Editing Time travel (section)

=== The grandfather paradox ===
{{main|Grandfather paradox}}
A common objection to the idea of traveling back in time is put forth in the grandfather paradox or the argument of auto-infanticide.<ref name="horwich">{{cite book|last1=Horwich|first1=Paul|title=Asymmetries in Time: Problems in the Philosophy of Science|date=1987|publisher=MIT Press|location=Cambridge, Massachusetts|isbn=978-0262580885|page=116|edition=2nd}}</ref> If one were able to go back in time, inconsistencies and contradictions would ensue if the time traveler were to change anything; there is a contradiction if the past becomes different from the way it ''is''.<ref name="NicholasSmith">{{cite encyclopedia|url=http://plato.stanford.edu/entries/time-travel/index.html#CauLoo|author=Nicholas J.J. Smith|date=2013|title=Time Travel|encyclopedia=Stanford Encyclopedia of Philosophy|access-date=November 2, 2015|archive-date=August 18, 2018|archive-url=https://web.archive.org/web/20180818152007/https://plato.stanford.edu/entries/time-travel/index.html#CauLoo|url-status=live}}</ref><ref name="lobo">{{cite journal|title=Time, Closed Timelike Curves and Causality|journal=The Nature of Time: Geometry|volume=95|pages=289–296|author=Francisco Lobo|year=2003|arxiv=gr-qc/0206078v2|bibcode=2003ntgp.conf..289L}}</ref> The paradox is commonly described with a person who travels to the past and kills their own grandfather, prevents the existence of their father or mother, and therefore their own existence.<ref name="sagan-nova" /> Philosophers question whether these paradoxes prove time travel impossible. Some philosophers answer these paradoxes by arguing that it might be the case that backward time travel could be possible but that it would be impossible to actually ''change'' the past in any way,<ref name="unchangeable">{{cite web|author=Norman Swartz|title=Time Travel: Visiting the Past|url=https://www.sfu.ca/~swartz/time_travel1.htm|date=1993|access-date=February 20, 2016|archive-date=August 18, 2018|archive-url=https://web.archive.org/web/20180818151754/https://www.sfu.ca/~swartz/time_travel1.htm|url-status=live}}</ref> an idea similar to the proposed [[Novikov self-consistency principle]] in physics.