Why do all presumptions of the existence of UFOs assume we're on the same time and space scales? From the space perspective, if the universe is boundless then the odds of us recognizing another life form are zero because it could be a million times larger or smaller than us - it certainly wouldn't be on our scale. And it may move around a million times faster or slower than us - again something we're not going have the ability to perceive. Or maybe it passed through a billion years ago.