What is the purpose of this meditation and the theory behind it? Normally as we go through the day, Qi is rising up and being expended, it is lost entropically. This occurs through engagement of the senses with the world, mental states, and emotions, which in turn effect breathing, the physical movement of Qi. Entropy is a measurement of relative disorder in a system, the energy lost as a byproduct of producing work, the inefficiency of the system. The system in question is the human, and the ultimate goal of that person, and all that lies in between. The Dantien, which means Elixer Field, is the part of us that needs to reach this goal, while logic and intelligence, and effort and strain appear to be what moves this achievement nearer to fruition, it is actually the intelligent Qi already in the Dantien that actually organizes and completes the intention. The Dantien reduces loss of energy, it cultivates the efficiency of the system on its way to completion. Once Qi is centered here, it becomes a routing bay, from which all impulses return and usher forth. All worldly actions harmonize with this center and come from the vitality gathered here.
There are actually three Dantien, each with a different role in this alchemy. The Lower Dantien is the one most commonly referred to by the plain term "Dantien". The Lower Dantien is responsible for transmuting Jing, the most dense and physical vital essence into Qi, which is available energy. Jing is often linked to fertility, the production of gametes (haploid cells containing half of our DNA for the purposes of conception), and the health of the legs, bones, and marrow. It is linked to the durability of our tendons, and the general power behind all functions. The normal processing of the Way is a gradual loss of Jing as we move from our conception to our death, acquiring the dust of the world which muddies the original near-immortality we have as babies. At our height of sexual maturity, our JIng is ready to be passed on to conceive a new baby. I believe the reducing of the 46 chromosomes into the 23 present in a gamete is a refinement process following the Way, giving only our best genes to the next generation. The process can also go the other Way, returning our genetic state back to its most adaptable state, and redistributing this to our own body. Meditating on the Lower Dantien begins this process of stopping the outflow of Jing and creates the base from which the reverse Way of life can occur.
As babies we naturally breathe from this location, the belly expands freely, and life force coalesces around this center as the body develops. When people age they often forget about this and breath shallowly, filling only the chest. When proper Dantien breathing is established an effortless wave emerges from deep in the lower nervous system which acts as a vacuum acting on the respiratory mechanism. The Dantien naturally pulls in what it needs based on body instinct.
When practicing Tai Chi and Qi Gong breathing should always happen from this point. This allows Qi to release and travel where it needs to with the postures and gestures. The Lower Dantien is associated with the japanese Hara, known as the place one splits in the committing of Hara-kiri (Seppuku). It may also be tied to the Hindu Swadhisthana, or Sacral Chakra.
When you have some available time to practice meditation, give this practice a shot, instruction for which is found in the video above. See the results for yourself in meditation and in the world. Stay tuned for further steps on the path of Daoist meditation.