Gene Boggs > SETI-Drake-0.0201 > SETI::Drake
Module Version: 0.0201

# NAME

SETI::Drake - Estimate the number of interstellar communicating civilizations

# SYNOPSIS

```  use SETI::Drake;
\$d = SETI::Drake->new(
R  => \$stars,
fp => \$planets,
ne => \$support,
fl => \$life,
fi => \$intelligence,
fc => \$communication,
L  => \$lifespan,
);
\$n = \$d->N;
printf 'You are ' .
(\$n > \$threshold ? 'opt' : 'pess') .
"imistic: %0.2f\n", \$n;```

# DESCRIPTION

A `SETI::Drake` object answers the question, "How many detectible, intelligent, interstellar communicating civilizations might be out there, in the galaxy?" by providing a single method, `N()`, which is a prediction based on the product of seven factors. In other words, this module does nothing more than multiply seven numbers together.

According to NOVA, Drake's values were:

```  R  => 5,     # Number of stars formed per year.
fp => 0.5,   # Fraction of those stars that form planets.
ne => 2,     # Average number of those planets that can support life.
fl => 1,     # Fraction of those planets that actually do develop life.
fi => 0.2,   # Fraction of those planets that then evolve intelligence.
fc => 1,     # Fraction of those planets that develop interstellar communication.
L  => 10000, # Average lifetime (in years) of an interstellar communicating civilization.```

According to Wikipedia, Drake's values were:

```  R  => 10,  # Annual rate of star creation in our galaxy.
fp => 0.5, # Fraction of those stars which have planets.
ne => 2,   # Average number of these planets that can potentially support life.
fl => 1,   # Fraction of the above that develop life.
fi => 0.1, # Fraction of the above that develop intelligent life.
fc => 0.1, # Fraction of the above that communicate.
L  => 10,  # Expected lifetime (in years) of such a civilisation.```

On Cosmos, Carl Sagan computes it this way:

```  R  => 400_000_000_000,  # Number of stars in the Milky Way.
fp => 1/4,  # Fraction of stars that have planets.
ne => 2,    # Worlds suitable for sustaining life per system.
fl => 1/2,  # Fraction of suitable worlds in which life does arise
fi => 1/10, # Fraction of worlds where intelligent life evolves.
fc => 1/10, # Fraction of worlds that produce a technical civilization.
L  => 1/100_000_000, # Chance that we might destroy ourselves tomorrow.```

# METHODS

## new

`  my \$d = SETI::Drake->new(\$arguments);`

Return a new SETI::Drake instance. If no equation variables are provided, Frank Drake's choices (from his 2004 chalkboard video interview on Nova) are used.

## N

`  \$N = \$d->N;`

Return the value of the Drake equation:

`  N = R* x fp x ne x fl x fc x L`

## TO DO

Use Math::BigRat.

http://www.youtube.com/watch?v=0Ztl8CG3Sys - Carl Sagan explains it.

http://www.setileague.org/general/drake.htm

http://www.pbs.org/wgbh/nova/origins/drake.html

http://en.wikipedia.org/wiki/Drake_equation

http://www.hawking.org.uk/lectures/life.html

http://setiathome.berkeley.edu