Is there anybody out there?

While watching the history channel this evening, i was fascinated by incidencts that were attributed to  UFO . There was a scene in which a craft was captured by a camera moving at high speed next to a jet plane, and although the craft was visible through the camera lens, it was invisible to the naked eye. This phenomenon was explained by the suggestion that perhaps the craft emits x-rays and other light ranges that are within the range (wavelength) of a camera but out of range of the naked eye. Is there a possibility that extraterrestial craft are constantly zooming past us while we are blissifully unaware of their presence? Has anyone out there encountered any evidence of exstraterrrestial beings?