It is generally accepted that we live in the present. The past has passed and the future is still to happen... Therefore:
We cannot change our past and the future is still uncertain.
That means also that nobody can really know what will happen in the future. You could make educated guesses, but knowing for sure is impossible, as that would require that in some way or another the future should already exist.
The idea that the future already happened is impossible to comprehend. Besides, the thought that the future is known, fixed or pre-defined could easily lead to wide spread fatalism.
If the future however, is not fixed, it cannot be known and then predicting it with accuracy is consequently impossible and as a result true prophecy cannot exist either. However, history tells us about many prophets that supposedly received true prophecy.
The well-known prophet Michel Nostradamus, born 1503 in France, left us with almost a thousand prophetic quatrains. The book of Nostradamus has recently attracted renewed interest as people link current world events to his prophecies, suggesting that he knew our future. But how can that be possible? If he really did know, then how did he get that information? According to his own writing he used occult practices to receive messages from an occult source, although he never revealed in detail how he managed to do such thing.
People who believe Nostradamus realy predicted the future base their belief on the contents of his quatrains and a possible relationship with historic events. But how can we ever accept or understand the idea that someone from the 16th century could have known his own and our future. It definitelly does not fit into the accepted theory about time regarding the correlation between past, present and future.
This site explores a number of theories that would allow for the existence of true prophecy.
The basic idea being, that if the 'character of time' turns out to be different than our intuition that it should be a single straight line without break or branching point, it would possibly allow for activities like building a time travel machine and traveling backwards in time or even sending a time traveler to the future.