Thank you Randy. This is how Ki is taught in my dojo. Your explanation bears repeating, so I quote it in entirety.
Heard the saying that a beginner tries to control his opponent with strength, and an intermediate aikidoka tries to control his opponent with speed, and an experienced aikidoka tries to control his opponent with Ki. A master, however, controls his opponent with his own mind. It is a real magical phenomenon, I like to say, as practiced by Penn and Teller.
Psychologists may be getting closer to explaining how it works by explaining some kinds of learning through Mirror Neurons. No "Spock/Vulcan" mind-meld required. Just get and control your opponent's attention to get a direct line to their brain motor control:
In my opinion and by my experience in the martial arts I believe the ability to project KI as an energy force is not real. Sorry, Yoda! Good movie but not Aikido.
However, if you feel KI is the ability to mentally and emotionally and perhaps spiritually connect to another human being. That I believe. Having established that connection the other individual knows beyond a doubt that when I atemi to his face that I am coming to his face and am going to go through it leaving him with only two choices. He moves out of the way or gets punched really hard. In his moving, if I stay connected and press toward him directing him to his weakest support his balance begins to fail and continuing to press the attack he will fall to the ground. On the way down he must continually believe he has to go down or he will get punched really hard on the way down to the floor. So he constantly continues to evade breaking his balance all the way to the floor.
Imagine a bear coming at you and is right on top of you but has not physically touched you yet I think he will break your balance and send you to the ground without touching you. Get the idea? That is a Grizzly bear no touch throw.
I believe the connection and intent and continuing the attack is crucial and if the Uke sees it, feels it, believes it he will get the hell out of the way. That is a real no touch throw.
If you line up a bunch of guys and the first in line is connected and you affect him the others who are connected to him will also be affected. However to do it at a range that he feels no real physical threat it won't work unless he feels a connection even at a nonthreatening physical distance. His mind can be affected causing him to subconsciously sway and begin to break his balance. Those physically connected to him will also be affected.
Imagine he is first in line and all his five buddies behind him are touching him and connected to him and as he comes over the rise he sees the Grizzly bear standing up and charging at him full force with bared teeth and claws coming down. What do you think will happen?. That is another Grizzly bear no touch throw for all of us nonbelievers.
Bottom line, it is about connection and staying connected breaking his balance all the way down to the ground by affecting his mind and emotions and his survival instinct. As someone said above have a guy ignore that instinct he gets the punch. Most people are not that stupid but I have had attackers rush in ignoring everything and charging like a bull. Try an energy ball on him! That guy you must connect to him and break his balance and take him down.
Food for thought.