Avengers: Endgame is in no small part responsible for me writing The Chronoversal Compendium. I checked my timestamps and it turns out I started writing the weekend it came out. What was so special about Endgame that I needed to write a 400-page book? Two things: First off, it put time travel front and center in pop culture again. Endgame is, as of 2021.06.06, the top grossing movie of all time. Second, there was a surprising amount of dissent in discussions about how time travel worked in the story. Time travel was both popular and not well understood, a perfect topic for a textbook!
So, with MCU’s Loki premiering this week, I thought it would be good to talk about what started my journey into time travel and clear up the misconceptions around Avengers: Endgame. Loki’s head writer Michael Waldron has said that a ton of effort was put into solidifying the MCU’s rules for time travel in the series, and they expect it to stand up to scrutiny and answer any outstanding questions and controversies. I am anxious myself to see whether or not this is true, and I expect some of the following information to be overruled by the series, so this will probably change in the future. Anyways, the following is a rough excerpt from The Chronoversal Compendium, so you can think of it as a sneak peek! Lastly, if some of the time travel terms seem unfamiliar, check out my glossary post. Now, without further ado, onto our analysis.
Documenting the time travel events in Avengers: Endgame is pretty straightforward, since we see all but a few of the traversals on screen. Two key events tell us that time travel must be Branching: Loki escapes with the Space Stone in 2012 (leading to his series) and Thanos’ forces disappear from 2014 and are destroyed, never to return (we see Thanos die two different deaths). Therefore, time travel cannot be on a Single Static Timeline.
The most obvious timeline diagram would look something like this:
- We start with Ant-Man exiting the Quantum Realm (he entered it and got trapped at the end of Ant-Man and the Wasp). As he was going forward in time, he ends in the same timeline he started, the primary branch that becomes Timeline A.
- Hawkeye is sent back in time to test the time travel equipment, creating Timeline B
- The plan is formulated and the Avengers head to their various destinations
- Nebula, War Machine, Hawkeye, and Black Widow head back to 2014, branching into Timeline C.
- Rocket and Thor go to 2013, branching into Timeline D.
- Ant-Man, Iron Man, Hulk, and Captain America go to 2012, creating Timeline E.
- Thanks to a spinoff-related mishap, Iron Man and Cap have to go back to 1970, creating Timeline F.
- The Avengers (along with the evil Nebula-C) return to their native era, leaving Nebula-A on Timeline C.
- Nebula-C opens a tunnel back to Timeline C, and Thanos’ forces from Timeline C come pouring into Timeline A
- After a bunch of stuff happens, Captain America journeys back to each of the Timelines C-F and returns the Infinity Stones.
- After returning all the stones, Cap goes back to 1948, branching into Timeline G.
- After having lived a happy life, Cap returns to Timeline A to pass the torch.
The branching is pretty straightforward, but there are also a few outstanding questions, narratively. First, there is a curious issue of how much time passes in different timelines between trips. Hulk’s discussion with the Ancient One indicates that very little time will pass in any given branch timeline between the Stones being taken and being returned. A fair amount of time passes in Timeline A between the stones being acquired, the battle with Thanos, Iron Man’s funeral, and Cap finally leaving to take them back. Conversely, several decades elapse in Timeline G before Cap returns to Timeline A, only a few seconds after he left. We can conclude that time travel is possible to any future point on a previously visited timeline, provided there’s no intervening travel.1
When Hulk encounters the Ancient One in 2012, she tells him that removing the Infinity Stones from their native eras causes branches in time and Hulk responds that bringing them back eliminates the branches. The implication is that when Captain America returns the Infinity Stones, all of the extraneous timelines are cut off. However, the existence of the Loki series implies that Timeline E continues even after Captain America returns the Stones.2 If we are being generous, this scene describes one mechanism for timeline splitting–Infinity Stone removal–but it leaves open the possibility of other mechanisms, such as time travel.
What happens to the Captain America native to Timeline G, who was still frozen in the ice in 1948? Well, since we don’t really see much of Timeline G this is left open. Clearly he doesn’t end up with the same Peggy Carter as Cap-A does. We might assume that Cap has him found at some point.
One thing I won’t really address in detail is the initial temporal experiments moving time through Ant-Man. The ability to age and de-age a person is largely outside the purview of what we would consider time travel, so we will attribute it to the misapplication of “quantum energy”, as seen in Ant-Man and the Wasp, where quantum energy can be used to create a variety of essentially magical effects, like as healing.
Chronoportation (how time travel is achieved) in Endgame is pretty flexible. The travelers enter the Quantum Realm, and with the proper equipment they can choose any time and location to exit from. For the most part, it seems to work like a time catapult, with a large platform serving as the launcher and the travelers being shot through time. They are then able to recall directly to the platform a few moments after having departed.
However, in the case of Iron Man and Captain America going to 1970, as well as Cap’s various traversals to return the Infinity Stones, there are definite cases where the platform is not needed for departure. The platform was involved in the initial departure from Timeline A for all these journeys, but subsequent traversals did not use it.
So what was the purpose of the platform? In the name of plausible deniability, we aren’t told, but we can speculate some possibilities:
- It is a power supply to open the initial tunnel. Subsequent traversals may then be less energy-intensive.
- It is a relay, like a positioning beacon, that the traveller can use to reorient themself. Tony describes the wristbands as quantum GPS, so it makes sense there would be a “satellite” for positioning. They might even use it as a quantum hub, so Tony and Cap return for a microsecond to Timeline A before swinging back out to Timeline F.
- It is used for coordination. Iron Man and Hulk had a good idea of how everything worked, so it offloaded the calculations to a central location for the less technical members.
- It helps modulate time travel order. We notice that Nebula-C has to contact Timeline C for Thanos-C to come to Timeline A. This is perhaps because it takes a long time for Thanos-C to prepare his forces to invade, and by that time, the Avengers would be returning the stones. By dialing in, Nebula can call later in Timeline C and bring Thanos before that happens.
In almost all instances, travelers returning to Timeline A arrive on the platform except for when Cap returns from Timeline G. This may be because the travelers used recall functionality to return to exactly where they came from. When Cap returned, he likely had the help of Hank Pym-G and Tony Stark-G to reprogram the time travel equipment.
Ripples, Not Waves
“Imagine time as a stream, right? And we are sticks that were thrown into it… The water… it moves around us”
“But it ends up in the same place”
“Right! Now too many sticks thrown into it would create what is called a dam and that’ll change the direction of the water forever and that is bad, so as long as we can avoid that we would be able to splash around a little bit.”
―Deke Shaw and Coulson
One interpretation of time travel in the MCU is the idea that time travel can lead back to the same timeline if the arrival doesn’t change anything, or more generally, anything big. If the arrival makes ripples, they fade; if it makes waves, they split. If the changes to the past don’t obviously change things, then it simply turns out that they didn’t. Hulk’s talk with the Ancient One implies that this is the case, largely due to the influence of the Infinity Stones.
Notably, the writers and directors of Endgame as well as Agents of SHIELD had varying ideas about this, which has led to a fair amount of consternation.
This presents us with a lot of potential problems, because it means that the same time travel mechanism can generate two different forms of time travel with no apparent reason for the difference. The technical workings are inconsistent with no apparent governing reason. It also implies that the timeline doesn’t split until the pivotal change happens (like a linchpin); but linear causation tells us the split must happen at the arrival since this event was set in motion by the arrival. Historical Inertia keeps the timeline in an unstable equilibrium that is easily broken.
Nevertheless, this seems to be the intention of Markus & McFeely in Avengers: Endgame, so I’ve reformatted the earlier diagram to match:
So we can see that Timelines C and E are the only timelines that differentiated enough to branch, while the rest of the traversals kept enough intact to still take place on Timeline A.
Time Travel in the Rest of the MCU
Judging primarily by revenue, Avengers: Endgame is the most well-known instance of time travel in the Marvel Cinematic Universe, but it is far from the only one. So here I’ll briefly touch on time travel as seen in the rest of the MCU.
We shouldn’t forget the first instance of time travel in the MCU is the sending of a person into the future. Captain America is frozen in ice for 70 years, cryogenically preserved, and experiencing nearly no proper time flow. This method, of course, would not work for a baseline human; his ability to withstand the cold is attributed to the Super Soldier Serum. We have a basic intrauniversal trip to the future on a single timeline.
Lest we forget, however, that James Buchanan Barnes was also the subject of similar time travel, being forcibly recruited into the Winter Soldier program and put into suspended animation over the years. In fact, since Bucky was captured before Cap went under, technically he was the first to experience this form of time travel.
The Time Stone itself functions differently from time travel through the Quantum Realm. As an Infinity Stone, it theoretically has enough energy to reshape the universe under its own power, as though by magic. In fact, we primarily see it being used by a mage–Dr. Strange. We see the Time Stone used in 3 ways: Retrieving the past or future state of an object, creating a time loop, and rewinding the universe.
The entire concept of time being concentrated into a solid ingot raises questions of what “time” means in the context of the MCU. As far as magic goes, the simplest explanation is that the Time Stone has enough power3 that it could simply reshape the universe as if time had changed. However, since it is said to specifically govern the actual flow of time in our universe, we should take it to mean that it can legitimately shuffle temporal states within the timeline. Without seeing how the overall structure of spacetime is affected, the result is apparently a Dynamic Timeline (the timeline is not set, it can be altered).
In effect, the object is isolated and its state is dragged to the present from a different point in the timeline to the present. The Book of Cagliostro and an apple are both affected by this ability. The past state being brought to the present doesn’t bring any causal irregularity. It is akin to using magic to repair the object or sending something into the future.
We don’t know how the future state is determined. We only see it briefly used on an apple before the scene is departed: several bites suddenly appear in the apple before it rapidly rots. Given how flexible the spell is, and using the Dynamic Timeline as a baseline it seems likely to be based on a version of the timeline that would happen if the spell had failed.
Similar to moving time through Ant-Man in Endgame, the effect is based on the application of a vast and little-understood power source, giving it a lot of leeway in what it is capable of.
Dr. Strange effectively creates a checkpoint and a trigger to return to the checkpoint. While the universe is physically returned to the state of the checkpoint, the memories of the beings involved are retained. Each iteration simply overwrites the timeline. It can be further noted that the universe in which this is enacted does not have the same conception of time, confusing Dormammu when our universe’s time is invoked.
Rewind & Pause
Time in the universe is reversed, although fundamental forces–e.g., gravity–seem to behave for those still moving forward. Proper time moves forward for those following the spell backward through time. Those who have been isolated with the spell replace the native versions–Dr. Strange, Wong, Mordo, and the Zealots don’t encounter copies of themselves in the past. Since the Zealots’ abilities are tied to a different dimension, they can resist this effect.
In Infinity War, Dr. Strange looks into 14,000,605 possible futures. We are not told in what manner he observes these futures, or how Thanos’ use of the Time Stone might impact Strange’s own. The Directors insinuate that the function is similar to the Time Loop function, in which Strange must personally experience them, in which case Strange was either exaggerating or has remarkable mental fortitude. The Ancient One does something similar, in which she looks into the future (though she apparently cannot see past her own death. Of course, the same might be true of Strange, depending on how we interpret “dusting”).
The simpler method to achieve this would be simply peering into the future. The sheer act of pulling information back in time would then create a new version of the timeline, so a new future could be viewed then. That would create a new timeline, and so on and so forth.
For example, Strange has plan A and looks into the future of version A of the timeline, where he sees they fail. So he comes up with a plan B4, leading to version B of the timeline. Now he looks into the future and sees Timeline B is also a failure. So he comes up with plan C, and so on.
Agents of S.H.I.E.L.D.
As of this writing, Agents of S.H.I.E.L.D. is the single longest franchise within the MCU, and it has a commensurate plethora of time travel in various forms. Thanos’ snap is never referenced, though. Perhaps this takes place on Timeline C.
Charles Hinton, Robin Hinton, and Raina are Inhuman prophets5. Their prophecies come to them passively, and each one occurs unerringly. We can surmise that these prophecies come from within their timelines, as though from a Single Static Timeline.
The Framework & Time Stream
The Framework is a simulation of the real world, à la The Matrix, with a few specific changes implemented, effecting an alternate timeline. There was explicitly magic involved in its creation6, so its accuracy could be arbitrarily high. If someone went back in time and made these changes, this could very well be identical to how the timeline would play out. This whole thing plays out in a supercomputer, so it isn’t really its own timeline, it’s a Phantom Timeline created by a hyper-extrapolator.
The Chronicoms had access to a computer with apparently similar predictive capabilities called the Time Stream. We don’t learn much about how it works, just that it was able to predict possible futures.
The Time Di’Alla
The most intricate time travel in S.H.I.E.L.D. is due to a white monolith called the Time Di’Alla. Adding in the Space and Creation Di’Allas, these monoliths come from an alternate dimension and have functions similar to Infinity Stones. We get to observe three separate timelines created by using the Time Di’Alla.
This is where we spent the majority of the series. Led by Robin’s prophecies, the team is sent to the future, where the Earth has been shattered by a gravitonium reaction after a battle between Quake and Graviton. They are met with information that insinuates they will make it back to the past, but that they cannot save the Earth–that they are stuck in a time loop on a single timeline.
As foreseen, they do make it back to the past. Things are apparently on course to repeat Timeline 1, however they do eventually manage to save the Earth. The events are somewhat confusing, as many shared events indicate we have not left Timeline 1, such as:
- Fitz and Simmons take several daredevil risks, including playing Russian roulette with poison, knowing they can’t die yet because they have yet to have a child like they do in the future.
- Yo-yo’s arms are chopped off, as they were from her future self.
- Yo-yo’s future self told them they’d already tried to change the future and it just ended up the same.
It appears the timeline is static, or at least elastic, until finally one decision (giving Quake power boost rather than trying to save Coulson) results in SHIELD triumphing over Graviton. One would think that if that could change, why couldn’t anything before it? If the timeline was Elastic, the biggest change would be the hardest to make rather than the easiest.
Ultimately it seems the team was in an unstable time loop. The ability to share information between timelines was limited, so while they may have thought they were changing things from the previous timeline, they might have only been making small changes. They had reached a nearly stable point, where the changes to the past resulted in nearly the same future, but the butterfly effect was enough that eventually one small change made it through to the end.
This implies the first few loops were probably very different from the final ones, and that the Di’Alla was able to branch timelines through Robin’s prophecies. Prophecy, being a form of time travel, should be able to branch the timeline when the information arrives. Her visions still come from a future, but the Di’Alla could branch the timeline before that future comes to pass.
SHIELD and the Chronicoms went back in time and battled to change the timeline, resulting in a timeline very different from the previous. Thanks to advances in quantum tech, the team is eventually able to travel between Timeline 3 and Timeline 2. This implies there are similarities between how the Di’Alla works and the Quantum Realm time travel from Endgame.
At one point when traveling through the Timestream (as in inter-temporal space, not to the Chroniton Time Stream device), the team gets trapped in a time loop. The mechanism is unclear, as it is based in the interactions of multiple kinds of supertech, though.
I have not watched The Runaways yet, but I intend to eventually. Sorry!
This all, of course, generally ignores what we are going to learn in Loki. Personally, I would anticipate branch timelines being cut off in some way. The events are incompatible, so they couldn’t exactly rejoin the main timeline, but perhaps their energy could be returned when the universes are destroyed. I guess we’ll just have to find out!
2021/ 07 14 Addendum: Now that Loki Season 1 has wrapped, I have an up-to-date post on its effect on the temporal mechanics of the MCU.
- In The Compendium I refer to this mechanism as quantum leader, because the events of a timeline aren’t set until they are observed or interacted with by a separate timeline.
- As mentioned before, the Loki series will likely overwrite some of this information.
- Being an Infinity Stone, it has ostensibly infinite power. In this context though, we mean “power” as in physical energy.
- Of course, he could also look into the future before he even comes up with the new plan to see what the new plan is going to be.
- Inhumans are a race of humans with superpowers (a little bit like the X-Men). This propensity is due to genetic engineering done by Kree millenia ago.
- The extent to which magic is involved is unclear. At the very least, AIDA was supernaturally inspired to build the Framework.