There is a theory which states that if anyone discovers exactly what the universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable. There is another theory which states that this has already happened.

There are of course many problems connected with life, of which some of the most popular are: Why are people born? Why do they die? Why do they want to spend so much of the intervening time wearing digital watches?

One of the major problems encountered in time travel is not that of accidentally becoming your own father or mother. There is no problem involved in becoming your own father or mother that a broad-minded and well-adjusted family can’t cope with. There is no problem about changing the course of history - the course of history does not change because it all fits together like a jigsaw. All the important changes have happened before the things they were supposed to change and it all sorts itself out in the end. The major problem is quite simply one of grammar.