What happens when you take the flat earth hypothesis and raise it to the third power?
For starters, you gain a whole new appreciation for the predominantly up/down gravity of our good-ol' fashioned spherical world. According to Discovery News's Robert Lamb:
A hypothetical cube world...would feature six square faces and you'd only encounter up/down gravity toward the centers of these regions. As you traveled closer and closer to the edge, it would feel like you were walking up an incline and it would be difficult to stand up straight because the gravitational pull would draw you toward the center of the massive cube, which wouldn't lie directly beneath your feet.
The thought experiment is in reference to an announcement issued at the end of the 19th century by mononymous Swiss astronomer Arndt, who claimed to have discovered a cubical planet.
Lamb is summarizing physicist Theodore Vankirk's response to Arndt's outrageous claim as it first appeared in the November 16, 1884 edition of The New York Times.
You can read more about the implications of a six-sided earth over at Discovery News