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How many alien civilisations are there?

In 1961, astrophysicist Frank Drake wrote the famous 'Drake Equation', which he used to estimate that there are 10,000 extraterrestrial civilisations in our galaxy that are capable of making contact with us. Nearly six decades later, astronomer Seth Shostak from the SETI Institute in California and zoologist Matthew Cobb from Manchester University in the UK discuss the likelihood that his estimation is accurate.

(Image: Milky Way galaxy, Credit: ESO/S. Brunier.)

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4 minutes