There must be aliens in the universe, if you have to say that there is no aliens in the universe, then congratulate you still stay on the earth is the center of the universe of the point of view, there is no need to look down. The universe has many people, who do not know, if the universe as a huge white paper, that the earth is one of the small point, the sun is also a point, there is an endless point on this page, from the point of view of probability, the infinite point will have a few or even more points are the same function, This function is called the object can survive on the planet. The simplest example is the examination of our students, why the same score, this is the probability, even if the probability of a small, large base (infinity point), there will be a repetition. So don't think about self-centered thinking that there's going to be aliens.
From the perspective of human thinking that there must be aliens in the universe, take us now, the number of human beings more and more, one day the earth will be overloaded. Can't keep so many people, how do you think, to live, you will want to find the new World (that is, the newly viable planet), the premise is, of course, under the conditions permitted by science and technology, then why do not you want to think, if our ancestors were brought from another planet to the planet to survive, reduce the survival burden of the ancestors. Just because our technology does not reach that level, the human beings on other planets may not be able to do it, just as you told 100 years ago or 1000 years ago that the computer, cell phone, they would believe, they will not believe. If we consider the progress of science and technology as a line, then we are just a point in the line, both the technology is more advanced than we have the technology behind us. Don't be so self-centered.
There must be an alien presence in the universe.