latteholic

If you're using Dark/Back to The Future's rules to judge the time travel, then yeah, indeed, it's bad, very bad even... nothing is consistent.
But if you're using Stargate SG-1's rules they work.

JG's trip to the past: he met with TY, but when he returned to his original timeline, he returned to TY who has no memory of ever meeting him in 2010 --> exactly as what OW said in his lecture because now there are 2 universes where TY remembered meeting him in 2010 (the person didn't get into an accident because he has been warned) and the original universe where she doesn't have that memory (the person still got into an accident and lose her/his leg)

The trip with TY is slightly different because now she is traveling to the future. So that universe will have 2 different futures from the moment she set foot in 2021 (but I won't get into the weeds with that one because that's adding more dimensions and will complicate things). The 2020-2021 timeline will not change in that universe.

Now it's exactly OW's example in again:
TY is now the person who knows that an accident will happen to her at a certain time in the past, so she can go back to the past, tell herself to avoid that accident (warn JG, etc). That results in a universe where the person didn't get into an accident (or JG didn't die on October 2020) and a universe where the person still got into an accident and lose her/his leg (JG was still killed in October 2020).
And this is why now TY can delete the picture on her/his phone, and JG can drop that USB without having to worry that these 2 things need to happen so that it's consistent with the 2021 future because they are now 2 different universes with different futures

I think if you look up the "many universes theorem", things prolly would make more sense. Director Oh explains how the mechanism works, but I feel that people have their own prior assumption on *how* the time travel *should* work and I think that makes it confusing.
It's like trying to calculate an area of a circle but forcing the formula of triangle area to calculate it and then hoping to make sense if it.

Actually here is a paper that talks about it: https://arxiv.org/pdf/1907.04178.pdf. Skip to page 52, under section 7.3 Multiple Timelines (don't worry this section doesn't have math, it just talks about how the multiple timelines work).

Yes! I think you nailed it when you said that she wasted time moping about a guy instead of exploring the mechanics of the time travel. That is a noble prize^2 experience right there and she completely wasted that! It's also frustrating to watch her crying in front of JG's niche when she already knew that she time traveled to the future and will return back to 2020, so she still have a chance to fix things/save him from dying. 30 minutes were wasted on her crying over something she can potentially change.

Whoever thought that it's a good idea to add romance into this should be eliminated from all parallel universes - because all it does is making the characters becoming one- dimensional, stereotyped melodrama leads.

Yes, I feel like the need to add romance to the story is now dictating how the characters behave towards certain situation or certain situation are written to fit that. This results in things starting to become inconsistent, and characters not behaving as what they were originally written to be. I missed those parts where TY would talk about her research and what she thinks of the physics implications of something, we don't have that anymore in the last 2 episodes, and we only have 6 episodes left and she still hasn't figured out how to open up a wormhole.

I think the topics that you brought up are important. But they are also very complicated concepts and require very careful consideration on the application otherwise they will lead to very confusing physics.

One thing to remember when you bring up paradox is that the law of physics doesn't allow for any paradox to happen. If a paradox happened then that indicates incomplete understanding/knowledge on the physics side. The Schrodinger Cat is precisely this. It's a thought experiment that is used to illustrate that if you try to apply the superposition principle (a particle having multiple states at the same time) from quantum physics theory on macroscopic objects and force them into one state when you make a measurement, then things get weird (there's also some important details about conscious observers that I'm skipping here for sake of brevity): you have a cat that both dead or alive inside a box, and you force that cat to be dead or alive when you open the box (a paradox). To make sense of that situation, a physicist then came up with the idea of many universes. In this case, the universe we are living in is not limited to 1 reality which forces the idea of the cat being in a limbo of both dead and alive, but instead, now you have 1 universe where the cat is already dead inside the box and another universe where the cat stays alive, thus removing the paradox of cat being both dead and alive at the same time.

In the context of this episode, we are now talking about a universe where JG died (2021) and JG survived (original universe). So in the same vein, the bootstrap paradox won't happen here, because the many universes interpretation now allows us to have a universe where JG dropped the USB (original universe), and another universe where he kept the USB (2021). One universe where TY deleted the picture of both of them (original universe), and another universe where she didn't delete the picture (2021).

I wish both female leads were not written mainly as these 2 jealous women fighting over 1 guy. At first, it was funny, but because they've been dragging this for far too long, it's just annoying. I really like Do Yeon from ep 9-10. From ep 9, I think we can learn why she comes across as too overbearing towards JG. Mostly because she's the one who's been teaching JG how to behave in social settings and that's why he became more socially aware/more polite compared to his 2010 character. She's like a nagging mom, but that is what she's been doing in the last 10 years. Also in both episodes, she puts every clue together and basically figured out the time travel/parallel universe by herself even when JG is holding information from her. It's a shame that they have written this smart female character only to reduce her into this typical jealous second lead for the sake of "forced/teased romance"

I agree, I'm just trying to say that different to the tracking device, their intention doesn't go against the mechanism here with the post-it notes, it's genuinely bad editing and prop mistakes which ended up confusing viewers.

I keep changing my idea of how this goes based on how the story proceeds. And I'm at a point where I don't think a time loop needs to happen for JG to be born. There already a version of him existing in at least one universe because TY already time-traveled, so 2020 TY doesn't need to time travel again, meets Min Hyuk in 2050 and returns to 1992 to give birth to JG. That part already happens in at least 1 universe.

Yes, they made a lot of bad editing choices here that ended up confusing viewers. In theory, TY shouldn't have that memory. But I don't know why they keep showing that scene where she's holding JG in her arms... maybe to remind the audience that that is what going to happen? Which is kinda insulting at this point, lol. They expect us to follow the mechanism of time travel, but then keep showing that scene in case we forgot what happened in 2020 (which could be another parallel universe/the future of the original universe)

yeap for that one I agree that that is definitely a plot hole

2:50 assuming this is when TY enters the house... I think they are forgetting the props
6:16 is bad editing and they were being inconsistent with the props. If you look at the scene, the color tone of the wall between 2020 and 2021 are different. They split the screen and were showing the wall in 2020 as JG put up the post-it notes, that it looked like TY is picking up the notes as they appear one by one (and they made another mistake here on the number of post-its). But in the end, they showed the 2020 wall with 3 post-it notes, which are then faded into the 2021 wall where TY picked up the remaining note. Then when JG left that house, they showed those post-it notes again, implying that those stayed on the wall for a year which was then read by TY in 2021. I watched this scene a couple of times because I couldn't believe they made this mistake XD. But when I watched it again, it's clearer that that was not their intention, but then the editing made it look like the post-it notes were delivered in real-time.

I think that's a result of bad editing, because when you watch the scene... they split it so that the wall covers the past (the color is more muted compared to the color tone in 2021, which matches the color tone in 2020). And when she returned to 2020 and compared notes, the post-it from the future already faded. Why the notes are still there and the furniture is covered up is another thing, but the fact that the post-it exists in 2020 and stays until 2021 doesn't mean the time travel mechanism is wrong? It's true that there are other plot holes as others mentioned such as the tracking device, but I think the post-it notes scene appears as a plot hole because of genuinely bad editing (which I don't think would cause a problem in another drama where time is linear and limited to 1 universe, because we are so accustomed to the concept that when you change something in the past than the future will change as well, e.g. Signal)

Also, I don't think they ever set the rules that you can't go back to your original universe after time traveling to another timeline/parallel universe? (I could have missed this part, and it would appreciate it if you can point me out the part where that was mentioned). I think so far, both JG and TY always return to their own original universe after traveling to the past/future (although TY's returning to 2020 is another unexplainable mechanism, it's more fantasy than sci-fi to me), clients from Alice also always return to their original universe, and at the beginning, MH returned to his original universe. They didn't explain this explicitly so far, but I tend to think of the wormhole as a bridge. It takes you to another universe in the first place but you always return to your original universe. It's only the time coordinate that changes.

I think another version of him exists in the 2010 universe that he time traveled to before and now another parallel version of him who's supposed to die in 2020 exists in the 2021 universe that TY time-traveled into.
But yes he won't exist in every parallel universe like everyone else.

I'm most likely missing something here, because I didn't pay enough attention during the scene that TY and JG were being dramatic together. but why is the post it notes scene is a plot hole? My understanding is that he wrote and attached that note in 2020 and they stayed there until 2021 when TY read them?

the bad editing is referring to the post it notes, because when TY came back to 2020, those post it notes are still there -> so it stays for a year, then was read by TY. But yeah the tracking part, I missed that... mostly because the crying scene becoming too annoying for me...

oh you are right! I didn't pay attention to that. I thought he went there because they were talking before about her visiting the house if she ever time-traveled to the future. Yeap! definitely a plot hole!
(I stopped paying attention when things got a bit dramatic XD)

at which part did that happen? What I know is that JG was just able to track TY when she was already returning to 2020 at the ossuary... They were not able to track her during that period when she was in 2021

One thing I'm trying to figure out: TY's real name is supposed to be Jang Tae Yi and not Yoon Tae Yi, right? If the 2050's Tae Yi is also Yoon Tae Yi, then that means she was also adopted by the current family...

she's talented in physics, but could be clueless in everything else.. She also doesn't have too many friends and so she barely has filters when talking/too blunt. But you're right, the directing could be done different. Those characteristics fit the reality, but it's not entertaining to watch, and it's the directing/writing fault to accentuate her weakness episode after episode after episode rather than her strength.