Everyone knows what energy is, right? Take a few seconds to define it yourself.

You might have defined energy as it relates to heat or electricity (usable power) or how much juice you have to run around the block (the capacity for doing work). Or maybe you thought of brain power (intellectual energy) or Einstein's famous equation, E=mc2 (energy equals mass times the speed of light squared; in other words, energy and matter are essentially one).

But there is another type of energy discussed that falls outside these typical definitions. It is known as subtle energy— energy running around and through the human body that conventional scientific instruments cannot detect. Yet these energies are central to popular healing practices such as traditional Chinese medicine.  

Energy practitioners believe that disruptions of these subtle energies result in mental and physical illnesses and other undesirable states. You have probably heard the term chi, the Chinese word used to describe this energy, often associated with acupuncture. Other names include prana, ki and dosha. Some refer to subtle energy as biofields.

While invisible to most, some people, such as intuitive healers, claim to be able to see, feel or sense subtle energy. Also, various instruments have been developed that, according to their inventors and enthusiastic users, can detect and measure subtle energy.

So, if subtle energy is by no means proven to everyone's satisfaction, why does it remain a viable theory? Why is it growing in popularity in Western health practices? Because techniques based on subtle energy seem to work, often more powerfully and effectively than anything else the practitioner has tried, including the "proven" methods.