Excel Spreadsheet of Drake's equation
IIs anybody out there?
Space is big! Really big! There are 150,000,000 stars in our galaxy and at least 1,000,000,000,000 galaxies in the Universe. That's 150,000,000,000,000,000,000 stars. Current research indicates that about half of them should have planetary systems. Our planet appears to have evolved life as soon as it could. That's the good news.
We cannot think of a way in which we could communicate with other galaxies. The closest similar sized galaxy to our own is Andromeda at 2.2 million light years. Even if we could traverse the enormous gap with a radio signal, we would have to wait a minimum of 4.4 million years for a reply.
So conversations with aliens will have to be restricted to the Milky Way. Even that is 100,000 light years across.
Coming up with an equation for working out if their are alien civilisations to talk to, is relatively easy. The hard part is deciding the values of the figures you insert into it. The first person to come up with an equation was Dr Frank Drake in 1961. It looks like this:
N = N* • fs• fp• ne • fl • fi • fc • L
There are several versions of it. The key to this one is at the bottom of the page. You can download a spreadsheet version on the left. Spreadsheets are great for experimenting with the figures and watching what it does to the likelihood of making first contact.
If you fancy joining the search for extraterrestrial
intelligence, try downloading the SETI@home program from the University of
California. This gets your computer to analyse data from the
Arecibo Radio
Telescope.
You can even download a free planetarium program, Distant Suns 4, which will
show you where each packet of data you process ha come from.
Perhaps a more likely way of detecting life on other planets will be detecting the chemicals created by life. The European Space Agency's Darwin mission plans to do this and is due for launch in 2015
N = The number of civilizations in The Milky Way Galaxy whose electromagnetic
emissions are detectable.
N* =The number of stars in our galaxy in the region of 150,000,000,000
fs = The fraction of those stars that are of Sun type. Thought to be between
0.02 and 0.10
fp = The fraction of those stars with planetary systems. Current findings
indicate 0.5
ne = The number of planets, per solar system, with an environment suitable for
life. Although Venus and Mars may have had, they didn't stay the course. So the
maximum is probably 1, but more likely is a i in ten chance so 0.1.
fl = The fraction of suitable planets on which life actually appears. Could be
all of them.
fi = The fraction of life bearing planets on which intelligent life emerges. The
dinosaurs ruled the world for over 100 million years and never invented a radio.
So it's anyone's guess.
fc = The fraction of civilizations that develop a technology that releases
detectable signs of their existence into space. Probably all of them.
L = The length of time such civilizations release detectable signals into space.
Anyone's guess. The Universe has been going for 13 billion years and we have
been broadcasting for 100 years. The spreadsheet converts this to a fraction of
the age of the Universe. If we destroyed ourselves tomorrow this figure would be
a fraction of 1/(13,000,000,000/100) or 1/130,000,000th = 0.000000007 and if
that were the norm, it would make the chances of contactable alien civilisations
extremely unlikely.