I believe there exists one supreme being - the absolute infinite - a dynamic force that governs the world and universe. It is an unseen spiritual power that vibrates and all other powers fade into insignificance beside it. So, therefore, it is absolute!...I shall call it "Reiki"... Being an universal energy from the Great Divine Spirit, it belongs to all who seek and desire to learn the art of healing. - Hawayo Takata

The term Reiki consists of Two Japanese words, 'Rei' and 'Ki'. Rei=cosmic or universal energy and Ki=basic life force energy, so Reiki is considered as a form of force or energy which is the unison of universal energy and basic life force energy. If reiki is universal life force energy, it follows that we are also reiki beings and part of that very energy, which creates the whole universe including us.

Although we cannot define or measure Reiki like other energies, namely light, electricity, heat etc, we can prove the presence of reiki with various indirect tests.

Reiki shows positive effects in stress-related conditions, like allergies, heart conditions, high blood pressure and chronic pain.

In another study, a simple magnetometer measured magnetic fields emitting from the hands of a healer. These fields were 1,000 times greater than the strongest human biomagnetic field.
In eighteenth centuries 'Quantum Mechanics' and 'Nuclear Force' were unknown to us, but today we know that 'Nuclear Force' is one of the four important forces of nature, governing our universe.

So it can be that our scientific apparatus are not sensitive enough to measure this subtle form of energy. Who knows, one day technology will reveal the true nature of reiki and it will become a part of our life.