Recently, Elkement a.k.a. the Subversive Element, did a nifty little analysis of Time Travel in Movies. Let me just say that, even though she hasn’t nearly covered all of the possible material 100+ years of cinema and TV have to offer (how could anyone, really, in a life’s time), the analysis itself is quite thorough. It also had the side effect, I can’t say whether it is beneficial or not, that it got me thinking.
So, yes, the title. Paradox and Tautology. Most of you folks should be familiar with the first term. If I were to step into a time machine that took me 60 years into the past, and I accidentally became one of my grandfathers, that would be a paradox. Everyone agreed?
All of you, those who have agreed with my former statement, can leave now. They have failed. It would have been a paradox had I killed my grandfather, thus preventing my father’s birth, and consequently, my own. If I became my grandfather, well, I wouldn’t have prevented my own existence, but caused it. This kind of causality loop is very much related to the logical loop named Tautology, and because Paradox is also a logical/philosophical term that has been transmuted to explain time travel, I argue that Tautology is also a valid Time Travel Term.
How did I come by this deliberation? Less than a year ago, my pal and I watched the Bill and Ted movies. For those who don’t know them, Bill and Ted are arguably the stupidest and worst musicians the world has to offer. So, who would’a thunk that some guy from the future comes to help them pass their history class, so Ted isn’t sent to Cadet school, thus preventing the best band ever and the 800 years of peace and music? So, they need help to not fail school from a future that wouldn’t happen if they failed? And the only reason for this future to be possible is the feasibility of time travel… anyway, my pal identified this logical structure as a paradox, and my overworked brain (I just returned home from the night shift) had to pick this up now, because Elkement talked about time travel categories in movies.
Of course, Tautology and Paradox in Time travel are not mutually exclusive. If you were your own grandfather, but got yourself killed before your father’s conception, or your father before your own, I’d say reality is FUBAR
I really just pretend to know stuff 
Thanks for the pingback! As philosopher Dan Mullin – who had triggered my post – commented: We would need a well-funded international research project to sort this out.
I am also intrigued by the logic (or not) of time travelling, not so much about the ‘physics’ actually.
Re the ‘grandfather’s paradox’ – I tend to state becoming your own grandfather is no less paradoxical than merging with your own younger or older self as it happens in movies (classified as 1 in my theory) all the time.
Exactly, though (almost) the entire point of this post was that the “Grandfather Paradox” isn’t actually a paradox 😉