UFOs have been a source of great mystery for a long time. There have been UFO sightings dating back to previous century. Some even claim that man has known the presence of UFOs for thousands of years.

Why are they talked about so much?

Several features make UFOs interesting. They have been reported to travel at mind-boggling speeds and take sharp turns. Some appear as dazzling lights while others have the ability to vanish in the atmosphere.

What do UFOs look like?

UFOs come in all shapes and sizes. Cylindrical, cigar shaped, spherical etc. The most common of them all are saucer shaped.

How do they levitate?

One thing is for sure. UFOs use extremely advanced technology. The two ways that I can think of how UFOs levitate are:

Magnus Effect

Whenever a cylinder or sphere rotates in an airstream lift is produced.

These UFOs may be using Magnus effect to generate lift.

Anti-gravity

Everything in nature has its opposite. Whether they are animals or human beings or atoms. Scientists have even discovered a "thing" called anti-matter. May be there's an opposite for gravity also i.e. anti-gravity.

Where do they come from?

From Earth's interior

Some people theorize that Earth is hollow and has openings at poles and one can enter the hollow part by traveling through these holes. Modern science claims that Earth's core has a lot of iron.

Hollow earth believers say that since we have never been to the core of the earth therefore it cant be proved that earth contains iron in its core. They also present several "proofs" about hollow earth. They say that UFOs are really the aircrafts used by people living inside the earth, who according to their claim are much more advanced than those living over the surface.

From Outer Space

Some people claim that these UFOs belong to the alien species living at far off planets, well away of humankind's reach. They also say that these UFOs use teleportation as means of transportation.

From hangars of very advanced nations

My opinion about UFOs is that they are the handiwork of advanced nations of the world. May be these UFOs are used to keep tabs on other less developed nations of the world. Humankind's ambitions are limitless. One can expect anything. World scientists are making things possible which have been considered impossible, for many many years. And now with the help of high speed computers and advanced softwares the process of research is touching new heights.

Very high speed and stealth are the essential characteristics that any spy plane should possess. Governments of all the advanced nations have denied even the existence of their high-tech aircrafts e.g. The American Airforce denied the existence of F-117 Nighthawk for several years.