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# Is there anybody out there?

## Are we alone? It’s one of the fundamental questions about space. Are there other civilisations out there living their lives and looking at their stars wondering, as we do, if there’s anyone else out there?

Computer scientists are playing their part in the search for extraterrestrial intelligence. They contribute to the development of space probes, and deep space imaging devices such as the Hubble space telescope. Computers process the massive amounts of data that come from radio telescopes. Scientists have even used maths in an attempt to compute the probability of discovering intelligent life out there. Perhaps the most famous of these is the Drake equation.

## The Drake equation

The Drake equation was developed by scientist Frank Drake around 1960. It looks a bit complicated but is really quite simple. The equation is a series of numbers multiplied together, and each number is related to a factor that could influence our ability to detect intelligent life in the galaxy. Why are the numbers multiplied together? Here’s a simple example. Suppose there were 10 possible planets, and we believed only one in 10 (0.1) planets on average could support life, then N, the number of planets able to support life, would be 10 x 0.1 = 1 planet. All that the Drake equation does is to take more numbers (called factors) to multiply together, each factor filtering down the number of intelligent civilisations possible. So let’s look at the equation.

## N = R *x* fp *x* ne *x* fl *x* fi *x* fc *x* L

Here N is the number of civilisations in our galaxy with which it might be possible to communicate, that support intelligent, technically advanced life. On the other side go the seven factors that affect the answer. R is the average rate of the formation of stars in our galaxy, while fp is the fraction of those stars that have planets orbiting them. For stars that have planets, ne is the average number of them that could potentially support life. fl is the fraction of these inhabitable planets that actually go on to develop life at some point. fi is the fraction of the life-bearing planets that have intelligent life. We’re getting closer now: fc is the fraction of civilizations whose technology leaks detectable signs of their existence into space, such as TV or radio. Finally, L is the length of time such civilizations actually release their detectable signals into space. Lots of factors, but what’s the answer?

## And the answer is?

No one can agree on the answer to the Drake equation. Science is constantly discovering more about the formation of planets, stars and the evolution of intelligent life, and the factors keep needing to be updated. Estimates for the number of civilisations out there for us to detect have varied from 5,000 to the most recent estimate of around 3.

Some have argued that many of the astronomical factors, such as star and planet formations, are quite large, and that the real problem is in L, the amount of time intelligent civilisations release detectable systems. Space is vast and signals travel at the speed of light, so distant inhabited planets would need to be active for a considerable time to make their detection possible. Some pessimistically believe that intelligent life that has arrived at a high level of technical ability will discover nuclear fission. Acting as a sort of galactic IQ test, unleashing the potentially destructive power of the atom may have led to nuclear war, and the end of their civilisation – a rather depressing thought! Of course no one knows for sure. That’s one of the arguments against the Drake equation. Science needs to be provable, and since there’s no easy way to prove or disprove the Drake equation, is it more science fiction than science fact?

## Drake and the Fermi Paradox

The Drake equation is related to another famous statement called the Fermi paradox. A paradox is a statement that leads to a contradiction. For example, the statement 'this statement is false' is a paradox. Ask yourself what you know if it is true and what you know if it isn’t – which is it?

The Fermi paradox says that since the universe is apparently so ancient and huge, there ought to be lots of technologically advanced alien civilisations so they should be easy to spot – except we haven’t found any.

Perhaps the answer to the Fermi paradox is related to the Drake equation, and the same filter that reduces the number in the Drake equation is responsible for the Fermi paradox.

Computer scientists are using increasingly sophisticated models, running on supercomputers, to try and better understand the formation of stars, planets and galaxies. These simulations can then be tested against real astronomical observations where available, so perhaps one day we will have a better idea of the factors in the Drake equation. Of course in the meantime, as computers worldwide process millions of observations from the night sky, perhaps it will be a computer scientist who helps us uncover the first proof of intelligent extraterrestrial worlds. Will the 21st century be when it all changes?