Fermi paradox

Proposed by physicist Enrico Fermi, the Fermi Paradox attempts to answer one of the most profound questions of all time: 'Are we the only technologically advanced civilization in the Universe?'. The Drake equation for estimating the number of extraterrestrial civilizations with which we might come in contact seems to imply that we should not expect such contact to be extremely rare. Fermi's response was that if there were very many advanced extraterrestrial civilizations in our galaxy, then, "Where are they? Why haven't we seen any traces of intelligent extraterrestrial life?". Those that adhere to the premise behind the Fermi Paradox often refer to that premise as the Fermi Principle.

Table of contents 1 The Controversy 1.1 Is There Extraterrestrial Life? 1.2 The Rare Earth Hypothesis 1.3 The Drake Equation 1.4 Current Data 2 The Argument Over the Premise Behind the Fermi Paradox 2.1 ET Phone Home 2.2 The Anthropic Principle 2.3 Freeman Dyson's Contribution 2.4 Extraterrestrial Colonization 3 Several Possible Explanations

The Controversy

The commonly held belief that the universe has many technologically advanced civilizations combined with our observations that suggest otherwise, appears to be paradoxical, suggesting that either our understanding or our observations are flawed or incomplete.

Is There Extraterrestrial Life?

Many people would like to believe that extraterrestrial life exists and that there are many planets in our own galaxy that harbor life. Others, however, believe that our current knowledge of both chemistry and of biology strongly indicates that life is an exceptionally improbable thing to arise spontaneously. "Strong life" proponents counter that because life arose on Earth as soon as the crust cooled, life itself must be intrinsically linked with terrestrial planet formation. More current data on this issue seems to support this second view. There is now relatively less controversy on this particular issue, due to the confirmation of the rapidity of the origin of life on our own planet, the fact that life is much hardier than was once thought, that planet formation seems to be fairly common, and that conditions to support bacterial life seem to exist elsewhere in our own solar system. However, the issue of whether intelligent life develops as readily as simpler forms is still an open question.

The Rare Earth Hypothesis

An emerging line of thought even argues that multicellular life may be exceedingly rare in the universe because of a probable rarity of Earth-like planets. This line of reasoning has been dubbed the Rare Earth hypothesis[?] and relies on that fact that many improbable coincidences converged to make complex life on Earth possible. For example, the Earth just happens to have an axial tilt, period of rotation, and proper mix of light to heavy rock types in its crust to best support a vigorous hydrological cycle[?]. The reason we are so blessed is because of a chance event: the collision between the young Earth with a Mars-sized body 4,450 million years ago. This giant impact sent much of the felsic rich mantle of Earth into orbit, thus forming the moon, setting Earth into a much faster rotation, and creating our characteristic axial tilt. In addition, the removal of such a huge amount of light-rock types (felsic rock) allowed for the formation of the first ocean basins (which are composed of the heavier mafic rock types). Furthermore, the presence of different crustal rock types allows for the existence of plate tectonics, which is a vital component of the carbon cycle. The collision had to occur at a very precise angle; too direct and Earth would have been obliterated, too shallow and the Mars-sized body would have been deflected. This is just part of the Rare Earth hypothesis.

The Drake Equation

Those people who believe in the more optimistic assumptions used in the Drake equation proposed by Dr. Frank Drake and the even more optimistic assumptions given by Dr. Carl Sagan, add that intelligent life is also common in the Universe. Some state that by making what they feel are reasonable assumptions and arguments we can ascertain that if life is possible at all, then the universe is so vast that it should not only be possible, but almost certain that there are large numbers of extraterrestrial civilisations in the Universe. However those people who adhere to the premise of the Fermi Paradox believe that, due to a lack of evidence to the contrary, in all probability, humans (as a technologically advanced species) are effectively alone in at least our part of the Milky Way Galaxy. They further say that since we cannot yet determine the variables of the Drake Equation with any real confidence, we cannot determine the numbers of extraterrestrial civilizations based solely on this equation. We must therefore, they argue, rely on data collection - which is only now beginning to be collected in a significant manner. Only then can we even begin to presume what the values of each of the variables in the Drake equation are, they say.

Current Data

Our solar system if seen from a radio telescope within a few tens of light years away would seem unusual for the huge amount of radio waves being emitted from what appears to be an otherwise unremarkable main sequence star. One can presume that a similar solar system civilization nearby would be immediately characterized as unusual by us.

Radio and observational data have for several decades been collected and analyzed by such projects as Project Ozma[?], the Search for Extraterrestrial Intelligence (SETI), and the various projects searching for extrasolar planets. So far the SETI data seem to indicate that we are the only radio-transmitting species in at least that portion of our part of the Galaxy that has been surveyed; there are no known main sequence stars with unusually bright radio emissions. In addition, to date, the majority of the extrasolar planetary systems that have been found appear to be harsh environments for advanced life-forms.

Some people contend that these results probably have a significant amount of sampling error: that we are searching the wrong radio frequencies in SETI and that we can more easily find planetary systems with planetary orbits and configurations that are less stable than our own. Still other people contend that we are probably the only spacefaring species in at least our galaxy; otherwise we would be awash in their radio transmissions, and have already been overrun by early colonization efforts.

The Argument Over the Premise Behind the Fermi Paradox

ET Phone Home

Some of those who subscribe to the Fermi principle state that given enough time to develop, the radio transmissions of any sufficiently advanced civilization will begin to outshine their parent star in the radio part of the spectrum. Further, the Law of Mediocrity[?] states that physical laws are the same throughout the Universe and the development of anything within the Universe has to follow these laws. Since the use of the electromagnetic spectrum for information transmission is relatively cheap and easy, one would expect any technological civilization to take advantage of at least a part of this spectrum during their development. We have been actively searching for extraterrestrial signals for almost 30 years with projects such as SETI and have been passively listening to radio static for nearly 100. During this entire period we have yet to hear any confirmed alien broadcasts nor have we observed any main sequence stars with unusual electromagnetic radio signatures that might indicate a technological civilization.

Those that believe the galaxy has many technologically advanced civilizations counter that the extraterrestrials may simply be using a medium other than radio or they eventually choose to hide their transmissions for some unknown reason. This could very well be so, proponents of the Fermi Principle say, but only if there are very few such civilizations in both space and time and they very quickly abandon radio as a means of data transmission. Either way, they say, if there were very many of these civilizations their transmissions would make a large impact on at least some part of the electromagnetic spectrum for at least some part of their development. They further state, that if there are as many advanced extraterrestrial civilizations as Drake and Sagan have estimated, then their presence would be made obvious by their transmissions.

The Anthropic Principle

Those that believe the Fermi Principle also state that from the Anthropic Principle one can see as a logical fallacy the following statement: "With billions of galaxies and countless trillions of planets in the Universe, intelligent life must exist somewhere besides Earth. After all intelligent life happened here, so why not on many of the trillions of other worlds? It is illogical to think that we are the only one." With the Anthropic Principle, Fermi Principle adherents say, one can quickly point out that if a particular planet is the only planet out of the trillions that has intelligent life on it, it would be certain that the people there would assume that they couldn't be the only planet with intelligent life. They would think that, given the sheer numbers of other worlds, there must be others like themselves in the Universe. However, the Anthropic Principle makes it necessary to gather additional information before such an assumption could be made.

Freeman Dyson's Contribution

Popularized by Dr. Freeman Dyson, a Dyson Sphere is an opaque shell around a star. Such a shell would be created by advanced alien civilizations that wished to harness as much of the radiant energy of their sun as possible. The exact design of the Dyson sphere was not specified; it could consist of billions of independent solar collectors and space habitats or be a single unified structure, but in any case it would be made of solid matter and would intercept most of the star's emitted light to re-radiate as waste heat. A star surrounded by a Dyson sphere would thus emit a distinctive black body spectrum without the strong emission lines that incandescent stellar plasma exhibits, probably with its peak unusually far into the infrared for a star of its size. With this speculation, he advised astronomers to search the night sky for unusually colored stars, which, he postulated, could only signify highly advanced and intelligent life. No such stars have yet been found.

Some adherents to the Fermi Principle state that it is highly unlikely that all advanced civilizations would not eventually take full advantage of the power source of their home star, and in doing so changing the electromagnetic signature of their sun.

Extraterrestrial Colonization

They furthermore argue that, from what we know about life's ability to overcome scarcity and colonize new habitats on our own planet, we can reasonably assume that life elsewhere will follow similar principles. Given this, Fermi Principle adherents state that any advanced civilization will almost certainly try to seek out new resources and colonize first their solar system, and then surrounding solar systems. Several writers have tried to estimate the amount of time it would take for such a civilization to colonize the entire galaxy. What they have determined is that it would take 5 to 50 million years to accomplish this feat [1] (http://www.sciam.com/2000/0700issue/0700crawford) - which is a tiny amount of time on even a geologic scale (not to mention a Galactic one).

Several Possible Explanations

A common concept used in the scientific method to test the validity of certain ideas is Occam's Razor. Occam's Razor states that the explanation for a given phenomenon that has the fewest assumptions should be preferred over more complicated ones.

All this draws us to a few possible conclusions, say adherents of the Fermi Principle: that sentient civilizations destroy themselves before harnessing the power of their star (a very real possibility); that the overwhelming majority of sentient civilizations never develop space age technology; and finally, that as a technologically advanced species, we are alone in our part of the Cosmos. The simplest explanation, say adherents to the premise behind the Fermi Paradox, is the last one.

Science fiction authors have proposed another possible explanation -- that someone, or something, is destroying intelligent life in the universe as fast as it is created. This theme can be found in novels such as Frederik Pohl's Heechee novels, Fred Saberhagen[?]'s Berserker novels and Greg Bear's The Forge of God.

Another possible explanation is that advanced civilizations would construct multiple concentric Dyson Spheres around their stars, each one radiating less energy than the next smallest one, with the outermost sphere radiating energy at close to the background radiation. These would be essentially unobservable from any distance. See Matrioshka Brains[?] - http://www.aeiveos.com/~bradbury/MatrioshkaBrains/MatrioshkaBrains.

see: paradox