Novikov self-consistency principle: Difference between revisions

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Revision as of 16:01, 9 October 2022

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Among the co-authors of this 1990 paper were [[Kip Thorne]], [[Mike Morris (physicist)|Mike Morris]], and Ulvi Yurtsever, who in 1988 had stirred up renewed interest in the subject of time travel in general relativity with their paper "Wormholes, Time Machines, and the Weak Energy Condition",<ref>{{cite journal | first=Kip | last=Thorne |author2=Michael Morris |author3=Ulvi Yurtsever | journal=[[Physical Review Letters]] | volume = 61 | issue=13| pages=1446–1449 | doi= 10.1103/PhysRevLett.61.1446 | title= Wormholes, Time Machines, and the Weak Energy Condition | year=1988 | url=http://authors.library.caltech.edu/9262/1/MORprl88.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://authors.library.caltech.edu/9262/1/MORprl88.pdf |archive-date=2022-10-09 |url-status=live | bibcode=1988PhRvL..61.1446M | pmid=10038800}}</ref> which showed that a new general relativity solution known as a [[Wormhole#Traversable wormholes|traversable wormhole]] could lead to closed timelike curves, and unlike previous CTC-containing solutions, it did not require unrealistic conditions for the universe as a whole. After discussions with the lead author of the 1990 paper, John Friedman, they convinced themselves that time travel need not lead to unresolvable paradoxes, regardless of the object sent through the wormhole.<ref name = "time warps">{{cite book| first= Kip S. | last= Thorne|title=Black Holes and Time Warps: Einstein's Outrageous Legacy|url=https://archive.org/details/blackholestimewa0000thor| url-access= registration | quote= Polchinski's paradox. |year=1994|publisher=W. W. Norton|isbn=978-0-393-31276-8|pages=[https://archive.org/details/blackholestimewa0000thor/page/510 510]–}}</ref>{{rp|509}}

[[File:Grandfather paradox billiard ball.svg|thumb|right|upright=0.7|"Polchinski's paradox"]] [[File:Causal loop billiard ball.svg|thumb|right|upright=0.7|Echeverria and Klinkhammer's resolution]]

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===Quantum computation with a negative delay===

Physicist [[David Deutsch]] showed in 1991 that this model of computation could solve NP problems in [[Time complexity#Polynomial time|polynomial time]],<ref name="Deutsch1991">{{cite journal | first=David | last=Deutsch | url= http://journals.aps.org/prd/abstract/10.1103/PhysRevD.44.3197 | title= Quantum mechanics near closed timelike lines | journal = Physical Review D | volume = 44 | issue = 10 | year=1991 | doi= 10.1103/PhysRevD.44.3197 | pages=3197–3217 | bibcode=1991PhRvD..44.3197D | pmid= 10013776}}</ref> and [[Scott Aaronson]] later extended this result to show that the model could also be used to solve [[PSPACE]] problems in polynomial time.<ref>{{cite journal|journal=Scientific American|date=March 2008 | first= Scott | last= Aaronson| title= The Limits of Quantum Computers |pages=68–69 |url= http://www.scottaaronson.com/writings/limitsqc-draft.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.scottaaronson.com/writings/limitsqc-draft.pdf |archive-date=2022-10-09 |url-status=live | via= scottaaronson.com }}</ref><ref>{{cite journal | first1= Scott | last1= Aaronson | first2= John |last2= Watrous | url=http://www.scottaaronson.com/papers/ctc.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.scottaaronson.com/papers/ctc.pdf |archive-date=2022-10-09 |url-status=live | title=Closed Timelike Curves Make Quantum and Classical Computing Equivalent | journal = Proceedings of the Royal Society A | volume = 465 | year=2009 | issue = 2102 | doi= 10.1098/rspa.2008.0350 | pages= 631–647 | bibcode=2009RSPSA.465..631A|arxiv = 0808.2669 | via= scottaaronson.com}}</ref> Deutsch shows that quantum computation with a negative delay&mdash;backwards time travel&mdash;produces only self-consistent solutions, and the chronology-violating region imposes constraints that are not apparent through classical reasoning.<ref name="Deutsch1991" /> Researchers published in 2014 a simulation in which they claim to have validated Deutsch's model with photons.<ref name=RingbauerEtAl2014>{{cite journal| first1= Martin | last1= Ringbauer | first2= Matthew A. | last2= Broome | first3= Casey R. | last3= Myers | first4= Andrew G. | last4= White | first5= Timothy C. | last5= Ralph|title=Experimental simulation of closed timelike curves|journal=Nature Communications| date= 19 June 2014| volume= 5| doi= 10.1038/ncomms5145|arxiv = 1501.05014 |bibcode = 2014NatCo...5E4145R| pmid= 24942489| page= 4145}}</ref> However, it was shown in an article by Tolksdorf and Verch that Deutsch's self-consistency condition can be fulfilled to arbitrary precision in any quantum system described according to relativistic [[quantum field theory]] even on spacetimes which do not admit closed timelike curves, casting doubts on whether Deutsch's model is really characteristic of quantum processes simulating closed timelike curves in the sense of [[general relativity]].<ref>{{cite journal

| last1 = Tolksdorf

| first1 = Juergen