Here's a quote from Zhuang Zi's "Inner Chapters" (4th century BCE)
"There must be some primal force,
but it is impossible to locate.
I believe it exists, but cannot see it.
I see its results,
I can even feel it,
but it has no form."
This is a reference to chi, but if you think about it, applies equally today to something we all take for granted - gravity. Scientists can tell us the effects of gravity, and there are numerous gravitation theories, but no one has found the "gravity particle" or any other energetic evidence of what makes gravity work. So it's not surprising that science can't really explain the energy healing arts either. But the information at the following links is a really good start!
The Human Energy Field
The Science of Energy Healing