Our universe is a huge place, possibly infinite. within this vast space rein trillions upon trillions of stars, and they form, trillions of trillions of galaxies, clusters and supper-clusters of galaxies as fare as the eye can see. I have seen photographs where the galaxies are so numerous that their images overlap and form an even shade of gray. Surely, within an infinite universe there are an infinite number of stars and therefor an infinite number of planets, hence an infinite amount of life. It is extremely unlikely that we are the only life in the universe. though I must concede, we could be the first, after all, someone has to be first. though I doubt if we are the first because according to the famous drake equation, there has been ample time since the beginning of the universe for other life to have formed.
The argument about whether there is life in the universe is mostly an academic one. the universe is a huge place, the distances between the suns is so distant that even if there is other life in the universe the technical difficulty, never-mind the odds, of making contact is so hard that we will probably never make contact. So for all practical purposes, we may as well be alone.
Another thing is this: even if aliens visited us how would we know? an observing party from Alpha Centaury could slide in in a black, radio silent ship, park up between Venus and the sun on the daylight side of the Earth, and we would never know. After-all, the moon disappears from view once a month as it goes new. we barely have the technology to image an asteroid from earth. how do you think we will see an alien ship!
There is this common misconception that the astronomers are constantly looking out into space looking for asteroids and other near earth dangers. Even though there have been great strides towards this in the last decade. It is still far from the truth. There are surveys being done but it is only by a hand full of individuals who really haven’t got a chance of seeing every thing due to the shear enormity of the task. a few tens of asteroids have been picked up by such surveys but nothing has actually been imaged from earth. Any one of these objects could have been an alien ship. Well, why not!