Editing Temporal paradox (section)

==== Variants ====
{{anchor|Retro-suicide paradox}}{{Anchor|Hitler's murder paradox}}
The grandfather paradox encompasses any change to the past,<ref name="NicholasSmith2">{{cite encyclopedia |title=Time Travel |encyclopedia=Stanford Encyclopedia of Philosophy |url=http://plato.stanford.edu/entries/time-travel/index.html#CauLoo |access-date=November 2, 2015 |date=2013 |author=Nicholas J.J. Smith}}</ref> and it is presented in many variations, including killing one's past self.<ref name="horwich">{{cite book |last1=Horwich |first1=Paul |title=Asymmetries in Time: Problems in the Philosophy of Science |date=1987 |publisher=MIT Press |isbn=0262580888 |edition=2nd |location=Cambridge, Massachusetts |page=116}}</ref><ref name="stanford backward2">{{citation |author=Jan Faye |title=Backward Causation |date=November 18, 2015 |url=https://plato.stanford.edu/entries/causation-backwards/ |encyclopedia=Stanford Encyclopedia of Philosophy |access-date=May 25, 2019}}</ref> Both the "retro-suicide paradox" and the "grandfather paradox" appeared in letters written into ''[[Amazing Stories]]'' in the 1920s.<ref name="Nahin 1999">{{cite book |last=Nahin |first=Paul J. |url=https://archive.org/details/timemachinestime0000nahi_m8y6 |title=Time Machines: Time Travel in Physics, Metaphysics, and Science Fiction |date=1999 |publisher=Springer-Verlag |isbn=0-387-98571-9 |edition=2nd |location=New York |access-date=2022-02-19 |url-access=registration}}</ref> Another variant of the grandfather paradox is the "Hitler paradox" or "Hitler's murder paradox", in which the protagonist travels back in time to murder [[Adolf Hitler]] before he can rise to power in Germany, thus preventing [[World War II]] and the [[Holocaust]]. Rather than necessarily physically preventing time travel, the action removes any ''reason'' for the travel, along with any knowledge that the reason ever existed.<ref>{{cite book |last1=Brennan |first1=J.H. |url=https://books.google.com/books?id=UBf_HjZHUxkC |title=Time Travel: A New Perspective |date=1997 |publisher=Llewellyn Publications |isbn=9781567180855 |edition=1st |location=Minnesota |page=23}}</ref>

Physicist John Garrison et al. give a variation of the paradox of an electronic circuit that sends a signal through a time machine to shut itself off, and receives the signal before it sends it.<ref>{{cite journal |last1=Garrison |first1=J.C. |last2=Mitchell |first2=M.W. |last3=Chiao |first3=R.Y. |last4=Bolda |first4=E.L. |date=August 1998 |title=Superluminal Signals: Causal Loop Paradoxes Revisited |journal=Physics Letters A |volume=245 |issue=1–2 |pages=19–25 |arxiv=quant-ph/9810031 |bibcode=1998PhLA..245...19G |doi=10.1016/S0375-9601(98)00381-8 |s2cid=51796022}}</ref><ref>{{cite book |last1=Nahin |first1=Paul J. |title=Time Machine Tales |date=2016 |publisher=Springer International Publishing |isbn=9783319488622 |pages=335–336}}</ref>