No one has "seen" gravity, either. The best we can hope for is to observe the effects of a particular force or influence...either by getting bonked on the noggin by an apple, or by uncovering the fossil remains of progressively more complex organisms.
To deny that gravity has not been scientifically observed is totally ludicrous. If you wish to see it for yourself though, just go on top of a 20 story building and jump. You will observe it very clearly.