This is not a proof but it is a strong clue. The vast majority of all people who have ever lived, in all nations, cultures, races, and religions, have believed in life after death. The vast majority of the sages, or wise men, have taught it through the centuries. All the religions of the world teach some form of it. And above all, Jesus clearly taught it. If all these people are wrong, then you have to be a snob, for only you and your very small circle of unbelievers are right while the rest of the human race, including the best and wisest people who have ever lived, have all been wrong about this crucial question.