hyperexponential technological growth.


Continued next post ...



posted on May, 11 2010 @ 07:08 PM
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Continued from previous post ...


It may be that once intelligence emerges in a species, it develops an irresistible technological drive. If we consider the time intervals required for our civilization to advance from one significant technological point to another, e.g. discovering fire; learning to process metals; the industrial revolution; flight; nuclear energy; space travel; electronics; etc; etc. At each step in this technological acquisition curve, the time intervals to the next advance shrinks at an ever increasing rate.
There is absolutely no reason to assume that this curve stops with us. There may be as little as only a few hundred years between the start of an industrial civilization and the the eventual rise of machine intelligence. Beyond that, any further speculation is impossible. Vinge, Joy, Kurzweil and others have described this process of ever decreasing time between one major technological stage and the next as the Singularity..

It may be that the kinds of civilizations we might communicate with have remaining 'life expectancies' of only a few hundred years before Singularity. During their short existence, they produce only the kinds of radio output that we produce. Upon entering Singularity, their radio emissions abruptly stop and they go silent.

One can then ask what happens to those post-Singular civilizations? Assuming Singularity occurs, their level of technology would be so great that presumably they would no longer be vulnerable to natural threats. So why then would they lack the ability or motivation to settle the galaxy? An immediate and simple explanation is that no biologically based culture, survives Singularity.



6 - Prone to annihilation before they achieve a significant level of interstellar colonization
It must be almost a given that if extraterrestrial civilizations do in fact exist, that they must inevitably face a variety of threats to their existence, just as we have and still do, here on Earth. These threats may come in many different forms such as competition or predation from other species, potential gradual or sudden adverse changes to the environment (for example, due to the onset of an ice age), or a sudden cataclysm, such as the impact of an asteroid or comet, a massive stellar flare, or the eruption of a nearby gamma-ray burster, capable of causing a mass extinction or even a complete planetary sterilization.
Such threats are not necessarily exclusive to natural causes or events as in addition to these natural dangers, many more of a self-generated nature may also arise to confront an intelligent race once it has achieved a substantial level of technology.
The following are some examples of such hazards and dangers that presently confront our own civilization:
Large-scale nuclear or biological war
Global epidemics of lethal disease resulting from the emergence of antibiotic-resistant pathogens
Environmental disasters stemming from a combination of industrial pollution, over-population, and destruction of natural habitats, climate change (warming or cooling)
Depletion of the ozone layer
Unforeseen side-effects of new technologies, such as genetic engineering

Both Shklovskii and Sagan have pointed out two other potential scenarios confronting any rapidly developing technological civilization.
In the first, a technological civilization destroys itself (see above self-generated threats) soon after achieving interstellar communication capability - possibly sometime within the following 100 years.
In the second, a technological civilization learns to live with itself soon after achieving such communication capability. If it survives more than a further 100 years, it will be unlikely to destroy itself afterwards. In this case, such a civilizations lifetime may be measured on a stellar evolutionary timescale i.e more than 10 million years.
However, since we can't even begin to predict the short-term future fate of our own civilization, we are in no position to say whether advanced civilizations tend to survive for long periods or whether they self-destruct soon after acquiring the means to communicate over interstellar distances. Furthermore, even if such technological races, on the whole, are fortunate enough and manage to overcome any problems of their own creation, it is certainly not clear how often natural disasters would tend to purge a world of its life and intelligence.



7 - Interstellar travel is impossible
This explanation clearly fails as no known principle of physics or engineering rules out interstellar spaceflight. Scientists have devised many methods by which interstellar distances may be crossed (ion, nuclear, light sail, etc) and have even envisaged propulsion strategies that might reach 10 to 20 percent of the speed of light, thereby permitting travel to nearby stars in a matter of decades.
More advanced forms of propulsion, such as the interstellar ramjet are technically not too advanced over what we are currently capable of building. It's been estimated that a dedicated effort by the U.S. government, much like the Apollo program, could put a probe in orbit around Alpha Centauri within a century. The majority of this time would be required to make the transit instead of developing and launching the probe.


Continued next post...



posted on May, 11 2010 @ 07:08 PM
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Continued from previous post...


8 - Interstellar travel is possible but is not very economical
Suggestions have been proposed that perhaps attempted galactic colonization might prove to be to large of a resource investment for a civilization or that it might present to much of a strain on a society over the time period required to achieve it. However, this assumes that the colonization effort would need to be "manned" but this does not necessarily have to be the only way that expansion and colonization could be accomplished. An alternative option is through the use of von Neumann or self reproducing automated systems colonization. This form of colonization is based upon a ship (or ships) capable of autonomously reproducing itself in the target system and launching copies of itself at the next set of target systems. The great advantage of this system is that, once launched, its ongoing propagation throughout the galaxy does not require resources or any other input for that matter, from the civilization that launched it. A von Neumann colonization wave would even survive the death of its parent civilization and would be almost impossible to stop.

Based on a von Neumann expansion program, a conservative (i.e. slow expansion rate) estimate of the amount of time required to colonize the galaxy is still only on the order of millions of years. While this seems like a very long time indeed, it is a very short period when considered on the astronomical scale. One needs to remember that it has been four billion years or so since the appearance of life on Earth. In that four billion years all it would take is for just one single civilization to decide to embark on a program of Galactic expansion. And that would mean that they would now occupy Earth, not us.



9 - Interstellar communication is impractical or there is a preferred mode of communication which we don't know about yet
At our current level of technology, the fastest means we have of communicating between 2 distant locations is by modulating various specific regions of the electromagnetic spectrum, whether this be light in the form of a modulated laser beam or by modulating radio frequencies such as microwaves, tv, etc. But irrespective of the type of signaling method employed, we are still limited by the 'known' laws of physics to a communication speed not exceeding the speed of light. For relatively short distances such as those within our solar system, the time lag between sending a signal and receiving a response can be measured in minutes or even hours, but is still acceptable. However, for extraterrestrial civilizations attempting to communicate with each other across many light years, the resultant and unavoidable time lag incurred could amount to tens, hundreds or even thousands of years and would be prohibitive. In fact when communicating over enormous distances, the sending civilization may no longer even be in existence when the reply arrives.
Another limitation is that the number of bits (i.e. data) that can be transmitted on a given frequency, over a given area, is fixed by a combination of physics and information theory. So radio waves are incredibly limited for long distance communication as there just isn’t enough broadcast bandwidth available to go around.

And this assumes that electromagnetic radiation is the best and only method by which to communicate across interstellar distances. Given our present level of physics, we are unable to categorically state that there can be no faster communication method - we simply don’t know enough. And if some form of faster than light communication is possible, it makes sense for that to be the “threshold of interest” for extraterrestrial civilizations. Rather than worrying about detecting another's radio broadcasts with it’s centuries to millennia turn around times, it would make more sense to wait until their understanding of physics develops sufficiently to employ these superior communication methods.

One can also ask how long an extraterrestrial civilization that uses electromagnetic waves for communication will even remain visible to other civilizations. How long will the Earth's radio/tv footprint be detectable? A few decades ago we thought the visibility would last a long time - ever more powerful TV stations and radar installations were being built, and these are the strongest signs of our existence. But there is only so much bandwidth in the useful electromagnetic spectrum. To transmit ever-increasing amounts of information, portions of the spectrum must be shared. This is only possible if signal strengths are reduced so that transmissions on the same frequency do not interfere with one another. The textbook example of this paradigm is the cellular phone system. This inevitable signal strength reduction means we are well on our way to becoming invisible to the remainder of the galaxy.
This is a rather counter-intuitive result, but a real one, and ultimately means that the detectable lifetimes of technological civilizations may be much shorter than we had estimated.



10 - We are a protected species. Either developing species in general are protected or ours in particular is
What's the likelihood that all advanced civilizations would refuse to colonize inferior and less well developed societies? To assume that a technologically advanced civilization is similarly morally or ethically advanced is simply that, an assumption. After all, why should an alien civilization's morals and ethics be compared to, or even assumed to be similar to our own? It is not a law of physics that the correct moral or ethical thing to do is to respect or honor the existence of other civilizations, let alone "lesser" life forms. As our own history has shown time and time again, we as a species have never been overly concerned with the rights of lesser advanced cultures on our own planet. e.g. European colonization of North America and Australia.

Once again it is an issue that it only requires just one civilization somewhere, sometime deciding that it is the only valid civilization and having the means and the willpower to back it up.



11 - The first technological civilization to have developed subsequently eliminates all potential developing rival civilizations
Could the lack of evidence for additional extraterrestrial civilizations be purely and simply because they've been eliminated one by one as potential rivals to an existing race ?

Should intelligent life have first appeared in the galaxy, say just shortly after the formation of the galaxy, the danger of potential rival civilizations developing over time must have been obvious. It seems reasonable if this first race was essentially paranoid, was space faring and had sufficiently advanced technology, that they would have been in a unique position to have done something about such a possibility.
Any intelligent race presents an unpredictable danger to all other races. Even worse, the danger is probably not from one of the races which is willing to communicate but rather from one which is not - one which is totally unknown.


Continued next post...



posted on May, 11 2010 @ 07:09 PM
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Continued from previous post...


SUMMARY

Based on the earlier described contingencies that could potentially impact on or inhibit an advanced civilizations capacity or will to colonize the galaxy, it follows that any attempt to resolve the Fermi Paradox must rely on assumptions being made regarding the behavior of other civilizations. For example, they might destroy themselves first, they might have no interest in colonizing the galaxy, or they might have strong ethical codes against interfering with primitive life-forms. Many SETI researchers, as well as others who are convinced that extraterrestrial civilizations must be common, tend to dismiss the implications of the Fermi Paradox by an uncritical appeal to one or more of these sociological considerations.

But they face a fundamental problem. Each of these attempted explanations can only be considered plausible if in reality, the number of extraterrestrial civilizations is small. If the galaxy has contained millions or billions of technological civilizations, it seems very unlikely that they would all destroy themselves, be content with a sedentary existence, or agree on the same set of ethical rules for the treatment of less developed forms of life. As has already been pointed out, it would take only one technological civilization to embark, for whatever reason, on a program of galactic colonization. Indeed, the only technological civilization we actually know anything about--namely, our own--has yet to self-destruct, shows every sign of being expansionist, and is not especially reticent about interfering with other living things. And based on a historical perspective, would have no qualms about embarking on stellar expansion and colonization when the opportunity and means eventually presents itself.

Therefore, one can state that there are primarily only four conceivable ways of reconciling the absence of evidence indicating the existance of extraterrestrial civilizations with the widely held view that advanced civilizations should be extremely common.
Perhaps interstellar spaceflight is infeasible, in which case extraterrestrial civilizations could never have come here even if they had wanted to.
Perhaps extraterrestrial civilizations are indeed actively exploring the galaxy but have not reached us yet.
Perhaps interstellar travel is feasible, but extraterrestrial civilizations choose not to undertake it.
Perhaps extraterrestrial civilizations have been, or still are, active in Earth's vicinity but have decided not to interfere with us.
If we can eliminate each of these explanations of the Fermi Paradox, we will have to face the possibility that we are indeed, the most advanced life-forms in the galaxy.

The first explanation clearly fails. No known principle of physics or engineering rules out interstellar spaceflight.

For the same reason, the second explanation is problematic as well. Any civilization with advanced space technology would be able to colonize the entire galaxy on a cosmically short timescale. For example, lets consider a civilization that sends colonists to a few of the planetary systems closest to it. After a sufficient period of time has elapsed and those colonies have established themselves, they send out secondary colonies of their own, and so on. In time, the number of colonies begins to grow exponentially. We begin to observe a colonization wave front moving outward with a maximum speed determined by the speed of the starships and by the time required by each colony to establish itself. In addition, as the wavefront expands, more new settlements will quickly fill in the volume of space behind this wave front.

Assuming a typical colony spacing of 10 light-years, a ship speed of 10 percent that of light, and a period of 400 years between the foundation of a colony and its sending out colonies of its own, the colonization wave front will expand at an average speed of 0.02 light-year a year. As the galaxy is approximately 100,000 light-years across, at this expansion rate, it would take no more than about five million years to colonize it completely. Though a long time in human terms, this is only 0.05 percent of the age of the galaxy. Compared to the estimated age of the galaxy, this expansion/colonization process is essentially instantaneous. The greatest uncertainty is the time required for a colony to establish itself and spawn new settlements. If we use the time that it has taken human civilization to develop to the stage of acquiring spaceflight, then a reasonable upper limit might be 5,000 years. In that case, based on that 5,000 year figure, full galactic colonization would take approximately 50 million years. Again, compared with the age of the galaxy, still a very short period of time.

So, the implication is quite clear: the first technological civilization with the ability and the inclination to colonize the galaxy could have done so before any competitors even had a chance to evolve. In principle, this could have happened billions of years ago, when Earth was inhabited solely by microorganisms and was wide open to interference from outside. Yet no physical artifact, no chemical traces, no obvious biological influence indicates that it has ever been intruded upon. Even if Earth was deliberately seeded with life, as some scientists have speculated, it apparently has been left alone and in isolation since then.

Despite the vastness of the endeavor, I think we can identify a number of reasons why a program of interstellar colonization is actually quite likely and advantageous to the colonizing species. For one, a species with a continuous history of colonization on its home planet would be more than likely to continue such behaviour once it achieves the capacity to venture into space. Moreover, we need to also consider that colonization might be undertaken for reasons such as political, religious or purely on scientific grounds. In fact, the last seems especially probable if we consider that the first technological civilization to evolve would, by definition, be alone in the galaxy. It would most likely embark on its own version of SETI and when such searches proved negative, it might then initiate a program of systematic interstellar exploration to find out why.

So where does all the foregoing potential explanations leave us in our attempt to explain one of cosmologies greatest and as yet, still unanswered mysteries ? In spite of all the advances since Fermi posed his famous paradox almost 60 years ago, we have hardly added to our knowledge base and essentially find ourselves in basically the same position today. The only way to eventually resolve this ongoing mystery is by continuing to explore our cosmic surroundings in greater detail.

Ultimately however, we may have to accept the inevitable conclusion that we can find NO evidence for other extraterrestrial technological civilizations ... that we are indeed completely alone. In that case, we may have to conclude that it is entirely up to us alone, and has become our ultimate destiny as a technological species, to embark on the exploration and colonization of the galaxy.


So in conclusion, I'll finish off by asking once more, the very same question that I asked in my OP ...

Where are they ?




Continued next post...


[edit on 11/5/10 by tauristercus]



posted on May, 11 2010 @ 07:09 PM
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Continued from previous post...


REFERENCES


Annis, James. "An Astrophysical Explanation for the Great Silence," Journal of the British Interplanetary Society, 52, 19 (1999).
Baird, John. The Inner Limits of Outer Space. Hanover, N.H.: University Press of New England (1987).
Ball, J. A. "The Zoo Hypothesis," Icarus, 19, 347 (1973).
Bracewell, R. N. "Communications from Superior Galactic Communities," Nature, 186, 670-671 (1960). Reprinted in A.G. Cameron (ed.), Interstellar Communication, W. A. Benjamin, Inc., New York, pp. 243-248, 1963.
Bracewell, Ronald N. "The Opening Message from an Extraterrestrial Probe." Astronautics & Astronautics, 11, 58-60 (May, 1973).
Brin, G.D. "The ‘Great Silence’: The Controversy Concerning Extraterrestrial Intelligent Life," Q.J. R. Astr. Soc., 24, 283-309 (1983).
Christian, James, ed. Extraterrestrial Intelligence: The First Encounter. Buffalo, N.Y.: Prometheus Books (1976).
Clarke, Arthur C. "The Sentinel." In Expedition to Earth. New York: Harcourt, Brace and World (1970).
Dyson, F. "Interstellar Transport," Physics Today, Vol. 21, No. 10, 41-45 (Oct. 1968).
Dyson, F. J. Letter, Scientific American, 210 (4) (April 1964).
Dyson, Freeman J. "The Search for Extraterrestrial Technology." In R. E. Marshak, ed.,
Feder, J., Fractals, chapter 7: "Percolation," 104-148, Plenum Press, NY and London, 1988.
Fogg, M.J. "Temporal Aspects of the Interaction among First Galactic Civilizations: The ‘Interdice Hypothesis,’" Icarus 69, 370-384 (1987). Freitas, R. A. "Extraterrestrial Intelligence in the Solar System: Resolving the Fermi Paradox," Journal of the British Interplanetary Society, 36, 496-500 (1983).
Freitas, R. A, Jr. "There Is No Fermi Paradox," Icarus, 62, 518-520 (1985).
Hart, M. H. "An Explanation for the Absence of Extraterrestrial Life on Earth," Quarterly Journal of the Royal Astronomical Society, 16, 128-135 (1975).
Kuiper, T.B.H., and Brin, G.D. American Journal of Physics, 57, 13 (1989).
Mallove, E. F. & Forward, R. L. (1972) Bibliography of Interstellar Travel and Communication, pp. 16-21. Reseach Report 460, Hughes Research Laboratories, Malibu, Califomia.
Marx, G. (1963) Astronautica Acta, 9, 131-9.
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+4 more 
posted on May, 11 2010 @ 07:23 PM
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There's been hundreds of thousands of spacecraft sightings just in recent times, and the recorded history of older cultures provides hundreds, if not thousands, more. Many speak in no uncertain terms about visitors from other planets, like the Dogon tribe and their visitors from Sirius B.

All those people know we're being visited by them, and so do the governments of the world, because they've psychologically conditioned everyone to think something so plausible is ridiculous. The only people who don't are those who look to the media for what to believe.



posted on May, 11 2010 @ 07:33 PM
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Great work tauristercus.

Here is my own poorly formed
andwer to the Fermi paradox and aliens.

(12) Due to the limitations of light speed the only
way aliens can visit us is to beam energy signatures
to our planet. Which they have done for thousands of
years, even millions. They are called plants. In the future
when we can do it, we will be able to experience other planets
as plants ourselves. The problem is that we don't treat our
visitors very well and the word has gotten out about us.
So even our very close cousins won't come visit us
in person. "All they do is eat or burn us."
Can't blame them really.


David Grouchy



posted on May, 11 2010 @ 07:36 PM
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reply to post by tauristercus
 


Dear tauristercus

Wonderful thread.

My take on this is this. If the human race is to survive in the future we must and I mean must occupy other planetary systems. That is it we just must.

So that cuts out a bit of your of your quandary.

That is assuming that we make it and do not exterminate our selves, agreed this is likely as I see it right now.

Why have we not heard them? Simply the speed of light is too slow. If a race of hi tech beings occupy two star systems they have found a quicker means of communication. What well obviously we have not found it yet.

Anyway that is by 2 cents worth so far.



posted on May, 11 2010 @ 07:37 PM
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Originally posted by Risen
There's been hundreds of thousands of spacecraft sightings just in recent times, and the recorded history of older cultures provides hundreds, if not thousands, more. Many speak in no uncertain terms about visitors from other planets, like the Dogon tribe and their visitors from Sirius B.

All those people know we're being visited by them, and so do the governments of the world, because they've psychologically conditioned everyone to think something so plausible is ridiculous. The only people who don't are those who look to the media for what to believe.


The purpose of this thread was not to dispute or deny the many instances over the years of 'alleged' sightings of what have been 'interpreted' as alien spacecraft but rather to highlight the seemingly incomprehensible fact that there is absolutely ZERO substantiated evidence, whether on Earth, in the solar system or in the galaxy of other extraterrestrial civilizations.
As pointed out, statistically, the galaxy should literally be crawling with signs, evidence and artifacts of these other civilizations and yet nothing has been found.

As for these claims that these visiting spacecraft are evidence of actual extraterrestrial civilizations out there, then one is hard put to explain just why we can see a spacecraft visiting us, but can see no other evidence out there of a supporting civilization. After all, if they're capable of visiting Earth, then they're more than capable of expanding throughout the galaxy and colonizing it. I don't for one minute believe that they just recently acquired space travel capability and the first thing they did was head straight to Earth for a visit !



posted on May, 11 2010 @ 07:38 PM
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I do believe there is other life out there. If you look at all the life that has existed on earth. Only one has become intelligent enough to begin to fathom the idea of talking to other intelligent beings.

That does not play well for there being lots of intelligent life out there.

Life may indeed be abundant in the universe but intelligent life may be an aberration.



posted on May, 11 2010 @ 07:44 PM
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Originally posted by MAC269
reply to post by tauristercus
 



My take on this is this. If the human race is to survive in the future we must and I mean must occupy other planetary systems. That is it we just must.

I totally agree with you that sooner or later, whether by choice or necessity, that we as a species absolutely will expand out into the galaxy. We've shown throughout our species history that we're an expansionist species and that given the opportunity to do so, then we definitely will.




Why have we not heard them? Simply the speed of light is too slow. If a race of hi tech beings occupy two star systems they have found a quicker means of communication.

I don't believe the speed of light really is an appreciable factor in galactic colonization. As has been shown by many people, even at speeds substantially slower than light speed, the entire galaxy could be colonized in less than 50 million years ... and thats theoretically by just one species. If more species embarked on colonization, then the galaxy would be totally overrun in just a few million years.
So if it's possible and there are one or more extraterrestrial species out there, the question once again is why does the galaxy appear to be completely deserted except for we humans ?



posted on May, 11 2010 @ 07:48 PM
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Originally posted by Xeven
I do believe there is other life out there. If you look at all the life that has existed on earth. Only one has become intelligent enough to begin to fathom the idea of talking to other intelligent beings.

That does not play well for there being lots of intelligent life out there.

Life may indeed be abundant in the universe but intelligent life may be an aberration.

Absolutely right ... but then we have the unfortunate situation where we humans apparently become the center of the universe.
This goes entirely against physical cosmology and the Copernican principle that states that the Earth is not in a central, specially favored position. More recently, the principle has been generalized to the relativistic concept that humans are not privileged observers of the universe.



posted on May, 11 2010 @ 07:52 PM
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reply to post by tauristercus
 



Intelligent life is abundant and all around you but with your primitive physics and constipated scientific approach; you are still to stupid to recognize it.

You have only been out of the trees for a short time in the grand scheme of things.

One of your very perceptive authors, a Mr. Clark said something to the effect that
"Any sufficiently advanced technology is indistinguishable from magic.


Look there!



posted on May, 11 2010 @ 07:55 PM
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Originally posted by davidgrouchy
Great work tauristercus.

Here is my own poorly formed
andwer to the Fermi paradox and aliens.

(12) Due to the limitations of light speed the only
way aliens can visit us is to beam energy signatures
to our planet. Which they have done for thousands of
years, even millions. They are called plants. In the future
when we can do it, we will be able to experience other planets
as plants ourselves. The problem is that we don't treat our
visitors very well and the word has gotten out about us.
So even our very close cousins won't come visit us
in person. "All they do is eat or burn us."
Can't blame them really.


David Grouchy


Maybe we must stop eating plants =), that is what have them angry with us.



posted on May, 11 2010 @ 07:59 PM
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They are right here.

There are countless numbers of craft with millions of 'off-Earthers' in our area at this time in history. Wouldn't you want to witness the end of a 26,000 year cycle of humans to see how it will turn out?

It's the Blockbuster of the millenia.



posted on May, 11 2010 @ 08:06 PM
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reply to post by tauristercus
 

So the Real Roswell Crash that happen 3 Years before Enrico Fermi created Fermi Paradox, are allows Majestic 12 and MIB to Perfectly Conceals the existence of the Extraterrestrial, so this makes Fermi Paradox to Happens



posted on May, 11 2010 @ 08:36 PM
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reply to post by tauristercus
 


Dear tauristercus

No sorry I have not been clear.

The reason we have not heard them is because the communications speed are faster than the speed of light using some other method other than radio that we have not found yet.



posted on May, 11 2010 @ 08:38 PM
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I to think life is out there but once intelligence arises and gains technology
it quickly ends up destroying its self . and not nesserly through war.
but to gain intelligence in the first place there has to be a natural drive for it of life stagnates at a lower lv . for instance a predator only has to be smart enough and fast enough to get its pray and its intelligence is devolved one step ahead of its prey this must be true if it cant out smart out run out think its prey it dies .
now the prey only needs enough to out run out hid its predator .
going by this it would seam humans are a paradox but no were the one in a billion combination predator prey .
we started as a animal that was a prey animal live in trees devolved good visual skills and memory for land marks as we needed to see wich tree and fruit was ripe and rember were and when its was ready.
this cause us to evolve a good bite of intelligence but we were still animals
and would have stayed at that lv if not for a climate change .
in just a 100 years the trees we needed to live all died off maybe a comet hit maybe a drought what ever caused it suddenly there was savana were there use to be forest now is were the funkey part happened it was eather evolve or die time .
ok no fruit trees left no place to easily jump and hid left . so we changed our diet to meat more and more became predators and quickly learned the advantages of standing on two feet to see more around you get a running start .
so now you take a animal thats smart veg add in the intelligence need to become a predator and dobble its smarts and wala now its smart enough witha big enough brain to start evolving beyond nature each generation adding to the mix more and more till well us.
the problem with this is this animal is part predator wich means it kills to live now come on people we have been smart for 250k years or more and yet we still kill and have used our intelligence to take killing to whole new levels. theres no way we will ever get interstellar flight as we will destroy our self's long before we achieve that.
but even without the self destructive nature of intelligence ,(would a smart wolf have been different?) at not even lv 1 civilization we will destroy our very planet we need in order to live again long before we can achieved lv 1 .
our planet is less then a 100 years from total environment collapse now.
and saying 100 years is realy giving more then its likely to take . were so close now it could happen tomorrow .
now if every intelligence follows this pattern and nature says it must then wile we may not be alone we will never find that advance race we all dream of as there is none as they destroy them self's before they accave interstellar flight.
were a fluke but even with a million flukes the end is extinction.
there's no animal not one that wont eventually fall to this fate. and most don't last long at all





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