There was an episode of The Twilight Zone involving time travel and as it turned out some things can be changed but other events can't and it seems to me it's possible to avoid the time paradox.  For example, at first someone else was the father and Sarah raised him by herself. At some point Skynet is created starts the war and after losing sends the terminator back in time to kill her. Kyle goes back in time and becomes the father of John creating the time loop.
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The Terminator movies leave us with a sort of "chicken or the egg" problem.  Let's review some key facts   In 2029, Skynet sends a T-800 back to kill Sarah Connor In 2029, John Connor sends Kyle Reese back to 1984 to protect Sarah Connor In 1984, it is heavily implied (though I don't recall any explicit confirmation) that Kyle Reese impregnates Sarah Connor who later gives birth to John Connor. In the final battle, the Terminator is destroyed but one of his processors and hand survive. In 1995, it is revealed that Cyberdyne recovered/acquired the remnants and Miles Dyson is on his way to creating the first version of Skynet.    So, in this scenario, we are led to believe we are in a time loop. John sends Kyle -> Kyle fathers John and inadvertently leaves technology responsible for Skynet -> John sends Kyle... round and round we go.  But much like the chicken or the egg, someone had to have created Skynet before the time loop actually started. Has this ever been addressed?  Corollary: Who was John's father in this original timeline?
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I was recently reminded of sci-fi short story which I read quite some time ago (several decades, possibly) which was entirely a monologue.  The narrator is talking to two professors and it's revealed that they stole something technical from him.  Either the secret to time travel directly or something that could be extended into time travel.  During the story it becomes clear that the narrator has learned to manipulate time travel to such an extent that he was able to alter events so that he could not only win over his rivals, but in such a way that they'd be psychologically identical, so he could gloat over their downfall.  The resolution, according to my memory, was the narrator had taken over the religious order the rivals had created, and done so in such a way that the rivals were now seen as heretics and the story ends with the populace showing up with torches and pitchforks to take down the rivals.
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In Star Trek: Voyager, episode 23 of season 4 (), the episode begins with a civilization unknown until now. They claim to hold the ruins of the USS Voyager, which has otherwise contributed to the history of this civilization in a negative way, whereby Captain Janeway formed an alliance with the enemies of the people in question.  In the historical reconstructions of this event, we see many parts belonging to the ship, such as the Doctor.  This one -- having been deactivated during all these years -- still seems to be several centuries ago. The Doctor is therefore considered as the last "living" witnesses of this war.  The USS Voyager was considered a heavily armed warship with a restless and violent crew. The Doctor has done everything to set the truth about that time, and finally, all ends well, history is approved.  However, what is really going on? In the other episodes, the Doctor is always present, as well as the crew members, and the USS Voyager. At the end of the series, they all return to Earth.  What about this episode that seems to be out of the scope of the story?    I couldn't find any explanation about this episode, except that we could consider it as a separate story, but it doesn't really make sense to put an episode that has nothing to do with it in the middle of the series (even if it's very good and fits in pretty well).  I don't think this question is a duplication of , because this one is about the whole episode, as well as what really happened to the crew.
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I recently rewatched  And noticed a lot of new things that left all kinds of plot-holes and questions. I'm willing to accept plot-holes and Deus Ex Machina type explanations at times for entertainment sake, but there was one item that I wondered about.  David Levinson saves the day by figuring out that they can upload a computer virus into the alien ships that will disabled their defenses and allow the humans to damage their ships. Ok, great. He and Cpt Steven Hiller fly to the mother ship, he somehow is able to communicate through some sort of signals with the alien system, and upload the virus which is made up of some sort of injected code which he pastes into a console.  This leaves me wondering if any attempt is made in the movie or from someone involved in creation the movie to explain how earth technology is able to interact with alien technology. Is there a quote from a film maker? Is there a deleted scene where they mention how it works? Even if they say its midichlorians, this different than simply not addressing it.
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PART 1: I was reading the article  Wikipedia. I couldn't understand this line:       "if the two events are causally connected ("event A causes event B"), the causal order is preserved (i.e., "event A precedes event B") in all frames of reference."     Is this an assumption or a consequence of STR? Please explain.       Note: My question consists of 2 parts this is the 2nd part. Below is a genral version of my previous question question:.   PART 2: Let there be three events $A$,$B$ and $C$ s.t: $C$ is the result of Simultaneous occurrence of $A$ and $B$. In other words $C$ occurs iff $A$ and $B$ are simultaneous. Now as we know in STR any two events separated in space are not simultaneous in different frames. So In some frames $C$ will occur and in some $C$ will not occur which will cause paradox. I tried many thought experiments to make such a paradox but i failed. In all the experiments that i thought i could not break the causality even by breaking the simultaneity because everytime the fact: "all signals move slower than light" preserved the causality.    So why causlity remains preserved always? Is it due to the fact that nothing can move faster than light?
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In Fringe's season 1, the episode  (1x13) shows how  travels on VertusAir flight 718. We witness how he develops some strange symptoms, withdraws into a lavatory and transforms into a porcupine-like monster.  At the end of season 3, Peter "switches" the timeline (changing the past and making the present continue in a different timeline henceforth) from blue- to orange-verse. Various statements throughout the 4th season indicate time (the date) was not reset; Olivia and Walter have been working on Fringe cases for some three years etc. - hence it is safe to say that season 4 plays 3 years after season 1.  Then, in the episode  (4x16), the events from 1x13 happen again, up to the point of Bowman's transformation, which this time doesn't happen (not aboard the plane, anyway). As far as I can tell, great care was taken to exactly recreate the events from the season 1 episode, including hiring the same actors to play the flight attendants once again ( and ), so obviously this is supposed to be the same event with slight changes.  Peter, as well as Olivia - who is in the process of regaining her memories from the blue-verse -, remember the events from 1x13 and note the difference that Bowman's transformation happened later this time, implying that in the orange-verse, everything related to flight 718 played out the same way, except for the small difference that the transformation happened a bit later.  BUT ... all of this happened 3 years later!! Is there any explanation for this?  How unlikely is it that in the orange-verse timeline, Marshall Bowman is on the very same flight with the very same flight attendants 3 years after the same would have happened in the blue-verse? Mind you, this is not a "small change" in the course of events while mostly everything else stays the same.  So, why did Peter and Olivia realize the transformation happened a tad later in the orange-verse timeline, but were not baffled by the fact that essentially the same events as in the blue-verse happened, but three years later?  EDIT: Not only the flight and the flight attendants were the same in both episodes. The passenger next to Bowman was the same, an elderly lady played by  both times, as well. Moreover, the transcripts of  and  reveal that the dialogue between Bowman, the passenger next to him, and the cabin crew is the same down to the lines of text until the moment of transformation.  Interestingly, the announcement by the captain in the beginning seems to be different - starting the inflight movie + selling headsets vs. circling before beginning the final descent + selling snacks. On the other hand, this could be presumed to be a slight retcon, as in 4x16, it was crucial for the plot that the plane would be close to landing, and starting the inflight movie would not make much sense right before landing.
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Since the first Terminator failed, Skynet sent back .  Another strategy would have been to send back multiple Terminators. Why was that not attempted? Was there a cost (e.g. power) to sending them back in time?
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I just finished watching Into the Universe with Stephen Hawking (2010). Specifically the third episode titled 'The Story of Everything.'  In the episode Hawking is explaining the mainstream theories of the events just after the Big Bang. What confuses me is that he just said at the beginning that the laws of physics were different and time (among other things) did not exist as we know it during this early stage in the life of the universe, but then goes on to say certain events took certain amounts of time.  I don't know if the numbers match, but the same issue exists on .  How can we even guess the time frames of these events if time itself is largely dependent on the current state of the universe?
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So you've failed once, so you send back your shiniest poly-mimetic alloy terminator, but it fails because the resistance sent back a reprogrammed T-800! You know, or could reason that the T-800 would have to have encountered the targets of the T-1000, and they would have become familiar with each other as they evaded your near perfect killing machine.  Why not send back another with real infiltration programming (the T-800 is supposedly an infiltration unit, no?) so that it spends some time getting Connor to grow familiar with him, fooling him into thinking they are chased and then when he least expects it, the unit turns on him.  Is Skynet not capable of thinking in this out of the box manner? Did it not have enough T-800s to send back? Was it just designed by a physicist, and thus brute-forced every problem?
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In Book 1, Artemis et al escaped from the time stop by drugging themselves to sleep.  In the same time stop, Julius Root "accidentally" plugged Briar Cudgeon with a tranquilizer dart.  Cudgeon fell asleep, but did not disappear from the time stop.  Why not?
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Temporal Agents were supposed to keep eyes on timeline. Whenever timeline was altered and Temporal Agents failed to prevent it, it was due to advanced tech of other factions of Temporal Cold War.  Narada was powerful in front of 24th century tech &amp; past, but not in front of 31st century tech. And, it had no Temporal tech (that's why Nero didn't try to return back to 24th century). So, there was no way for them to escape detection etc.  Why didn't Temporal Agents stop Nero?
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I have been trying to find the title of this kid's movie involving these 2 scenes and the best description from what I can remember. Each of the scenes are connected by the use of the watch but in two different time periods in 1980s/1990s and then in the past.  First it’s about two best friends (I think both are male) who both set their wrist watches at a certain time to remember to watch a TV show (I think wrestling?) each week and after confirming the exact times on their wrist watches they say yeah air alright and possibly high five.  The show somehow had to do with time travel to the past. Only one of the friends goes back but I'm not sure how. While being stuck in the past and trying to solve a problem to help the people in the past, his alarm for the TV show goes off and he remembers the title of the TV show by hearing the alarm uses the battery to solve the problem. The watch didn’t cause the time traveling only that the battery of the watch was used in the past after traveling there.  But other then those scenes I don’t know the whole main plot and around the time it came out in the early 90s or late 80s.  It's not A Kid In King Arthur’s Court.
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The reason given in the movie Looper for sending targets to the past is that it is difficult to dispose bodies.  From ,     Thirty years into the future in 2074, time travel is invented, but is   immediately outlawed. However, because by that point tracking   technology has rendered it nearly impossible to dispose of bodies   secretly, crime bosses turn to time travel to send their targets to   the past to be killed using "loopers": hired guns paid in silver to   kill whoever is sent to them.   When trying to capture old Joe, they kill his wife. So how did they dispose the body of his wife? Or is it difficult to dispose bodies only in US and not in China? And they came for old Joe only because the Rainmaker wanted to close the loops?  Could someone explain? What am I missing?
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From this answer: , I'd like to quote this:     The paradox energy essentially creates a shielded fixed point in time. That particular region of 1938 New York can neither be changed nor visited by the Doctor or the TARDIS. The Doctor mentions trying to penetrate such a fixed point could conceivably destroy New York or potentially the planet.   Okay, so The Doctor can't land there to at least visit Amy and Rory. Well, can't he land outside New York and then, well, take a little walk to them?  Edit: Why can't it be visited by the Doctor anyway?  And, even if the Doctor himself can't walk into New York, surely Amy and Rory could go outside, no? So in Amy's afterword she would have said "Meet us in X place outside NY >_>", so it is just a matter of the Doctor going there and waiting for them to come.
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In Blade Runner 2049, so why is Dr. Ana Stelline in a bubble?  To clarify I'm not asking about her supposed weakness that has her in a bubble.  I mean if she is the key link to both sides issue, then why is she in a bubble.  We basically have two sides opposing each other in this sci-fi.  One side is driven to find the child so that they can make more slaves faster.  The other side so that they can have children and become "more than human" and have freedom.  Both sides have placed huge importance on the child.  One side to protect her, the other to obtain her and dissect her, or whatever, to figure out how this was possible.  I fail to understand how the side that has her in a bubble, making memories, is moving forward with their (the replicants') plan?  She's now 30 years of age and they are no closer to finding out how to have children of their own.  Are they just having sex with each other for 30 years hoping to hit the jackpot again?  Is she just important to them because she's naturally born... I mean they lead us to believe she's more important than that yet, they're not using her in any way to figure it out.  Given, I'm not sure how they could without putting her through some type of distress.  But 30 years now and she's still in there and their whole plan of a rebellion is hanging on the hope of having kids some day..
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Hypothetically, if you were to travel say, 6 months into the past with no spatial displacement, you would end up floating in space because the Earth would be on the opposite side of the sun.  I know when it comes to sci-fi, they can't account for everything and I don't expect them to. So I'm not nit-picking or anything, I'm just wondering if this is something that has been addressed to any detail, as it seems like it would have to be a major component of any time travel.
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Spoilers ahead! Plot points are revealed here, I'll put the deeper plot points in spoiler boxes.  Time travel features heavily in the plot of Endgame. Correct me if I'm wrong, but the MCU seems to subscribe to a multiverse of sorts. This makes any alterations to the past fine, and the "present" people making those changes return to the future they left from unaffected.  So, the plan is:      pop into the past to gather the Infinity Stones, wield them to perform a reverse snap, then pop them right back where you found them as if they'd never left at all.   This plan succeeds. However, as a result,      the pre-snap Thanos journeys into the future to protect the job he has yet to do, and is defeated in the process. This means that, although the Stones are placed back in their respective times (the Cap's last job before retiring), there's now a universe short of Thanos.   So, my question: is there now a universe out there in which the snap never occurred as well as several of the Avenger's adventures (anything after 2014, I think that's where Thanos travelled from), while at the same time there is a universe (the one we see in the films) in which all of the events of the MCU films transpired?  A further point, we're told that traveling back to kill a baby Thanos wouldn't work because they'd still be in the timeline they left from upon return (the snap one), while the other timeline would exist to no benefit of their own. This is why the mission was never about killing a pre-snap Thanos - your own past is unchangeable, the snap is locked in. Therefore, the Thanos that travelled to 2023 is forever locked in to travelling to that point and being defeated, meaning the time he came from must no longer have him.  This could also explain how the universe that we watch through the movies has a Gamora now. Because she came from a timeline in which Thanos never sacrifices her, she can be alive (remember, we're told that there's no way to reverse the sacrifice made to retrieve the Soul Stone - the only way she can be alive is if she's from a universe where she was never sacrificed (i.e. no Thanos after 2014)).