The ancient Greek philosopher Democritus put forth the wave and corpuscle theories to explain telepathy. In the 19th century, the British chemist and physicist William Crookes, thought telepathy rode on radio- like brain waves. Later in the 20th century the Soviet scientist L. L. Vasilies proposed the electromagnetic theory. The American psychologist Lawrence LeShan proposed that each person has his or her personal reality, and the psychics and mystics share separate ones from other people which allow them to access information not available to others. In conclusion telepathy, like the other forms of psychic phenomena is elusive and difficult to test systematically.
Enough evidence is available to reasonably substantiate the phenomenon does exist.
But, quantifying it seems to be another matter. The phenomenon is closely connect to the emotional states on both the sender and receiver which creates difficulty in replicating experimental results. Attitudinal factors also influence the phenomenon. The best that researchers can hope for is to have supportive and receptive subjects in experiments that produce similar results. Neither one nor the other coincidence can be explained by causality, but seems to be connected primarily with activated archetypal processes in the unconscious.