The grandfather paradox is well-known and has a good dramatic hook, but it's a rather ineffective controlled experiment. The Polchinski Paradox gives us a time travel paradox based purely on laws of motion, without any of that tiresome free will. Plus, it involves billiards.
Most people here have heard about the Grandfather Paradox. Most people here have also read at least one time-travel story in which people either take out or attempt to take out Hitler. But if we have one, can we possibly do the other?
What if all the Large Hadron Collider's recent woes are more than bad luck and technical problems? Two noted physicists speculate that the future may be pushing back on the LHC to avert the disaster of observing the Higgs boson.