As is known to all, Aliens only exist in movies. However, some people believe in aliens. In my opinion, there is no aliens because we haven't any evidence to prove.
Firstly, living beings need three elements - proper temperature, water and air. No other planets have such conditions except for our globe. The only discovery of living trace is that on Mars, but just some marks. These marks could only shows that there probably had been living beings, but now, they died.
Secondly, if there are aliens, where are they from? Why don't they connect people on the world? Global famous scientist cannot even explain such questions. Because from thousands of year, no evidences shows aliens had once communicate with people.
Lastly, rumors which concern about aliens or UFO is just imagination. We have heard all kinds of legends, news or information about aliens and something like UFO. Some people even said they had seen such aliens. But until now, no one had taken real photos or show any conclusive clues. Some story about them is only guessing and dreaming.
In a words, we haven't find aliens now. But I believe, maybe hundreds and thousands years ago, aliens will appear and make friends with us.