All These Worlds Are Yours - Part 3
How many "Goldilocks" or Earth-like planets are there? Without being able to survey other planetary systems in detail we can only estimate this value based on largely untested theories of how stars and planets form. A recent hand-waving estimate (http://news.bbc.co.uk/1/hi/sci/tech/7891132.stm) suggests there is one for each star, making perhaps 300 billion of them in our galaxy. I think this is perhaps optimistic, but we have to wait for the real data to decide.
Once you have an Earth-like planet, what are the chances that life will develop on it? What is the chance of that life developing intelligence, civilisation, technology, spaceflight? What are the chances of that planet being close enough to us, and both our civilisations lasting long enough to detect a signal from the other? These questions have been combined into a single statement known as the Drake Equation.
N = N* x P x E x L x I x C x t/T
N is how many alien civilisations we can potentially contact within our galaxy.
N* is the number of stars in our galaxy.
P is the fraction of those stars with planets.
E is the average number of planets per star that may support life.
L is the fraction of planets that do develop life.
I is the fraction of lifeforms that develop intelligence.
C is the fraction of intelligent lifeforms that send signals into space.
t is the length of time these civilisations send signals.
T is the age of the galaxy.
Most of these terms are impossible to even estimate with our current knowledge. We only have one example of life developing on a planet, one example of life developing intelligence - the inhabitants of Earth. A single data point does not a useful graph make. The Drake Equation is not a part of science like the Theory of Relativity or Maxwell's laws, but it is a useful starting point for understanding the conditions for meeting extra-terrestrial life.
Once you have an Earth-like planet, what are the chances that life will develop on it? What is the chance of that life developing intelligence, civilisation, technology, spaceflight? What are the chances of that planet being close enough to us, and both our civilisations lasting long enough to detect a signal from the other? These questions have been combined into a single statement known as the Drake Equation.
N = N* x P x E x L x I x C x t/T
N is how many alien civilisations we can potentially contact within our galaxy.
N* is the number of stars in our galaxy.
P is the fraction of those stars with planets.
E is the average number of planets per star that may support life.
L is the fraction of planets that do develop life.
I is the fraction of lifeforms that develop intelligence.
C is the fraction of intelligent lifeforms that send signals into space.
t is the length of time these civilisations send signals.
T is the age of the galaxy.
Most of these terms are impossible to even estimate with our current knowledge. We only have one example of life developing on a planet, one example of life developing intelligence - the inhabitants of Earth. A single data point does not a useful graph make. The Drake Equation is not a part of science like the Theory of Relativity or Maxwell's laws, but it is a useful starting point for understanding the conditions for meeting extra-terrestrial life.
Labels: space
posted by Cobweb | 20:40
2 Comments:
shouldn't there be something in that equation to account for the potential for overlap (or not) of t/T for our civilisation vs the "other" civilisations? Or have I not understood how t/T works (this is more likely, given that I'm not a mathematician)?
I should have made it clearer - the number N is the number of contactable civilisations in the galaxy at any one moment. Considering the relatively tiny amount of time over which our civilisation has been listening to space, we can estimate it as "one moment". Should we last for millions of years, we would have to alter the equation. There are other factors which perhaps should be included - a civilisation existing right now in the galaxy is not much use if it's 50,000 light years away, and even if it had been broadcasting for 50,000 years the signal may be too weak for us to hear.
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