When the protagonist overcomes the odds and makes it to Jupiter, he's pulled into a "vortex" and a trippy psychedelic sequence begins, watching weird cosmic occurrences that he's not able to wrap his brain around because the human mind is restricted to three dimensions. Without going into much detail, the protagonist passes away and gets reincarnated into "the star child", the next evolutionary step for our species. He's then guided back to earth by one of the monoliths, similar to the one that's shown in the beginning of the movie.