Theories about extraterrestrial life

The alien and UFO phenomenon is so widespread and present in our modern times that it looks difficult to make even a cautious opinion. There are many theories about where aliens come from, but there is no absolute proof. Some speculate that aliens come from other planets, while others suggest different dimensions. Le it be abduction,  crop circles, or strange lights in the sky, ... a formal synthesis of the origin of such a wide array of phenomenon is almost impossible. Here, we will examine evidences, theories scientifically as well as esoterically.