Welcome to the Fermi Paradox Wiki


Since Fermi was credited with his question re the event described above in 1950, other physicists have reconsidered it. Stephen Hawking ends his lecture "Life in the Universe" with a similar observation.  
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If the argument about the time scale for the appearance of life on Earth is correct, there ought to be many other stars, whose planets have life on them. Some of these stellar systems could have formed 5 billion years before the Earth. So why is the galaxy not crawling with self designing mechanical or biological life forms? Why hasn't the Earth been visited, and even colonized.

Notice that Hawking explicitly introduces two terms into the mix: self-designing and mechanical. The self-designing can also be applied to biological life forms, as we could engage in genetic engineering of ourselves if we engaged with the ethical issues.

The paradox of this question is that the scenario that is painted is so blindingly obvious and apparently incontravertible given what we know about the nature of life and its ability to propagate exponentially and fill every available niche. It is this lack of clear evidence of alien forms of life that is the puzzle. Why is there no evidence ?

We do not have Fermi's calculations that went through his head that day in 1950. But it is easy enough to construct a reenactment.

There are at least 200 billion stars in the Milky Way. If only 1 in a hundred host a planet supporting life, maybe not even anything like Earth, then there could be 2 billion planets out there that support life of some kind. Planets of this kind will have been around in the Milky Way Galaxy for at least 8 billion years. The Earth has only been formed for 4 billion years and life has developed on it in that time. Life supporting planets have existed in these numbers in the galaxy from 8 billion years ago to now so even 4 billion years ago billions of intelligent civilizations should have formed on these planets. Possibly 1 per planet. That makes 2 billion civilizations formed up to 4 billion years ago. By now those planets are gone, they have been consumed by their exploding star and that civilization lost if it did not learn to become a self-sufficient space-faring reproducing redesigning civilization. The debris from those supernova explosions reformed into new star systems such as our own with new planets and life developing a new and beginning to explore space travel.

But rather than get complicated with multiple generations of civilizations let us just stick with the 2 billion civilizations figure as a bare minimum. But stars are long distances apart

To travel from where they are to us here on Earth they might have to travel half way round the galaxy. This is a route of roughly 300,000 light years. They would spot Earth as a life supporting planet as soon as they analysed its atmosphere, so finding us would not be too difficult. But at a speed of perhaps 1000 years per light year distance it could take 300 million years before they reached Earth. But this is true for all of the 2 billion civilizations. They should all have been able to visit Earth in the course of 1 billion years. If 2 billion civilizations visit us over 1 billion years it means that we would get visited 2 times a year on average !! So where are they ?

Maybe Fermi used a different line of reasoning, but he came to a similar conclusion.

Since then more careful assessments of the abundance of intelligent life in the Milky Way Galaxy have been worked out. All of these have been so imprecise as to be no more informative that the rough guess above, but the lines of reasoning do allow us to address the issues underlying this paradox.

The most recognized is the Drake Equation.

The Drake Equation



Note that the Drake Equation is an attempt to determine the number of civilizations in our galaxy with which communication might be possible, the Drake Number N. This is quite a different figure from Fermi's question of how many civilizations could have visited Earth or be visible to us. But it is part of the answer to Fermi's paradox.

But the Drake Equation presents only one view of the Fermi Paradox. It is a mistake to consider the Fermi paradox only through the lens of the Drake Equation. Other formulations of the Fermi paradox need to be considered. Relying on only one formulation of a nebulous issue is a sure way of never engaging with it productively. Our own history is littered with formulations, such as the the Ptolemaic System that, while adequate, were fundamentally wrong. Repeating this kind of mistake holds up the progress of our civilization.

Therefore we need to consider Alternative Lines of Argument to the Drake Equation

However the Drake Formula does form a useful agenda with which to start consideration of the Fermi Paradox. However this agenda should never be considered as fixed and other alternative agendas should be sought out. And we need to add Fermi's question "Why cant we see signs of their having visited?"

Reasons for pursuing the Fermi paradox

Fermi's paradox is not just an intellectual exercise. Millions of dollars have been spent on seeking out alien life by looking for broadcast communications. Billions of dollars are being spent to identify nearby planets that may support life. This money is not being spent because we expect to travel to these planets anytime soon. It is being spent because these planets may have information about technology which we are currently unaware of which will give us a boost. The number one technology which we need to develop to make us space-capable is Cold Fusion - the controlled generation of energy by hydrogen fusion.

A second important reason is the possibility of eco-collapse on Earth which will make our civilization unsustainable and we will fall back to another Dark Age. We need to develop counter-measures for this event especially in the face of significant Global Warming compared to what we have experienced in the last 5000 years. One of these counter-measures is space-capability either for ourselves, suitably genetically modified, or for an intelligent machine civilization capable of redesigning itself and reproducing itself. Stephen Hawking's nod in this direction is motivated by the threat that global warming poses. If we could happily believe that we would inhabit this planet, untroubled, for a billion years, such options would probably not occur to us.

The fleeting nature of intelligent civilization also turns out to be a major limiting factor in the Drake equation. If we take the lifetime of a civilization that can communicate across space to be 10,000 years against the life of the Milky Way Galaxy at say 8 billion years then the limiting factor is .0000025. This is by far the most limiting factor in the Drake equation and ensures that we will never make make contact with alien beings. 10,000 is the figure that Drake used in 1960.

Drakes guesstimate produced a figure of 10 current civilizations in the galaxy. If they were evenly distributed around the galactic disc, they would be roughly 30,000 light years apart. (expr 60000*2*3.14/10) If we picked up a message from one, it is likely they would already be extinct by the time we received it. If we survived long enough to visit that planet we would find only ruins. We certainly could not communicate with them to advance our own science.

This implies that we are in fact truly alone in the galaxy, and that we are faced with the predicament of our imminent extinction before we have a chance to engage with other life in the galaxy. A sobering scenario.

If we can make steps to ensure the survival of our civilization, at whatever cost, then we can possibly reframe our view of our place in the galaxy and our likelihood of making contact with alien life. However resources and time are running out on us.

Drake Equation Considerations

Drake R* factor- The average rate of star formation in our galaxy. Milky Way Star Formation

Drake L factor - The length of time that technological civilizations release detectable signals into space.

One way of calculating R* is to take the number of stars currently in the galaxy Drake N* factor) and divide by the age of the galaxy Drake Tg factor.

(R*) * L --> (N*) * (L / Tg)

Drake gave L as 10,000 years and Tg as about 8 billion years. This last phrase cancels time out of the units of the Drake Equation but gives a factor of 10000/8000000000 -> 1/800000 -> .00000125 which is a very restrictive fraction.

Drake Fp factor - the fraction of stars that have planets

Drake Ne factor - the average number of planets that can potentially support life per star that has planets

Drake Fl factor - the fraction of the above that actually go on to develop life at some point

Drake Fi factor - the fraction of the above that actually go on to develop intelligent life

Drake Fc factor - the fraction of civilizations that develop a technology that releases detectable signs of their existence into space

Additional factors that need to be considered to address Drake's question of detecting communication from alien life

Drake formed the equation on the basis that Earth's radio signals might be seen by others in the galaxy and our presence noted. But we would have to broadcast load and clear for that to happen. We broadcast a large amount of radio signals but these are basically carrier waves. They would be impossible to decode. As we move to more directional communications using microwave and laser our broadcast emissions reduce. In addition we are developing highly compressed encoded data streams that can be transmitted in second bursts, rather than broadcast continuously. This means that our own communications are becoming more difficult to spot. While this impacts on the Drake Equation, it does not effect the Fermi Paradox.

Empirical Observation of Alien Civilization

One of the problems we face when looking at the Universe is that we tend to view it as a clock-work world, as though created by some great designer, that goes through its motions according to basic Laws. Therefore we try to explain all phenomena by using this model. We are negligent in looking at life-based processes causing natural phenomena.

A good local example is global warming on Earth. It is with some difficulty that people are understanding that mankind is causing this effect. But there is still general lack of understanding that life process will cause this effect to increase at an exponential rate. Most scientific studies still view global warming as a linear process, as though it were caused by some linearly based natural process.

So when we consider what the Dark Matter in the Milky Way is made of, we implicitly exclude the possibility that it might be caused by 4 billions of years of intelligent life in the Milky Way. In fact we entertain some ludicrous logic to avoid considering this option.


The problem here is that to make-up the mass of all the dark matter requires huge numbers of brown dwarfs, and even more Jupiter's or rocks. We do not find many of these objects nearby, so to presume they exist in the dark matter halos is unsupported.

The above webpage then goes onto present a whole range of natural explanations that are even less supportable and in some cases demonstrably impossible.

Whether there is evidence that supports their existence is one thing. But the way this is expressed in the webpage implies that the hypothesis is unsupportable, which it most definitely is not. It is these kinds of twisted forms of expression which can make us avoid seeing evidence of intelligent life even if is in front of our noses. Indeed such statements are so irrational that one has to wonder if thee is not a conspiracy in the scientific community to disguise the true nature and prevalence of alien civilization in our galaxy.

The factor that most prevents us from discovering alien civilizations is our own refusal to engage in the rational that visible could be caused by life processes (which can be recognized by their exponential growth properties) and instead try to explain phenomana purely by "natural" Laws (such as linear and inverse square functions) which do not involve expontentials.

Observing Radio and Visible Light signals

The SETI Projects (Search for Extra Terrestial Intelligence) have focused on observing a band of radiowaves that is generally quiet in nature and so is useful for technological civilizations to broadcast on. Nothing has been observed despite almost continuous observations being made since 1960 with Drake's first SETI program, Project Ozma. However the Drake equation suggests we may have to watch for 300 years.

There are now many SETI projects watching radio frequencies on the assumption that technological civilizations will use radio broadcast. However most of these can only scan within a few hundred light years and the rough estimates for the Drake Equation suggest that the nearest intelligent civilization may be thousands of light years away.


The Search for Extra Terrestial Artefacts attempts to search for objects on space.

Initially it posits that extra terrestial probes may be stationed in the Solar System at Lagrange points. So far nothing has been found for Sun-Earth or Earth-Moon. However it is far more likely that such probes would just pass through until they found something of interest. The frequency of extra terrestial probe visits might be quite long so a permanently posisitoned probe might not arrive for a 1000 years.

There is also the question of whether large satships would enter the Solar System. If such intelligent civilizations had a high regard for the preservation of life, and we would assume they would or else we are in trouble anyway, then they would have to consider if they could enter the Solar System without causing a arge asteroid to be nudged in Earth's direction at some future point in time, with the annihilation of life on Earth as a realistic outcome. If they could not do this safely they would not enter.

It should be possible to determine some limits as to what maximum mass of starship or probe can safely enter and leave the Solar System, even down to the safest trajectory. This might tell us what and what to look for.

When we consider this issue it is understandable that we might not find any alien starships in our neighbourhood, but that this is no reason to assume they do not exist in large numbers.

For this very reason, the logical place to look for such starships is in the dark halo where there is no evolving life, or closer to the galaxy hub where it is too energetic to be hospitable to the development of life. Analysis of the Velocity Curve of the Milky Way would seem to support this.


Traces of targeted asteroid mining on asteroids and comets could also be utilized for the search of ETI.

Examination of the evolution of Self Replicating Machines (SRM) indicates that they would mine their home star system asteroids and comets. However for interstellar travel they would need to resort to cold fusion technology or risk resource depletion and extinction. Therefore we should not expect to see evidence of asteroids being mined, but we should still look. It is more likely alien visitors will graze on Neptunes gases leaving little trace of the visit. It is even more likely they will not enter the Solar System with a ship that has mining capability.

This leads us to other discussions which also seek to explain the lack of evidence for extra terrestial intelligence.

Direct Planetary Observation

The Kepler Mission is now looking closely at a sector of stars in the Milky Way. Derivative projects are following up with more detailed analysis of stars which Kepler identifes as having planets.

Explanations for the Lack of Evidence of Aliens

Fermi's paradox is not based on the assertion that if we look hard enough we should find some alien life. Fermi concluded that if there was alien life, it should have been around for billions of years and it should be manifestly obvious to us. But even after 50 years of preliminary searching we have not found a thing to suggest there is any out there.

Fermi's Paradox is based on the Mediocrity Principle. This principle is the reverse of the Egocentric Principle which governed Western Culture for thousands of years and which asserted that mankind was uniquely special and the center of a Universe made solely for our habitation. The Mediocrity Principle asserts that there is nothing prohibitively special about mankind, Earth or the Solar System. We know that our Sun is not a particularly unique star in the galaxy. We can presume that other Sun-like stars (G2) in the galaxy may have Earth-like planets. There is nothing to suggest that life cannot develop on those planets, that is there is nothing so special about Earth, that it is the only Earth-like planet in the galaxy on which life can develop. If we apply the Mediocrity Principle over the lifespan of the Galaxy it seems inevitable that intelligent life has developed millions of times over, to a space-faring level, and that the galaxy should be so full of Alien life that we should not have to search for it. It should be in our face. But it isn't. Why not ?

If we take a firm grasp on the Mediocrity Principle there are only four reasons why not.

1 Intelligent technological species quickly use up their resource base and become extinct, before they ever achieve emancipation in space. Figures of less than 500 years are quoted for us at present. This does not mean that mankind becomes extinct, but that our technological civilization does and that we revert to a Dark Age. This is equivalent to saying that L should be 500 rather than 10,000 years

2 Intelligent technological species avoid encroaching on areas of the galaxy where life is developing, i.e. the habitable zone of the galaxy. There are a number of reasons for this to happen. This is an extension of the Zoo Hypothesis.

3 Intelligent technological species rapidly evolve into forms which are not mass-based. These may be information based, light based or energy based. Such civilizations may may well be beyond our technology to detect or recognize. However we should seriously explore this conjecture and come up with possible paths for exploration of this and possible ways to test for the presence of such beings in our midst. If this is the only viable long-term path for our evolution then we need to find out about it. This transmutation should not be confused with the Singularity Event which is merely a transmutation from human intelligence into mass-based computer intelligence that will probably occur here in 2021.

4 They are here and are observable but the evidence is being suppressed and denied. When scientists start making irrational explanations on webpages you have to begin to wonder if there is not a coverup conspiracy. And at the Freudian level there is certainly reason for our unconscious mind to prevent us from observing phenomena which indicate evidence of alien intervention. However this hypothesis should be able to be disposed of in a few years.

Other reasons become apparent if we relax the mediocrity principle and look at the details more carefully. It may be that our Solar System is a rather more special collection of planets than we currently understand. This means that the various factors in the Drake Equation get smaller to the point where the number of intelligent civilizations reduces to less than one.

This means that we are unlikely to ever communicate with aliens, but we could still come across the artefacts of extinct civilizations, either in space or on habitable planets. Even in this situation, the mediocrity principle suggests that Earth has been visited in the past by aliens unless the Zoo Hypothesis is correct.

As the likelihood of finding intelligent life in the galaxy reduces, so do the prospects of our continued survival.

If more research proves that N is becoming prohibitively small, then at some point we must take a deep philosophical breath and say that we have no future in space and that we should just learn to live within our own means on this planet. Other intelligent species on this planet have been forced into this position because they live in the Ocean.

If we are not prepared to accept this outcome, not matter what the value of N shifts to, then the smaller N gets the more determined we will have to be to become a space-faring civilization, and on whatever terms that may be.

The Drake L Factor

Drake initially estimated the L factor to be 10,000 years. Many have considered this to be optimistic. But it is also limited to the extent that the civilization may communicate in a way the we can detect. There are good reasons to believe that this will be a short time. Possibly less than 1000 years.

The reasons for this are to maintain information integrity, security and privacy in a situation where there are multiple civilizations moving about the galaxy. We can expect any such civilization to be highly secretive about their communication streams, though maybe not so secretive about their actual existence. Therefore there would be no way that we would receive communications from them accidently. We might be subjected to viral information probes though. We should watch out for such events.

This means that for mankind l is already 100, but may never exceed 200 years. In 100 years we may have decided to tunnel all our communications. However this does not mean that mankind is not a technological presence in space for the next 10,000 years at least.

Therefore to answer the Fermi paradox we need another time, the Drake Lf Time, which is the average time that an intelligent technological civilization may exist for. We can replace the L in the Drake equation for Lf to get something more applicable to Fermi's original question. But if we again use the figure of 10,000 years we are still left with the fact that if we try to visit such a civilization, we will find it has been extinct for thousands of years.

If L is 100,000 then there may be 100 civilizations and the nearest will be 60,000 * 2 * 3.15/100 = 3,000 light years away. To have any kind of real-time conversation with them would require sending a Bracewell Probe there and have it send the information back. Travel time would be 3,000 * 100 years and the communication back a mere 3,000 years. This is a 300,000 year project. Obviously L must be greater than 100,000 if we are to make contact with viable alien civilizations.

If L is 1,000,000 then there may be 1000 civilizations and the nearest will be 60,000 * 2 * 3.15/1000 = 300 light years away. This is a little beyond the fringes of our current ability to peer at exoplanets. The Bracewell probe would then take 30,000 years to complete its mission. This means that if aliens picked up on our existence we could expect their Bracewell Probe to turn up here in 30,000 years time for a chat.

If L is 10,000,000 then there may be 10,000 civilizations and the nearest will be 60,000 * 2 * 3.15/10,000 = 30 light years away. If they spotted changes in Earth's atmosphere consistent with life-forms entering an industrial era they could send a probe here and it would arrive in 3,000 years. But this means that we would have 2 intelligent civilizations in our neighbourhood that might themselves have been around for 5,000,000 years. It is impossible to imagine what they might have evolved to over that period. Given 5,000,000 years of technological development it is highly likely that they would have transmuted into another form of existence.

This figure of 10,000,000 years matches close enough to the projected lifespan of galactic scale SRM civilizations. It is entirely understandable that they may not wish to communicate with us if they are so far developed. It is quite possible that if we visited them we would discover a fabulous techonology which was extinct, abandoned, by an intelligence that had shifted to another plane of existence. Any space-faring civilization that lasted for 10,000,000 years would have had time to fill the galaxy with machines, using up a large chunk of the mass of the galaxy in the process, but it would have had the sense to park the machines in the dark halo.

As you can see, this sequence of figures gives us no clear window in which we can expect to make contact with alien intelligence. No matter which way we look at it either there are too few and they are too far away to reach, or they are close but too advanced to interact with us.

Consequently we must assume that we are on our own, regardless of how many intelligent alien civilizations there are out there. We must also assume that we must be in for the long haul - meaning continually progressive technological advancement for the next 100,000 years at least. This includes cold fusion technology as an early requirement.

Feasibility of Technological Advancement

The Mediocrity Principle can lead us astray in presuming that if other civilizations have achieved emancipation in space, specially if we find evidence of it, that we can achieve the same. However some planets can be more mediocre than others and some star systems likewise, and some stellar neighbourhoods also. It may be that we do not have the resources necessary to mount a complete technological advance. It may stall somewhere, and our efforts will be wasted. We need to answer the question of whether we should be Earth-bound conservationists or space explorers as soon as possible by undertaking a forward plan of development as far as our imagination will allow and look for problems which may prohibit success. We would then be in a better position to decide to what extent me should commit to technological advancement and space exploration. We also need to learn to be good conservationists or we may have no future as biological beings.

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