One of the major problems encountered in time travel is not that of accidentally becoming your own father or mother. ...
The major problem is quite simply one of grammar, and the main work to consult in this matter is Dr Dan Streetmentioner's Time Traveller's Handbook of 1001 Tense Formations. It will tell you for instance how to describe something that was about to happen to you in the past before you avoided it by time-jumping forward two days in order to avoid it. The event will be described differently according to whether you are talking about it from the standpoint of your own natural time, from a time in the further future, or a time in the further past and is further complicated by the possibility of conducting conversations whilst you are actually travelling from one time to another with the intention of becoming your own father or mother.
Most readers get as far as the Future Semi-Conditionally Modified Subinverted Plagal Past Subjunctive Intentional before giving up: and in fact in later editions of the book all the pages beyond this point have been left blank to save on printing costs.
The Hitch Hikers Guide to the Galaxy skips lightly over this tangle of academic abstraction, pausing only to note that the term "Future Perfect" has been abandoned since it was discovered not to be.
Also, look at this: http://www.bbc.co.uk/dna/h2g2/A1126595
I think I worked this out the other day, and both of the above resources are making it unnecessarily complicated. It depends on whose time line you're referring to. If you're talking to Person X, who is responsible for Event Y (which is in your future, say, World War III), and person X (as you're talking to them) has already done it, you'd say "You started World War III", because you're referring to their time line and they've already done it.
If you're talking to a third party, Person Z, about this: if Person X is familiar to both of you, or is present, and you're refering to X at a specific time (say, the present), then you say "Person X started World War III." If you don't know person X or are just talking about them in general (or if World War III is the main focus of the sentance and not Person X), then you say, "Person X will start World War III."
Using the example from the Restaurant at the End of the Universe example, no matter where you are, you'd describe the event in the past tense since you're referring to your own timeline.
I think this works for most cases, as long as Person Z knows that Event Y occurs in their future. (I suppose, for clarification, you could institute a system of "Futurepresent", "Futurepast", "Presentfuture," "Nowpast," etcetera, where the first word refers to the starting location [Future, Present, Past, Now], and the second refers to where you are from then [Future, Past, Present]. But that seems messy, and my idea seems to work as long as you explain yourself or as long as Person Z is in the know.)
Am I oversimplifying? Does it make sense? What do you guys think about the issue?'
(In before "Time travel is impossible".)