Some 2600 years back, some saint induced prana into the stone. It is called prana pratishta. There is a Devi energy in it. This Mother Divine energy (in the stone) came to the Adishakti Appaji, and has been there for the last 20 years with him. Any question you ask, it responds. Suppose you ask, 'Will I get married next year, if yes then becomes heavy, if I won't then become light, and then the stone become light or heavy depending on the answer. Only Adishakti Appaji is eligible to touch this "Divine Stone".
The stone becomes as heavy as Mountain weight; you cannot even lift it if the answer is no. If the answer is yes, then you can lift it like a feather. Vice versa is also applicable. Something can become as light as a feather, or so heavy that you cannot even lift it off the ground. It's a challenge to science.
He is a God (He is the incarnation of Lord Krishna)
Yes. Modi will become the Prime Minister of India (This great Historic event took place in front of Sri Sri Ravi Shankar Guruji)