This question has been confusing human beings for over thousands of years. Maybe Newton, Einstein and Tesla couldn’t figure it out even throughout their whole life’s work. When the rover Curiosity landed on Mars for the first time, people all around the world expected to meet new "friends" from another world, but unfortunately, they realized that Mars is a silent world without any living creatures. I don't know the purpose of the people who persevere to look for aliens, maybe it is because of all these sci-fi (science-fiction) movies that give us enough material what aliens may look like. But most of them are carbon-based creatures, but what if they are silica-based creatures, could we find them? So, this is a boring question and it makes no sense to look for an answer. If they exist, they must live thousands of lightyears aways so that neither us nor them can reach each other’s' planet. If they don't exist, we are the only creatures in the universe, we must pursue our own goals without wasting time looking for other forms of life.