Editing Time travel (section)

==== Interacting many-worlds interpretation ====
A variation of [[Hugh Everett]]'s [[many-worlds interpretation]] (MWI) of quantum mechanics provides a resolution to the grandfather paradox that involves the time traveler arriving in a different universe than the one they came from; it's been argued that since the traveler arrives in a different universe's history and not their own history, this is not "genuine" time travel.<ref>{{citation|title=Time Travel and Modern Physics|date=December 23, 2009|author1=Frank Arntzenius|author2=Tim Maudlin|url=http://plato.stanford.edu/entries/time-travel-phys/|encyclopedia=Stanford Encyclopedia of Philosophy|access-date=August 9, 2005|archive-date=May 25, 2011|archive-url=https://web.archive.org/web/20110525025650/http://plato.stanford.edu/entries/time-travel-phys/|url-status=live}}</ref> The accepted many-worlds interpretation suggests that all possible quantum events can occur in mutually exclusive histories.<ref name="many-worlds">{{cite web|url=http://plato.stanford.edu/entries/qm-manyworlds/|title=Many-Worlds Interpretation of Quantum Mechanics|date=January 17, 2014|access-date=April 26, 2017|last1=Vaidman|first1=Lev|archive-date=December 9, 2019|archive-url=https://web.archive.org/web/20191209220612/http://plato.stanford.edu/entries/qm-manyworlds/|url-status=live}}</ref> However, some variations allow different universes to interact. This concept is most often used in science-fiction, but some physicists such as [[David Deutsch]] have suggested that a time traveler should end up in a different history than the one he started from.<ref name="deutsch">{{cite journal|last=Deutsch|first=David|author-link=David Deutsch|year=1991|title=Quantum mechanics near closed timelike lines|journal=Physical Review D|volume=44|issue=10|pages=3197–3217|doi=10.1103/PhysRevD.44.3197|pmid=10013776|bibcode=1991PhRvD..44.3197D|s2cid=38691795|url=http://pdfs.semanticscholar.org/8e99/3e3e9b0952198a51ed99c9c0af3a31f433df.pdf|archive-url=https://web.archive.org/web/20190228075930/http://pdfs.semanticscholar.org/8e99/3e3e9b0952198a51ed99c9c0af3a31f433df.pdf|url-status=dead|archive-date=2019-02-28}}</ref><ref>{{citation|author=Pieter Kok|title=Time Travel Explained: Quantum Mechanics to the Rescue?|url=https://www.youtube.com/watch?v=uz9eLjO2BrA |archive-url=https://ghostarchive.org/varchive/youtube/20211211/uz9eLjO2BrA| archive-date=2021-12-11 |url-status=live|date=February 3, 2013}}{{cbignore}}</ref> On the other hand, Stephen Hawking has argued that even if the MWI is correct, we should expect each time traveler to experience a single self-consistent history, so that time travelers remain within their own world rather than traveling to a different one.<ref name="Hawking warp"/> The physicist Allen Everett argued that Deutsch's approach "involves modifying fundamental principles of quantum mechanics; it certainly goes beyond simply adopting the MWI". Everett also argues that even if Deutsch's approach is correct, it would imply that any macroscopic object composed of multiple particles would be split apart when traveling back in time through a wormhole, with different particles emerging in different worlds.<ref name="Everett MWI">{{cite journal|last=Everett|first=Allen|title=Time travel paradoxes, path integrals, and the many worlds interpretation of quantum mechanics|journal=Physical Review D|volume=69|issue=124023|pages=124023|year=2004|doi=10.1103/PhysRevD.69.124023|arxiv=gr-qc/0410035|bibcode=2004PhRvD..69l4023E|s2cid=18597824}}</ref>