Alien Life Lesson

A couple of weeks back I was asked to help plan a lesson on alien life to a GCSE class. In our 20 minute brainstorm we came up with what’s below and I suitably pleased with house the lesson went that I’d share our quick thoughts on this.

Alien life and SETI (Search for Extraterrestrial Intelligence) is part of GCSE science, in particular it is a physics topic. For this we decided that it would be quite interesting to add a bit extra to make the subject a bit deeper.


For a starter we got the students to look at the Drake Equation, yes I know this isn’t the most scientific and indeed some of the numbers are hard for the class to comprehend (doing this as group work would lead to differentiation giving a variety of information or different parameters for the more able to answer). The Drake equation is good fun as it exposes the students to a wide range of different numbers and the large scale of astronomy. It also has some interesting social issues in there. The idea that society could transmit, or retrieve, a signal for thousands of years is very thought provoking especially when you bring in the idea of 60 years or so for our society. So, you might be think, what is the Drake Equation? Simply the Drake Equation allows one to estimate the number of detectable civilizations in our galaxy. This was put together in 1961 by radio astronomer Frank Drake.

The Drake equation states that:

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


N = the number of civilizations in our galaxy that can be communicated with
R* = average rate of star formation per year in our galaxy
fp = fraction of those stars that have planets
ne = average number of planets that can potentially support life per star
fl = fraction that develop life at some point
fi = fraction that develop intelligent life
fc = fraction of civilizations that develop a technology that releases detectable signs of their existence into space
L = length of time for which such civilizations release detectable signals into space

Drake used the following:

R* = 1/year
fp = 0.2-0.5 (
ne = 1-5
fl = 1 (100% will develop life)
fi = 1 (100% will develop intelligent life)
fc = 0.1-0.2
L = 1000-100,000,000 years

They roughly concluded that N ~ L and somewhere between 1000 and 100,000,000 civilizations in the galaxy.

Using more recent, and less optimistic numbers gives much lower values, very sceptical values give very small values of N: 10^-20. So we would probably be alone in the whole Universe. A good discussion of these parameters is given over on wikipedia (maybe a chance for some research work?).

After this we went on to get the class to discuss how we would communicate and how we could detect alien life, what we are looking for, how we are doing this and why should we do this. This was done in groups with ideas discussed as a whole group. The students then went on to think how we could terraform Mars, in essence answering the question: what do we need for life?

We finished off by getting the students to calculate how far out into space the first radio signals that man sent into space will have now gotten? This is a nice link into history and the Berlin Olympic game of 1936 and the first TV signal sent into space. The students were asked, after being reminded what the speed of light is in SI units, how far the radio signal would have gone. This is of course the current year – 1936 light years. It was interesting to see how close the students got to the correct answer in metres. This could have been extended if they had been time via a list of nearby stars and to calculate how many stars are in that region.

I feel this lesson was a bit different to their normal work and they got to touch on many different aspects of physics and the world around them.


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