Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Where do CTCs go?

  1. Nov 30, 2007 #1
    OK, I've read a lot of articles on Closed Timelike Curves, and they all say confusing things. Take this part off of Wikipedia for example:

    Orbits around high-density objects with extreme gravitational forces are an example of such a closed loop. An object in such an orbit would repeatedly return to the same point in spacetime if it stays in free fall.

    And which point in spacetime would that be? I'm starting to get the feeling that going on a Closed Timelike Curve would not send you to a requested time.

    That's what I'm confused about. What point in spacetime would the object go to? Would it go to multiple points?
  2. jcsd
  3. Nov 30, 2007 #2


    User Avatar
    Staff Emeritus
    Science Advisor

    A CTC would be a "time loop", i.e. for instance the fictional idea in "Groundhog day" or "12:01" (if you've seen either of those movies).

    However, it seems extremely doubtful that there would be any "memory" of pervious iterations of the loop in reality, unlike in the fictional treatments.

    The fictional treatments might correspond best to an almost-but-not-quite closed timelike curve. A true CTC would be totally closed and unable to evolve (at least classically).
  4. Nov 30, 2007 #3

    Chris Hillman

    User Avatar
    Science Advisor

    If you mention WP, link to the article, but its NOT A RELIABLE SOURCE

    Hi, TimeCurtis2289, welcome to PF!

    You should have said: see the Wikipedia article on Closed timelike curve, which reads in part:

    Sure, that's nonsense: even in regions of spacetimes which do contain some CTCs, most timelike curves (possible world lines) are not closed.

    Wikipedia is inherently unstable and unreliable; since I am a former Wikipedian who cofounded what turned into this WikiProject, my criticisms (far too complex and far too OT* to discuss here) cannot be easily dismissed as the product of failure to understand how WP (doesn't) work or as arising from hostility towards the stated goal of Wikipedia.

    [*I claim the paragraph above is not at OT as some might think since the OP seems to have implicitly criticized the dubious utility of WP in this thread :wink:]

    IMO, you shouldn't ever behave as if you think it might be a reliable source; it is not and most likely never will be. If you are willing to swear a solemn oath that you'll never use WP again, I can elaborate on what pervect said.

    (I'm kidding. But only just barely.)
    Last edited: Nov 30, 2007
  5. Nov 30, 2007 #4
    OK, I'll admit, Wikipedia was a horrible source to go to. I won't use Wikipedia ever again!
  6. Nov 30, 2007 #5

    Chris Hillman

    User Avatar
    Science Advisor


    Do you have enough background in gtr to follow a discussion of some specific examples of CTCs in specific exact solutions such as the Van Stockum dust?
  7. Nov 30, 2007 #6
    gtr? what's gtr? I'm new to this science thing, I used to be a filmmaker, and I'm using the filmmaker thing as a disguise.
  8. Nov 30, 2007 #7
    GTR = General Theory of Relativity.
  9. Nov 30, 2007 #8
    Yes I read an article that told me about that weird ball and rubber model and another that explains the special relativity theory. I understand both the general theory of relativity and special relativity.
  10. Dec 4, 2007 #9
    well, are you going to explain or not? Sorry if i'm acting impatient.
  11. Dec 4, 2007 #10


    User Avatar
    Staff Emeritus
    Science Advisor

    That's not really answered Chris' question, though: reading an article "about a weird ball and rubber" is not, I suspect, enough background on which to understand a response. We shall wait and see, however.
  12. Dec 4, 2007 #11
    Basically, I read about the general theory of relativity, and I understood it.
  13. Dec 4, 2007 #12


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Can you provide a specific reference to what you have read?
  14. Dec 4, 2007 #13
    I read http://archive.ncsa.uiuc.edu/Cyberia/NumRel/GenRelativity.html" [Broken]
    Last edited by a moderator: May 3, 2017
  15. Dec 5, 2007 #14


    User Avatar
    Staff Emeritus
    Science Advisor

    OK, do you know that CTC stands for "Closed Timelike Curve".

    I'll assume there's nothing that strikes you as mysterious about a closed curve. (Though perhaps that's a bad assumption. It's not particularly clear to me how to answer "where does a closed curve go?" - does the question even make sense?).

    Now, if you know what a closed curve is, and you also know the difference between a timellike and a spacelike curve, I think we're home free and you'll be able to answer your own questions. Otherwise, you might have to ask "what is the difference between a timelike curve and a spacelike one?".
  16. Dec 5, 2007 #15
    Yeah, it's an object's worldline that turns into a loop. Like tiing the two ends of a string together.
  17. Dec 5, 2007 #16


    User Avatar
    Staff Emeritus
    Science Advisor

    Yep, the worldline of an object is an example (one of the best examples) of a timelike curve. And if you have an actual object that follows a particular CTC, the object's worldline would be a closed curve.

    While there is certainly a lot more to GR than "rubber sheets", you seem to have a perfectly good understanding of what a CTC is.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook