This element Agni is not just the fire that we know. Fire is only a modification of Agni. Agni is that state of matter, which is in the process of becoming fused or grossified. Matter from a simple state, under certain conditions begins to get fused to form heavier or denser forms. This process of fusion of matter particles to produce heavier forms releases great quantities of heat and light radiations. This heat and light radiation is Agni. This Agni is produced in the sun and in every star. The sun or each star that we see at night is the chemical laboratory where simpler forms of matter (mostly hydrogen atoms) are getting fused to form heavier forms of matter e.g. Helium, Carbon, Oxygen, etc. releasing huge quantities of light and heat. This light and heat radiations from the sun on reaching the earth gets trapped in all objects animate or inanimate, more in some and less in others. In inanimate objects these trapped radiations under certain stimulus creates fire. In animate objects these radiations perform many chemical and biological processes for its growth and decay.
Vayu is always translated as air. Air definitely contains vayu but vayu is not air. Air is better classified under Apah as mentioned earlier. Vayu is that state of matter in which it exists in its simplest form. Clouds of hydrogen atoms in enormous masses float in inter-galactic space. These simplest material atoms along with all the other independent sub-atomic particles form the Vayu element. So vayu is matter in its simplest form before its grossification into heavier forms.
It is that state of matter, which is in the borderline between energy and matter. It is that state where energy is constantly getting converted into sub-atomic matter particles and matter particles are getting dissolved back into energy. At this stage called akash matter and energy are indistinguishable, the quantum level of matter of modern physics. Akash is, therefore, the screen, the background, the medium, the container, the space where matter particles are created, maintained and then dissolved. This Akash is the borderline between the physical universe and the subtle astral universe. The physical universe is composed of matter, which exists in five different states as explained above, and the astral universe in made of Prana energy.
The physical body is composed of the above five elements. Yoga stresses that health of the physical body can be maintained only if all these elements are kept in the body in a pure state. Great care, therefore, is taken to ensure we consume the right food, pure liquids, expose the body to proper sunlight, do regular exercise, practice deep breathing and have proper sleep and relaxation.
Pranamaya Kosha (Energy Body/Aura)
The physical body or Annamaya Kosha is permeated both within and without by Pranamaya Kosha. The word,
'Pranamaya' means formed of Prana. Prana is the subtle life force that keeps the physical body alive. So
'Pranamaya Kosha' is the body composed of Prana energy which is responsible for bringing life to the physical body. This body is inside the physical