In our solar system? Yes, it's just 7 billion of us, some animals, and one green/blue rock.
In our galaxy? Maybe. There is definitely potential for there to be alien life, it's just a long way away. Then there is always the possibility that we are the first intelligent civilizations in the Milky Way galaxy.
In the universe? Odds are that there are millions of other intelligent civilizations. The speed of light and the amount of distance to cover is a big reason why they probably haven't visited us and we will probably never visit them.
Indeed. I don't see how we can even get a reasonable bound on the exponent of P(alien life). That kind of uncertainty behaves counter-intuitively - multiplying it by the size of the universe leaves it essentially unchanged.
