How many alien worlds exist?

Have you ever wondered if "we" are alone in the universe, and if not how many alien civilisations may be out there? Well, you'd not be alone. In fact, there's an equation, called the Drake equation, that lets us calculate how many alien civilisations there may be. The BBC has a nice interactive graphic that lets you play with the Drake equation to calculate your own figure. There's also a gr eat TED Talk on the subject. from The Universal Machine http://universal-machine.blogspot.com/ Universal Machine post to email (CS blog)