12.1 Drake equation
astronomer Frank Drake tried to summarize the factors that would determine whether any attempt to detect
intelligent extraterrestrials could succeed.
He came up with a simple equation that, at least in principle, could be used to calculate the number of
civilizations existing elsewhere in our galaxy (or in the universe at large) from which we could
potentially get a signal.
The Drake equation, as it is now called, does not give us a definitive answer for the number of
transmitting civilizations. Rather, it lays out the factors that are important in determining this number.
Number of civilizations N( HP) *f(life)f( civf(* now)
N HP is the number of habitable planets in the galaxy.
flife is the fraction of habitable planets that actually have life.
fciv is the fraction of the lifebearing planets on which a civilization capable of
interstellar communication has at some time arisen.
fnow is the fraction of the civilizationbearing planets that happento have a
civilization now, as opposed to, say, millions or billions of years in the past.
To summarize, the Drake equation gives us a way to calculate the number of civilizations capable of
interstellar communication that are currently sharing the Milky Way Galaxy with us. As such, it provides a
useful way of organizing our thinking about the problem, because it tells us exactly what numbers we need
to know to learn the answer. Indeed, it suffers from only one significant drawback: We don’t know precise
values for any of its terms!
The evolutionary argument in favor of widespread intelligence is based on the phenomenon of
convergent evolution, the tendency of organisms of different evolutionary backgrounds that occupy
similar ecological niches to resemble one another. (ex. Eyesight, streamlined body form for sharks and
natural selection often produces analogous adaptations.
intelligence—the way an animal processes information—is subject to natural selection
Those animals whose brain mass falls on this line are said to have an encephalization quotient
(EQ) of 1, which means a typical allotment of mental ability for creatures of their size. If their brain mass falls above this line, then it seems reasonable to suppose that they are capable of more
elaborate behavior. Creatures whose brain mass falls below the line are presumably less mentally agile
than average animals in this sample. The EQ, the brain mass relative to the value on the line EQ = 1,
as an indicator of general intelligence.
measuring EQ has the advantage of being fast and easy. EQ also has the advantage of being something
we can compute for extinct species
Carniv orous animals that need to hunt down their meals generally have higher EQs than leaf eaters, and
animals that lavish care on their offspring score higher than those that ignore them.
Humans are not closely related to dolphins in an evolutionary sense, so the fact that they have also
developed large brains suggests that there is real survival value in cleverness, and that there are many
ways that nature can produce it.
Was this a lucky accident, or was it inevitable that some culture would develop modern technology?
Again, a single example—what happened on our own planet—cannot guarantee that science and
technology will be common in the cosmos, even if high intelligence is.
SETI means "Search For Extraterrestrial Intelligence"
One of these pioneers was Guglielmo Marconi (1874–1937), generally celebrated as the man who made
radio practical. The other was Nikola Tesla (1856–1943)
Teslamost enduring legacy was the use of alternating current (AC) for distributing electrical power.
“whistlers,” electrical noise created by distant lightning discharges. (which Tesla mistook as greeting from
1920s, the signals that Marconi heard may also have been “whistlers” from distant lightning, or possibly
garbled U.S. Navy broadcasts of which he was unaware.
They were conducted at relatively low frequencies, which have problems penetrating Earth’s ionosphere—a
layer of the upper atmosphere that consists of particles ionized by sunlight
The beginning of modern SETI is gener ally attributed to two physicists working at Cornell University. 1959
Giuseppe Cocconi and Philip Morrison That range of transmit ted frequencies is called the bandwidth of the signal. As a practical matter, the
bandwidth is governed by how much information the broadcast contains. (ex. Radio