Thought experiment. Lets say that you've created a closed loop time machine.

The machine can transmit matter and data across time, but only as far back as the point it became active. You turned it on an hour ago and discover a flaw that is too late to repair. So you step in and travel back to right after you turned it on to tell yourself how to fix it. You meet yourself from one hour ago and discover you've created a causality loop. In an hour, younger you will become you and travel back to this point. Given what you know will happen in one hour, do you fill that time having sex with younger you?