.
Drake Equation - (also known as the Green Bank equation or the Sagan equation) is a famous result in the speculative fields of xenobiology, astrosociobiology and the search for extraterrestrial intelligence.
This equation was devised by Dr Frank Drake (now Emeritus Professor of Astronomy and Astrophysics at the University of California, Santa Cruz ) in the 1960s in an attempt to estimate the number of extraterrestrial civilizations in our galaxy with which we might come in contact. The main purpose of the equation is to allow scientists to quantify the uncertainty of the factors which determine the number of extraterrestrial civilizations. In recent years, the rare Earth hypothesis, which posits that conditions for intelligent life are quite rare in the universe, has been seen as a possible refutation of the equation.
The Drake equation states that:
where:
N is the number of civilizations in our galaxy with which we might expect to be able to communicate at any given time
and
R* is the rate of star formation in our galaxyfp is the fraction of those stars that have planetsne is average number of planets that can potentially support life per star that has planetsfl is the fraction of the above that actually go on to develop lifefi is the fraction of the above that actually go on to develop intelligent lifefc is the fraction of the above that are willing and able to communicateL is the expected lifetime of such a civilization for the period that it can communicate across interstellar space.
Fermi Paradox - the apparent contradiction between high estimates of the probability of the existence of extraterrestrial civilizations and the lack of evidence of contact with such civilizations.
The extreme age of the universe and its vast number of stars suggest that extraterrestrial life should be common. Considering this with colleagues over lunch in 1950, the physicist Enrico Fermi is said to have asked: "Where are they?" Fermi questioned why, if a multitude of advanced extraterrestrial civilizations exist in the Milky Way galaxy, evidence such as probes, spacecraft or radio transmissions has not been found. The simple question "Where are they?" (alternatively, "Where is everybody?") is possibly apocryphal, but Fermi is widely credited with simplifying and clarifying the problem of the probability of extraterrestrial life.
There have been attempts to resolve the Fermi Paradox by locating evidence of extraterrestrial civilizations, along with proposals that such life could exist without human knowledge. Counterarguments suggest that intelligent extraterrestrial life does not exist or occurs so rarely that humans will never make contact with it.
A great deal of effort has gone into developing scientific theories and possible models of extraterrestrial life and the Fermi paradox has become a theoretical reference point in much of this work. The problem has spawned numerous scholarly works addressing it directly, while various questions that relate to it have been addressed in fields as diverse as astronomy, biology, ecology, and philosophy. The emerging field of astrobiology has brought an interdisciplinary approach to the Fermi paradox and the question of extraterrestrial life.
Zoo Hypothesis - one of a number of suggestions that have been advanced in response to the Fermi Paradox, regarding the apparent absence of evidence in support of the existence of advanced extraterrestrial life. According to this hypothesis, aliens would generally avoid making their presence known to humanity, or avoid exerting an influence on human development, somewhat akin to zookeepers observing animals in a zoo.
Adherents of the hypothesis consider that Earth and humans are being secretly surveyed using equipment located on Earth or elsewhere in the solar system which relays information back to the observers. It is also suggested that covert contact will eventually be made with humanity once humans reach a certain level of development.
The Great Filter - Humanity seems to have a bright future, i.e., a non-trivial chance of expanding to fill the universe with lasting life. But the fact that space near us seems dead now tells us that any given piece of dead matter faces an astronomically low chance of begating such a future. There thus exists a great filter between death and expanding lasting life, and humanity faces the ominous question: how far along this filter are we?
Combining standard stories of biologists, astronomers, physicists, and social scientists would lead us to expect a much smaller filter than we observe. Thus one of these stories must be wrong. To find out who is wrong, and to inform our choices, we should study and reconsider all these areas. For example, we should seek evidence of extraterrestrials, such as via signals, fossils, or astronomy. But contrary to common expectations, evidence of extraterrestrials is likely bad (though valuable) news. The easier it was for life to evolve to our stage, the bleaker our future chances probably are.
*PooF*
This equation was devised by Dr Frank Drake (now Emeritus Professor of Astronomy and Astrophysics at the University of California, Santa Cruz ) in the 1960s in an attempt to estimate the number of extraterrestrial civilizations in our galaxy with which we might come in contact. The main purpose of the equation is to allow scientists to quantify the uncertainty of the factors which determine the number of extraterrestrial civilizations. In recent years, the rare Earth hypothesis, which posits that conditions for intelligent life are quite rare in the universe, has been seen as a possible refutation of the equation.
The Drake equation states that:
where:
N is the number of civilizations in our galaxy with which we might expect to be able to communicate at any given time
and
R* is the rate of star formation in our galaxyfp is the fraction of those stars that have planetsne is average number of planets that can potentially support life per star that has planetsfl is the fraction of the above that actually go on to develop lifefi is the fraction of the above that actually go on to develop intelligent lifefc is the fraction of the above that are willing and able to communicateL is the expected lifetime of such a civilization for the period that it can communicate across interstellar space.
Fermi Paradox - the apparent contradiction between high estimates of the probability of the existence of extraterrestrial civilizations and the lack of evidence of contact with such civilizations.
The extreme age of the universe and its vast number of stars suggest that extraterrestrial life should be common. Considering this with colleagues over lunch in 1950, the physicist Enrico Fermi is said to have asked: "Where are they?" Fermi questioned why, if a multitude of advanced extraterrestrial civilizations exist in the Milky Way galaxy, evidence such as probes, spacecraft or radio transmissions has not been found. The simple question "Where are they?" (alternatively, "Where is everybody?") is possibly apocryphal, but Fermi is widely credited with simplifying and clarifying the problem of the probability of extraterrestrial life.
There have been attempts to resolve the Fermi Paradox by locating evidence of extraterrestrial civilizations, along with proposals that such life could exist without human knowledge. Counterarguments suggest that intelligent extraterrestrial life does not exist or occurs so rarely that humans will never make contact with it.
A great deal of effort has gone into developing scientific theories and possible models of extraterrestrial life and the Fermi paradox has become a theoretical reference point in much of this work. The problem has spawned numerous scholarly works addressing it directly, while various questions that relate to it have been addressed in fields as diverse as astronomy, biology, ecology, and philosophy. The emerging field of astrobiology has brought an interdisciplinary approach to the Fermi paradox and the question of extraterrestrial life.
Zoo Hypothesis - one of a number of suggestions that have been advanced in response to the Fermi Paradox, regarding the apparent absence of evidence in support of the existence of advanced extraterrestrial life. According to this hypothesis, aliens would generally avoid making their presence known to humanity, or avoid exerting an influence on human development, somewhat akin to zookeepers observing animals in a zoo.
Adherents of the hypothesis consider that Earth and humans are being secretly surveyed using equipment located on Earth or elsewhere in the solar system which relays information back to the observers. It is also suggested that covert contact will eventually be made with humanity once humans reach a certain level of development.
The Great Filter - Humanity seems to have a bright future, i.e., a non-trivial chance of expanding to fill the universe with lasting life. But the fact that space near us seems dead now tells us that any given piece of dead matter faces an astronomically low chance of begating such a future. There thus exists a great filter between death and expanding lasting life, and humanity faces the ominous question: how far along this filter are we?
Combining standard stories of biologists, astronomers, physicists, and social scientists would lead us to expect a much smaller filter than we observe. Thus one of these stories must be wrong. To find out who is wrong, and to inform our choices, we should study and reconsider all these areas. For example, we should seek evidence of extraterrestrials, such as via signals, fossils, or astronomy. But contrary to common expectations, evidence of extraterrestrials is likely bad (though valuable) news. The easier it was for life to evolve to our stage, the bleaker our future chances probably are.
*PooF*