Hey, I must say I've become quite fascinated with the concept of ki, and although I'm new to martial arts in general I believe its very real. Now, I do believe that people give credit to ki when ki had nothing to do with it (not sure how much, but it seems like it so far). I'm soon to be taking some Tai chi classes to begin understand it more fully (and from what I hear about people in it, their utilization of ki(chi/Qi) can be very powerful.
Those that deny its existance though, I'm curious how long it took you to come up with that conclusion...? Afterall, did you simply assume its not possible? or did you spend 20years with guidence to try and understand it without success? Because, if it was the former I personally wouldn't rule out the possibility of its existance. Humans are capable of some extremely powerful things, and to simply assume something isn't possible is a fast route to limiting your potential.
As for the unliftable body "trick", I've had a shodan 90lbs girl demonstrate it to me... and, she started by letting me which was very easy. Then, same posture, stance and everything she was unliftable, and yes I lift with my legs, good posture, etc.. I suppose relaxation and a steady mind were the cause of her suddenly being unliftable, but regardless it went from super easy to impossible against all my strength (lol and no she didnt jump with it the 1st time.. felt about 100lbs, and i lift weights). By the way, her arm dont bend or raise either lol unless she wants it to... lots of it in the mind from what I've experienced.
Good luck in your pursuits of ki.
P.S. If you dont think its possible to do then, for you, it wont be.