The thought waves transmitted by human mind are described to be some kind of electrical impulses of brain waves of specific wavelengths. These are attracted and received by the field of compatible currents (impulsive flow) of the transmitted brain waves.
 
The rhythm of the thought waves of pure, saintly mind would naturally match with that of the receiver if the latter too has similar character and piety of thoughts and sentiments.
Albert Einstein’s brain used to continuously emit alpha waves even when he was deeply engrossed in solving complicated problems of mathematics or was asleep…. It may be noted the alpha waves are emitted in a state of sharp alertness of the mind
Thus, despite being engaged in the work at hand, or in deep thinking, Einstein’s mind used to be always prepared and receptive to the cosmic signals of compatible ideospheres.
 
It should be noted in this context that we are living in an infinite ocean of prana (eternal cause of vital energy). It is the continuous impulse of this eternal force that is the source of all activities and motion in nature. Our existence as living beings too is a manifestation of this subtle power. The prana existing in us is also present in others and is omnipresent in the limitless expansion of the universe. Thus, we are all subliminally linked together by the currents of praña. It is an stimulated or intensified flow of praña induced in one’s mind that makes possible the transmission (and reception) of compatible thought waves from one place to another without any medium.

-  From 'The Extrasensory Potentials of Mind' by Pandit Sri Rama Sharma Acharya.