Headscratchers / Tenet

Time inversion regarding the dead

• If someone were to take a person who just died (or even died a long time ago, so long as the corpse is mostly intact) and put them in the inversion machine, would they come back to life? Or would it be a situation where the body heals but the "soul" or some equivalent remains dead?
  • Keep in mind that Kat still had a scar from being shot in the chest, the only thing that actually changed was that she didn't have poisoning. My guess is that someone would not come back to life.
  • No. When someone or something is inverted, it only moves backwards through time from an outside perspective; the object's subjective time still runs forward, from its point of view everything else is reversed. Thus, an inverted corpse would continue to decompose normally in its subjective, inverted, timeframe. It's only to an uninverted observer that it would appear to become 'fresher'.
    • In fact the movie contains a possible example of this. Neil dies while inverted, taking a bullet for the Protagonist. His corpse must also be inverted, and it was already there when Ives and the Protagonist arrived in the room. Assuming the body was never recovered (because the logistics of retrieving and then deliberately placing an inverted corpse at the site of its death are just too much to think about right now), it would have lain there for uninverted years, apparently decomposing in reverse, until eventually, as seen, it stands up (from the frame of reference of the uninverted characters) and takes the bullet that killed it.
• How did Protagonist have a "years-long" friendship with Neil? He either recruited Neil in the future, or in the past, and either of these would need one of them to spend years inverted - Protagonist to go back and recruit Neil, or Neil to get back to the events of the film... how does one spend years inverted?
  • There's a rather interesting theory that Neil is actually Kat's son. If that's the case, then The Protagonist could have watched over the boy as he grew up, befriended him once he was old enough, and formally recruited him into TENET when he was ready.
  • Being very bored most likely. Tenet most likely has a bunker or some such with a lot of inverted air, food and entertainment to pass the time. Not the best life for sure, but it's for the Greater good. However Neil probably could leave from time to time to play his part in some of Tenet's future operations, like saving the Protagonist's life back at the opera.

Duplicate Kats

• Are there now two Kats in the "present" at the end of the film? Which one do we see outside the school? Where is the other one? Are there two Protagonists as well?
  • There's only one Kat. She kills her husband, then dives off the ship. This version is the one that younger Kat saw. Presumably elder Kat stayed hidden until the point in time she went through the inverter and resumed her life. It's fair to say the Protagonist did something similar.
    • But if she shot Sator she couldn't have been shot by him herself, meaning she never would have gone through the turnstile in the first place...
    • The only thing that makes sense to me is that the Sator she shot was a formerly-inverted Sator who traveled back to before the holiday then uninverted to be shot by Kat.
    • That is correct. Kat says her husband vanished that particular day, from which the Protagonist and Neil conclude he was directing the opera attack (it was on the same day) and indeed we see his helicopter leave the yacht when older Kat arrives. Furthermore, the Sator she shoots is familiar with the Protagonist and recognizes the "despair or anger" line, proving he has already lived through the other events of the movie.
  • There is only 'one' Kat, but it is possible for multiple time-shifted instances of the same person to exist in the same 'clock-time'; for example, Kat sees herself jumping from the yacht, and there's a point where three instances of the Protagonist exist simultaneously at the Oslo freeport; his 'original' self, his future inverted self, and his future uninverted self.
  • Something I was wondering about that was whether past Kat would have to merge with future/present Kat. Past Kat would go through the same events as her future self, but when would Past Kat stop existing?
    • There would be no literal 'merging'. Past Kat, who unknowingly saw her future self jump from the yacht, would eventually invert and become the Future Kat that jumps from the yacht, and presumably Future Kat would step into Past Kat's place once Past Kat inverts, picking up where she left off, as it were.

Inverted car physics

• When cars are driven forwards in inverted time (the Protagonist's silver SAAB, for example), are they being driven in reverse gear? If so, how can they keep up with cars traveling in forward gears?
  • They would be in forward gears, they would only appear to be reversing due to the inversion. If you really want to melt your head, try to imagine what it would be like for an inverted driver to drive an uninverted car (as is the case with the Protagonist during the second half of the car chase, if I understand right)... but now I think about it the inverted Protagonist's car was facing the other way ('backwards' to the direction of travel) during the 'handoff', and since I don't think the car itself was inverted it would have to be in reverse gear and now I don't know what to think.
    • Then the silver SAAB must have been inverted as well, given its behavior during the forwards van heist.
    • Then I'm choosing to believe that the Saab was an inverted vehicle left behind by Sator and his goons, since they apparently have access to inverted vehicles, again as seen during the truck heist scene.
    • This would explain why when Sator drops his lighter on the gas the fire goes from it to the car as if they're going in the same direction in time, but then it wouldn't make sense for the Protagonist to suffer hypothermia rather than explosive death.
    • The movie also shows that inverted bullets have a severe poisonous effect when they hit non-inverted people and that inverted people are unable to breath normal air, so that's just another effect of the in-universe properties of inversion: it affects other things than just the course of time.

Storing inverted materials

• In a normal timeframe, where do inverted objects, such as those shown in storage early in the movie, come from? From the object's frame of reference, it goes through a stile and becomes inverted, then is collected and put into storage... but what happens to it after that? The inverted object has no point of origin in the normal past. Does it go on apparently travelling back in time indefinitely?
  • From the objects frame of reference, it’ll carry on until it rots away/degrades into nothing
    • The big question is, how was it put into storage from it's perspective? Invertedly (yes I’m using that) it was taken out of storage and put into the ground by Laura (assuming she found it) but Invertedly how did it get into storage? From normal time perspective, someone will have to take it out of storage and put it somewhere for it to end up returning to its point of origin in time.
  • I agree that yes, an inverted object will decay away in its own frame of reference (apparently appearing from nowhere in normal time), but yeah, the question is where would it be when it reverse-decays? A good example of this is the inverted bullet that almost hits the Protagonist during the opera raid. There is a visible bullet hole, and the bullet emerges from it. Has the hole been there with the bullet in it since the opera house was built? Did no-one notice or try to repair it? How did the hole even appear, since the building material isn't inverted?^note For that matter, why do bullet holes exist from inverted bullets in uninverted material? Effect follows cause normally for the material, and even if the bullet is inverted the impact happens at the same clock-time, so wouldn't the bullet hole appear 'normally' too, though possibly as a strange hole where the bullet effectively bursts out rather than slams in? Where, and this is the main point, was the bullet before it was in the hole, in the building? Could it have been in the ground, and then 'fallen', inverted, like the Protagonist 'dropping' the bullet, into the building material as the building was constructed?
    • And yes, it's also worth noting that someone would have to bring an inverted object to a time stile at some point for it to have arrived as an inverted object, in the same way that the characters who pass through a stile to invert will see their inverted self 'return' to the stile on the other side.
  • From what I can understand (and it's not much), an inverted object such as a bullet has its apparent impact appear once a person has the intention of using it for its desired goal. The bullet hole in the opera house chair only appeared immediately before the shooter had the intention of "firing" the gun. Of course, I could be completely wrong, but the movie basically tells you not to think that hard about it because honestly I don't think even Nolan understands how it works.

Catching a Bullet pt 1

• So when Laura shows the protagonist the wall, she has him pick up a gun and catch the bullet coming out of the all. But two problems present themselves. Firstly, how did the inverted bullet get in the wall in the first place. Assuming the wall is also inverted was it just built with bullet in it?
  • The bullet got in the wall when the Protagonist fired it. It will remain/has remained in the wall until/from the moment it will be/was extracted from it or decompose(d) to nothing.

Catching a Bullet pt 2

• So Laura has the protagonist catch the bullet, but how did she know he was the one who fired it and could thus catch it? Relatedly, who fired the bullet anyway? Presumably from the bullet's perspective the Protagonist fired it, but he never actually does, so how does this causality work out?
  • The protagonist did fire the bullet. He squeezed the trigger and everything. Laura "knew" he was the one who fired it because she told him to, if she hadn't told him to fire this particular bullet wouldn't have been fired in that particular hole.. Just like catching the bullet who inverse-fall. You do the action because you know you did/are going to do it.

Tenet, the organization

• So what is their setup? They recruit the protagonist and then provide him no assistance until later on while putting him up against their most dangerous target. He in fact tracks them (meaning Tenet high command) down himself via the bungee scene. What's their organization and what's their plan to run this operation?
  • According to Neil, the organization's motto is most likely "What's happened, happened.", so their operation procedure seems to just be 'do whatever they have to and hope for the best'. Since it's eventually revealed in the end that The Protagonist himself is the founder (or at least a high-ranking member) of the organization in the future, he probably sends specific instructions to his agents in the past to just recruit his past self for the mission and let everything solve itself, since he already knows his past self's going to succeed even with little assistance. Stable Time Loop ensures that. So there's no need to do anything more than what had already been done.

Returning Kat to Oslo

• Why did they need to return Kat to Oslo? It makes sense that they can't re-use Sator's turnstyle, but for the finale to take place they clearly had other turnstyles or they couldn't have inverted all of their troops.
  • "Need to know basis and you don't" + "what's happened happened" that Tenet has a turnstyle and its location are its most important secret so Ives wouldn't be willing to let Sator's wife know it just yet and Neil saw the Protagonist's future self at Oslo so he knew he'd go back there eventually and realized this was why.

Logic of inversion

• So let's consider the pane of glass in Oslo with the bullet holes in it. It was shot by the inverted protagonist so presumably those bullet holes exist throughout it's entire past. So they just appear when it was melted and made without anyone thinking to not install it. The same problem persists with the flipped Saab that would have had to sit on the highway for all of time before the action scene.
  • The movie clearly shows the cracks slowly forming over time after they enter the room, same with the cracked rearview mirror in the Tallinn chase, you weren't paying attention.
  • To try and break things down based on Neil's explanation that inversion involves going against the flow of time:
    • Think of space-time as we experience it as a river. Like the water in the river, space-time always moves forward.
    • An inverted individual firing an inverted bullet would be like a human throwing something against the flow of the river. It will make a splash that goes back a certain distance, but the effects will eventually disappear as the river keeps flowing.
    • So, the damage from the inverted bullet will travel back a way so that the hole (instead of existing all throughout the glass pane's past) seems to appear from out of nowhere some time before the actual hit happens. The hole and the damage will then disappear once we approach the moment the inverted individual pulls the trigger. IIRC, we see the cracks in the glass shrinking, showing that the damage is being reversed by the flow of time.
    • Also, remember the inverted Protagonist's stab wound. It suddenly appears while he's traveling in the cargo container back to Oslo, but disappears once the forward-moving Protagonist inflicts the wound.
    • But this makes no sense. If the injury is inflicted by a 'forwards' knife then the wound should be moving forwards on inverted Protagonist up util he became inverted in the future at which point it wither disappears—or continues onto non-inverted Protagonist. Either way he would have noticed at some point. If it is more about the direction of the injured party, then inverted Protagonist would have no wound until he was stabbed from his perspective. As we see the wound running forwards and go with this explanation then why does the wound appear so suddenly? This also calls into question the nature of the inverted shot Kat suffers, the injury having a linear progression on her no matter which way she is going, though Protagonist is stabbed while inverted and by himself, maybe making his injury of a different nature. but in both cases the attacker is inverted (though the status of the weapons is unclear.)
    • As for the Saab, it's not simply sitting on the highway waiting for events to happen. Think of it like a boat traveling up our river. The Protagonist is forcing the Saab against the stream. The moment the car flips and comes to a halt would be like the boat's engine cutting out. The momentum against the stream would stop and the boat gradually starts getting pushed back. What we're seeing when the forward-moving Protagonist approaches the flipped Saab is two opposing flows meeting (—> <—, as it were) and the greater flow of forward-moving time pushing ahead as we see the inverted actions playing out.
    • This implies that the car just, from a forwards perspective, appeared or faded into existence as a crash in the middle of the road? Or that the wreck somehow was pushed with the current into forwards time—which shouldn't be a thing at all as it would cause too many problems with the rest of the logic of inverted objects—and existed both as a moving car and a wreck at the same time and without actually meeting.
  • So, at the beginning of the scene, there are bullet holes in the glass pane. This troper thinks this is a mistake. From the point of view of the inverted bullet: the bullet is fired from the gun / the bullet flies from the gun to the glass pane / the bullet strikes the glass pane / Due to impact, there is a hole in the glass pane / the bullet falls to the ground. From the point of view of the glass pane: the bullet un-falls from the ground and strikes the glass pane / Due to impact, there is a hole in the glass pane / the bullet flies from the glass pane to the gun / the bullet is un-fired. The bullet hole appears because of the impact between the bullet and the glass pane. But the glass pane is not inverted, therefore the hole (effect) should appear AFTER impact (cause). Therefore, at the beginning of the scene, the glass pane should be intact. The bullet holes should appear only after impact, later in the scene. This is not what happens in the movie. In the movie, the bullet holes exist before impact and disappear after impact.
  • Even if it is the case that the inverted elements 'time out' after a certain distance back into the past, there's an issue - can an inverted item's interactions affect themselves? Take, for example, the Oslo scene in the vault. The bullets are in the glass when the protagonist enters. So, what if he shot the person coming out of the turnstile? The bullets would never be fired into the pane of glass, and there's a unstable time loop leading to a universe-destroying paradox. This should imply that there is no ability to change the timestream, and that everything that occurs is predestined - the bullets only hit the glass in those points because the protagonist saw where they'd hit, so wasn't caught by surprise by the guy coming out of the turnstile, etc. The problem with this is that the stakes of the film's plot are based on an inverted nuclear weapon... which could not be used. By the logic that we've already seen, if it was at any point going to be used, it would have already been used, and affected the past. You can see the same thing with the car chase - the protagonist couldn't have chosen not to be inverted and drive to that particular spot, because he already had done.
• So an inverted!bullet can be un-dropped but does that mean it cannot be dropped? If it is running backwards then a drop from its perspective is an un-drop from yours, but if you drop it then from its perspective you have un-dropped it, which defies physics in the same way if it were going forwards. If you put a inverted!bullet in a gun and try to fire it then does that mean it cannot be fired for the same reason? From its perspective it is being un-fired.
• Nobody else has raised this, and this wasn't answered in the movie, but if you invert a radioactive object, presumably from a "normal" perspective it is becoming *more* radioactive over time, not less. This has some pretty disturbing implications for the destabilizing effect of an inverted nuclear bomb. However, there is another secondary implication: Neil argues that the act of inversion and interacting with inverted objects causes them to ultimately push against the huge inertia of "normal" time's arrow: that is, over a long enough interval an inverted object could lose its inversion. As such, any would-be dirty bomb maker could take a spent nuclear fuel rod, invert it, and in doing so reverse all the beta decays to the point where the reactor had initially gone into steady-state operation, making the rod much more radioactive than should be, and have no fear of it going on forever as eventually the rod would "un-invert", and at that point the nefarious individual could handle the rod with all normal tools without fear of it suddenly jumping into their hand.
  • The film clearly establishes that an inverted object can only logically exist in the universe *prior* to the point at which it was inverted, that's why Sator inverting at Tallinn causes him to "vanish" from a red-entropy perspective, by definition a blue-entropy object can only progress from the future to the past the same way a red-entropy object can only progress from past to future. You can invert a sample of radioactive material but only if you could find both the red and blue versions of it and place them into opposite ends of the turnstile at the same time, at which point the material would appear to make a "u-turn" on the timeline and both versions would disappear from your present and future. So an inverted nuclear rod would indeed appear to increase in radioactivity, but only to a point where it matches the original uninverted sample, at which time it would deterministically have to have been inverted: It's not like its magically gaining more energy out of nowhere, the observed increase in radioactivity is just the same dissipation of energy it would otherwise experience just playing out in reverse from our perspective.

Where do inverted objects spatially go?

• So let's say I take a rock that is traveling through normal time and I put it in a turnstyle and invert it but not myself. From my perspective does the rock disappear? If not, would it have always existed traveling backwards meaning even while I put the rock into the turnstyle, it would already have been in there. I assume this has something to do with why the the going in and coming out parts of a turnstyle are always separated but still...
  • The Turnstile wouldn't invert the rock unless you found the future, inverted version of the rock and put it in the blue side of the turnstile at the same time that you put the original rock into the red side, that's why Ives has to explain the proving window to the Protag. A good way to visualize it would be an object traveling in a given direction along a timeline before "bouncing" off of a turnstile to begin going in the opposite direction instead: It's passing over the same portion of the same timeline, just at a different point in its personal worldline.
  • Do you remember the scene where Sator flees Ives and his men into the turnstyle and seems to disappear? The Protagonist asks where he went and Ives answers "into the past." If something enter a turnstyle they seem to disappear from the point of view of other people going forward in time, and 'inversely' if they enter the turnstyle while inverted, they seem to spring from nothing just like the Protagonist suddenly appeared to Neil and his older self in the Freeport. So, if someone were to put a rock in a turnstyle without going to they'd see the future version of the rock on the other side of the proving window when they arrive and it falling inside the turnstyle as they put it in and then it would seem to disappear.

Kat being a loose end

• In the ending, Priya tries to have Kat killed because she's a loose end who knows about the world-ending Algorithm, the same reason why Ives tries to kill The Protagonist and Neil after the final battle but decided to give them a Mercy Lead instead. Problem is, if Priya is indeed working for Tenet, which is founded by The Protagonist in the future, wouldn't The Protagonist's future self specifically instructs Priya to leave Kat alone? Granted, the fact that Priya is killed by The Protagonist's present self in the first place means she has no chance to make it out alive since Stable Time Loop is a thing in the setting, but let's say it wasn't or someone decides to Screw Destiny, couldn't The Protagonist's future self instructed Priya to leave Kat alone so nobody has to die needlessly? The Protagonist's present self has an excuse since he knows what he's doing with the Algorithm and knows better than to use it for nefarious purposes like Sator, and he could evade Ives's attempts to eliminate him with the skills he has. Kat is just a civilian who's only tied up in the whole plot because of her connection to Sator, so why is she considered a threat now that Sator is dead? To prevent the Greater-Scope Villain from getting to her again? She doesn't even know how time inversion works beyond what she went through during the story, and the pieces for the Algorithm isn't even with her. Tenet already had them secured. Moreover, even with Priya dead, there's no guarantee that Ives or any other Tenet agents would go after Kat again, forcing The Protagonist to basically fight his own agents to protect her even as he attempts to build the organization that he fights against in the meantime.
  • My guess is that Priya is acting on her own in the last scene, possibly defying the Protagonist’s orders and is being overzealous.

Sator's dead drops and the dual futures of inverted objects

• Here's a question that applies to most inversion (including the bullet in the demo), but most obviously to Sator's dead drops. At future time x, the dead drop is inverted and buried in Russia. For the dead drop, time runs opposite: (x-1), (x-2), so on. Up until time = 0 when it is unearthed by Sator, it has been in the ground. Now, (non-inverted) Sator and company unearth the dead drop at time = 0, and move it to the ship. So where is the dead drop at time = 1? time = 2? It is both in Sator's possession and buried which is a paradox.

• Put simply: an inverted object is traveling forward in time, it's future is our past. Any interaction with said object could not possibly shift it's trajectory since to do so would be to alter the objects already established path. Inverted objects should be entirely immovable and unalterable to someone is un-inverted.
  • You Already Changed the Past, any interaction by uninverted persons is already part of the object's timeline. the problem with your description of event is the idea that Sator and his men are taking the inverted gold out of the ground rather than putting it in. Here is how it most likely work: the future decide to send gold to Sator so they bring it to a turnstyle and invert it along with some people, to the uninverted future people, the gold and the inverted people seem to disappear (just like Sator seemed to disappear in Tallin), "then" the gold is buried where it travels back in time and from its point of view is picked up by Sator and his crew who bring it one of his turnstyles and uninvert it and then it is spent on whatever Sator wants to spend it on. From Sator's point of view both the inverted and uninverted gold appears at the turnstyle (just like how the Protagonist seemed to appear from nowhere in Oslo), the univerted gold is taken to be used as normal gold and the inverted one transits on his yacht and is put in the ground for the future. So at time=1 the inverted gold is inside the time capsule.
    • I think you're misunderstanding the problem slightly. Sator uninverted, so how can he possibly pick the gold up and take it to a turnstyle? In doing so he's moving forward in a period where the gold is already in the ground. Let's set it up practically. At 3:00 PM I invert a gold bar and bury it. At 2:00 PM Sator digs it up. We know that 2:00-3:00 it's buried, so at one time can Sator possibly move it and uninvert it?
    • Maybe I am misunderstanding something basic, but doesn't this just mean that there are two instances of the gold? At 2:00-3:00, the gold is both in the box AND in Sator's possession?
    • He picks up the inverted gold at the turnstyle and puts it in the ground (from the perspective of the gold he picks it up from the ground and brings it to the turnstyle). This does not work for the first one though. Beats me.
    • A possible workaround for this is that to retrieve the gold, Sator inverts, then goes to the location and digs it up, and then brings the gold and himself back to the turnstile to re-invert. From a non-inverted perspective, this would see Sator emerge from a turnstile in reverse, placing the gold into the ground, where it will remain until it is un-buried in the future and un-run through a turnstile. You are absolutely right about this, and naturally, it would make the entire plot of the film impossible to begin with.
    • And this workaround would work...if he had some means of getting a turnstyle before opening that capsule, but the flashback makes it clear that was not case (and how could it be?)
    • The papers included with the first drop he digs up could have included instructions to sell the gold to a trader, build the turnstyle with the profits and from then on use the turnstyle to invert for collecting dead drops (as suggested above). a later message from the future might have than told him to go back to the original trader and reacquire the original gold and bury it somewhere the future could retrieve it. Its a bit convoluted, but from the gold's point of view the future people mint the gold bars, and take it through a turnstyle so they can bury it, an 'old' Sator digs is up and gives it to a trader for a while, before a 'young' Sator retrieves it and buries it in the Stalsk-12.
    • Not a part of the movie, but this would probably have been so much easier if there was a mechanism that automatically uninverts objects if they were unearthed.

Inverted weapons, Inverted bullet holes

• I was thinking how does someone use inverted weapons, like Protagonist's bullet test. They could only be used in places where inverted bullet holes already existed? Or how do you place the bullet holes in advance? Which all doesn't sound practical. Then I realized this isn't really an issue if the user is also inverted as well. But that still doesn't answer the question, where did the bullet holes come from from normal time's perspective? Do cracks that just happen to look like bullet holes appear when the glass windows are made that will be involved in the fights in the future? And people just use it for construction? Why did nobody notice and wonder about the very big hole in the opera house and fix it?
  • This really stood out to me too. The logic of the film generally works if you assume there's absolutely nothing beyond what's shown in the film, but thinking of it with real world implications it falls apart. The only answer that really makes sense is yes, the wall in the opera house and any class shot was built with bullet holes in it from the start of its existence and no one ever bothered to fix it.
  • Answering my own question and based on this Reddit thread, seems like the best answer is that they just appear at some point before the cause. Sort of like how things can seemingly just appear from the turnstiles. And as if the physical effects of inverted objects are fighting back against normal flow of time, but gets stopped eventually.
  • As that Reddit thread points out that just leads to further questions. Namely if inverted things have an expiry date then how can things come from hundreds of years in the future. Even the people we see going back in time a week is more time then logic would dictate the bullet holes could exist without causing problems.

Overlaps in the turnstile

• When someone uses the turnstile there appears to be doubles. From the outside perspective wouldn't they "bump into each other" kinda like imagining your mirror self is blocking you when you push a mirror? From the user's perspective the instant your time reverses, aren't you perfectly overlapped with your present and past self down to the atomic level before you can separate and walk out into the separate rooms?
  • It's just a simple case of Time and Relative Dimensions in Space, two version enter at different ends of the machine from one perspective and exit at opposite ends from another.
  • In the movie, we see characters enter and exit turnstiles from different openings. This implies that the inversion process involves some sort of physical movement from entry to exit so that there won't be an overlap.
  • Furthermore, Ives tells Protagonist to watch the "Window of proof" before entering the turnstile, and not to enter the turnstile if he doesn't see his future/past self (dependent on the timeline) because if he doesn't see them, he won't be able to go back into the timeline he's currently in. So because he waited before going into the turnstile, there wouldn't be an overlap- remember, as Clemence's character says at the beginning of the film when describing the process of the inverted bullets, "from your point of view, you caught it, from the camera's point of view, you dropped it". Hence why the window is there, it's meant as something of an entropic mirror effect.

Inverted eyes and light

• Should it be possible for inverted people to see anything? As light won't be bouncing off objects to enter their eyes? Or even stranger, would photons be coming out of their eyes instead?
  • The light itself isn't inverted, so it would still bounce off objects (inverted objects or otherwise, light doesn't really have to care what motion and object has since it is practically instantaneous) and enter the eye, just like you can still catch a bullet. What happens inside the eye is much more questionable. I would say that once it's inside the eye it's treated like inverted light, but given we know oxygen that enters the body continues to function normally and is thus lethal. So idk.
  • On second thought, of course light from the sun won't be inverted. But as for the latter part, from a normal point of view, an inverted person's brain signals would travel back through the nerve to the eye, then create a backwards moving photon? Their line of sight would become visible? Is that right?
  • Answering my own question: It would seem that the only way this would work is the characters using inverted flashlights, just like needing inverted air. And they'd strictly only be able to see things flashed by it. But I understand that'd be so impractical for the characters and the audience.
  • I hope to have a big write up of tenet physics at some point. For light, the way you see is that light hits a pigment molecule and excites it, the excited molecule than sets off a nerve signal. To see using opposite time light, all that is needed is that the light can transfer energy to the pigment, once this happens, a nerve signal goes and you can see. A "flames cool you" situation is unlikely since less than excited pigments don't exist. The most likely hiccup is if "pigment excites magically like bullet damage appearing, than emits light" is the sequence. (So no actual answer, but the movie's physics isn't consistent) Most cameras use a similar "light excites something, which sends a signal" principle, so would work or not work along with eyes.

Inverting the world

• Why do the bad guys want to invert the entire world in the future? Sator suggests it's because of environmentalism to stop global warming or something...but how does that in any way make sense? You invert the world and you invert all the carbon already inside the world. The fact that it's a greenhouse effect is the entire point. It seems to me that inverting the entire planet would just have the effect of making space travel really weird to deal with, making meteorites really confusing (there'd be no reason for meteorites already on Earth to shoot out into space, and meteors approaching Earth wouldn't be effected until they reach Earth's atmosphere, where in they'd crash down, which from the perspective of the people would be them shooting up, but then there wouldn't be any impact craters at the time of inversion because it's occurring from space from before the inversion and oh dear I've gone crosseyed) and eventually in thirteen billion years the universe would end. Which isn't a great deal considering the universe is projected to live far far longer than it has up until this point.
  • I'm not sure if you’re reading too much into it or not, but from the sound of things in the movie the people of the future want to invert the earth to collide it with the uninverted earth. Remember the conversation about Anhilation? Sounds like they want to go that plantwide, the second the earth is inverted it will occupy the same timespace as the earth moments before it was inverted. Which creates a paradox for those in the future, if the earth was destroyed in their past then how can they exist in their present?
  • That makes no sense. If that were the case then everything inverted would collide with itself on the moment of invertion, unless those machines are capable of literally plucking them out of existence entirely and putting them in a different place. There must be a point, even if it's between the two machines where something has to go from x1, y1, z1, t+ to x1, y1, z1 t-.
  • Sator describes the future Earth as being all but destroyed due to climate change. The planet-wide inversion is a desperation move by the future parties funding Sator's operation, while Sator doesn't care if it works or annihilates humanity, since he's planning on taking his own life to set the inversion in motion.

Freeport, Round 2

• When the Protagonist goes to the freeport after he's been inverted, he's pushed under the metal door by an exploding jet engine. If the engine isn't inverted, shouldn't the shockwave be traveling in "reverse" and thus pull him closer instead of pushing him away? Also, when he grapples with his past self, why does he shoot the window? He knows by this point in the film that he shouldn't harm his past self for fear of causing a paradox, so... does he shoot because he knows he had to dodge the inverted bullets the first time he ran through this fight?
  • The Protagonist is inverted, not the word around him, it just seems that way to his inverted senses. Think of it like the bullet drop in the beginning of the movie: The Protagonist makes a reverse-dropping motion which causes him to catch the inverted bullet, the opposite of what would have happened were the bullet travelling in forward time; at the freeport the reactor explodes causing it to attract the inverted protagonist, the opposite of what would have happened were the Protagonist travelling in forward time. From the bullet point of view, the Protagonist dropped it; from the (inverted) Protagonist's perspective, the explosion pushed him in. As for the windows, muscle memory?
  • For the jet, a couple possibilities:
    • The jet spinning up may have sucked air in, which in reserve time means pushing the protagonist away.
    • The pressure wave from the explosion still pushes away from the engine, whether it is moving forward or backward.
  • For shooting the gun: the standard explanation is that he misses on purpose so that his forward self can't use it (Also why he disassembles it.) Presumably, he doesn't want to take a chance his normal self gets his hands on a loaded gun and fires, changing the timeline and injuring himself. Outside the story, inverted gunshots and disassembly make obvious to the audience that gas mask man is inverted: a pure hand to hand fight wouldn't be so clear.
  • Considering he kept missing his shots to the right, maybe he was trying to move the fight closer to the turnstyle so that he could jump into it.

Who Would Make &/ Use Such a Doomsday Weapon?

• So a scientist, for reasons never explained, invests a weapon that can end the world, possibly the universe, and possibly in all times simultaneously. The why is a question in itself but why was the weapon manufactured and not destroyed along with the notes on how it was made? Why was it not destroyed along with the notes but sent back in time—where other people could still use it? Somehow this weapon became known about along with its devastating consequences, but there are people who would use such a weapon? Sator is mad, but the organisations of the future seem to be a co-ordinated group who must all think this is a good idea—who could ever think that and why? Are they some kind of well funded doomsday cult?
  • As Neil explains, the future people helping Sator seem to think they have found a way to make the grandfather paradox work. Tenet believes that the algorithm being used would destroy all time but the people in the future believe their time would be preserved. As they're the ones who created the algorithm they may even have reasons to think so (maybe it does not work according to the exact same principles as the turnstyles) and are willing to bet on it. The scientist designed the algorithm possibly as a Manhattan project sort of thing and then got a Heel–Face Turn or just came up with the theory and wasn't expecting anyone to put it to practice. As for why she sent the thing in the past rather than just destroy it, it was for the same reason nobody ever destroys the Artifact of Doom, there wouldn't be a movie if they had.
    • If the future people think their Earth would be preserved then what is the point of destroying Earth in the past? Presumably they think their world won't be affected but isn't that the whole point? They are doing this to stop their future of a Earth ravaged by global warming, but even if Earth does survive then it would now be a version where the past never happened and maybe have no humans on it, defeating the purpose. Deleting history if it doesn't alter the present is pointless.
  • The comparison to the Manhattan Project only emphasizes how reckless this is, too. Contrary to what the film says (...can fiction please stop popularizing this really horrifying urban legend?), the Manhattan wouldn't proceed with the Trinity Test if there was even a 0.0003% chance of it igniting the atmosphere, and they proved (again, before the test) that it was effectively impossible. It's obviously just a "This needs to happen for the movie to exist" thing (same as the Artifact of Doom not getting destroyed), but trying to use the Manhattan Project to justify it only makes it more obvious how idiotically reckless the bad guys are being.
  • I assume that the physical components of the Algorithm are made of some future super-material which is practically indestructible, so the future scientist's best available option was to invert them all and hide them in the past.
  • As to why a future civilisation would want to invert the whole world: the reason given by Sator, reversing climate change, is invalid, as by reversing the planet then everyone in it would also be inverted, never experiencing from their point of view any reversal. The only possible reason would be to avoid an actual exo-planetarial threat - there's a planet-busting meteor headed for earth, or the sun exploding/extinguishing, or a nearby supernova, and inverting Earth is the only way they've found to avoid reaching that extinction event.
  • Inverting the Earth wouldn't help if the sun was exploding, as it would continue to orbit the same exploding sun. You'd need to invert the sun itself to stop that one.

The collected aftermath of the future war

• So early on we see the scientist's collection of junk that she thinks is the aftermath of a future war. But where does it all come from and where does it go? in the future, the object's past, the stuff must be used in order to be the aftermath of a war, so it must all leave the collection to get to the battlefield—but how? Do an inverted clean-up crew collect it all and take it to the gallery and put it all into place while the collector watches as, from her perspective, it is all suddenly taken away? If there is a clean-up crew then why not just invert them the right way and keep them dispose of them? And from a forwards perspective where does the collection come from? The objects won't be going anywhere by themselves so someone must move them as they are acquired, maybe bought on the black market due to their strange properties? But this is so strange my mind cannot even begin to contemplate where inverted!objects go in such a situation!
  • Their entropy is inverted (blue) so from a red-entropy perspective they begin to materialize out of the background disorder of wherever they ended up, then they get found by the CIA and stored at Barbara's lab, then the lab gets destroyed or whatever and the end up scattering out to wherever they got inverted in the future. From their own perspective they get built and inverted in the war, then they gte pulled back to the lab before the scientists take them and replace them wherever they were originally found to degrade and fall apart according to their own entropy.
  • Possibly Tenet's (or a future version's) people (possibly inverted) got them and stuck them in storage, so that the scientist(s?) in their past could examine the items and help prepare.

Plutonium location

• How does the plutonium get from the opera to the convoy? Did it get reclaimed by the government after the prologue?
  • Probably. It's possible Sator's attack got disrupted, and Ukrainians managed to grab the object, or the Protagonist's original contact was wrong and Ukrainians got to the CIA team.
    • The opening scene is deliberately very ambiguous as to who is fighting who, as its main purpose is actually to just establish the themes and tone of the "Twilight World" that the rest of the film is set in, the same way the opening scenes of Inception and the Dark Knight both set up elements of the plot without contributing anything directly.
• How does Sator get his hands on the plutonium after the Tallinn heist? The Protagonist steals it, inverted-Sator gives chase, the Protagonist tosses the box to inverted-Sator and the plutonium into the Saab driven by inverted-himself, he gets taken to Sator's building while inverted-him "drives back" to the building (leaving for the chase from inverted-his perspective) with the plutonium in the Saab, the Protagonist lies about the location of the plutonium to inverted-Sator, Sator arrives and inverts himself, and then the Protagonist inverts himself. Sator inverted himself in real time before the Protagonist, so in inverted time, he would've inverted himself after the Protagonist, and the inverted-Protagonist left in the Saab before inverted-Sator left the building or Sator arrived, so even if they'd known the plutonium was in the Saab, they couldn't have searched it.
  • The standard argument (Based on logic, and the backwards version of Sator's original radio call in the chase scene) is that Sator's non-inverted people pick up the piece after (in forward time) inverted Protagonist entered the inverted car. (One of the tropes here describes it.) Tenet agents inverted themselves, and probably left, so would not have been around to guard the car if they'd known.
• Or perhaps, combining the two... (Deep breath) Some of the armed forces in the prologue are Sator's men. They know about the existence of the plutonium from inverted-Sator coming back to that period, who already knows about the existence of it from the Protagonist telling him about it during the catamaran scene. They steal the plutonium and put it in the Algorithm. Once Tenet secures the Algorithm, they arrange for the plutonium to be given to the government, where it will be moved on that convoy and wind up in the Saab. After the Protagonist inverts himself for the Tallinn chase (a period we don't see in the movie), Tenet retrieves the plutonium from the Saab and secrets it away somewhere.
  • Problem with this model: The path of the plutonium in this version is Opera —> Algorithm/Stalsk —> Ukrainian government —> Talinn chase —> tenet. In this model, the plutonium is no longer of immediate concern to anyone, Sator doesn't need it (because he already had it from the opera and had a completed algorithm), Tenet either screwed up badly (If they needed to keep it hidden, giving it to Ukraine instead of hiding it was a bad mistake) or has no need to worry, as the rest of the algorithm is neutralized.
    • Your timeline is backwards, that segment of the Alg. was inverted from the Tallinn freeport and then taken back to Stalsk 12, the version at the Opera is essentially fresh off the turnstile after being inverted in the far future and inserted into Russian nuclear stockpiles to travel backwards to the present.
      • That's the movie timeline. The timeline the previous response is arguing with is the original bullet point in this section, not the original movie.

What actually arms the algorithm at the end?

• Tenet is trying to get the algorithm out from underground near the end, and Ives and Protag are still worried/consider Sator's death early when they are still underground and he dies. However, the algorithm does not activate at any point. So what actually sets it off, and what makes it safe? (It seems maybe the explosion is what sets it off if Sator's dead man switch has tripped, but they were still pretty close when the bomb blew up. container is another possibility, but the algorithm was never in it after Ives and Protag got to it.)
  • It does nothing in the present day. It's meant to be dug out of the explosion site and be used in the future. I imagine there's a big, complicated machine there with a hole for the completed Algorithm to be inserted into. Sator's death just wrote a message revealing the location of the explosion site. But even thinking in a timey-wimey way, it's not clear to me if the time of Sator's death and retrieving the Algorithm mattered.
• The movie certainly wants us to think Sator's death matters, but logically it shouldn't. His death sets off the nuke that records the position of where the algorithm is. Centuries later some future bad guys dig it up, use it in their timey machine and destroy reality. If at any point before the bad guys dig it up the protagonists move it, then it doesn't matter, the future bad guys can't use it. So logically they could have waited for Sator to die and all his mercenaries to burn through their pay checks and stop caring about this weird time conflict they've signed on for, and then dug it up and moved it still centuries before the future villains can use it. The movie tries to get out of it by saying that the weapon's power would transcend time and erase the past, but that also doesn't make sense as Sator's death wouldn't be a trigger that would cause the future bad guys to get the algorithm. All his death would do is cause them to check a specific place. So long as the protagonists fully intend to move it at some point, and eventually do, the future villains will never find it.
• The Algorithm isn't "armed", it isn't the superweapon itself its just a schematic for how to build such a weapon.

The fight in the climax

• In the climax, the red team and the blue team execute a temporal pincer operation. I saw the scene a couple of times, but I don't understand this: who were they fighting against? It made no sense to me what they were actually trying to achieve there. "Need to know and you don't", maybe?
  • They were fighting against Sator's men. The troper writing this agrees the scene wasn't shot well, including not showing much or any enemies on camera (I understood the overall battle actions after a YouTube video, though this doesn't fix some other issues. Grr, missed opportunities there....but this isn't a review). They were trying to fight their way to the opening of the tunnel where the Algorithm was, clear Sator's people nearby, and get the main team/strike team/whatever you call them in without anyone noticing.
    • The movie clearly establishes Rotas as having a large paramilitary component beefed up with funding and technology from the future. And most real life engagements rarely have anyone closer than a few dozen yards, just because everyone is too busy not getting shot to smile and wave for the camera or whatever it is you're complaining about doesn't mean its a bad scene.
  • The goal of the blue team was to gather information such as enemy locations, important locations, finding out they have a turnstile etc. The goal of the red team was to protect the blue team and using what they learned from them to execute the mission to supposedly disarm the bomb. The real goal of all this is just to have a distraction while Ives and Protagonist retrieve the Algorithm in secret. It was Sator's men they were fighting against. It'd make realistic sense that the enemy would make themselves hard to see in battle.
  • One line of dialogue that didn't get enough of a highlight or explanation was during the red team briefing, where Ives says (effectively) "For most of you, your mission is to fail to disarm the bomb." The vast majority of the red team and blue team soldiers were acting as if they were trying get to the location of the bomb that Sator was using to bury his dead-drop, so they could disarm it. Sator's men were fighting to prevent them from doing so, so that the dead drop would go as planned. At the end, both ends of Sator's temporal pincer movement were able to report that the bomb did go off and claim victory, not realising that it had only been cover for the Protagonist and Ives to swipe the algorithm out from under the bomb.

Stopping Kat's car

• Why didn't Kat hit the brakes on the car she was trapped in herself? She appeared to just have her hands bound, not tied to the chair she was in.
  • She was having trouble wiggling her way forward to hit the (lock? whatever was on the siderest), so brakes would have been harder to get to most likely.
    • The subtitles confirm that the button she pressed was for unlocking the doors.
  • I assumed that her hands were in fact tied to the chair, and we just couldn't see it very clearly.
  • The better question is why the protagonist bothered jumping across at all when they could've just had Neil drive in front of the vehicle's path and brake to gradually slow it to a stop.
  • If you believe that the cars were inverted during this scene, rather than just being driven by inverted drivers, then there's another possible explanation. If Kat had been able to try the brake of the inverted car (and maybe she did, in the time before the protagonist caught up with her) it would only have caused the car to go faster. (From the car's perspective: it was going at the speed the protagonist saw it at, and that was after a period of time with the brake depressed, so before then it must have been going even faster.)^note I'm not sure if that matches what was shown onscreen, but in any case any situation with inverted drivers driving non-inverted cars just doesn't work out in terms of the physics. The cars are reacting to the positions of their pedals, not the direction they are moved.

Chasing Sator

• The heroes and several agents of Tenet pass through Sator's turnstile, and the Protagonist decides to chase Sator on the highway. But couldn't the team just ambush Sator as he exits the turnstile? Since they went in the turnstile after him, in inverted time they would come out before him and therefore could just wait until he arrives and walks right into their hands.
  • Sator had a bunch of other guys there, Tenet probably doesn't want to risk fighting them.
  • Tenet capturing Satori also changes everything that happened before:. Satori wouldn't have been in the car to grab the case, and quite possibly wouldn't have gotten protag to the turnstile for interrogation, so a tenet that tried to capture him would have run into a different situation.

Neil's death unnecessary?

• After the final battle, Neil leaves to invert and unlock the gate for the heroes, which will lead to his death. But what's to stop the other heroes from just inverting too and going to the gate with him? With backup Neil would have far better odds of surviving instead of going there alone.
  • Because Neil already knows he has to die, "what's happened's happened." Plus he was only one out the three who'd be able to work the lock and Ives needed to make sure nobody could see the Alg. and live to tell the tale, if they tried to invert they would by Neil's logic get separated at some point before reaching the hypocenter at which point they would risk Ives or the Protag falling into Rotas hands.
  • A related question is why Neil uninverts after seeing Volkov instead of just telling the red team as planned, and maybe than heading into battle again to help them. Answer to the original headscratcher might be stable time loop, plus they know that they stopped Sator, so no point in possibly messing with timeline. Tenet selects agents willing to self sacrifice, making Neil's death more acceptable. (Obvious outside the movie answer is to create drama.)

Senses while inverted

• So the writers wanted to look smart and include how you can't breathe air while inverted so you need a supply of inverted air but this is rather selective. If you continue this line of logic then an inverted person shouldn't be able to see as light is still moving forward and unable to hit their eyes for them to see anything. The same goes for sound, the soundwaves are still moving forwards. Maybe air is different for how it interacts with the body but an inverted person should be blind and deaf as well as suffocating.
  • The physics of the movie is tricky and not consistent, or just weird, but it does make sense that inverted air wouldn't be breathable while inverted light and sound are fine. For air to be breathed, it has to be pushed into the lungs, have oxygen diffuse into the blood, diffuse into the cells, than chemically react with body stuff. All of these steps are tricky, breathing itself might be doable since expansion and contraction is symmetric, so oxygen would enter on the exhale, from the air's view the lungs are expanding. Diffusing is a straight up entropy based process, chemicals will spread out in their own time direction. An inverted person would see oxygen seeming to move from their cells into the air. What really messes up respiration is reacting inverted air with something else. Which way chemical reactions go is also straight up entropy based, so a chemical reaction between opposite time chemicals is hard to work out: whether it happens, how much energy it makes, whether that energy can be harvested. Quantum effects also come into play, which I don't understand well, it's possible a normal and reversed time atom or particles don't interact the same way same time ones do. A body might by able to use food and air inverted from itself with reactions happening in reverse and harvesting energy, but reverse time oxygen diffusing out of the body and doing who knows what inside is a good recipe for bad or weird things that don't produce usable energy.
    • Sound and light are simpler. Force and pressure seem to work fine inverted, so sound works, the pressure wave pushes against ear components as normal, but since the person is going backwards to the air, the pressure pattern seems reversed and you have backwards sound. Light probably works, but could go either way. Vision works by a photon hitting a chemical in the eye, being absorbed and exciting said chemical, than the excited chemical sets off a nerve signal. It might be an inverted person has the chemical get excited from nowhere and emit light, like the bullet holes/mirror/wound appearing from nothing. It is also possible that a nerve signal appears from nothing creating vision and moving towards the eye, or that the light seems to move backwards but still excited the eye, setting off a nerve signal and working normally from the person's view from there. Either way, they could see since a nerve signal existed.
    • Hopefully all that makes sense. Tenet's physics is clearly "what looks right on camera" and what works in story logic, the microscopic stuff or how energy, force, chemicals, etc. work wasn't as important.

Taking a sledgehammer to the Algorithm

• A formula translated into physical form that can't be copied or communicated. A black box with one function. So, besides separating the nine pieces, why not just take those pieces to separate corners of the world and take a sledgehammer to them? Smash them, cut them, melt them, and turn them into useless pieces of slag? Then you can hide what's left.
  • Because they had to hide it by inverting it, that's why Priya said to "continue the Algorithm's journey into the past." Even if they did smash it the people in the future would still be able to comb the world for the remnants, then they'd only need to plant an inverted tracker for Rotas to follow backwards to a point before they smashed it.

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