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At the beginning of Avengers: Endgame, there was exposition dialog explaining the rules of time travel this movie was working under.

Banner explained that modifying the past will not alter the present. This movie does NOT work like Back to the Future, and they even mentioned that specific film.

They said that going back into the past and removing the Infinity Stones would not change the effects they had on the present.

Taking an object from the past wouldn't remove it from the present, so you would expect the opposite to be true: going back in time and leaving an object behind would not be adding it to the present.

Then, right at the end:

Steve Rogers went back in time, and chose not to come back. The other characters then encountered a very old Steve Rogers.

Doesn't this break the rules?

Something was left behind in the past (Steve Rogers himself), but he should not have appeared in their timeline.

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    @NigelFds I sympathize with the script writers. The crucial thing they had to include was a handover of the shield from Steve Rogers, and to demonstrate that Steve lived a happy and fulfilled life. And they had to convey this in a way that had dramatic impact. I can understand if they chose to break the rules, and hope that we wouldn't notice or care that much :-) – Andrew Shepherd Apr 29 at 23:26
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    You assume the rules are correct in the first place. Banner didn't even figure out proper time travel, that was Tony, so why accept his off-the-cuff explanations as canonical rules? – zibadawa timmy Apr 30 at 3:31

11 Answers 11

30

Even though he was living his life with Peggy in the alternate timeline, once he was done he could probably have used another mechanism entirely to return to his own. For instance, his alternate timeline presumably has a sorcerer supreme who possesses the time stone, so he could go and ask for a favor, or might have simply made it part of the arrangement when he returns the time stone to the Ancient One in the first place.

This also allows him to provide Sam with a replacement for the shield destroyed by Thanos, which he apparently got by trading Mjolnir.

Edit:. this article basically confirms that he lived with Peggy in a branch timeline and used unspecified alternative means to get back to the 'prime' reality.

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    Using unspecified magic, he popped over to visit the narrative's timeline from his parallel timeline. I actually think you've provided the most plausible and consistent answer. – Andrew Shepherd Apr 26 at 6:10
  • Didn't cap have a fixed shied when he left? I am no sure now – Andrey Apr 28 at 3:23
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    @Andrey - he has the time stone. Presumably he's able to use it to reverse the status of the (broken) shield and return the stones to their original forms. – Valorum Apr 30 at 21:37
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    @Valorum or they can just hop to Wakanda where there is no limit of vibranium. It's not a big deal – Andrey May 1 at 14:26
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    Trading Mjolnir? Surely he needs to put the hammer back with the Aether or Thor's going to struggle for the rest of The Dark World. – OrangeDog May 4 at 15:23
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They said that going back into the past and removing the Infinity Stones would not change the effects they had on the present.

They were saying that you can't change the past, it's already happened so what your trying to alter is actually your future. Therefore Steve never changed his past but his future i.e. it is his post Tony snap that is old not pre Endgame self. So, for himself specifically he never changed the past.

There is another thing at play with time travel here though and that is the Infinity Stones, they hold the timeline together and keep it on the correct course. When you remove them from their timeline that's when alternate timelines are created as explained by The Ancient One. As The Infinity Stones are all within their correct timelines nothing changed and so history remained the same... apparently.

Chistopher Markus has said that Steve lived in the main timeline when he went back to the past and rejects the alternate timeline theory.

Fandango: So people are asking... Does this mean an old Captain America was hanging out this whole time while another Captain America was saving the day?

Christopher Markus: That is our theory. We are not experts on time travel, but the Ancient One specifically states that when you take an Infinity Stone out of a timeline it creates a new timeline. So Steve going back and just being there would not create a new timeline. So I reject the "Steve is in an alternate reality" theory.

I do believe that there is simply a period in world history from about '48 to now where there are two Steve Rogers. And anyway, for a large chunk of that one of them is frozen in ice. So it's not like they'd be running into each other.

Fandango, EXCLUSIVE INTERVIEW: THE 'AVENGERS ENDGAME' WRITERS BREAK DOWN THE BIGGEST MOMENTS IN THE MOVIE [SPOILERS!]

The only thing that could be different here is Peggy, her timeline would be potentially different if she spent her life married and with Steve rather than apart from him. So, this part might break the time travel rules with regards to Peggy but with regards to Steve I don't think it does.

I'll have to have more of a think about how to explain the Peggy part as all this sort of stuff hurts my head.

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    Holy moly, I think that Loki did something very bad :O – Dhon Joe Apr 25 at 12:40
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    I worked my brain into a pretzel thinking about Peggy, while answering this question: scifi.stackexchange.com/questions/210701. The theory that Peggy was married to Steve all along, in the prime timeline, is not contradicted by any on-screen info. If that were true, then Steve going back in time to rejoin her would not have altered her past, as that past had already occurred. Steve would merely be fulfilling her past. Although I originally thought that Steve's actions did not follow the time-travel rule set down in Endgame, I now think it's possible that the rule was followed. – Rob Apr 25 at 20:54
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    @Rob so when Peggy is gazing longingly at photos of Steve during Agent Carter, she’s actually just thinking “What does that perky bastard want for dinner tonight?” – Paul D. Waite Apr 26 at 10:08
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    @DhonJoe: “I think that Loki did something very bad” — as far as we know, Loki didn't remove the Space Stone from the timeline, as he didn't have access to time travel. – Paul D. Waite Apr 26 at 12:36
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    For The Good Place fans, Peggy and Steve's relationship happens in the dot above the i in Jeremy Bearimy. ;) – Paul Apr 27 at 16:25
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This article details a Q&A event in China with the Russo brothers.

Here's the relevant material. Quoted text is from the Russo brothers. Unquoted italicized text is by the author of gthe article:

So does that mean there are two Captain America’s in that alternate timeline?

“Yes, there were two Captain Americas in that reality. It’s just like what Hulk said, what happened in the past has already happened. If you go back to past, you simply created a new reality. The characters in this movie created a new timeline when they went back to the past, but it had no effect to the prime universe. What happened in the past 22 movies was still canon.”

That’s why Hulk promised The Ancient One that they’d return the Infinity Stones, so as not to mess up what she and the people in her reality considered their own prime timeline. Basically, this allows for multiple realities to exist in the Marvel Cinematic Universe, just as Marvel Comics has various realities that allow for different versions of characters to exists and eventually crossover and meet each other. The Russos explained it further by again referencing the final scene with Cap:

“Both Ancient One and Hulk were right. You can’t change the future by simply going back to past. But it’s possible to create a different alternate future. It’s not butterfly effect. Every decision you made in the past could potentially create a new timeline. For example, the old Cap at the end movie, he lived his married life in a different universe from the main one. He had to make another jump back to the main universe at the end to give the shield to Sam.”

So what did Steve Rogers have to do in order to time travel back to the primary timeline and give Sam Wilson his shield? That’s a question that we may get an answer to down the road. Because apparently there are still some details Anthony & Joe Russo aren’t willing to reveal. The directors were also asked when Steve Rogers traveled back to in order to dance with her, and they said:

“We can’t answer it for now, this is a story that happened in an alternate reality. Maybe it will be revealed in the future.”

4

It seems to be that yes, they broke the rules. However I will provide a backdoor for hand-waving.

See also: Why didn't this character die even though they shot this person in Avengers: Endgame?


I posted the following to "Is there a grandfather paradox in Endgame?"

As Banner explains, they cannot change their past:

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.

In other words, whatever change they do in the past will not ripple to the future. Thus, killing Past-Nebula does not translate to Present-Nebula being death.

In fact, they are two different realities. The Ancient One explains:

I'm sorry, I can't help you Bruce. If give up the time stone to help your reality I'm dooming my own.

So, how did the realities diverge? The Ancient One continues:

The infinity stones create what you experience as the flow of time, remove one of the stones and that flow splits.

The thing is, this already happened when Thanos destroyed the stones. That event allowed the realities to split.

End of the answer posted to "Is there a grandfather paradox in Endgame?"


The Ancient One continues:

Now, this may benefit your reality, but mine not so much. In this new branch reality, without our chief weapon against the forces of darkness, our world would be overrun, millions would suffer.

I strongly belive that the Ancient one is hinting that without the time stone they do not have the means to stop Dormmamu and his dark dimension from taking the universe.

Banner explains:

Once we have got the stone we can return each one to the moment they were taken. So, chronologically, they never left.

That being the motivation to return the stones to the moment from where they were taken.


However, if they are different realities, how did the old age Steve Rogers appear? First I have to back track... this is where they got the stones:

During the film they jumped to:

  • 1970: New Jersey. Steve and Tony got the Space tone.
  • 2012: New York. Scott got the mind stone, Bruce got the Time stone. Steve and Tony went to (see above).
  • 2013: Asgard. Rocket and Thor got the Reality stone.
  • 2014: Morag. Rhodey got the Power stone. Nebula, you know.
  • 2014: Vormir. Clint got the Soul stone. Natasha, you know.

They said they had to return the stones to exact moment they left. Which would mean they have to travel to each of the moments where they left the past to return to the present... they didn't do that.

At the end of the movie they send Steve Rogers back in time. However, he was carrying all of them. They would have all entered at the same point in the timeline.

If Steve Rogers first went to

  • 1970: he replaced the Space stone. The replacement would have been the Space tone that appears afterwards. Steve keeps the duplicates of the other stones.
  • 2012: he returned the time stone to The Ancient One. The replacement is the one that Doctor Strage got. Steve also gave the mind stone to Hydra. Hail Hydra! The replacement is one that gave power to Wanda and Pietro. Steve keeps the duplicates of the other stones.
  • 2013: he injected the Reality stone to Jane Foster. Steve keeps the duplicates of the other stones.
  • 2014: he left the Power stone in the ruins of Morag How he got there? The replacement was found by Peter. And Steve left the Soul stone in Vormir. Did he meet Red Skull? The replacement is what Thanos retrieved. Steve keeps the duplicates of the other stones.

Even if the did not leave the stones in the same place, at any moment in time where he could have gone first, there were duplicate stones. Regardless of which one was first, he must have gone to each of those moments to leave the stone until there he had none left.

That is my hand-waving: who knows what duplicate stones do to the flow of time?

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    There is no duplicate stones, Cap returned the stones at their places the same moment they were taken, so there is no duplicate. they just borrowed them – Dhon Joe Apr 26 at 14:13
  • I think the answers that claim that the final scene didn't break the rules of time travel have either misunderstood the situation or are making up excuses for the film's mistake. I think this answer addresses the actual question in the most factually accurate way. – Sigma Ori Apr 28 at 8:24
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    @DhonJoe In 1970 every stone except the space stone already exists. Cap shows up with every stone plus the space stone. Therefore every stone but the space stone has a duplicate. Similarly for any other ordering. – zibadawa timmy Apr 30 at 3:30
4

I think you misunderstood the ending: if it was the way you tell it, yes, it breaks its own time travel rules.

What I understood is that Captain America lived his life in the "other" past (other timeline) and then came back when he was old: I remember Bruce Banner saying something about Cap' having used its device to come back. That way, it doesn't break the rules.

Edit to clarify my point of view

Let's say our heroes are in universe A.

When they borrowed the stones from the past, it created another universe. A universe where Loki escaped after the battle of NY, where Sitwell thinks Cap' is with Hydra, where Thanos never snapped etc. Let's call it universe B.

At the end, Cap' went in the past to give back the stones in universe B, but in this universe, Loki still escaped, Thanos still never snapped etc. After getting old, Cap' came back in universe A but didn't "teleport" in the spot where they wait for him. He "teleported" a little further on the bench.

If he hadn't used his device to come back in the universe A, he would never be there.

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    Sam said: "Where is he?" Banner replied: "I don't know, he blew right by his timestamp, he should be...", Sam: "Get him back", Banner: "I'm trying", Sam: "Get him the hell back", Banner: "I'm trying...", Bucky: "Sam..." (old age captain america reveal) Bucky: "Go ahead". – Theraot Apr 25 at 14:17
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    I may remember incorrectly the discussion between Hulk and the others, or maybe the translation was bad (I've seen it in french). The discussion you posted, is it from your memory or do you have any source ? – LP154 Apr 26 at 13:31
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No, Banner says you can't change your own past. Not that you can't change the past. In Roger's case, his life followed a linear passage of time with no conflict. It just so happens that part of that path of that time overlapped from 1945 to 2019.

Rogers doesn't change his past life. There is no reason to believe that the older Rogers, from the future, hasn't been sitting at home with Peggy and his kids for the last several decades watching the world unfold.

0

The rules can still work if the following assumptions occured:

We are seeing 2 Realities A & B.

  1. The snap removed "Reality B" Thanos + army from "Reality A" and back to "Reality B" without memory of the events that occured.
  2. The scene from old man Rogers onwards is in "Reality B" NOT "Reality A"
  3. If we were to be shown the events of "Reality A" from the Rogers time jump onwards, Rogers would not have reappeared as an old man and they would have assumed that rogers chose to remain in "Reality B" thus "Reality A" continues without old man Rogers.

Easy

0

I see it as this: everything they’ve done up to 2024 in this film is already done on this MCU timeline and according to the rules established earlier in the film are set in stone in our present (hence why the plot revolves around time travel to retrieve the stones and return to the future and not to just kill Thanos in the past instead). So when Steve goes to return the stones, he stays in 1945 to live the life he missed out on with Peggy, and keeps his 1945 self from being frozen in the first place, allowing the past Steve Rogers to live a normal life, being older and deliver the message after everything enfolds. In this theory, it wouldn’t break the time travel rules set up earlier, and is sorta hinted at when Cap fights himself and the Bucky knowledge gets the attention of past Cap.

That’s my theory anyways.

0

Yes.

Spoiler Alert!!!

What Banner says about changing the past is true, but the end result is false.

Banner tells the group you can't change the past because it's already happened, so what you're trying to alter is actually your future. So if the group went back and stopped Thanos from wiping out half the Universe, then the events that led up to them going to the past would never have occurred, i.e., The Hitler Paradox. That's basically saying you can't change events that you were a part of, or events that affect you; e.g., I go back to 1989 to warn my parents about my sister dying from meningitis. I was conceived 2 months after she died, so preventing this would either erase me from existence, or create a Hitler Paradox because I'd have no reason to go back to the past; that is, unless I stabilise the timeline by creating a Predestination Paradox/Temporal Causality Loop by leaving a message in the past to be read by me in the new timeline instructing me to go back to September ’89 in April 2024, warn my parents, and leave the message in the past, therefore closing the loop.

The outcome of the movie has some major flaws because, despite retrieving the Infinity Stones from the past, several things happened in the past that would make it so that what we see at the end of the movie should be erased from existence. When 2014 Thanos and the 2014 Black Order are brought to 2023 by 2014 Nebula, they're all killed when Iron Man snaps his fingers and they never return to their own time period, so anything involving Thanos and the Black Order between 2014 and 2018 should no longer exist – such as Loki, Heimdall, and Gamora's deaths. Plus Steve staying in the past erases the events of Agent Carter, plus all the events involving Peggy Carter that we've seen throughout various films.

If this were "The Flash", I'd say Time Remnants. However, based on what happens in the end, we're either looking at a timeline that, once time catches up, it will cease to exist, or the timeline has been split. So much was changed in the past that a lot of what we've seen between phases 1-3 should no longer exist. Examples:

When Marty goes back to 1955 and stops his parents' first meeting he endangers his own existence. Fortunately their first meeting is a fluxed point, it's their first kiss at the Enchantment Under the Sea Dance that's the fixed point that ensures Marty's existence. So he was able to ensure it happened, and Marty returned to 1985 twenty minutes before his Time Remnant goes back in time. However due to his parents coming together under different circumstances, Marty returns to a future with a different history to the one that he knows due to his actions in the past, so in order to keep this new timeline intact the Doc has to ensure that Marty's Time Remnant goes back in time creating a Predestination Paradox/Temporal Causality Loop.

When Barry goes back in time to get information from Eobard Thawne, his plan to keep the Timeline safe goes wrong due to a Time Wraith. He ends up having to reveal himself to the past versions of his teammates, and his past self. Fortunately what Barry changes in the past are all fluxed points so they're no threat to the timeline. However he returns to a future different than the one he came from. He returns to the future moments after he left, but when he returns, Cisco, Caitlin, and a reformed Hartley Rathaway are there waiting to combat the Time Wraith. Again creating another Predestination Paradox/Temporal Causality Loop.

As for Avengers: Endgame, the changes that are made in the past don't effect the present in the slightest except Thanos learning what is destined to happen with the Infinity Stones.

2012:

Due to Lang causing Stark to go into cardiac arrest, Loki ends up escaping with the Space Stone, so how long would Thor have been stranded on Earth? And how long would it of been before Loki was captured? Without the Space Stone, the Asgardian's couldn't restore the Bifrost Bridge.

Steve whispering Hail HYDRA to all those HYDRA operatives in the elevator would cause a massive change to the timeline because HYDRA would be under the impression Steve is working for them, therefore changing the events of CA: TWS, such as the elevator fight scene. Battling his past self would've also been a massive change if it weren't for the fact Steve's past self wasn't under the impression that present Steve was Loki, and due to having his memory altered by the Mind Stone.

2014:

Due to Natasha sacrificing herself to gain the Soul Stone, how would the stone be returned once it's been claimed? Therefore this would erase Gamora's sacrifice from the timeline.

2023:

Nebula should not have been able to kill her past self because it's more or less the Grandfather Paradox. However she's a cyborg, so her body could no doubt be repaired.

As I mentioned before due to Stark erasing the 2014 version's of Thanos and the Black Order, everything involving Thanos and the Black Order from 2014 onwards should be erased from existence.

Again as I mentioned before, Steve remaining in the past should've erased the events of Agent Carter, plus the events involving Peggy Carter throughout various films. If the Avengers required Steve's help in the future this would be more or less like creating a Marvel version of the british sitcom Goodnight Sweetheart.

Conclusion:

Whatever tragedy you think you've just averted time will find a way to replace it, and trust me Barry, the next one... is gonna be much worse - Harrison Wells/Eobard Thawne.

Time is like cement it takes time to set - Rip Hunter.

Whenever you alter the past those changes affect the present and get compunded in the future - Barry Allen 2056.

TBQH after Tony snapped his fingers erasing Thanos and the Black Order, we should've been taken back to the start of Infinity War except this time it's not the Q-Ship hovering above New York, it's the Statesmen carrying the Asgardians, and the Sakaaran rebels therefore a new timeline has been set like cement. With the threat of Thanos averted, time can replace it with something greater in the future.

Edit #1: Extra information.

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    “several things happened in the past that would make it so that what we see at the end of the movie should be erased from existence” — that's assuming MCU time travel works how you think it does. Based on what we see in the movie, it does not actually work like that. – Paul D. Waite Apr 26 at 12:37
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    “the Time Travel used in Endgame IMO is no different to the Time Travel used in Back To The Future” — you remember the bit in the movie where they explicitly say it’s different to Back to the Future? – Paul D. Waite Apr 27 at 21:16
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    “Any changes in the past affect the present and the future” — except in Endgame, as Hulk says, they don’t. Do remember that time travel isn’t real. Each fictional work decides how this entirely fictional concept works. Endgame decided, and told you what it decided right there in the movie. Stewie f—ing Griffin is not involved. – Paul D. Waite Apr 28 at 18:22
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    “by leaving something in the past e.g. A letter containing important infotmation to be delivered at a certain time, on a certain date in the future would allow the team to create a Predestination Paradox/Temporal Causality Loop therefore stabilising the Timeline”. Oh, is that how time travel really works? Because I was under the impression that it’s a fictional construct, and therefore entirely up to the authors. – Paul D. Waite Apr 29 at 9:03
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    Ah, right sorry — so you're saying how you think it should have worked. Gotcha. – Paul D. Waite Apr 29 at 16:30
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No, it doesn’t violate its own rules.

The timeline we’ve experienced throughout the whole MCU could be the alternate timeline that Cap travelled to. All the events happen identically in this timeline.

In the original timeline, cap never shows up and Sam, Bucky, and Hulk don’t see him. He’s travelled to a second timeline but doesn’t interfere with any of the events that have led us to the same point.

-1

Yes I agree, this breaks timeline rules. To answer your question; if Captain America goes back in time to live in the past and returns as an old man, then everything he did from 2012 onwards (as a young man) never happened. Thus breaking the timeline. Therefore this is a major flaw at the end of the film. Time travel storylines are always messy and contain flaws. This is a huge one.

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