He then returns to his original time, only to find that in killing the butterfly, he has changed history so much, that he has no world to come back to. All science fiction with a philosophical element is worth reading. Science fiction is very good for shaking up the grey matter in the brain. However, it does appear that while the future is very highly variable, the past is fixed for ever. No one can change the past, but any stuck emotional charges can be drained or abreacted out of the mind.
Abreaction is a psychiatrist's term for the therapeutic discharge of old, and obsolete emotion.
This is commonly in the form of laughter or tears, but not necessarily so. From time to time, past life incidents may surface. If one wishes to be a science fiction writer, then keep a similar book to the one used for the things one has done in this lifetime. Past lives are prone to many problems. People tend to remember, not their own past lives, for these were too uninteresting, but those of their heroes.