What are the rules and logic for time travel set in Loki?

Question

In this article by Vanity Fair, Michael Waldron talks about the rules for time travel set by Loki (2021):

Marvel already made its case for how time travel works in Avengers: Endgame, but that, Waldron points out, “is the way the Avengers understand it.” With a TV show it’s a little different. “I was always very acutely aware of the fact that there’s a week between each of our episodes and these fans are going to do exactly what I would do, which is pick this apart. We wanted to create a time-travel logic that was so airtight it could sustain over six hours. There’s some time-travel sci-fi concepts here that I’m eager for my Rick and Morty colleagues to see.”

This article was posted before Loki began airing. Now that Loki has finished airing and we've seen the full breadth of time travel involved in the story, what are the specific rules and logic that govern time travel in the TV series (and most likely also the larger Marvel Cinematic Universe)?

Avengers: Endgame had that excellent scene where they laid out the rules for time travel as the Avengers understood it and said it doesn't work like the Back to the Future:

Professor Hulk: I don’t know why everyone believes that, but that isn’t true. Think about it: If you travel to the past, that past becomes your future, and your former present becomes the past! Which can’t now be changed by your new future!

The only other scene I remember in Avengers: Endgame was the one where the Ancient One talks about not destroying timelines:

Ancient One: I'm sorry, I can't help you, Bruce. If I give up the Time Stone to help your reality, I'm dooming my own.
Bruce Banner: With all due respect, I'm not sure that science really supports that.
Ancient One: The Infinity Stones create what you experience as the flow of time. Remove one stone and that flow splits. Now, this may benefit your reality but my new one, not so much. In this new branched reality, without our chief weapon against the forces of darkness, our world will be over run. Millions will suffer. So, tell me Doctor, can your science prevent all that?
Bruce Banner: No, but we can erase it. Because once we are done with the stones, we can return each one to it's own time line at the moment it was taken. So, chronologically, in that reality, they never left.

In Loki, our understanding of time travel was stretched across the whole TV series and we didn't get an easy two scene explanation of how time travel worked. The episode where Loki gets oriented has a video that explains time travel and timelines as the Time Variance Authority understands it, but we learn more about timelines and how time travel works as the series progresses.

How are the rules of time travel in Loki similar to those in Endgame, and how do they differ? What new rules are created in Loki? What are the specific time-travel logic rules that Michael Waldron talks about in the article with Vanity Fair? What do the rules for timelines and time travel look like for the future Marvel Cinematic Universe films?

Answer 1

There's an important part of the TVA and the "time travel" we see in Loki that the other answers here miss: it exists outside of time and space.

What did you envision as the look for "Loki"? There's so much going on, and the TVA has its own unique mix of styles that adds to Loki's and the viewers' disorientation.

[...]

Loki, for example, when he's arrested, he goes through these processing rooms. And Kasra was like, "Oh, we should make them cubes that he like falls through." And I thought that was so funny. And the idea of having the cat in one of them because I really wanted the TVA to feel like it was a real challenge because it's this office environment, but it exists outside of time and space. Something with me and Kasra was always talking about what how do we make this feel like a real, living, breathing office space.

_{Salon, The existential crisis of "Loki"}

As such it would mean that the "time travel" we see in Loki from the TVA isn't actually time travel. What is actually happening is the Minutemen are jumping in and out of the timeline. There's no contradiction to the time travel rules setup in Endgame because the actions we are seeing are different to inner timeline time travel.

The rules that were setup for Loki weren't necessarily for time travel but rather for timelines. How do timelines work? How does the multiverse work? How does the Sacred Timeline work? etc. That is what had to be airtight not time travel because when you think about it that isn't really what is happening in Loki.

Answer 2

It appears that the rules don’t necessarily differ, it has just been explored more in Loki.

Consider that in Endgame, like the scene described in your question, we know that the flow of time creates new branches when the stones are removed. In Loki, we learn that these branches can happen for another reason, and that is seemingly that variants can cause these branches. Now, how other variants than just Loki (or the other Loki variants) really began is the real question. I predict we will have more insight into that in Multiverse of Madness, and I suspect that either Mordo or Scarlet Witch have something to do with it, but I digress.

It seems that the rules haven’t changed, we’ve just learned more about the flow of time and the multiverse in general. I suspect we will continue to learn more and it will all be built off of the foundation established regarding time travel in Endgame.

Answer 3

In the MCU any time travel is to an identical parallel universe. Thus no paradoxes but the new universe may proceed slightly differently. However the Hulk explains this in the worst way possible and people who should know better still don't get it. (The 1990s series Time Trax had the same rules. As did 2000s Art Bell internet conspiracy John Titor)

Anyway Ant-man and Tony Stark realized that at the quantum realm level of reality time travel is possible - it's part of the landscape at that level. What Loki demonstrated is that it doesn't take macro level time travel events like Avengers on a mission to split a universe. It happens all the time everywhere. Note I don't think this is the multiverse interpretation of Quantum physics vs Copenhagen. Rather I think I just means some quantum realm time travel took place. Maybe a neutrino or a photon took a wormhole to the past.

This provides a degree of freedom for anyone- but particularly Lokis- to make a different choice than what the sacred timeline had.

What Loki established is that an organization will jump to these parallel universes and delete the parts they consider divergent to the timeline they want. Hulk couldn't know that. Once the TVA stopped doing that a Fractal multiverse takes off and gets out of control for the next phase of the MCU.