h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

After some years of reading and watching science fiction books and films, I compiled a glossary of temporal paradoxes that I'd like to share with my colleagues of this forum. Some were conceived by famous (and not so famous) SF writers and some by myself:

1) Grandfather Paradox


-Perhaps the most famous temporal paradox. Sometimes called the Grandmother Paradox. It happens when a time traveler goes back to past to kill his grandfather (or grandmother) when he (or she) is still a child, so avoiding his own birth, and consequently his own travel to past to kill his ancestor. In general any change of History caused by a time traveler that impedes the own time traveler to go back to past to cause the change. It can be considered a special case of the History Alteration Paradox.


2) Accumulation Paradox


-It happens when you travel from several points in timeline to the same moment of past. There will be several duplicates of you at the arrival point.


3) Transit Displacement Paradox


-Time travelers while in time transit carry with them their own time - their present the exact way it was at the moment of their trip -, and cannot be affected by subsequent History changes occurred after their departure. They will suffer the effects only when they return to their present and are reintroduced in their time matrix, now changed.


4) Discontinuity Paradox


-It happens when you meet someone in past that you don't know yet, but he knows you, since he comes from a point of future after you have been introduced. Or the opposite, when you meet someone in past that seems not knowing you, because it's a version that you are meeting 'now' in past before he has been introduced to you in future.


5) Duplication Paradox


-It happens when you travel back in time, meet yourself and do something that avoid your past version to travel back in time as you did before, altering History and creating a permanent duplicate.


6) Final Paradox


-A paradox created by a time traveler that changes History in such way that time travel was never invented.


7) Law of Lesser Paradoxes


-If two mutually exclusive paradoxes can happen simultaneously, it will happen first the less paradoxical.


8) History Alteration Paradox


-It happens when you travel backwards in time and change the past, and consequently History. You can change your change later, editing History.

9) Propagation Paradox


-This paradox involves the speed in which the History alteration will propagate itself along the Continuum. It can be instantaneous, or follow an arbitrary rate, or it can depend on a probability of the change be irreversible.


10) Retroactive History Paradox


-It happens when people of the future, that had not been born at the time of events already happened and historically registered, end up being revealed protagonists of those same events.


11) Objects and People Loop Paradox


-It happens when an object or a person are trapped in a time loop, like the clock of the movie 'Somewhere in Time'.


12) Repetition Loop Paradox


-It happens when you don't travel in time in the traditional way, but when you revive an arbitrary interval of time, like in the movie 'Groundhog Day'. Two paradoxes are involved here, the repetition loop itself and the fact that the person in the loop keeps his memories after each loop.


13) Cumulative Duplication Paradox


-It happens when we remove an object or person from a certain point in the time line and we transport them to other instant of time, and later we return to one moment immediately previous to the first removal and we repeat the process, placing the person or object near the first 'duplicate'. We can repeat indefinitely this operation creating a series of duplicates.


14) Metabolic Paradox


-It happens when a time traveler loses his body temporal integrity in the past due to his metabolism, that causes him to exchange his original atoms by atoms from the past.


15) Timeshift Paradox

Similar to the Metabolic Paradox, but with different causes and consequences. It happens when a time traveler spends a long period of time in the past. Since he is not part of the past time matrix, there occurs a spontaneous exchanging of all his atoms by atoms from the past, eventually creating a new individual with new memories. History changes, and the time traveler's original timeline vanishes.


16) Mnemonic Paradox


-It happens after a Discontinuity Paradox or a History Alteration Paradox that involves the own time traveler, when he can have memories of two or more different timelines.


17) Continuum Paradox


-It involves the concept that everything that happened or will happen is already registered in the Continuum, even the own time travel. Taking into account this fact, for example, a time traveler that would visit a specific point of past several times along his life would find all his duplicates there since the first visit. This paradox affects several other paradoxes and even the concept of free will.

I also wrote an article called 'Temporal Paradoxes in Science Fiction, that can be found in www.intempol.com.br/news/temporal-paradox.html.

Comments are welcome.

Best regards,
Eduardo Torres
Rio de Janeiro, Brazil