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The Fermi paradox. Are there any extraterrestrial civilizations?

The Fermi paradox. Are there any extraterrestrial civilizations?

The Fermi paradox, named after Italian-American physicist Enrico Fermi, is the apparent contradiction between the lack of evidence for extraterrestrial civilizations and various high estimates for their probability (such as some optimistic estimates for the Drake equation).

The following are some of the facts that together serve to highlight the apparent contradiction:

There are billions of stars in the Milky Way similar to the Sun.
With high probability, some of these stars have Earth-like planets.
Many of these stars, and hence their planets, are much older than the Sun. If the Earth is typical, some may have developed intelligent life long ago.
Some of these civilizations may have developed interstellar travel, a step humans are investigating now.
Even at the slow pace of currently envisioned interstellar travel, the Milky Way galaxy could be completely traversed in a few million years.
And since many of the stars similar to the Sun are billions of years older, the Earth should have already been visited by extraterrestrial civilizations, or at least their probes.
However, there is no convincing evidence that this has happened.
There have been many attempts to explain the Fermi paradox, primarily suggesting that intelligent extraterrestrial beings are extremely rare, that the lifetime of such civilizations is short, or that they exist but (for various reasons) we see no evidence.

Although he was not the first to consider this question, Fermi’s name is associated with the paradox because of a casual conversation in the summer of 1950 with fellow physicists Edward Teller, Herbert York and Emil Konopinski. While walking to lunch, the men discussed recent UFO reports and the possibility of faster-than-light travel. The conversation moved on to other topics, until during lunch Fermi allegedly said suddenly, “But where is everybody?” (although the exact quote is uncertain).

 

History
Fermi was not the first to ask the question. An earlier implicit mention was by Konstantin Tsiolkovsky in an unpublished manuscript from 1933. He noted “people deny the presence of intelligent beings on the planets of the universe” because “(i) if such beings exist they would have visited Earth, and (ii) if such civilizations existed then they would have given us some sign of their existence.” This was not a paradox for others, who took this to imply the absence of ETs. But it was one for him, since he believed in extraterrestrial life and the possibility of space travel. Therefore, he proposed what is now known as the zoo hypothesis and speculated that mankind is not yet ready for higher beings to contact us.That Tsiolkovsky himself may not have been the first to discover the paradox is suggested by his above-mentioned reference to other people’s reasons for denying the existence of extraterrestrial civilizations.

In 1975, Michael H. Hart published a detailed examination of the paradox, one of the first to do so :27–28:6 He argued that if intelligent extraterrestrials exist, and are capable of space travel, then the galaxy could have been colonized in a time much less than that of the age of the Earth. However, we see no evidence they have been here, which Hart called “Fact A”.[:6

Other names closely related to Fermi’s question (“Where are they?”) include the Great Silence, and silentium universi (Latin for “silence of the universe”), though these only refer to one portion of the Fermi Paradox, that we see no evidence of other civilizations.

Original conversation(s)

At Los Alamos National Laboratory in the summer of 1950, Fermi and co-workers Emil Konopinski, Edward Teller, and Herbert York had one or several casual lunchtime conversation(s).

Herb York does not remember a previous conversation, although he says it makes sense given how all three later reacted to Fermi’s outburst. Teller remembers seven or eight of them at the table, so he may well be remembering a different previous conversation.

In one version, the three men discussed a spate of recent UFO reports while walking to lunch. Konopinski remembered mentioning a magazine cartoon which showed aliens stealing New York City trash cans, and as he wrote years later, “More amusing was Fermi’s comment, that it was a very reasonable theory since it accounted for two separate phenomena.”

Teller remembered Fermi asking him, “Edward, what do you think? How probable is it that within the next ten years we shall have clear evidence of a material object moving faster than light?” Teller said, “10–6” (one in a million). Fermi said, “This is much too low. The probability is more like ten percent” (which Teller wrote in 1984 was “the well known figure for a Fermi miracle”).

At lunch, Fermi suddenly exclaimed, “Where are they?” (Teller’s remembrance), or “Don’t you ever wonder where everybody is?” (York’s remembrance), or “But where is everybody?” (Konopinski’s remembrance).

Teller wrote, “The result of his question was general laughter because of the strange fact that in spite of Fermi’s question coming from the clear blue, everybody around the table seemed to understand at once that he was talking about extraterrestrial life.” York wrote, “Somehow . . . we all knew he meant extra-terrestrials.”[note 4] However, Emil Konopinski was not emphatic that he immediately knew Fermi was referring to possible aliens, merely writing, “It was his way of putting it that drew laughs from us.”

Regarding the continuation of the conversation, York wrote in 1984 that Fermi “followed up with a series of calculations on the probability of earthlike planets, the probability of life given an earth, the probability of humans given life, the likely rise and duration of high technology, and so on. He concluded on the basis of such calculations that we ought to have been visited long ago and many times over.”

Teller remembers that not much came of this conversation “except perhaps a statement that the distances to the next location of living beings may be very great and that, indeed, as far as our galaxy is concerned, we are living somewhere in the sticks, far removed from the metropolitan area of the galactic center.”

Fermi died of cancer in 1954. However, in letters to the three surviving men decades later in 1984, Dr. Eric Jones of Los Alamos was able to partially put the original conversation back together. He informed each of the men that he wished to include a reasonably accurate version or composite in the written proceedings he was putting together for a previously-held conference entitled “Interstellar Migration and the Human Experience.”

Jones first sent a letter to Edward Teller which included a secondhand account from Hans Mark. Teller responded, and then Jones sent Teller’s letter to Herbert York. York responded, and finally, Jones sent both Teller’s and York’s letters to Emil Konopinski who also responded. Furthermore, Konopinski was able to later identify a cartoon which Jones found as the one involved in the conversation and thereby help to settle the time period as being the summer of 1950.

 

Basis

The Fermi paradox is a conflict between the argument that scale and probability seem to favor intelligent life being common in the universe, and the total lack of evidence of intelligent life having ever arisen anywhere other than on the Earth.

The first aspect of the Fermi paradox is a function of the scale or the large numbers involved: there are an estimated 200–400 billion stars in the Milky Way[25] (2–4 × 1011) and 70 sextillion (7×1022) in the observable universe. Even if intelligent life occurs on only a minuscule percentage of planets around these stars, there might still be a great number of extant civilizations, and if the percentage were high enough it would produce a significant number of extant civilizations in the Milky Way. This assumes the mediocrity principle, by which the Earth is a typical planet.

The second aspect of the Fermi paradox is the argument of probability: given intelligent life’s ability to overcome scarcity, and its tendency to colonize new habitats, it seems possible that at least some civilizations would be technologically advanced, seek out new resources in space, and colonize their own star system and, subsequently, surrounding star systems. Since there is no significant evidence on Earth, or elsewhere in the known universe, of other intelligent life after 13.8 billion years of the universe’s history, there is a conflict requiring a resolution. Some examples of possible resolutions are that intelligent life is rarer than we think, that our assumptions about the general development or behavior of intelligent species are flawed, or, more radically, that our current scientific understanding of the nature of the universe itself is quite incomplete.

The Fermi paradox can be asked in two ways. The first is, “Why are no aliens or their artifacts found here on Earth, or in the Solar System?” If interstellar travel is possible, even the “slow” kind nearly within the reach of Earth technology, then it would only take from 5 million to 50 million years to colonize the galaxy. This is relatively brief on a geological scale, let alone a cosmological one. Since there are many stars older than the Sun, and since intelligent life might have evolved earlier elsewhere, the question then becomes why the galaxy has not been colonized already. Even if colonization is impractical or undesirable to all alien civilizations, large-scale exploration of the galaxy could be possible by probes. These might leave detectable artifacts in the Solar System, such as old probes or evidence of mining activity, but none of these have been observed.

The second form of the question is “Why do we see no signs of intelligence elsewhere in the universe?” This version does not assume interstellar travel, but includes other galaxies as well. For distant galaxies, travel times may well explain the lack of alien visits to Earth, but a sufficiently advanced civilization could potentially be observable over a significant fraction of the size of the observable universe. Even if such civilizations are rare, the scale argument indicates they should exist somewhere at some point during the history of the universe, and since they could be detected from far away over a considerable period of time, many more potential sites for their origin are within range of our observation. It is unknown whether the paradox is stronger for our galaxy or for the universe as a whole.

 

 

 

 

Source: WIKIPEDIA

Image: https://gr.pinterest.com/pin/392024342544337022/



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