One of the most Enduring questions in Astrobiology is, is There anyone out there? By anyone, that means extraterrestrial
intelligence. Could we find another intelligent
civilization in The galaxy or in the universe at large? Well, one of the first people to really
think About this and apply these ideas was Frank
Drake. An American astronomer and astrophysicist,
a Pioneer in the search for
extra-terrestrial intelligence. In 1961, he wrote down an equation that's
become rather famous. And has now become known as the Drake
Equation, To try and estimate the number of Communicative civilizations there might be
in the universe. Of course one of the first things we have
to do is to define what A civilization is and there are a number
of ways that we might do that. We might define a civilization as a group Of organisms that have built certain
certain technology. Maybe they've built cities or something
else. But of course if we're going to detect an Intelligent civilization they need to be
transmitting signals to us. So, from an operative point of view, We might simply define an intelligent
civilization As a civilization that is able to Communicate with us, for example, using
radio waves. So the Drake Equation is about trying To estimate the number of communicative
civilizations. What are the terms of this equation? So, this is the Drake Equation and it's
made up of a number of factors. And we have to estimate values for those
factors To be able to put them together to
estimate the total Number of communicative civilizations in
our galaxy, or perhaps in the universe. The first term, R, is the rate of
Formation of suitable stars, suitable
stars for life. But we know that G stars are suitable for Life because our own star is a G type
star. There might be other stars that are also
suitable For planets with intelligent life, for
example, N stars. Now at the moment we don't really know
enough about the Types of stars that can give rise to
intelligences on a planet, But we need to work out the rate of
formation of Suitable stars to be able to put that term
into the equation. So that's clearly one forthcoming
challenge to Astrobiologists. The next term is the fraction of these
stars with planets. A few decades ago, this was pure
speculation, we just didn't know Of planets around other stars. Now, with an increasing quantity of data, About planets orbiting distant stars, we
can begin To get a more accurate estimate of The number of stars that actually host
planets. And so we can begin to put some estimate
on this this term in the equation, FP. Once we know that, we then have to know
the number of Earth-like worlds Per planetary system. And again, at the moment we don't know
exactly What this number is, but as we increase
the search For Earth-like planets, and by that I
mean, rocky, terrestrial Type planets that could host liquid water
and even biology. Then we can start to put that number into
the equation. The search for extrasolar planets around
other stars in particular the Recent search for earth-like planets,
around other stars is bringing us closer To a time where we can actually estimate A number that could go into the Drake
Equation. Once we have that number, we then need to Work out the fraction of these planets
where life develops. We just don't know enough about the origin
of Life, what conditions are required for the
origin of life, To be able to work out the fraction of
planets
That are habitable that do actually give
rise to life. And this again is a challenge for
astrobiologists To work out what really were the
conditions for the origin of life. How likely or inevitable is it, that these Conditions be met on other planets that
are habitable. And so, what fraction of planets will
inevitably give rise to life? That's another term that we don't have an
accurate number for that we would Need in order to be able to work out, the
solution to this Drake Equation. Once we know the Number or fraction of planets where there
is life, we then need to be Able to work out the fraction of Those planets where intelligence life
evolves and develops. And again, in the moment, that's entirely
speculation. We don't even know whether there are
planets in our galaxy or In the universe that have life, let alone
whether they have intelligent life. But if we were to be able to work that
out. If we were to be able to look at enough
earth like planets around Our stars, assess them for their potential
for life, and Assess whether they could support
intelligent life, we could then Move on to the next term in the Drake
Equation Which is the fraction of those planets
that are communicating. And the only way that we can really work
that out, is to try And pick up signals from other planets Where there are interment civilizations
that are communicating. And then finally, the last term in this Equation is the lifetime of communicating
civilizations. This is a term that constrains the Total number of civilizations, that are
attempting To communicate by taking into account the Fact that these civilizations might have
finite lifetimes. Civilizations might destroy themselves. For other biological or technological
reasons, they may come To an end after a certain length of time. We would need to take
That into account to work out the total
number of communicative civilizations. So this Drake Equation contains some terms
that we can be More accurate about, for example the
fraction of stars that have planets. Some terms we really don't know anything
about at the current time Such as the number of habitable worlds
that give rise to intelligent life. But the Drake Equation is a Very interesting way of thinking about
astrobiology. It's a very interesting Way of ordering our thoughts. And ultimately it's the equation that we
will need To be able to estimate a value for, in Order to be able to know whether the
search For extraterrestrial intelligence is an
initiative that's worth undertaking. When Frank Drake first came up with this
equation, he estimated that there are 10,000 communicative civilizations In our
galaxy, based On the numbers that were known then. Of course Trying to come up with more accurate
numbers is a very difficult thing to do. But astrobiologist need to use the Drake
Equation to try and formulate A more accurate assessment of the Number of communicative civilizations in
the galaxy. Given the number of planets that have been
observed around other stars, and The numbers of Earth-like planets that are Beginning to be detected around other
stars. We might expect that this number will
change, possibly even upwards, Over the coming decades. Although, again, we still don't know, even
if there are many Earth-like planets in the galaxy, how many
of those might support intelligence. So what have we learned? Well, we've learned, of course, that we
don't know whether there Is anyone out there, but by coming up with
this equation, The Drake Equation, we have some sort of
method of trying to Quantify or estimate the numbers of
communicative civilizations in the galaxy. The equation depends upon many factors,
many factors that
Depend upon the the formation of planets
around stars. The formation of habitable conditions on
those planets And the emergence of life and eventually
intelligent life. When Frank Drake first attempted to come
up with a value that Results in this equation he estimated 10,000 communicative civilisations in the
galaxy. This equation is a Very good way of underpinning our search
for Extraterrestrial intelligence and trying To find out where the extraterrestrial Intelligence fits in with astrobiology.
