[donh]

Oh, come on. If you want to go forward, you got's to throw something backwards. Newton's laws rule. All else is window dressing. Go get in a rowboat and row against the current--it's pretty obvious. Pressure differentials sound pretty dern cool, but it's just a different, and, unless you design high speed craft, pretty distracting way to re-organize how you think about the distribution of forces, which in no way frees you from the fundamental requirements of the equal-and-opposite law.

[Doctor Stochastic]

If you want to go forward, you got's to throw something backwards. Newton's laws rule.

Correct. Except in Hollywood where one can shoot someone with a recoilless pistol and have the target fly backwards as if struck with a 500lb sandbag.