The existence of alien intelligent life form.

Two thousand years ago, people thought the Earth is the center of this universe and human was the only intelligent life form in this world. Later, people discovered the vastness of the universe and found the Earth is only one of the countless planets. Then, logically it becomes interesting to find whether there are some other intelligent life form in other planet.

Personally, I believe there are some other intelligent life forms existing at remote planets in the universe, just like us. However, I don't think we are able to find them and contact them, and vice versa. Human, as one species living on the Earth, faces the same fate as other species. Eventually, human species will start extinguish one day and the culture developed at that time may not reach the level to perform inter-planet journey in an efficient way, i.e., we are not able to go to other planet as described in the movies.

The other intelligent species at other planets face the same situation.

We are not alone, however, we are lonely from the sense that we cannot contact other intelligent life form in other distant planets.