The release of Harry Potter and the Cursed Child has brought the conversation about quantum mechanics in the Wizarding World back into the limelight. In this essay, I will attempt to make sense of the way Time Travel in Harry’s world actually works, and give a bit of explanation to the way timelines are altered. This is in no way an exhaustive lesson in theories of Quantum Mechanics, I am not a physicist, just a big Sci-Fi and Fantasy fan eager to start a discussion on the way Time Travel works in these stories I love.
There is no way to have a thorough conversation on this topic without talking about the events in the story of Cursed Child, so if you haven’t read or seen it yet, and you don’t want to be spoiled, you should read the book before reading this essay.
Seventeen years later, the debate rages on
In a recent post here on the Lexicon, Steve pointed out again the long time official answer as to why Harry never went back in time to save insert name here:
- Doing so is very dangerous, resulting in death of the traveler or something much worse
- Would be very difficult as all the time turners could only go back in time a maximum of 5 hours, severely limiting the window that could be used to save someone
- Was impossible after OP36 because the time turners were all destroyed in the Battle of the Department of Mysteries.
That essay was written shortly before Cursed Child came out, and quickly spawned a lively debate in the Pensieve regarding Time Travel in Harry Potter’s world. Perhaps Steve used an Experimental Time Turner to jump back and write such a timely article right as the whole conversation about time travel was about to become super relevant to fans once again.
In the play, Harry’s son Albus, and his best friend Scorpius Malfoy decide to use an Experimental Time Turner to travel back in time to the Triwizard Tournament to save Cedric Diggory from his untimely demise. This is of course a crazy idea as it is a major change in the timeline with lasting repercussions throughout recent wizarding history. But this is not why some fans are up-in-arms about the story. Many fans are upset because based on the one time we visibly see time travel in the novels, it seems like it shouldn’t be possible to actually change time at all.
Following Lupin’s transformation into werewolf form and Wormtail’s escape in PA20 Harry is attacked by Dementors near the lake. The Dementors were prepared to administer the Dementor’s Kiss to finish him off when he was saved by the casting of a patronus from the other side of the lake, Harry sees the caster, who looks like his father. A short while later Harry and Hermione use Hermione’s Ministry Time Turner to travel back in time 3 hours to save Buckbeak and Sirius from being executed. After waiting and hoping to see his father appear, Harry realizes that the person he saw cast the Patronus was himself, and then casts the patronus, saving his past self from the Dementor’s Kiss (PA21).
Fans for ages have used this experience as “proof” that in the Harry Potter Universe, you cannot actually change time, you can only be a participant in it. The fact that Harry witnesses himself doing something he hasn’t done yet is what is known as a Predestination Paradox, or Causal Loop. Rather than try to fully explain a Causal Loop, I’m going to give you the example by renowned theoretical astrophysicist and cosmologist Igor Dmitriyevich Novikov:
the billiard ball moves in a path towards a time machine, and the future self of the billiard ball emerges from the time machine before its past self enters it, giving its past self a glancing blow, altering the past ball’s path and causing it to enter the time machine at an angle that would cause its future self to strike its past self the very glancing blow that altered its path.1Wikipedia contributors. “Causal loop.” Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 7 Jul. 2016. Web. 10 Aug. 2016.
The basic gist is that Harry was saved by his future self, had he not been saved by his future self, he would have had his soul sucked out and would not have been available to travel back in time to save himself in the first place. What makes this a paradox is that the first time around, before any time travel happened, Harry would have died due to the Dementor’s Kiss before he ever had a chance to go back in time and protect himself.
The problem with this is, it is not actually consistent with Hermione’s description of the effects of time travel in the very same chapter:
“Don’t you see? Professor McGonagall told me what awful things have happened when wizards have meddled with time. . . . Loads of them ended up killing their past or future selves by mistake!” (PA21)
What McGonagall described to Hermione, and she in turn was describing to Harry, is what is known as the grandfather paradox, the other great temporal paradox people debate and theorize about. Unlike the predestination paradox where effect precedes cause, in the grandfather paradox effect can in effect prevent cause. To keep with the billiard ball example, here is an example by theoretical physicist Joseph Polchinksi:
a billiard ball heading towards a time machine; the ball’s older self emerges from the time machine and strikes its younger self so its younger self never enters the time machine. 2Wikipedia contributors. “Grandfather Paradox.” Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 1 Dec. 2007. Web. 10 Aug. 2016.
The classic example of the grandfather paradox is an individual going back in time and murdering his own grandfather, thereby preventing his own birth. Since this person was never born, they were never able to travel back in time in the first place, and thus couldn’t kill their own grandfather. Thus creating a paradox.
In Cursed Child, Albus Potter goes back in time and sets in motion a sequence of events that culminates in Voldemort winning the Battle of Hogwarts instead of losing it, resulting in the death of his own father Harry before Harry could have a chance to marry Ginny. Albus effectively wiped himself out of existence, but once he had erased himself, he had no opportunity to go back in time and cause those events in the first place.
The common argument to solve the paradox, is that every time the past is changed, a new alternate timeline is created, while the original timeline continues the way it was before any change in the timeline took place.
Which is it?
Paradoxes are by their very nature difficult to talk about. The Oxford Dictionary defines a paradox as:
A statement or proposition which, despite sound (or apparently sound) reasoning from acceptable premises, leads to a conclusion that seems logically unacceptable or self-contradictory” 3“paradox, n. and adj.” OED Online. Oxford University Press, June 2016. Web. 10 August 2016.
How can the saving of Harry be reliant on him going back in time in the first place? How can someone prevent their own birth and still be able to actually prevent their own birth? In both cases the paradox would seem to destroy itself.
So which is it, can effect precede cause? Can an effect prevent the cause from happening in the first place? Can both temporal problems work? Is it possible to have a time travel model that can have both predestination paradoxes and grandfather paradoxes?
Time Travel in Cursed Child
Time travel in Cursed Child, creates several Grandfather Paradoxes, matching McGonagall and Hermione’s warning from PA21, and does not appear to follow the example of a causal loop at all.
When Albus and Scorpius travel back to the first task disguised as Durmstrang students in an attempt to cause him to lose the tournament (in order to save his life), they are spotted by the Hermione of the time. Hermione then becomes distrustful of Krum, rejects his invitation to attend the Yule Ball with him, instead going to the ball with Ron as friends. Without the whole Krum jealousy, Ron never falls in love with Hermione, and they don’t get married.
As Cedric still dies, they try again, travelling back to the second task preventing Cedric from completing the task. This does save his life, but the clear sabotage doesn’t sit well with him, and he eventually becomes a death eater, killing Neville during the Battle of Hogwarts. In this timeline, Voldemort kills Harry and rises to full power, Albus Potter is never born, and Scorpius is left with the difficult task of undoing the damage caused by their meddling in time.
The Timelines in Cursed Child
After reading the book, I quickly realized I needed to draw out the timelines in order to make sense of them all. When all drawn out, I came up with between 7 or 8 timelines in the book (depending on if you see the last 2 timelines as a single timeline or not). In order to make sense of them, we’ve come up with the following names for them:
- Prime: The Original timeline, or at least the original timeline as of the end of Deathly Hallows (more on that in a bit)
- Roseless: The first changed timeline, in which Ron and Hermione never get married, and Rose is never born4Scorpius is devastated by this, contrary to the belief of shippers it is possible for Albus and Scorpius to have a close relationship without it becoming romantic, just as it was possible for Harry and Hermione to have a close relationship without it becoming romantic.
- Scorpion King: the second changed timeline5Hat tip to my wife Barbara for pointing out this is a great name for that timeline, in which Albus was never born, Draco is head of Magical Law-Enforcement, and Scorpius (known as the Scorpion King) is an athletic jerk who loves torturing mudbloods.
- Half-Repaired: The third changed timeline, in which Hermione once again goes to the ball with Krum (and so presumably may have married Ron), but Albus is still never born, and Scorpius is still the Scorpion King
- Repaired: The fourth changed timeline, main events are repaired to the prime timeline state, still technically an alternate timeline .
- Delphi’s Failure: Delphi goes back in time and attempts to stop Cedric from winning the tournament with Harry, in an attempt to restore the Scorpion King timeline. She fails to do so, but there is still a minor change in that Cedric sees Albus, Scorpius and Delphi, thinking they are one of the challenges of the maze.
- Message in a Blanket: Trapped in the past the day before Voldemort’s original downfall, Albus and Scorpius encode a message on Harry’s baby blanket in hopes of being rescued by their parents.
- The Duel in Godric’s Hollow: Where the original trio, plus McGonagall, Ginny, and Draco travel back in time to rescue Albus and Scorpius, and prevent Delphi from… saving Harry’s Mom.
Timelines 5 through 8 all are basically the same as the Prime timeline in any way that actually matters, but each of the 7 alternate timelines has differences from the one that preceded it (some much more drastic than others).
The changes in these timelines are consistent with the description of Time Travel on Pottermore (Pm), as well as the warning McGonagall gives Hermione which she then gives to Harry. The only thing they are not consistent with, is the event where the harry of PA20 sees the patronus cast by the Harry of PA21. That is the one and only example in canon of a causal loop, with far more examples of grandfather paradoxes prevalent in the story.
Both are True
Now the real world explanation is simply that the inconsistency in temporal paradoxes probably didn’t occur to J.K. Rowling who saw both paradoxes as possible. Are there ways we can make it where time travel can be used both in a causal loop sense and in a manner that allows for changes in the timeline? There are a few ways we can make sense of it. Let’s go through 3 possible theories as to how both methods of time travel can be true.
Safeguards in Ministry Time-Turners
The Pottermore article indicates the 5 hour rule
“As our investigations currently stand, the longest period that be relived without the possibility of serious harm to the traveller or to time itself is around five hours. We have been able to encase single Hour-Reversal Charms, which are unstable and benefit from containment, in small, enchanted hour-glasses that may be worn around a witch or wizards neck and revolved according to the number of hours the user wishes to relive.” (Pm)
It also then indicates that the ministry only operates time turners under strict guidelines:
Even the use of the very limited amount of Time-Turners at the Ministry’s disposal is hedged around with hundreds of laws. While not as potentially dangerous as skipping five centuries, the reuse of a single hour can still have dramatic consequences and the Ministry of Magic seeks the strictest guarantees if it permits the use of these rare and powerful objects. It would surprise most of the magical community to know that Time Turners are generally only used to solve the most trivial problems of time-management and never for greater or more important purposes, because, as Saul Croaker tells us, “just as the human mind cannot comprehend time, so it cannot comprehend the damage that will ensue if we presume to tamper with its laws.”
The Ministry Time Turners have safeguards in place in order to prevent time travel. While most of these seem to be legal, some appear to be built into the time turner itself. The Ministry Time-Turner is an encased Single Hour-Reversal Charm which is why each turn only goes back a single hour. Also note the charm is only a reversal, there is no way to spin ministry time turners the opposite direction in order to return to the present. It is distinctly possible the Hour-Reversal charm is a very specific form of time travel that requires stable causal loops, and that attempts to alter time, thus creating a paradox, would somehow be prevented.
As both the Experimental Time Turner used by Albus and Scorpius and the Golden Time Turner used by Harry and Draco both take you back into the past, and then return you, and as they can take you back far further than a few hours, they clearly do not contain “Single Hour-Reversal Charms” and as such may not ascribe to the same rules of temporal mechanics that the Ministry Time-Turner does.
The problem with this theory is it precludes free-will. Harry wants to barge into Hagrid’s hut and snatch Scabbers before he has a chance to escape. It is Hermione who prevents him from doing this, not any form of magical prevention. What would have happened had she not prevented him from attempting to change time at this juncture? We don’t know, but if we are to believe that there are safeguards in place that enforce time act as a single stream, it would have to be predestined that Harry could not try, in other words, he has no free will.
The concept of “Return”
As mentioned above, the Ministry Time-Turner does not have a concept of “return.” When you travel into the past using one of these necklaces you must wait out time until you arrive back where you came from. When changes in the timeline from Cursed Child seem to not set themselves until the travelers return to their point of origin.
As mentioned above the second time jump resulted in a change of timeline that erased Albus from history. Yet the traveling Albus did not disappear until they traveled back to the present. Since the Single Hour-Reversal Charm has no return, changes in the timeline might set immediately instead of upon completion of the journey, thus resulting in a more direct flow. This actually matches the alternate timelines argument people use to resolve grandfather paradoxes. Going into the past creates a new time thread, but until you attempt to return to your point of origin, you are still the you from the original timeline.6An interesting side note is that while Albus doesn’t vanish until he attempts to return to the present, when they mark the blanket, that time stream seems to set immediately. The notable difference here is that in this final alteration, the experimental time turner had been destroyed, preventing Albus from returning to the present at all. It is possible that once the return became impossible, time became a single flow once again.
It isn’t a Causal Loop at all
My personal theory is that we do not see a Causal Loop at all in PA20- PA21 at all, just something that resembles one. My theory stems from the premise that the Harry who sees himself cast the patronus is actually the Harry from the second timeline.
It is logical that there was an original timeline with no time travel at all in which Harry does not see himself cast the patronus. I have to assume that in this original timeline something else prevented Harry from having his Soul sucked out, otherwise he never would have been able to travel back in time. We then have a second timeline when he does. In this second timeline, the Harry from the original timeline decides for some reason to cast the Patronus and save his younger self from a fate worse than death, the Harry of the second timeline sees himself (thinking it is his father because he knows nothing of time travel yet), and then travels back in time creating a third time stream where he realizes his “dad” was really him, and completes the cycle.
There is actually some evidence to support this theory. The Harry hiding in the bushes waiting for his father becomes confused when dad doesn’t show up. I believe that is because this second Harry casts the patronus later than the original Harry did. It is even possible that the now third Harry was already unconscious at this point and didn’t even see the second Harry casting the patronus, thus resulting in an even more different fourth timeline where Harry no longer expects to see his father in the bushes.
Why would the first Harry choose to violate the temporal prime directive7I had to stick in a little Star Trek reference somewhere didn’t I? Actually there’s another one before this one but you probably didn’t notice it. to cast the first patronus when he would have already known that things would be ok without casting it? My theory would be that this first Harry, who we don’t really see had already done something resulting in a change in the timeline, and felt that in this altered timeline his past self was in danger that he wasn’t originally in (the whole “Loads of them ended up killing their past or future selves by mistake!” argument).
The logical change in the timeline is the arrival of the Dementors themselves. What is it that drew all of the dementors over to the lake that evening? It is possible they sensed Sirius, but Dementors generally only sense emotional state and Sirius had already changed into a dog. Perhaps they sensed a werewolf and decided to investigate, but why would they care?
My guess is that in the original timeline the Dementors didn’t attack Harry at all but Sirius is still captured. When this first Harry traveled into the past, he or Hermione did something that attracted the attention of the Dementors and when they go to attack his past self, he felt it important to save himself, perhaps realizing that he had clearly failed in his task and simply had to hope that his past self would get it right the second time.
Assuming that we do not see a Causal Loop in PA20-PA21, that implies that every time Hermione traveled back in time she was actually creating a separate timeline, one where she attended a class she didn’t attend in the previous timeline. This of course leads me to feel the need to do some math8as Steve poked-fun at me in Episode 17 of the podcast, “just shows what a nerd [I am]”.
How many timelines were created by our heroes during PA?
The difficulty of course is that we do not know Hermione’s complete class schedule, what we do know from PA6 is that at least one time during the week Hermione is scheduled to be in 3 classes at once (9 o’clock on Tuesdays, Divination, Muggle Studies, and Arithmancy). That means that at least once a week she needs to turn back time twice. We also know on Thursday, Hermione uses the time turner following Potions, because she vanishes and then Harry and Ron see her coming back up the stairs she just came up. We also know that by dropping 2 classes, she is able to give up the time turner at the end of the year.
Let’s therefore go with a conservative estimate of 3 turns a week at the start of the year and 2 turns a week following Easter. Estimating 35 school weeks 26 of which have the additional class, we come up with 96 times Hermione used the time turner for class. Add one more for the unauthorized alteration of time, one for my theoretical second loop through the same trip, and one for the original timeline and we come up with 98 different timelines9And you thought there were too many timelines in Cursed Child. As I said, this is a relatively conservative estimate based on the assumption of only 3 turns a week, we know that some classes are on multiple days, so it is possible the number is much higher than this.
Hermione’s age at the end of PA
An interesting side note while I was researching this essay was a question I found on stack overflow about how old Hermione would be at the end of Prisoner of Azkaban. Since Hermione is reliving hours throughout the year, she will have aged more than normal by the end of the year. Rather than come up with my own answer to this question, I for the most part agree with the math done by a bright individual named Kevin who came up with a total of 7 days, 12 hours of extra age. Be sure to check out his answer for the full breakdown.
There are still some temporal anomalies in Cursed Child that are hard to deal with. Here some temporal anomaly questions I’d love to see answered or fixed:
- Why is Delphi unaffected by the change in the timeline after the first jump? Delphi did not accompany Albus and Scorpius until the 5th jump, yet after Albus and Scorpius return from the first jump, she seems to be aware of the changes in the timeline.
- Why does Albus disappear in the second time jump? I touched on this one above. After all other jumps, Albus and Scorpius remain unaffected by the changes in the timeline, allowing them to notice the differences between the timelines and act accordingly. However when they manage to erase Albus from existence, Albus vanishes on return and comes back when that timeline is repaired.
So there you have it, my thoughts on the time travel in Prisoner of Azkaban and Cursed Child with my rationalization of how the time travel can still be consistent. But what do you think? Which of the 3 theories on how to make the time travel consistent do you believe? Perhaps you have a fourth theory that I didn’t even think of. Any theoretical physicists out there who want to expound on the simplistic explanations of Causal Loops and Grandfather Paradoxes? Please join me in the conversation in the Pensieve below and let me know what you think. I’m eager to read some other theories of temporal mechanics that I may not have thought of.
|↩1||Wikipedia contributors. “Causal loop.” Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 7 Jul. 2016. Web. 10 Aug. 2016.|
|↩2||Wikipedia contributors. “Grandfather Paradox.” Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 1 Dec. 2007. Web. 10 Aug. 2016.|
|↩3||“paradox, n. and adj.” OED Online. Oxford University Press, June 2016. Web. 10 August 2016.|
|↩4||Scorpius is devastated by this, contrary to the belief of shippers it is possible for Albus and Scorpius to have a close relationship without it becoming romantic, just as it was possible for Harry and Hermione to have a close relationship without it becoming romantic|
|↩5||Hat tip to my wife Barbara for pointing out this is a great name for that timeline|
|↩6||An interesting side note is that while Albus doesn’t vanish until he attempts to return to the present, when they mark the blanket, that time stream seems to set immediately. The notable difference here is that in this final alteration, the experimental time turner had been destroyed, preventing Albus from returning to the present at all. It is possible that once the return became impossible, time became a single flow once again.|
|↩7||I had to stick in a little Star Trek reference somewhere didn’t I? Actually there’s another one before this one but you probably didn’t notice it.|
|↩8||as Steve poked-fun at me in Episode 17 of the podcast, “just shows what a nerd [I am]”|
|↩9||And you thought there were too many timelines in Cursed Child|