Question: How likely is it that there is life on another planet somewhere?

Duncan McNicholl answered on 7 Nov 2017:

We don’t know, so to try and work it out a scientist came up with something that’s named after him: the Drake Equation. It takes a bunch of probabilities of different things happening and multiplies them together to get the probability of intelligent life existing somewhere in the galaxy. It’s a nice idea, but the problem is that we don’t know the probabilities of the different things happening, so we just have to make them up, and that means that the final answer can be anything from basically zero to nearly a hundred per cent.
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Something that I think is interesting is that we keep finding things that make it seem even less likely that life would evolve, like some scientists think that early life might have needed tides to evolve,, because the water coming in and out helps make a certain kind of reproduction work. But tides are caused by the moon, which is unusually big and unusually close to us, so maybe a planet has to have a really big close moon for life to evolve, and now there’s much less chance of finding a planet that’s just right out there, and much less likely for aliens to exist.