70,000,000,000,000,000,000,000 stars currently thought to exist in our universe.

You try and tell me that we're the only ones. Just try it.

But not all stars are the same size as our sun. Very few are. Still, most stars have a reasonable orbital area which is judged to have the right conditions for life. (Though some would say this is a prime example of carbon chauvinism.)

The real questions arise in the following forms;

How many races are within a distance we can reasonably make contact with?

How many races are within a distance we can reasonably travel to? (Largely this depends on whether or not there is a maximum speed limit, and whether or not we can circumvent it.)

How many races are within a recognizable span of evolution, both scientific and cultural? (Sure, we could probably work with a species with the equivalent of 10,000 BC quite easily, but 1,000,000 BC? Similarly, the future might offer even smaller scope - just a few thousand years could grant so much technology as to change a race beyond recognition. On a cosmic scale, it's unlikely we'll find many races close to our own, in this regard.)

How many races survive until the age of radio broadcasts, and how many of those until the space age, and how many of those survive until they establish self-sustaining colonies on other worlds? (Which I consider the point when a race has guaranteed survivability. A natural disaster of anything smaller than a star dying wouldn't take them out.)

But they are out there, I will stake anything on that. The chances of aliens not existing is so ridiculously remote as to make the question an exercise not in probability, but in comedy.