Are we alone in the universe?

Question: Are we alone in the universe?
- Keywords:
  aliens,
  universe
Asked by Beng to Pete, Natalie, Keith, Abbey, Aaron on 10 Nov 2015.
- Keith Franklin answered on 10 Nov 2015:
  
  No, I’m here!
  
  [I suspect we are probably not alone, but life on other planets will be so different to what we have here we might not even recognise it as life]
- Aaron Boardley answered on 10 Nov 2015:
  
  I can’t say for sure – but the universe is so big, with so many worlds, that I think there’s bound to be some form of life, somewhere.
  
  However, bear in mind what scientists mean by ‘life’ – trees are alive, bacteria are alive, microscopic creatures in the sea are alive, so just because there is life out there does not mean there are aliens with faces and brains that can travel around and communicate with us. That would be remarkable!
- Peter Burgess answered on 10 Nov 2015:
  
  I think it’s very unlikely that we aren’t.
  There’s a formula called the Drake Equation that tries to put a probability on extraterrestrial intelligent life.
  It’s basically a series of ‘What is the probability a star will have planets in orbit?’, ‘What is the probability those planets are in the habitable zone where liquid water can exist?’, ‘What is the probability that life will begin on a habitable zone planet?’, and ‘What is the probability that that life will develop intelligence?’ all multiplied by the number of stars to give an overall probability for intelligent life.
  Basically this last step of multiplying the probability for an individual star system to develop life by the billions and billions of star systems makes it extremely likely there is life elsewhere. Even if there’s a one in a million chance that still means there are thousands or even millions of inhabited worlds out there.
  
  A lot of the assumptions in the Drake equation are little more than guesses, and they are based on what we know now. Obviously the world humans know best is Earth, but as we get new evidence from the other planets of the solar system, comets, moons, and from extreme environments on Earth have tended to make life more likely. Next generation space telescopes might be able to find out what is in the atmospheres of planets orbiting other stars which could really give us some big clues as to whether life is present.
  
  Some of the most interesting candidates for extraterrestrial life in the solar system are moons of Jupiter and Saturn. In particular Europa, Titan and the newest ‘sexy’ moon, Enceladus which is a tiny moon of Saturn that is now thought to have geological activity and a sub surface ocean. Nobody knew much about Enceladus until the Cassini probe visited Saturn and it’s one of those wonderful discoveries which makes scientists go “Well that’s new… We didn’t expect that… What’s going on here???” in short, the whole point of doing science. Finding things out and getting a better understanding of the universe we live in.
- Natalie Garrett answered on 13 Nov 2015:
  
  As Peter and the others have said, if you look at the sheer vast numbers of planets in the universe, it is very likely that there is life somewhere else. However the universe is so flipping big, that we’re probably never going to see it :'(

Question: Are we alone in the universe?

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