Descartes dream paradox seems to have no solution, though it may help us understand some moral/political points of view.
Some concerns and a defense on solipsism as a moral framework.
The grandfather paradox is quite straightforward, and has many varieties. In the simplest version: if you were to build a time machine and use it to travel back in time and kill your grandfather before your parents (usually one of them) were consummated, you wouldn't have been born in order to build a time machine - and thus travel back in time in order to kill....
