I want to revisit an old subject that’s been talked about in this forum, but hasn’t really (to my knowledge) been adequately resolved. I am talking about the issue of the time-turner.

Specifically, what limitations there are or must be in play regarding the usage of time turners. We know in brief that time turners are devices that can take the user back in time up to five hours before activation; why then don’t we see extensive/more usage of such devices throughout the HP series?

J.K. Rowling herself had acknowledged this problem and attempted to come up with a fix to remove this awesome power by having all the time turners destroyed in OOTP. I think this is at best a short term fix, if even that, because presumably there might be time-turners in other places throughout the world besides the UK. Moreover, even if all the time-turners in existence where to be destroyed; the knowledge of their creation would presumably remain intact, and at any time an interested party might still be capable of (re)creating one.

Further, we still have the pressing issue of why time turners weren’t used more extensively before the OOTP. Why didn’t the ministry use time turners to stop Cedric’s death, or the death eater attack at the beginning of GOF?

To be clear this post is not about the manner of time travel utilized by time turners, but rather seeks to uncover some limitations inherent to time turner usage that would reconcile its use with the way it is presented/treated in canon. This post isn’t speculating about whether it is possible to use time turners to change the past, or whether time travel in the HP verse operates like a closed timelike curve, as was discussed here:https://forums.darklordpotter.net/threads/can-a-time-turner-change-the-past.39179/

However, I will quickly rehash the two main possibilities and discuss how they might impact the potential for time-turner usage and their limitations below.

Scenario 1:

Time travel is a closed timelike curve. Meaning that it is impossible to ‘change’ the past. No matter how hard the user tries, some physical/magical limitation will always prevent him/her from making an active change. Of course, one’s past presence might be seen to have already changed the past simply by being there, but it is presumed that the time traveler had always been there to begin with, and that his/her presence was simply ‘unknown’.

Scenario 2
(Parallel Universe approach):

It is possible to actively change the past. E.g. I see my friend die, activate my time turner, and prevent his death from taking place. He continues to live a long and prosperous life in the future. What this means is that I technically didn’t travel back in time to the same space-time continuum that I started from, but some very close analog to the thing (a parallel universe if you wish).

As will quickly become clear, the evidence in canon overwhelmingly supports this scenario.

As I see it, the first interpretation even if true does not solve the problem of time-turner usage. While a closed timelike curve would eliminate the possibility for one to change the past; time-turners would still grant the user a palpable advantage. For example, in the goblet of fire, whilst the ministry would no longer be capable of using their time-turners to go back in time and stop the culprits at the quidditch match; they could still follow them around whilst concealed and discern their identity for investigative purposes.

Similarly, whilst the ministry/OOTP couldn’t prevent Cedric’s death, they certainly could go back and observe the congregation of the death eaters and Voldemort’s return. Moreover, Voldemort couldn’t prevent the prophecy’s destruction, but he could observe it’s contents under an invisibility cloak at that very moment.

This also applies to investigations of recently committed crimes (e.g. Peter framing Sirius). Further, this isn’t just something that’s beneficial for investigative purposes. In a closed timelike scenario, it is possible to ‘set up’ the past in such a way so that you can influence the future, just like Hermione and Harry influenced the past in such a way to facilitate the escape of Black. So a detective couldn’t catch a criminal in the past if he was still at large, but she could devise a trap for the criminal in the immediate future by influencing the past.

Unfortunately, it looks like all the evidence indicates that scenario 1 is false. The close resemblance of the events in POA to a closed timelike curve was simply a coincidence. The existence of the Cursed Child play (granted that the method of time travel was unique), as well as J.K. Rowling‘s word: https://www.wizardingworld.com/writing-by-jk-rowling/time-turner
actively supports the contention that time travel change is very possible and real.

The books themselves also present the issue in such a way that changing the past, while inadvisable, is possible (hence why it is inadvisable). Needless to say, the plethora of evidence indicating an incompatibility between scenario 1 and the HP universe only makes the current problem of time turner usage much more severe.

So why then weren’t time turners used more extensively? Why wasn’t Cedric Diggory saved? Why don’t we see two Dumbledores dueling two Voldemorts at once, etc? We need to introduce some limitations on the usage of time turners that go above and beyond what is present in the books, but that still remain canon compliant. So what are some ways (canon compliant) that we can limit the usage of time turners to resolve this conundrum which make the most sense? I make some suggestions below, but I look forward to feedback and your opinions.

Possibility #1:

There are no inherent physical limitations to changing the past, but doing so comes with consequences due to to the existence of magical laws. Meaning nothing makes it physically impossible for you to enact a change, but there might be some unintended magical effects which dissuades the user from doing so (e.g. you will be vanished into nothingness).

Problems: Doesn’t limit scenario 1. Which as I described is still an issue for the way time turners are presented. Further, it doesn’t seem to be really backed up by Canon. While the characters go to pains to point out the potential consequences of changing the past (i.e. being seen) in POA, much of what is said seems to come across as timeline change being unwanted because changes in timelines are inherently unpredictable and because of the psychological effects implied.

In POA, Hermione said they shouldn’t be seen because their past selves might mistake what is going on for dark magic. In other words, the potential for misadventure is due to your past self accidentally killing you/dying from shock, and not because of some magical law which electrocutes you on the spot.

Further, we can infer from the fact that Hermione was given the time turner in the first place that the consequences can’t be too severe. Granted, Hogwarts is notoriously lenient when it comes to student safety, but it seems to be stretching matters entirely too far to say that the faculty would willingly grant a student a device which brings a ready and even likely potential for death or some other such bizarre outcome (e.g. the disappearance of Hogwarts itself).

Possibility #2:

The ministry has outlawed time turner usage; Hermione was the only exception.

Problems: Doesn’t explain away the potential for lawbreakers or death eaters to use such devices, and seems a bit of a cop out because we would want to know why such a device has been outlawed. Usually such a thing might be outlawed because it was dangerous, which of course is exactly the kind of limitation we are looking for. So possibility #2 will be reduced to some other possibility, which is the answer we want.

Possibility #3:

Because of the way time travel works; only one time turner in the universe can be used at the same time. This also avoid the infinite duplication problem: which is basically the problem that I can go back in time two hours, find my original self, who in turn time travels 1 hour further back. He finds the new original and they both wait 1 hour until I pop into existence. Now there are three of us (and three time turners), and we can go on existing and making more copies of each other at will.

This solution avoids this problem by having each time interval where a time turner is being used, be unique in that no other time turners are capable of functioning. So if I use my time turner to go back five hours, all other time turners will be non-functional for that five hour period.

This also makes it so that all time turners in the world have to be neatly coordinated by some world authority (e.g. the ICC), so that each user is granted a potential time slot. As such time slots will quickly come at a premium it now makes sense why we don’t see two Voldemorts dueling two Dumbledores. They can’t do so because some guy in China is currently time traveling to prevent some natural disaster taking place there. To be clear, this isn’t just some legal frivolity, but an actual magical/physical law enforcing such a thing.

Problems:
Preventing a bad actor from potentially ‘stealing’ a time slot, and this possibility also seems unlikely given how liberal Hermione was able to use the time turner. You would think that there would be more pressing needs worldwide for time-turner usage, that don’t revolve around a Hogwarts students academic achievements.

Possibility #4:

There are magical countermeasures that can be enacted to protect against the effects from magical time travel. For example, a geographical location can be warded to prevent all time-turner usage, or maybe there are spells that can target persons under the effects of the time-turner. So if two Dumbledores showed up to duel Voldemort, Voldemort can simply spell the second Dumbledore away back to the future present, and it is difficult or even impossible for anyone to prevent this (no matter how magically skilled).

Problem:
Doesn’t really take away the possibility for hidden/stealth time turner usage. It would still be possible for people to gain a great advantage using time turners to spy on others, or to lay the kinds of traps I was talking about. The only exception would be if it was common practice for most geographical locations of distinction to be actively spelled against such time-turner usage. For example, if Voldemort spelled the graveyard in GOF.

All in all I think this solution, despite being imperfect, is the best of the bunch. Alternatively, some combination of 3 and 4 might be interesting. Having extensive potential countermeasures might make time turners less useful, and might go some ways to explaining why Hermione had been granted so many time ‘slots’. In turn, possibility #4 puts even more limitations on the devices, which of course is beneficial to our problem.

 

It is a closed loop with some degree of determinism to it, I guess. Whole Cursed Child madness ignored, we can see in PoA that there is no changing past nonsense included, only a slight effect on the events occurring now. So while Ron is being dragged by Sirius and followed by Harry and Hermione there is also another Harry and Hermione saving Buckbeak. Nothing changed, nothing happened differently. In the said loop, Buckbeak and Sirius are always saved because Harry and Hermione would always go back in time to do so and everything that happened will always happen so.

If a change is about to occur, it would have already happened because of the few hours older you who went back to do something different and while that older you do the actual change, the present you will do the same he intended to do, but he will also use time turner every single time.

For example, why did Harry the traveler conjured Patronus to save himself and Sirius? He believes he saw his father doing so, and his curiosity leads him to the exact spot from where it was conjured. He arrives there and waits...and realizes that he actually saw himself, and is 100% sure he will succeed in doing so because he already did it.

 

I agree with you that scenario 1 isn't the case; all signs in PoA are that time turners can be used to change the past and that "closed loop" time travel is Ministry-directed best practice, not the only form of time travel possible. Hermione specifically notes in PoA that they must be careful to avoid changing the past.

However, I disagree on your idea of it being parallel timelines: rather, it is the single timeline which is being altered through multiple "reruns", and it is possible for previous "versions" of the timeline to be remembered/detected by wizards.

In terms of limitations, I think there are two: one magical, and one cultural. In particular, it's the cultural element which I think is missing in your consideration of the problem.

The magical limitation is the issue of consequences, which you raise but I think dismiss too quickly. For one, this is precisely the avenue JKR took on Pottermore:

So we see that time-travel against "best practice" is dangerous for both the traveller and for the fabric of time itself.

This passage is also why I say there is just the one timeline, which can be run through multiple times and altered: "changing the course of their lives so dramatically that no fewer than twenty-five of their descendants vanished in the present". It's not that those individuals vanished from history such that they were never born. If that had been the case, no one would know about them and no one would be able to conclude that they had vanished. Rather, they had existed in the first iteration of the timeline, but then a change was made such that they disappeared from the second iteration, which overrides the first; such change being detectable at the point of the time-traveller's departure.

As for why wizards are fine with Hermione having a time turner to attend classes, when it's possible that she could have destroyed time itself by using it badly? That's just how wizards are - but note that McGonagall did have to fight hard for Hermione to get one, and had to make some pretty strong arguments as to how responsible Hermione was.

Which brings us onto the cultural limitation. Whenever a person asks "Why don't wizards use magic X to achieve goal Y?" they almost always fail to consider this element. By doing so they are exercising a double standard, holding the wizarding world to a higher level of logical consistency than the real world.

The prime example is: why don't wizards use binding magical contracts to enforce law-abiding behaviour from all citizens and thus achieve a peaceful society? Personally I think the answer is obvious, and all you have to do to arrive at the answer is to consider what would happen in the real world if you proposed giving the government direct control of every person's free will. There would be an outcry; mass protests, and if necessary civil war to prevent it.

For some reason it never occurs to people that wizards may have a culture where people are unwilling to accept magic being used in certain ways.

Which brings us to time turners. The cultural limitation has a couple of different aspects.

The first stems from the existence of magical consequences to bad time travel. One imagines that most learned wizards would be aware of these effects and would wisely fear them for their unpredictability. So if you wonder: why did Voldemort never mess around with time to achieve his goals? My answer would mainly be: because Voldemort's not an idiot and he knows that any attempt to do so would almost certainly backfire.

The second stems from the culture of magic use. All signs indicate that wizards have a rustic aesthetic preference. They do not use magic to build floating cities or Towers of Babel; they do not wear clothes of fire and water rather than fabric; they do not even use light charms or heat charms to light and warm their buildings, preferring instead to use fire. Fundamentally, then: wizards choose not to use magic to its fullest extent to create what we Muggles might consider the optimal, most efficient society.

To be clear, this is not about wizards lacking logic. It's not "wizards are too stupid to realise that it's possible to do these things". It's about preference and societal norms. Wizards choose to reject those things because they enjoy the simpler life. Why use magic to travel to the moon when you can use it to grow some delicious strawberries? Why build a gleaming city of magic when the Leaky Cauldron already serves a lovely ale and hearty pies?

So even if time travel came without consequences, I doubt wizards would use it for anything significant. Using time travel for mundane tasks like doing extra homework, but rejecting its use in any way which would fundamentally alter the basis of society, is entirely in keeping with wizarding cultural norms surrounding the use of magic.

 

This is an interesting post Taure; I certainly agree with you that a cultural analysis was woefully deficient in my first post. That said; I think your mutual points of magical and cultural limitations are not really up to adequately solving the problem of time turner use for a few reasons I will get into.

On the topic of parallel vs single timeline:
I think we might have a different definition of what we consider a timeline to be, or a closed space-time continuum. When I said that changing the past implied one was operating in a close analog to ones one timeline; I was referring to a space-time continuum that the original user found herself in up until her departure. That is, a universe consisting of a series of objects and events that are held in a specific relation. By ‘timeline’ I refer to these specific objects/events and the relations between them that held up until the moment of time travel. Since one can change the past (by your own admission), it follows that the new timeline has new and distinct events from the one that the user emerged from (her future), hence by definition such a new universe/timeline cannot be the same as the old one.

I am sure what you had in mind when you said ‘timeline’ was in fact the universe of objects/events that were present before the time that the user traveled to (and not from which they engaged their time travel).

On magical limitations:
I deliberately did not include those effects that you mentioned precisely because they do not seem applicable to time turner usage (note where it reads that catastrophic consequences occur when people attempt to travel more than a few hours in the past). Hence, we still have an issue with actual time turner usage.

Note also that the catastrophic consequences arise not from meddling with the past, but are specifically mentioned to be a result of the longevity of the time travel involved. Also, in POA Hermione mentions that changing the past is bad precisely because it would be a significant psychological shock to meet your time companion, and not because of magical consequences.

Further, even if you stretch canon to say that changing the past does in fact have magical consequences; there is still a problem that I mentioned regarding the fact that time turner usage that doesn’t change the past is still potentially exploitative to a degree that we don’t see. Can this be solved by invoking cultural mores? Let us see.

Regarding Cultural limitations:
I think you nailed a great point by pointing out that cultural mores can readily explain why we don’t see general magical exploitation of the kind we might initially expect. That being said, I think the comparison to magical contracts is a disanalogy.

The important thing to remember here is that time turners are in regular use. And here is where I think the argument by cultural limitations starts to fall apart. The fact of the matter is that there are no cultural limitations to using time turners without changing the past because they are regularly used in such ways. Thus, if there is to be a social more against time turner use, it must be either directed specifically against the changing of the past, or against using time travel greater than a few hours (because of the magical consequences), and the latter is something I never had in mind.

If there is a cultural more against changing the past:
1) this doesn’t really apply to Voldemort and his death eaters
2) there are still problems with time turner use even of the kind that Hermione was doing.

So we would have to go further and propose that there is some kind of extreme cultural prohibition on just using time turners (without even influencing the past); to explain why the ministry doesn’t investigate past crimes etc..
It is certainly possible to take this approach and argue that Hermione is an exception, but we also need to invoke a magical limitation to explain why bad actors don’t exploit time turners.

This goes back to magical limitations when I pointed out that there is no canon evidence to really indicate that there are magical limitations to changing the past within the last few hours, and in fact a great deal of canon implication (Hermione stressing the psychological and not magical consequences) otherwise.

It is fine for the evidence to be underdetermined of course, that is what we are trying to solve here after all. But I think the problem of personal incredulity is not so easily dismissed. Saying that giving Hermione a time turner even though there is the potential for severe consequences (e.g. the vanishing of multiple persons) because that’s just ‘how wizards are’ doesn’t seem to me to square well with wizarding psychology.

Yes we know wizards are cavalier about safety and such things, but that’s precisely because they have magic which can so readily solve such problems. That doesn’t mean that they are cavalier about their lives however. Arguing that giving a student a time turner is acceptable in the face of such consequences is like saying it is perfectly conceivable that Dumbledore would have given away the horcruxes to a child to play with, because they were interested in it, and well who cares about the consequences of death from a potential curse/dark lord retaining immortality?

Perhaps that is a bit of an unfair comparison given that there is a perceived benefit to giving Hermione a time turner. But I would argue that a look at canon will tell you that wizards do care about using magic responsibly and the safety of their charges (e.g. Triwizard tournament age limit). What this tells us is that if there are to be magical limitations they cannot be too severe; certainly not if the kind where Hogwarts might potentially vanish etc... and if the magical limitations aren’t so bad; is it really plausible to think an actor such as Voldemort would be dissuaded from using them?

Lastly, addressing the issue of bad actors again; this problem must be explained away by invoking some magical limitation to changing the past (which as I explained, seems at odds with canon). Even then we still have the problem of why Voldemort didn’t use the time turner to observe the prophecy crashing etc...

The bottom line is that we are trying to come up with the best explanation. Your explanation can work only to a degree, it can solve almost all the problems except for why bad actors don’t use time turners without changing the past (in the way Hermione did). I suppose that is acceptable as long as we can come up with individual explanations for why Voldemort and other death eaters could not get their hands on time turners.

We just have to introduce some magical limitations which seem in conflict with the nuances of the text. And also introduce some crazy cultural mores (the equivalent of letting children play with nuclear bombs). I agree this can be done but it doesn’t really seem in keeping with the flavor of the text (regarding both the cultural and magical limitations you mentioned).

Far better I think to have some other approach like having magical countermeasures. After all, we are often told (HBP) that the reason wizards don’t do something is precisely because there is an opposing side that can use magic too. This is actually what I also prefer to explain away the lack of ubiquitous magical contracts (that there are magical defenses), and seems to be the approach Rowling has used in explaining other apparent discrepancies (e.g. veritaserum as universal truth-drug).

 

Two points:

1. By "alternate timeline" I took you to mean that the original still existed in parallel to the new, alternate timeline; that the time-traveller has created a kind of parallel universe which diverges from the original timeline rather than one which overwrites the original timeline. If that wasn't what you meant then we have no disagreement.

2. I'm not persuaded by your arguments that there aren't magical consequences to time travel; I think it's clear from the books that any changing of the past is considered extremely dangerous for the people involved - the only safe way to time travel is to ensure you create a closed loop. Any deviation from closed-loop is a recipe for disaster. The psychological impact of meeting yourself is presented as an example of the dangers of changing the past, not the final word on the matter.

3. I don't think the problem of "bad actors" is as big a problem as you present. The vast majority of "bad actors" are selective in their breaking of cultural mores; most bad actors still obey most norms. Even Voldemort, for example, never takes any action which would go so far as to break the Statute of Secrecy, even when conducting attacks on Muggles. I find it entirely believable that Voldemort would completely oppose the use of time-travel; not least because it could result in his own elimination from history, whether deliberate or accidental.

 

Yes we have no disagreement on the parallel universes in that case. I think 3 is right (e.g. Hitler being a vegetarian). I also agree with you that there are clear magical limitations to changing the past in certain contexts (e.g. more than a few hours time travel). It is obvious these are magical in nature and not just a consequence of peculiar causal laws in play (e.g. you vanishing because you killed your grandfather), because we see things like a four hour day etc...

Again the evidence is clear that these consequences are due to the longevity of the time travel involved. Does this mean there can’t be magical consequences to just changing the past in a more limited time window? No, of course you can invoke such limitations. What that leaves us with however is people not time traveling because of the risk of being caught.

So Voldemort doesn’t time travel simply to observe the past (already immensely exploitative, consider: he might have used a time turner in the atrium to lay a trap for Dumbledore with cursed objects, protective enchantments, and ten death eaters hidden under invisibility cloaks, all without changing the past) because of the consequences that he might mess up and be spotted.

This is fair enough, but ends up with time travel becoming synonymous with any other high risk activity. Like, barging into the ministry to begin with, which carried the consequences of him being seen and potentially captured/killed. Thus we might still expect time turners to be a part of the repertoire of the dark lord/others.

The fact that Hermione was given a time turner also puts an upper boundary on the degree of risk, or at least on the probability of risk. It is possible for there to be extreme consequences that have a relatively low probability of taking place. Thus, while the consequences established in Pottermore are extreme; the fact that Hermione uses the time turner in the first place implies the relative degree of risk (taking into account severity of consequence plus the probability of an accident) is not abnormally high. And this is being generous in extending the magical consequences established in Pottermore (unique to large-scale time travel) to apply to all changes in the past.

So for all the lauded risk, it seems less risky than doing something like dueling Dumbledore, and probably more akin to undertaking a triwizard task. Since Voldemort does engage in much riskier activity for perceived benefits, and since even non-changing time travel can carry huge benefits; it stands to reason that ‘time turner use is too risky for Voldemort’ is not an adequate explanation.

Invoking some kind of peculiar cultural more (i.e. never use time turners) that Voldemort specifically had but Hermione/the ministry didn’t might explain this away, but seems a tad far-fetched.

 

I haven't read all your comments carefully, but I don't understand the Pottermore explanation at all.

Why is the limit set to a few hours instead of days? Seems rather arbitrary to me.

So not only did she travel back five centuries, but she tried to travel forward as well? So the main example given to support the "shouldn't go back more than a few hours" is of someone going back centuries, and then traveling back to their own time. Meh...

I don't understand this at all. Why did 25 descendants vanished in the present, five centuries after the fact?

If changing the past with a time turner is possible, then she traveled back five centuries, changed some things living for 5 days in that past. The people whom she changed their life course ended up living their lives differently five centuries to the time traveler's past, which resulted in them having or not having children, with different people or whatnot.

So why would 25 people disappear five centuries later? If she changed the past, those people should never have existed in the first place.

Their parents shouldn't have existed, and their grandparents and so many others.

Why wouldn't other descendants at some point in those five centuries disappear, but the ones to go were the ones from the traveler's time?

How do we even know that their lives were changed in the first place? Looking back, history, if changed, can only have happened one way. To be aware of a change of course in the past in this way, means being aware of both versions of the past. But how could that be?

Many people seem to greatly dislike HPMoR and it has several flaws, but one thing the author dealt with greatly is the time turners I think.

 

I think the clear implication is that when the past is changed, wizards are able to remember the previous timeline(s).

 

But wouldn't that mean simply that they remember two versions of events, and no one would randomly disappear? Were those 25 people completely erased as in never having existed, and their parents and grandparents also?

What happened with their parents etc? Even this answer in pottermore that has come after the books seems poorly thought out to me.

The way it's been put (vanished in the present) seems a rather weird way of saying that wizards after the time traveler changed the past have simply two versions of events in their heads. Which by itself is rather strange, if one of the people who disappeared was your close friend and your life greatly affected by their presence in your life, not having them could have lead to a completely different life. All the knowledge gained, all the memories of happiness and sorrow would double? Instant x2 XP?

 

I think the system intended by the Pottermore article is fairly clear and works fine, so long as you don't come into it with preconceived ideas as to how time travel should function.

The present is a defined point in time, ever moving forward. If you travel back in time, your time travel does not make that time the present, even though it seems so subjectively for you. The present remains the time in what you now perceive as your future.

If you make any change in the past, it takes effect in the present, not in the time intervening between the past and the present. To define this more precisely:

Say you go back in time at 1 January 2020, to 1 January 2019. You stay in the past 3 days before you make a change on 3 January 2019. That change takes effect in the present, which is now 3 January 2020.

Essentially the idea is that the forward movement of time is universal, such that the time you spend in the past is mirrored by the progress of the "present".

 

Let's say Hermione getting the Time-Turner isn't a one-off occurrence and other students have gotten time-turners before. The power that a time-turner has can likely only be exhibited in the sense of "what has happened." So the reason Harry doesn't see three Harrys walking around is because he doesn't. If that makes sense.

Hermione is able to use it because its a secret and because it is for a menial task. They both use it because of the fact that the events surrounding his Patronus charm et cetera... were vague and ambiguous in themselves. Harry even states that the reason he was able to cast that charm was that he knew he was going to.

 

Ok, maybe I do have preconceived ideas about how time travel should function, though if you asked me I couldn't outline them clearly and I'd like to think that if a comprehensive explanation was given I'd be able to get it. I have opinions and understandings on several things but I don't think those prohibit me from seeing a different point of view when expressed clearly. In any case, my preconceived ideas about how time travel should function is that you can't change the past, so if changing the past is possible, I'm trying to understand how that would work, I don't have any ideas about how it should work.

How can the present not be subjective? I don't think there is present without it being someone's present. Are you saying you can't travel forwards in the future? If time travel is possible why would it be possible to travel only to the past? When I space travel I can take any direction after leaving my house, I'm not limited in any way. Why would I be limited when I time travel?

This seems super strange to me. Suppose I went back in time far enough in time to save the dinosaurs from extinction and somehow killed all mammals with a super powerful curse. You're suggesting that mammals and humans would evolve all the same, somehow overcoming my killing them off, and if I were to travel back to "the present" (30 july 2020) then all mammals including humans would instantly disappear and be replaced by...?
If there was no change in those 200 million years, but the change took effect in the present, was my saving the dinosaurs all for nought? Will they appear in "the present" despite not existing for 200 million years, as they were when I saved them?
With what you're saying no different evolutionary product (like lizzard people) can appear, since the only evolution that took place was the one that we both know as history, regardless of my killing off all mammalian life.

Or is it impossible that would undo yourself? There's no mention of such a restriction, and since what has happened in the interim cannot be changed it seems entirely possible to unmake oneself.

If you can explain the situation with my given example, or if you can think of a better one that illustrates what you're saying in a way that makes sense it'd be really helpful.

To get back to my space travel analogy, my house and my parents house are both well defined points in space. However the way my space traveling works, is that I have to get there someway. Even in hp world, apparition is a way of traveling through space. What you're arguing with time is that it wouldn't work like that at all. Instead, the two points in time I travel to and from are somehow linked bypassing all the time in between. Meaning that somehow my traveling linked those two times together? I don't get it.

edit:
What happens if in my example above I have the philosopher's stone and decide to live those 200 million years instead of traveling back to "the present"? How is that different from my traveling back? In one case I travel to the future slowly, in the other very quickly.

 

It doesn't sound like you have failed to understand the system, aspiring_failure. It just sounds like you would prefer it if it was a different system. Which is very much a you problem.

 

@Sesc I don't really see this "forward movement of time is universal" playing into time traveling. Do I have a POV problem or is it you who are picking two POVs ? Why pick the POV of people left behind? Let me use the original pottermore example to pick some more POVs: Let's look at it from the POV of the people whose lives where changed by their interactions with the time traveler. They are traveling linearly through time. Then let's look at it from their children's POV, and their children's children.


Alright, Taure I don't see how your comment is helpful. Maybe my understanding is great, but why is my disagreement me preferring it were a different system instead of weak points of the existing "system". I don't think there is "a system", just interpretations of some poorly thought and expressed ideas by JKR. The "forward movement of time is universal" is such an interpretation. And I think there are a million weak points trying to explain JKR as though she had a system in mind. Even in the pottermore example you gave there is no indication that time traveling to the past is bad for the traveler. Instead going back forward is.

Example of a weak point that you argue for:

In the pottermore example let's say A was friends with B (who disappeared due to time traveling stuff).

With B in A's life, A became an unspeakable doing research on magical theory or whatever.

Without B, A became a dark lord.

So now A has memories and knowledge from both his lives.

That does not make sense in the hp universe. But that is what your system supports.

 

Your objections are all based on setting out logical problems with the system. That's why I describe it as a you problem - the objections all stem from your need to make the system make logical sense.

There is no such need. The text is what it is, and it clearly states that if you make a change in the past, it takes effect in the present. You may think that doesn't make logical sense. But that just means that you think the text is illogical. It doesn't change what the text says.

The system is clear: if you change the past, it takes effect in the present. The question "what does canon say?" is answered simply by reading the text, and that's what it says.

Personally, I don't think that there is any way to write time travel (where you can change the past) in a way that stands up to logical analysis, simply because it's not possible to change the past. So I don't really think there's any worth in subjecting time travel stories to logical analysis of whether the system makes sense. They never will. So long as the system is clear, that's enough.

In the same way, magic isn't possible. We suspend our disbelief when it comes to the existence of magic; we do the same for the existence of time travel.

If, on the other hand, you wanted to object to the Pottermore text on the basis of how it sits with POA, that would be a discussion worth having. Because that is an objection based on the text, with the outcome that the system is not clear because we have multiple pieces of text to fit together.

But I think that discussion is also a very brief one: the two texts are just fundamentally incompatible. The specific incompatibility is the looped nature of Harry's PoA Patronus and the question of "if it's possible to change the past, rather than your time-travelling actions always being part of the timeline, how did Harry survive the first time around, without a Patronus there to save him?"

But to the extent that is inconsistent with the Pottermore article, it's also inconsistent with PoA itself, because within POA it's also the case that you can change the past if you're not careful. So within POA we also have the inconsistency of two time travel systems: one where you can change the past, another where your actions in the past are already factored into the present and therefore change is not possible. So the Pottermore article and Cursed Child added nothing new, they simply re-stated a problem which already existed in the text of POA.

 

This is clear enough, but I think part of the problem some of us (aspiring_failure) may be having concerns the exact causal connections between changes in the ‘past’ and changes in the present; which Sesc also alluded to. It seems to me that there are two possible scenarios which adequately explain the events, which I will outline below.

In scenario 1, the present is causally connected, in a discrete fashion, to the past time period (the five days) that the time traveler found herself in. But, importantly, the intervening time period (the closer past) is not causally connected to either the present or the time-traveler’s time period.

This explains how people can vanish in the present; their vanishing is directly caused by an event in the time travelers past five-day time period, and not a result of an intervening casual chain that stretches throughout the entire past timeline.

Alternatively, there is a continuous causal chain throughout the entire timeline between the time travelers time period and the present. In this scenario, people don’t suddenly vanish in the present. Rather, they never existed up until the present. At the moment the time traveler returns, (the present) people spontaneously gain the memories of the alternative past that they could have lived (including remembering the ‘vanished persons’).

The difference between scenario number 1 and 2 is that in the first, people live out the timeline of the time travelers origin (the one that included the vanished persons); retaining a memory of them all along only for them to spontaneously vanish at the moment the time traveler returns (the present).

In the second scenario, people live out the timeline where the persons were vanished, never knowing anything about them, only to spontaneously ‘remember’ this alternative vision of the past upon the arrival of the time traveler to the present.

Either scenario adequately explains why people know about past events pertaining to the time travelers original universe (for lack of a better word) while also being affected by the events created by the time traveler.

It seems to me from what you are saying that your picture of how time travel works would blend both scenarios; in that you state what happens in the time travelers past doesn’t effect the intervening past, but you also say that wizarding folk might regain certain memories at the time of the present time travelers return.

I think it is helpful to separate these two premises and realize that they aren’t necessarily logically entailed (and actually might be mutually exclusive; hence the problems you run into).

I actually think that J.K. Rowling has in mind a kind of scenario 1. The only disadvantage of the first scenario is that the notion of past isn’t really intuitive; in that we think of the past as being continuously causally connected to the present and future.

On the other hand, the disadvantage of the second scenario is that the time traveler originates from a kind of alternate/parallel universe that isn’t our own.

Edit:
I don’t think we have to give up and throw up our hands and say that time travel is inherently contradictory. That may well be true, but it might also be true that different people have different conceptions of what the ‘past’ or a ‘timeline’ is; for example as something not necessarily continuously causally connected to our present.

This is a bit of a cop-out, in that it means we are saying that the author didn’t really mean “past” when they wrote past. But I actually think this makes sense in that the topic is very complicated, and a person might have an intuitive feel for how time travel works which doesn’t necessarily comport with the standard definitions of what a space-time continuum is.

 

I don't think so. What you describe as scenario 1 seems to be the only possible reading of the text. The description of people disappearing in the present seems unambiguous: the people existed up to the time at which the person in the past made the change, at which point they ceased to exist in the present. You can only disappear if you first made an appearance.



Up to 3 January 2020, Female Stick Figure would still exist. You would be in the middle of a conversation with her, and at the moment that the person in the past made the change, she would disappear. And perhaps a new person pops into existence in her place.

 

Well yes, but we also need to take into account the author of the pottermore article. Who’s observing such effects and writing them down? Presumably the wizarding folk in the present (in universe). From their perspective, in scenario 2 they would suddenly gain the memories of the vanished persons, but of course after they’ve gained the memories they would feel as if they had known the persons their entire lives. It would very much be a case, from their point of view, of a person having spontaneously disappeared that they had known their whole lives. They would never know that they had actually ‘gained’ anything; unless they had some outside objective knowledge (perhaps from observing the time travelers effects).

Really the scenario is equivalent from the perspective of the wizarding folk; the only difference would be that ‘in universe’ a laplacian demon who theoretically ran back the causal chains of the events taking place would realize that in scenario 2 the memories described are fake ones, in that said persons never existed.

I suppose it ultimately comes down to how ‘objective’ you feel these Pottermore articles are. And whether you think that they are meant to be interpreted from the point of view of a wizarding denizen or not.