Closed timelike curve Puns

In recent years relativists have started to investigate previously discarded GR solutions, such as naked singularities, wormhole solutions, violations of the null energy condition, etc. In a similar way, I'm interested in these "time machine" solutions.

We all know about the grandfather paradox, but does this actually lead to any inconsistency in the equations? Or does everything work as usual?

Closed timelike curves are possible, at least mathematically, within some solutions of GR, e.g. in the Kerr metric describing a rotating black hole. These curves pose a big problem, in that causality breaks down; an observer on such a wordline would meet themselves from the past. From what I've read, this is "resolved" by the fact that these curves are hidden behind event horizons, so these curves cannot be observed from the outside universe.

This answer feels a bit unsatisfying to me. Sure it means us observers outside the event horizon won't have to worry about it, but what about an observer that travels into the event horizon of a spinning black hole? Would they actually be able to observe these violations of causality?

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Here's a pic

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I was curious about something involving Closed Timelike Curves. They're said to be exact solutions of relativity, but from my knowledge of them, it seems like they violate it. For example, you travel along a spacetime that makes you return lets say 1 minute into the past, but it takes 30 seconds. There's a nearby star that is not part of this spacetime, it's light is coming towards you. If you travel along the spacetime and return to the past, you are 30 seconds older but the light coming from the star is now 1 minute behind, further away from you. Doesn't this violate relativity, that the speed of light must always travel at the same speed?

I was wondering, what is the difference between a closed timelike curve and a time loop? Could it be possible for the universe to revert back to a previous state, and for a past moment to become the present again? Could the past be changed if this was the case? Is there any theory that suggests time could go backwards or loop back onto itself?

I've heard a lot about "non linear time" but I don't really find anywhere that explains it clearly.

Does string theory suggest time could be made to run backwards?

Hey. I'm just curious to knoew what wpuld it feel like to travel through a closed timelike curve geometric in spacetime. Would physics break down? Would you notice the looping pattern? Would our minds even be able to perceive it? Just interesting to think about.

Hi everyone :) I have a few questions about CTC. Specifically:

• What would CTC look like from the outside?

• Would every loop be the same?

• What would happen if the cause of CTC disappear? (e.g. Tipler cylinder stopped spinning)

These are all very interesting topics that I discovered recently. They all relate to Dark and may have been what a lot of the plot in Dark may have been built around. According to Wikipedia, a closed time like curve (CTC) is:

> In mathematical physics, a closed timelike curve (CTC) is a world line in a Lorentzian manifold, of a material particle in spacetime that is "closed", returning to its starting point. This possibility was first discovered by Willem Jacob van Stockum in 1937 and later confirmed by Kurt Gödel in 1949, who discovered a solution to the equations of general relativity (GR) allowing CTCs known as the Gödel metric; and since then other GR solutions containing CTCs have been found, such as the Tipler cylinder and traversable wormholes. If CTCs exist, their existence would seem to imply at least the theoretical possibility of time travel backwards in time, raising the spectre of the grandfather paradox, although the Novikov self-consistency principle seems to show that such paradoxes could be avoided. Some physicists speculate that the CTCs which appear in certain GR solutions might be ruled out by a future theory of quantum gravity which would replace GR, an idea which Stephen Hawking has labeled the chronology protection conjecture. Others note that if every closed timelike curve in a given space-time passes through an event horizon, a property which can be called chronological censorship, then that space-time with event horizons excised would still be causally well behaved and an observer might not be able to detect the causal violation.

Godel is a very interesting person to pay attention to, because he came up with the mathematical proofs that confirms the theoretical possibility of closed timelike curves:

> Einstein was aware of Gödel's solution and commented in Albert Einstein: Philosopher-Scientist that if there are a series of causally-connected events in which "the series is closed in itself" (in other words, a closed timelike curve), then this suggests that there is no good physical way to define whether a given event in the series happened "earlier" or "later" than another event in the series:

> In that case the distinction "earlier-later" is abandoned for world-points which lie far apart in a cosmological sense, and those paradoxes, regarding the direction of the causal connection, arise, of which Mr. Gödel has spoken.

> Such cosmological solutions of the gravitation-equations (with not vanishing A-cons

Full disclosure: 1) My grasp of the scientific world varies from "pretty okay" to "let me get on Wikipedia for a bit," but is definitely not "super." That said, as a failed writer, avid sci-fi and philosophy junkie, and a lover of weird brain gymnastics, I still find theoretical science (especially time travel) to be fascinating, even if I'm more likely to understand the broad strokes and not always the finer details. 2) I just finished playing Quantum Break, so that's rattling around in my head. (No story spoilers! The game just led me down the rabbit hole of time travel again, and plays with a few of these ideas, but right from the get go, and none of this will ruin your enjoyment of the game, which I personally really enjoyed.)

So, I'm trying to wrap my head around certain rules of (certain theories of) time travel, some of which are posited here. The most vexing rule for me is that "You can't travel back before the time machine was built," which relies on the theory of closed timelike curves.

Obviously, as a sci-fi fan, this is somewhat distressing. If a time machine was built in say 2005, that's the earliest point a person using that same time machine (as that time machine itself—and the placement of that machine?—is now the oldest fixed point of the CTC, right?) can travel back to, thus limiting anyone in 2016 to only 11 years of the past to travel back to.

Obviously, this assumes that there is one timeline, and because of that, anything that has already happened in my hypothetical timeline between 2005 and 2016 has already happened, whether or not someone traveled back from 2016 to 2005 to try to be meddlesome. (Right? Am I at least somewhat grasping this idea/theory?)

If I'm at least somewhat on track with the above (and don't be shy to say, "Well, yes and no..." or even "Did you ever stay awake during a physics class?"), my brain is stuck on a few points, and I would be very curious to hear what you all have to say about this.

If we stick with the CTCs/"can't travel back before the time machine was built/activated," sticking closely to the theories involved with this, a story using these would be a bit boring, yes? For example, if a person used the time machine today to travel back to 2008, they couldn't change anything due to the nature of the CTC—they couldn't prevent an event, ev

A CTC is a worldline of an object that essentially loops back to its own past, imagine it simply as the letter 'p', the curve being the bit where the person makes the trip back in time. I'm doing a project on these and I understand them quite a bit but there are a few problems I have encountered. Note this is all on the basis that CTCs actually exist, many say they don't.

1. Does a person on a trip through a closed timelike curve experience negative time? Again, imagine the letter 'p', the time axis is vertical and space is horizontal, so, for the trip going back, if they had a clock, would it tick negatively?

2. My main question, do they always require a specific geometry? CTCs are said to be seen in a very few specific GR equations, but they all seem to be based on the fact 'where spacetime does this', is warped spacetime the key to CTCs?

Thanks.

The idea of a self correcting paradox is the answer in and of itself. If I go back in time and try to kill my grandfather succeeding would cause me to never exist thus I would never be able to go back in time to kill my grandfather in the first place. This means that no paradox can ever occur in a close timelike curve because the paradox inducing timeline would be unavailable to the time traveler. Only those timelines that do not contain paradoxes would be accessible. This would only represent one end of the paradox scale. Think of it as the minimum side of a min/max scale. What then would be the maximum side of the scale?

Imagine an object falling towards a black hole. As the object approaches the event horizon, time begins to slow. As the object plunges over the razor thin event horizon an image of that object is permanently and forever fixed at the very edge of the event horizon as the object, and all of its mass, plunge deep down into the singularity. This would represent the max side of the min/max scale. In order for the image to ever be a erased from the edge of the black hole, i.e. the event horizon, the object's mass would have to be brought back out of the black hole and put back in the exact same position as the image; however, knowing that nothing can escape the black hole and it's intense gravitational pull, this also becomes self correcting. In other words no time traveler could, on the min side of the scale, violate the paradox self-correcting maxim because only those timelines that do not contain paradoxes would be available. Also, on the max side of the scale, no existing closed timeline curve could ever be reversed; such as: no image can ever be pulled back off of the event horizon because the mass from that image would need to be pulled out of an infinite gravity well singularity.

The event horizon of a black hole thus comes dangerously close to providing researchers with a truly testable solution to Closed Timelike Curves, aka paradoxes.

--Rulau

The ability to travel backwards in time is said to be impossible by most modern technomancers, arcanists, and researchers, but there are some rare accounts of such things. Recent research into quantum gravity and fringe cult philosophies open that possibly up again, but with a twist. A recent Stewart raid on a cult of Yog-Sothoth has unveiled enigmatic findings, some of which line up disturbingly with the timeline of the Gap. The esoteric nature of this knowledge, some researchers say, prevents more people from truly realizing the gravity of it.

The closed timelike curve is essentially a device or place connected to an another period in the past. Some think that these may be naturally occurring under certain cosmic conditions, and others believe it is possible to deliberately create one. They raise the potential of being able to consistently enter a point in the past, although some theorize that there is no risk of violating causality (or causing paradoxes that negate one's own existence). This is due to each trip back creating a new world-line, a new divergent reality.

The Stewart raid on the Church of the Gate and Key revealed a technomagical artifact called the temporal communicator. While the device was destroyed by the cultists during the radio, recovered notes reveal transcripts of curious conversation. These conversations say things the cultists could not have known, such as the time of the imminent raid. Even the cultists seemed skeptical about it until the last moment, which is why the device and records were still intact. The cultists stated that the messages came from the far future, when entropy had won its long battle against the cosmos. Curiously, the entity on the other end of the communicator claimed to be the same being as a lead cultist, only "post mortal" in that era.

Scholars of the Elder mythos note the similar accounts of the Great Race of Yith. The yithians were able to project their minds (and the minds of others) forwards and backwards in time millions of years. If so, they would serve as rare examples of psychic CTCs. Needless to say, this possibility has greatly excited many mystics and technomancers. The gods themselves said Golarion cannot be reached by technology or magic. A savvy mystic pointed out that perhaps psychic powers reaching across time may serve where magic and technology fail.

A dominant theory to explain the Gap is that the creation of the Drift caused some sort of cosmic realignment. Perhaps the Gap itself

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I found this article titled the "Experimental simulation of closed timelike curves" but I lack the background in physics to fully understand the article. Is it actually possible that scientists have found a way to send a single particle back in time?

EDIT: Article Link: http://www.nature.com/articles/ncomms5145

https://en.m.wikipedia.org/wiki/Closed_timelike_curve