<font face="Verdana, Arial" size="2"> But I’m wondering this: is this balloon feeling contained only within the physical body like a balloon animal where the skin is the edge (see teddy bear picture here): http://balloonguy.com/Who.html , or does the sense of the pung jin sphere extend beyond the physical edges of the body like, well, the shape of a balloon or a sphere?</font>
To me, it feels as if the moment-to-moment feeling is that of something that extends beyond the edges of the body, but the reality is that it is contained within the skin of the balloon.
One analogy that works for me is to think of a geometric curve that approaches a straight line that acts as “limit.” In theory, the curve will reach the limit when it is extended out to an infinite length. In approaching the curve, there is no abrupt point where the limit is reached or where the curve must make an angular change in direction; nevertheless, the reality of the limit and its “value” can become apparent even before the curve becomes very long.
For me, my skin, or rather the maximum extension of my tendons or joints, is the “limit” I approach. If I put in an “infinite” amount of energy, I will reach this limit, but can feel the approach of the limit with only moderate amounts of energy input.
Rather then a latex balloon, I think of a plastic bag. As you fill the bag with air, the shape it will ultimately take becomes clear before the bag becomes full. If you overfill the bag, something will leak, tear, or collapse and spoil its properties. The ultimate shape of the bag is designed by the mind as one particular manifestation of yi, but is brought about indirectly and naturally by the “peng pressure” operating through a loose framework of tendons. When the yi is changed, the design of the bag changes along with its properties and potential.
In the culmination of a posture like Deflect Downward, Parry, and Punch, I think there is a definite feeling of a forward limit to the punch, but without a feeling of an abrupt stopping point. If you are truly bringing the Qi from the Dantian, then it will expand outwardly in all directions. As much as you feel an extension of the fist forward, you will feel an extension of the right foot into the ground. The forward moving jin will be balanced by backward moving jin.
I realize that many use the term “explosive” energy to mean that Taijiquan can generate a great deal of force, but I think the qualitative aspects of this word may also be important. “Explosive force” is force that naturally expands in a sphere, as Chee Fatt has described. It can be shaped or focused to manifest itself in a particular direction, but the forces are actually always balanced.
<font face="Verdana, Arial" size="2"> You may imaging an explosion in slow motion, its energy does not travel in linear but an expansion of sphere or round. This way no matter how strong you exert your force outward (upward) against your opponent, he will not be able to counter with `chai jin' because there is no excess or overextend to one direction.</font>
I think this is a great point and a great way to practice. At heart, I think it is an aspect of zhong ding (“central equilbrium”). I also think, however, that if the other person’s relative level is high enough, he or she can always create the conditions to execute “chai jin” (or cai jin/ts’ai chin (“pluck energy”)) if he or she is better at zhong ding and can hold even closer to the “mean” of the energy interaction.