“Subtle energies” can be hard to explain. Elmer Green made a life-long study of them both as a scientist and as a mystic. One of my favorite ways to understand them was described by Elmer in, “Biofeedback and Human Potential”,
“A problem for many, however, arises with the word ‘spirit.’ Some feel that there is no such thing, or that in the absence of scientific evidence, we should not refer to spirit. Others say, the world is the world, the spirit is the spirit, and n’er the twain shall meet. To speak of the central nervous system as the abode of the gods is, in their view, sacreligious.
The late Indian existentialist and philosopher, Sri Aurobindo, resolved the difficulty, however. According to yogic theory, there is no problem because the infinite unknowable God (Brahaman), which lies behind all manifestation, can be known only as His body (Brahma) which IS all manifestation. And Brahma is composed, says Aurobindo (1955) of a continuum of energies from densest physical matter to most rarefied spirit. The twain meet because they were never separate. Aurobindo suggests that if we are embarrassed by the word ‘spirit,’ then we should not use it. Instead we should speak of the subtlest form of matter. On the other hand, if we are not embarrassed, then we can think of matter as the densest form of spirit.”
This quote is taken from “Biofeedback and Human Potential” by Elmer Green, Ph.D. in ENERGY MEDICINE AROUND THE WORLD, edited by T. M. Srinivasan, Ph.D., Gabriel Press, Phoenix, 1988.
The 1955 book by Sri Aurobindo is, THE SYNTHESIS OF YOGA.