You can't put a probability on something for which you have no data.
For something like Aliens you have the Drake equation, though the parameters are so unknown it renders it pretty meaningless. At least when talking about Aliens we have one example of life existing on a planet. For Supernatural things we have nothing that can be used to calculate a probability.
For something like Aliens you have the Drake equation, though the parameters are so unknown it renders it pretty meaningless. At least when talking about Aliens we have one example of life existing on a planet. For Supernatural things we have nothing that can be used to calculate a probability.