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Topic: Chronology protection conjecture

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	Chronology protection conjecture - Wikipedia, the free encyclopedia
		The chronology protection conjecture is a conjecture by the physicist Professor Stephen Hawking that the laws of physics are such as to prevent time travel ("closed timelike curves") on all but sub-microscopic scales.
		The idea of the Chronology Protection Agency appears to be drawn playfully from ideas in science fiction, such as Isaac Asimov's novel The End of Eternity, Charles Stross' novel Singularity Sky and the television series Doctor Who and Star Trek.
		The chronology protection conjecture might break down, and the anti-chronology protection conjecture might hold: There is no law of physics preventing the appearance of closed timelike curves.
	en.wikipedia.org /wiki/Chronology_protection_conjecture (368 words)

	Chronology Protection Conjecture
		It simply states that the universe will protect itself from time paradox by not allowing time machines to be made.
		It seems to me that this conjecture is rather contrived.
		There is another possibility when it comes to the universe protecting itself from paradox and it is nothing less than predestination.
	www.geocities.com /CapeCanaveral/Hall/5803/cron.html (1034 words)

	Goldbach & Hawking (Sherman's Thinkers) (Site not responding. Last check: 2007-09-07)
		This is, quantum theory is conjectured to prevent time travel by ruling out the existence of space-times with closed paths - paths that loop around on themselves and thus permit circular time with the obvious ability to construct time travel machines.
		This type of conjecture is different from Goldbach's conjecture in that it can be supported by experiments, and it can make predictions which can be tested, but it can only be proven to be real in the normal sense of scientific truth.
		Conjectures might not be proven, but that does not prevent them from being powerful forces.
	channels.lockergnome.com /it/archives/20050523_goldbach_hawking.phtml (996 words)

	Novikov self-consistency principle - Wikipedia, the free encyclopedia
		The Novikov self-consistency principle, also known as the Novikov self-consistency conjecture, is a principle developed by Dr. Igor D. Novikov in the mid-1980s to solve the problem of paradoxes in time travel.
		Stated simply, the Novikov consistency principle says that if an event exists that would give rise to a paradox, then the probability of that event happening is zero.
		From wormhole to time machine: Comments on Hawking's Chronology Protection Conjecture, which also addresses the Novikov self-consistency principle
	en.wikipedia.org /wiki/Novikov_self-consistency_principle (333 words)

	BTTF.com's Space-Time Continuum - Back to the Future Forums - View Single Post - String theory rules out travel into ...
		The best we have is Stephen Hawking's "chronology protection conjecture", which, in a nutshell, suggests that the universe has a built-in time cop.
		However, there are no time cops evident in the laws of physics, so at the moment the chronology protection conjecture is simply wishful thinking, a physicist crossing his fingers and hoping for the best.
		He decided to devote a lecture to dealing with the issues it raised, and then assigned chronology protection as a problem for his students to solve.
	www.bttf.com /forums/showpost.php?p=135456&postcount=1 (2943 words)

	Time Machines
		The chronology protection conjecture then can be construed as a subconjecture of the cosmic censorship conjecture, saying, roughly, that consistent with Einstein field equations, CTCs do not arise under physically reasonable conditions or else that the conditions are highly non-generic within the space of all solutions to the field equations.
		In the other direction, a very general chronology protection theorem will automatically provide a no-go result for time machines, however that notion is understood, and a theorem establishing strong cosmic censorship will automatically impose chronology protection.
		The most widely discussed chronology protection theorem/no-go result for time machines in the context of classical general relativity theory is due to Hawking (1992a).
	www.science.uva.nl /~seop/archives/win2004/entries/time-machine (7991 words)

	"Time Lords" - Time Travel (Site not responding. Last check: 2007-09-07)
		But at least one detailed model for a time machine has forced physicists such as Hawking to try and find some "chronology protection conjecture" that would ban time travel into the past.
		But until a Chronology Protection Conjecture arrives that makes the world safe for historians, it is a field that theoretical physicists will continue to pursue.
		But until a Chronology Protection Conjecture arrives > that makes the world safe for historians, it is a field that > theoretical physicists will continue to pursue.
	www.okka.biz /_Time_Lords-26239815-296-a.html (2937 words)

	Traversable Wormholes (Site not responding. Last check: 2007-09-07)
		For the purposes of this article I'll adopt Visser's conclusion that the CPC mechanism is generic and blocks all forms of time travel via wormholes, but permits the operation of wormholes for the purpose of FTL travel.
		The CPC mechanism says two holes disturb each other as they approach closer than their empire-time difference times speed of light eg two holes with an empire-time difference of a year can't approach closer than a light year.
		CPC forbids such travel by destroying lone wormholes that attempt to interpenetrate each others empires.
	www.aleph.se /Trans/Tech/Space-Time/wormholes.html (5622 words)

	Mahjoob.Com Forums - Time Travel
		However, this need not involve problems with determinism or free will, if the probabilities are very small, for histories in which space-time is so warped, that time travel is possible over a macroscopic region.
		This is what I call, the Chronology Protection Conjecture: the laws of physics conspire to prevent time travel, on a macroscopic scale.
		Thus it seems there may be a Chronology Protection Agency at work, making the world safe for historians.
	www.mahjoob.com /en/forums/showthread.php?t=110620 (5756 words)

	Should there be an international ban against time travel?
		I have also read the low-down on Hawkings "chornological protection conjecture." (In many places) HIS chronological protection conjecture is a conjecture that time travel is impossible.
		I'd risk saying that because his conjecture is only a conjecture, though, one which he whole-heartedly believes in (merely can't (or doesn't wish to take the time to) prove), when he did the lecture he went ahead and said something which was more moderate than what he actually believes, to avoid (what is happening here).
		Do you know what the chronology protection conjecture is? It is a lot more significant than a lecture, I assure you.
	www.surveycentral.org /?x=x&V=9786&ReSort=1 (4064 words)

	Matt Visser: Recent Seminars
		This is a short nontechnical talk on traversable wormholes, time travel, and Stephen Hawking's "Chronology Protection" conjecture.
		Stephen Hawking's "Chronology Protection" conjecture has stimulated considerable research over the last decade --- I will give an overview of where we stand.
		Originally it was hoped that classical or semi-classical physics would be enough to enforce chronology protection, but it is now becoming clear that the full theory of quantum gravity will be needed to provide guaranteed safety.
	www.mcs.vuw.ac.nz /~visser/seminars.shtml (1595 words)

	Wormhole (Site not responding. Last check: 2007-09-07)
		Many physicists, including Stephen Hawking (see Hawking's Chronology Protection Conjecture), believe that due to the problems a wormhole would theoretically create, including allowing time travel, that something fundamental in the laws of physics would prohibit them.
		However, this remains speculation, and the notion that nature would censor inconvenient objects has already failed in the case of the cosmic censorship principle.
		The quantum physics of chronology protection by Matt Visser.
	www.worldhistory.com /wiki/W/Wormhole.htm (1778 words)

	NOVA \| Transcripts \| Time Travel \| PBS
		But we can't be absolutely sure, we won't know absolutely for sure until we have the full laws of quantum gravity in our hands and we can explore just what they say about the end point of the explosion.
		That's, that's what conjecture is and, and the word conjecture in mathematics is often used as a challenge to future generations to try to prove or disprove.
		KIP THORNE: It's not a principle, it's not a theorem, it's a conjecture because we do not yet know for certain that there is a mechanism in nature that will always enforce it.
	www.pbs.org /wgbh/nova/transcripts/2612time.html (6830 words)

	Chronology protection conjecture (Site not responding. Last check: 2007-09-07)
		The idea of the Chronology Protection Agency appears to be drawn playfully from ideas in science fiction, such as Isaac Asimov's novel The End of Eternity and the TV series Doctor Who and Star Trek.
		Many attempts to generate plausible scenarios for closed timelike curves have been suggested, and all seem either implausible, or contradict other principles of physical law, or appear to be contradicted by experimental observations.
		Matt Visser, "The quantum physics of chronology protection" in The Future of Theoretical Physics and Cosmology: Celebrating Stephen Hawking's 60th Birthday by G. Gibbons (Editor), E. Shellard (Editor), S. Rankin (Editor) available online at " class="external">http://arxiv.org/abs/gr-qc/0204022
	www.sciencedaily.com /encyclopedia/chronology_protection_conjecture (334 words)

	Matt Visser: Research --- Technical details (Site not responding. Last check: 2007-09-07)
		Recently, Professor Stephen Hawking has formulated a conjecture, the "chronology protection conjecture", that addresses issues concerning the interplay between causality and the existence of traversable wormholes.
		(The conjecture essentially forbids the creation of time machines.) I have published a paper investigating this conjecture, with a view to: (1) extending some of the technical calculations of the renormalized stress energy tensor, and (2) seeking a better understanding of the physical mechanisms supporting the conjecture.
		A further outgrowth of this research is a general study of focussing and defocussing effects in Lorentzian spacetimes, as embodied in the behaviour of the van Vleck determinant.
	www.physics.wustl.edu /~visser/technical.html (3923 words)

	Science News Online (4/11/98): Evading quantum barrier to time travel by I. Peterson
		Their result indicated that such a combination of gravitational space-time and vacuum quantum state could not exist.
		Noting that result, Stephen W. Hawking of the University of Cambridge in England proposed the chronology protection conjecture, stating that physical laws do not permit the appearance of closed timelike curves.
		Self-consistent vacuum for Misner space and the chronology protection conjecture.
	www.sciencenews.org /sn_arc98/4_11_98/fob3.htm (606 words)

	New film updates time-travel tales - Science - MSNBC.com
		This goes to the age-old debate over causality protection — that is, the kinds of historical paradoxes that were just narrowly avoided in “Back to the Future.” In fact, Hawking has joked that his Chronology Protection Conjecture is an effort to “keep the world safe for historians.”
		Explaining how the rules of time travel apply in the world of “Timeline” would give away the story, but suffice it to say that Nahin was generally satisfied with the way Crichton handled the issues in the book, and intrigued to hear about some extra twists that set up the movie’s ending.
		History is history: One explanation is that changing the past would simply not be possible, based more on fundamental logic than on quantum physics per se: Anything that a time traveler was able to do would be accounted for in the historical record.
	msnbc.msn.com /id/3541435 (1460 words)

	Time Travel [Internet Encyclopedia of Philosophy] (Site not responding. Last check: 2007-09-07)
		According to his so-called Chronology Protection Conjecture, he claims that the laws of physics conspire to prevent macroscopic inconsistencies like the grandfather paradox.
		A "Chronology Protection Agency" works through events like vacuum fluctuations or virtual particles to prevent closed trajectories of spacetime curvature in the negative direction (CTCs).
		The "Chronology Protection Agency" actively prevents them from occurring.
	www.iep.utm.edu /t/timetravel.htm (7833 words)

	NOVA Online \| Time Travel \| Timespeak
		Physicists, on the other hand, call it a "closed timelike curve." Below, feast on the concepts and conjectures, the dialects and definitions that physicists rely on when musing about the possibility of time travel.
		If this list only whets your appetite for more, we recommend you have a gander at the book from which we excerpted this glossary: Black Holes and Time Warps: Einstein's Outrageous Legacy, by Kip S. Thorne (Norton, 1994).
		chronology protection conjecture: Stephen Hawking's conjecture that the laws of physics do not allow time machines.
	www.pbs.org /wgbh/nova/time/timespeak.html (887 words)

	Traversable Wormholes: Some Implications
		The CPC mechanism says two holes disturb each other as they approach closer than their empire-time difference times speed of light e.g.
		Circumstantial evidence indicates alien civilizations are very few and far flung in the universe.
		We have seen that whilst the construction of wormholes is technically very difficult the long-term payoffs are very great.
	www.futurehi.net /docs/Traversible_Wormholes.html (5608 words)

	[No title]
		Like the cosmic censorship conjecture, it has not been proved but there are reasons to believe it is true.
		The reason to believe that chronology protection operates is that when space-time is warped enough to make travel into the past possible, virtual particles moving on closed loops in space-time can become real particles traveling forward in time at or below the speed of light.
		As these particles can go round the loop any number of times, they pass each point on their route many times.
	suif.stanford.edu /~jeffop/WWW/hawking.txt (2095 words)

	Matt Visser Seminar Abstract (Site not responding. Last check: 2007-09-07)
		Tufts/CfA/MIT Cosmology Seminar, at Tufts: Matt Visser, Washington University Title: Hawking's chronology protection conjecture: current status and prospects Abstract: I will discuss the current status of Hawking's chronology protection conjecture.
		This conjecture states that no ``reasonable and realistic'' model for the universe based on the principles of (semi-classical) general relativity can possess or develop closed time-like curves.
		[This is a fancy way of saying that you can't build a time machine.] I shall discuss the conjecture both form the point of view of mathematics (proving theorems) and from the point of view of physics (to what extent do the theorems reflect physical reality).
	www-ctp.mit.edu /cosmo/y9596/2-13_abs.html (103 words)

	The SF Site Featured Review: The Future of Spacetime
		The universe wouldn't permit it -- which in essence is Hawking's Chronology Protection conjecture.
		Hawking speculates that the unfortunate time-traveler would be incinerated by (literally) a bolt from the blue.
		As you may know, a faster-than-light spaceship could also be used as a time-machine, another reason why most physicists think FTL travel is very unlikely.
	www.sfsite.com /11a/fs139.htm (787 words)

	Technological Progress
		Li and Gott had addressed the objections to the existence of spacetimes with CTCs ("Misner spaces"): previous calculations had shown divergences (i.e., inconsistencies) in the "renormalized stress-energy tensor of the quantum vacuum polarization".
		This subject matter is abstruse for Open SETI, but suffice to say that based on this problem, Steven Hawking in 1992 proposed the "chronology protection conjecture" that claimed that the laws of physics do not allow the appearance of CTCs.
		Li and Gott found a self-consistent vacuum for Misner space in which the renormalized stress-energy tensor is regular (in fact zero) everywhere.
	openseti.org /Progress.html (1865 words)

	The Disintegration of Possiblity
		Crudely, that means that any replacement for Newton's theory of the universe is restricted to adding terms which become significant in ranges for which Newtons' laws diverge from experimental observation.
		Physicists are concerned with the Master Theories, and with various conjectures about unfinished corners of an envisioned total picture (such as quantum gravity); and their work consists in the ornamentation of this subject-matter.
		The Protection Conjectures are supposed to save us from an insane reality.
	www.henryflynt.org /studies_sci/disposs.html (9357 words)

	Book Review - Vol. III No. 1 April - June 1995
		This theological artifice guides the very postulates of global general relativity: Hawking's chronology condition is supported solely by a formally identical reproduction of Augustine's fallacy.
		Conclusions about the beginning or end of time, which anyway do NOT follow from the postulates, are not, therefore, reliable.
		the grandfather paradox or Hawking's (1992) chronology protection conjecture, both aimed against the possibility that spacetime warps may be utilised for time travel, making the world "unsafe for historians".
	www.ignca.nic.in /nl_00812.htm (348 words)

	This Is Nit Picking Isn't It? - Page 5 - Bad Astronomy and Universe Today Forum
		There is a name for your theory of time travel; the Novikov consistency conjecture (a.k.a the principle of self-consistency).
		The Novikov self-consistency principle, also known as the Novikov self-consistency conjecture, is a principle developed by Dr. Igor D. Novikov to solve the problem of paradoxes in time travel.
		Stated simply, the Novikov consistency principle says that if an event exists that could give rise to a paradox, then the probability of that event happening is zero.
	www.bautforum.com /showthread.php?p=348445#post348445 (5620 words)

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