Elon Musk became the world’s first trillionaire on Friday — reaching a wealth milestone never before achieved in human history. But how much money is $1 trillion? The human brain isn’t built to comprehend such massive figures, so The Post is here to help paint a picture of the Tesla founder’s unimaginable wealth — and put it into context. If you were to stack one trillion one-dollar bills — each measuring just .0043 inches thick — it would reach more than one-quarter of the distance between the