HI Aswin, to create a anti-gravity effect you have to make a spacetime distortion ABOVE the space craft with the same mass as the earth because gravity is the distortion of spacetime due to the earths mass. Gravity can only pull not push, it's not a 'force' like electromagnetism that can be positive or negative. So to lift a UFO, you need to counter earth spacetime distortion above the craft, but you can't do that from within the craft, like you can't pull yourself up by pulling your own hair. Curious fact: the 'anti gravity generators' of the 'Bob Lazar 'UFO's when hovering point down, instead of up. The infamous element 115 he says powers the crafts was recently made in a Russian laboratory and was stable for... 90 milliseconds. Not very useful is it? Last but not least: Bob Lazar went under hypnosis ('regression therapy') back in the eighties and so all his 'lost memories' were retrieved. Every psychologist can tell you now that this technique is prone to induce false memories. Pour Bob, he's been led astray by his 'therapist', like so many other people who have been in 'regression therapy'.

If there was some kind of anti gravity, we would have known about it since every force in nature is visible in the plants an animals around us, even mangetism and electromagnetism, long before mankind discovered it. The had billions of years to evolve, and use it, if it was there.