What is 'grandfather paradox' which contradicts possibility of time travel?
Popularised by French journalist Rene Barjavel in 1943, 'grandfather paradox' contradicts possibility of time travel with a conundrum. It says if a man time travels, to a time before his parents' birth, and kills his grandfather, his parent would never be born. This means he wouldn't be born either and there wouldn't be anybody to time-travel and kill the grandfather.