Qi is a term from traditional Chinese culture, translating into modern English as “some sort of mystical cosmic energy or something”. It has been understood as things like “breath” or “spirit”, but the New Agers have got a hold of it now and they’re not letting go. (Damn those Westerners, with their bastardisation of an ancient dignified culture, and their technological advances, and their evidence-based medicine.) However, it doesn’t seem to be any less vague a term in either case.
“Energy” is a favourite term of the New Age movement despite nobody seeming to know what it means. (It’s not to be confused with the scientific concept of energy as a measure of ability to do work, of course. This use of “energy” actually means something and can be measured in useful ways; this is one reason why you don’t see many hippie physicists.) I can’t find a case of qi being much more precisely defined than this – it seems to just be some ethereal, non-physical, immaterial, abstract stuff, which has some place in our model of reality but not one that anyone can measure. It’s an extremely convenient formulation: its definition is so vague that just about anything can be claimed to be affected by it, but whenever empirical data fails to show up you can just say that “it doesn’t work that way”. Because there’s no consistent or well-defined way it does work, you can be as evasive as you like about the results.
Basically, qi is the force by which the “karate master” in this video knocks people out. Like when he waves his hands around that guy’s head without touching him and… nothing happens. But that’s a special case, because the guy may have had his tongue in a certain place in his mouth, which totally nullifies the effects. Yes, apparently that’s actually how it works. Also if you raise one toe and lower another, that’ll do it to. Wiggle your feet a bit and you’re totally safe from energy which would otherwise knock you on your arse. Oh, it also doesn’t work if you don’t believe in it. I don’t know how much more evident it needs to be that this is nonsense. Try maintaining a skeptical attitude to electricity while sticking a fork in a mains outlet, and see how far that gets you. (Note: do not actually see how far this gets you.)
Qi is also what the Kiai Master in this video is using to make people fall down by waving his hands… until he’s faced by someone who doesn’t buy into his crap, at which point he gets punched in the face.
Amidst all the blather about “life force” and whatnot, a number of seemingly testable claims about qi seem to be made. For instance, “I can exert a force to knock someone over by channeling this energy” is easily tested, and the above videos provide some pretty good disconfirming evidence. Even if the claim is something like “I can do all that, but only if the person isn’t moving their tongue or their toes in a particular way”, I can still imagine putting together a testing protocol where people’s extremities are carefully monitored as the power of the qi is supposedly flung their way.
Believers in pseudoscience are always keen to complain when people actually try and find out if the stuff they’re pushing really works, as if this is somehow unfair. But like anything else, if qi actually does something, then if you want us to believe it, you’ll have to tell us something it actually does, and then let us see whether it actually does it. If it could ever be convincingly demonstrated, then it wouldn’t matter that it’s all vague and mystical nonsense. If it works, it works.
It doesn’t work. It’s not there. The magic is nothing more than mentalism, the medical uses are nothing more than placebos. The long and illustrious history of qi as something widely believed in by millions of people who didn’t understand what it is, dating back to a time when you could expect to be dead by 30 and nobody had even invented the lever yet, isn’t very impressive in the face of absolutely no supporting evidence.