Higher Dimensional Science
In a recent discussion somebody posed an interesting question: "How can you be sure of the integrity and antiquity of the Bhagavad-gita? Could it not be a man-made scripture?"
From historical linguistics we can tell that ancient Sanskrit texts are very old. We know they go beyond the human mind, due to the subtleties and nuances of the conversations and descriptions. It would be impossible to cover such expansive topics, in such great detail over multiple volumes of books, and still remain consistent and comprehensible. It just wouldn't be possible according to the capacity of the human brain.
But that still doesn't prove much. The ultimate proof is in the spiritual science the Gita outlines. There is a certain hypothesis about life, a process by which one can directly perceive such truths and ultimately an observation where one actually experiences it. Whereas other spiritual paths seem to culminate in faith, the Gita starts with faith, and then moves on to higher dimensional science.