Microsoft Word Kurzweil, Ray The Singularity Is Near doc

The Drake Equation.
The SETI search has been motivated in large part by astronomer Frank Drake's 1961 equation 
for estimating the number of intelligent (or, more precisely, radio-transmitting) civilizations in our galaxy.
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(Presumably, the same analysis would pertain to other galaxies.) Consider the SETI assumption from the perspective 
of the Drake formula, which states: 
The number of radio-transmitting civilizations = N 
°
f
p
°
n
e
°
f
l
°
f
i
°
f
c
°
f
L
where: 
N = the number of stars in the Milky Way galaxy. Current estimates are around 100 billion (10
11
). 
f
p
= the fraction of stars that have orbiting planets. Current estimates range from about 20 percent to 50 
percent. 
n
e
: For each star with orbiting planets, what is the average number of planets capable of sustaining life? This 
factor is highly controversial. Some estimates are one or higher (that is, every star with planets has, on 
average, at least one planet that can sustain life) to much lower factors, such as one in one thousand or even 
less. 
f
l
: For the planets 
capable
of sustaining life, on what fraction of these does life actually evolve? Estimates are 
allover the map, from approximately 100 percent to about 0 percent.
f
i
: For each planet on which life evolves, what is the fraction on which intelligent life evolves? 
f
l
and 
f
i
are the 
most controversial factors in the Drake equation. Here again, estimates range from nearly 100 percent (that is, 
once life gets a foothold, intelligent life is sure to follow) to close to 0 percent (that is, intelligent life is very 
rare).
f
c
: For each planet with intelligent life, what is the fraction that communicates with radio waves? The 
estimates for 
f
c
tend to be higher than for 
f
l
and 
f
i
, based on the (sensible) reasoning that once you have an 
intelligent species, the discovery and use of radio communication is likely.

---

f
L
= the fraction of the universe's life during which an average communicating civilization communicates with 
radio waves.
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If we take our civilization as an example, we have been communicating with radio 
transmissions for about one hundred years out of the roughly ten- to twenty-billion-year history of the 
universe, so 
f
L
for the Earth is about 10
–8
so far. If we continue communicating with radio waves for, say, 
another nine hundred years, the factor would then be 10
–7
. This factor is affected by a number of 
considerations. If a civilization destroys itself because it is unable to handle the destructive power of 
technologies that may tend to develop along with radio communication (such as nuclear fusion or self-
replicating nanotechnology), then radio transmissions would cease. We have seen civilizations on Earth (the 
Mayans, for example) suddenly end their organized societies and scientific pursuits (although preradio). On 
the other hand it seems unlikely that every civilization would end this way, so sudden destruction is likely to 
be only a modest factor in reducing the number of radio-capable civilizations. 
A more salient issue is that of civilizations progressing from electromagnetic (that is, radio) transmissions to more 
capable means of communicating. Here on Earth we are rapidly moving from radio transmissions to wires, using cable 
and fiber optics for long-distance communication. So despite enormous increases in overall communication 
bandwidth, the amount of electromagnetic information sent into space from our planet has nevertheless remained fairly 
steady for the past decade. On the other hand we do have increasing means of wireless communication (for example, 
cell phones and new wireless Internet protocols, such as the emerging WiMAX standard). Rather than use wires, 
communication may rely on exotic mediums such as gravity waves. However, even in this case, although the 
electromagnetic means of communication may no longer be the cutting edge of an ETl's communication technology, it 
is likely to continue to be used for at least some applications (in any case, f
L
does take into consideration the 
possibility that a civilization would stop such transmissions). 
It is clear that the Drake equation contains many imponderables. Many SETI advocates who have studied it 
carefully argue that it implies that there must be significant numbers of radio-transmitting civilizations in our galaxy 
alone. For example, if we assume that 50 percent of the stars have planets (