Existance of UFO's depends upon the existance of the one who created UFO.
There are millions of stars in the Universe. That means there are so that many solar systems in the Universe. And each solar system has got 'n' number of Planets. So you have millions of Planets in our Universe.
Now among those million planets, question arises as to how many are earth like planets. It's not that hard to calculate. Simple proability reveals, out of those million Planets, let's assume that there are 30,000 earth like planets. Earth like planets means which can support life.
Now out of those 30,000 earth like planets,there is always a chance of alteast 6000 planets supporting Life.
That doesn't end there..
Not every Planet of those 6000 will support Intelligent life. Some may be just be simple life forms like Unicellular organisms.
So out of those 6000 planets, there is always a probability of around 3000 planets supporting Intelligent life! Level of Intelligence life may vary abruptly.
Some may be 'Human-like' and some like those shown in our movies!
There is always a proability that any of these Super-intelligent life forms may technology which we just can't imagine!
Humans totally depend on propulsion technology for achieving motion in air. Aliens may have found out a method of creating it own gravitational force along its flying object!! Nothng is impossible. Humans may also do it one day.
Who believed a thing like 'Aircraft' will exist on earth? No one imagined earlier! But now it's the fact.
One can't ignore the mere existence of UFO's. Now it's a matter of time when they visit earth.. or... HOLD ON........................
ARE THEY ALREADY HERE?!?