Someone once told me a story from Greg Egan‘s Axiomatic. The story, titled “The Hundred Light-Year Diary”, is about a future invention that allows people to send messages to themselves from the future. Every person can send about 100 words every day.
The protagonist of the story is a guy who has been writing a diary for his entire life and sending it back to his younger self. And naturally, the younger self has been reading the diary his whole life (of course not when he was just a little baby). The story starts when the protagonist meets his wife for the first time. But he has read about her already, and he knows everything they will do for the rest of their lives.
The protagonist has a friend, and in the diary it was predicted that in this friend’s wedding, he would have a broken arm. The protagonist and his friend knew about this ten years before it happened, and they even joked about it. There is nothing the friend could have done: the diary said that he would have a broken arm, so he will have a broken arm.
When the wedding day comes, however, it turns out that not only does the friend have a broken arm, he is also very badly beaten and is ‘sodomized with a bottle’ by muggers.
So, why did the protagonist not mention in his diary that his friend was nearly beaten to death? And why did the friend not send the truth of his mugging to the past? How honest can one be in one’s diary?