In Interstellar (2014) the human race seemed to be facing pretty poor odds until they discovered a convenient wormhole placed by an unknown entity expressed as "they". Later in the movie, we discover that

"they" are actually the human race in the future, reaching back in time to save itself.

The end of the movie gets a little wild on the physics end, and I'm happy to take that ending as is - no need for it to make sense - but one very basic detail does bother me:

How could the human race have gone back in time to save itself from circumstances that would have caused us to go extinct without our own help (the convenient wormhole)?

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    There is nothing wild about the physics. Highly regarded scientists have come out in defence of Interstellar. The wildest aspect of the movie is that clouds of ice can hang suspended. Even Neal Degrasse Tyson supported the physics of the film. – Venture2099 Mar 17 '15 at 0:42
  • If you don't like the wibbly-wobbly timey-wimey-ness of the ending, as I didn't, then I can point you to a blog post I read that offered a decent alternate ending, no paradox necessary. bit.ly/1YcnArN – DeHaan Jun 9 '16 at 17:35
  • backwards time travel is always a paradox. – DA. Dec 15 '16 at 19:15
up vote 43 down vote accepted

You pose an interesting question. It may indeed seem that this is a paradox since the humans couldn't have gone back in time to save themselves when they wouldn't have been saved in the first place.

But your problem is actually that you're searching a cause out of nothing where there is none. You are basically searching for the beginning of a circle. You assume that there could be an alternative timeline where humanity was not saved by the whole wormhole/tesseract stuff from its future self but then created the observed timeline by sending the message back. But such an alternative timeline does not exist and can't ever exist in the time concept of the movie, which follows the Novikov self-consistency principle in this regard. The point is that the timeline has always been this way and hasn't been created out of another timeline by some external influence, humanity has always been saved by its future self and will always safe its past self. If they hadn't saved themselves, they wouldn't exist to save themselves, as you realized yourself. You just have to stop looking for the beginning of what is a time loop, because there is no dedicated beginning, this time loop has always been part of the universe's unchangable time continuum.1

There is no point in reasoning about a reality where Cooper did not send the message to his daughter and himself in exactly the same way as he received them, since that is not the reality we're shown. It is not possible for Cooper to send other messages to himself than the ones he received or for the "Bulk Beings" to not open the wormhole in the future, since all that has basically already happened in Cooper's and earth's past. If he'd do it differently, he had received different messages in the first place. I know this may sound like a lame excuse or discussing away a supposed paradox just by its necessity. But it is really a fundemantally different approach of looking at time travel in contrast to, say, a different timeline whenever the past is changed. By saying that the past cannot ever in any slight way be changed -- and that's indubitably what the movie says -- the existence of any kind of paradoxa is basically avoided. One just has to accept the fact that the future 5D superhumans will at some point create that wormhole for us and will at some point create the tesseract for Cooper. Why they do this exactly is admittedly not answered by the movie, which just doesn't care about their reasons as they seem irrelevant here, but they certainly do it in exactly the same way as it already happened, because it happened in the way they did it.

This interpretation of an unchangable timeline is in fact a common way to avoid the problem of time paradoxa. A good other example for this is the movie Twelve Monkeys, where the end reveals

that the timeline has always looked this way and the young Cole has always seen his older self die.

And in fact when viewing that movie for the first time, it immediately struck me as one of the most plausible time travel movies ever, since it avoids any kind of paradox present in many other time travel movies by the simple consequence that the exact flow of events cannot ever be changed at all and every kind of time travel is already part of the causality chain that led up to it, even if in a circular way. (I have to add though, that discussions on this site have since made me doubt the unchangability of timelines in Twelve Monkeys a bit. But nevermind, Interstellar with its perfectly consistent depiction of a completely unchangable timeline can now take its place.)

1 If you want a more metaphysical term for this, call it fate, but don't take that too seriously, I'm still talking about an entirely physical interpretation here and nobody wants to steal your free will ;-).

  • Comments are not for extended discussion; this conversation has been moved to chat. – Napoleon Wilson Jan 24 '17 at 20:28
  • Have I misstaken the movie? I always understood it that way, that in the end, they actually entered a black hole, not the wormhole. And since we don't know whats going on inside of a blackhole, they actually made the gravity thingy of it make time run in another direction and that's how they made the time travel. Not by the wormhole. – Zaibis Dec 6 at 7:45
  • @Zaibis Yes, they entered the black hole at the end and with the weird stuff in it communicated a message to the past (they didn't "make time run in another direction", though). But...the answer doesn't say anything about entering the wormhole at the end either. So you might have mistaken the answer more than the movie. ;-) – Napoleon Wilson Dec 6 at 10:35
  • Seems like, yeah – Zaibis Dec 12 at 5:22

The most logical answer to me is that Brand (towards the end of the movie) has succesfully accomplished plan B on the third planet and the humans that came out of that were the future humans that later on either evolved or understood 5D, and therefore knew how to access the different dimensions of time, and were able to create the tesseract in order to save the original human race, which they (Cooper and Brand) didn't save in the original past. "They" knew from history that Cooper was going to go in the black hole and that's why they created the tesseract and put it in the there, so Cooper could send the message and save the original human race. Later on, Cooper helped Brand in executing plan B when his daughter told him to go to brand.

Cooper said "They didn't put us here, we brought ourselves here". So the future humans probably knew that there would be a wormhole that would appear at that time and that Cooper and the team would go there and do what they did. Cooper was really going to go in the black hole which was where they placed the tesseract And the rest is history.

  • Yet, this seems to contradict the single unchangable timeline and the unchangability of the past depicted in the movie. If Cooper did not land in the tesseract in the "original" timeline, why would he end up at NASA at all in the first place? And why would his doings inside the tesseract on the "second try" recreate the exact chain of events of his "original past", including the messaging of the quantum data that supposedly not happened in the "original past"? – Napoleon Wilson Feb 6 '15 at 10:18
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    In the original past, Cooper was working for NASA, just like what happened in the new past. "They" didn't create the worm hole. They just put the tessaract in the black hole. Thus, Cooper working for nasa in the original timeline. The only difference is that in the first past, there was no tesseract in the black hole and when Cooper went in, he died, and the rest of the human race afterwards except for Brand and plan B. With this knowledge, the future humans put the tesseract in the black hole because they knew from the past (original timeline) that Cooper was going to go into the black hole. – Edward Scissorhands Feb 6 '15 at 18:45
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    Also, if they were depicting unchangability of the past, then the whole thing would have been pointless anyway. They did change the past. They did it when Cooper seccesfully sent the message across to save the human race. They did save the human race. It was the point of the whole movie. That's why they built the tessaract in the first place. So yes, the past can be changed in the movie, through accessing different dimensions of time, like what they showed Cooper in the tessaract. – Edward Scissorhands Feb 6 '15 at 18:45
  • When you change the past, you either change the events that happen in the future as well (see looper, back in the future, time cop), or an alternate reality is created. – Edward Scissorhands Feb 6 '15 at 22:35
  • Wait, you're right about one thing. How did Cooper get the message from his future self if he wasn't really going there in the first place? He only went there because Cooper future sent him the coordinates. If he didn't get the coordinates, he wouldn't go to NASA. If he didn't go to NASA, he wouldn't be able to go and send himself the coordinates. Nolan owes us all an explanation. Or maybe there isn't one. – Edward Scissorhands Feb 6 '15 at 22:59

How could the human race have gone back in time to save itself from circumstances that would have caused us to go extinct without our own help (the convenient wormhole)?

The reason this is so difficult to answer is that you've included the words "back in time".

There is no linear time in this movie. There is no past, and no future. There are creatures, primarily humans, in the movie which experience time linearly, and have no ability to move around in time except at a fixed (perceived) pace.

Consider two walls on a road, traveling like vehicles, spaced apart from each other about 3 feet (1 meter), moving down the road. You are between the walls, and must move with them down the road. You do not have the ability to go around or over the walls, nor visibility to see what's beyond them - only what you see in the 3 feet of ground, and what's above and to the sides. You suspect that the walls aren't infinite, but you don't have the tools or ability to climb over or around the walls. So you are pushed forward, and you can't go "back" to places you've already been, nor "forward" to places you'll eventually come to.

Now change it slightly. Put the walls in the ocean, and put a fish there. It doesn't even perceive the need for tools or techniques to go over the wall - it just swims up and over. In fact the wall isn't an obstacle at all. It can fully utilize all three dimensions, and even when resting there's no need for it to move at all along with the walls.

The walls are irrelevant to the fish.

We perceive time as these walls. We can't travel to the past or the future. We don't have the ability to stop the walls or move outside the walls.

But a being that perceives time in the same way we perceive places can go to anywhen, the same way we might travel to anywhere.

In the same way that you have the monitor placed on your desk in a certain position so you can use it - it belongs there - the wormhole is placed in a certain when. That when is neither "before" or "after" any other when. It's just a when, exactly the same as your monitor is not "before" or "after" any other where. It's just a where. All where's exist without an ordering. You might perceive two monitors, one in "front" of the other as having an order, but if you move yourself around them, the order changes and isn't any less or more relevant.

So all whens exist. Some beings perceive whens in a particular order, but that doesn't mean that these whens actually have an ordering anymore than we see wheres as having an ordering.

Once you move past that perception and accept and perceive that all whens are unordered, the same as all wheres are unordered, then the wormhole exists in that when and where. Someone created it, and put it at that when. There was no before or after it was placed - it's placed at a when, and exists there. It will "always" exist there, despite the fact that "always" has lost meaning since it has never not been at that where and when.

In other words, 4 dimensional humans already exist "now", they've "always" existed, and will "always" exist. In the same way you move a glass of water from the kitchen to your desk, they created a wormhole and placed it at a when and where. It's there at a when. We can't perceive it, "yet", but it's "already" there at a when, "always" was there at a when, and "always" will be there at a when. To them, there is no time. Just wheres and whens.

So the real question is - How did we break through or go outside those walls? Not when - it doesn't matter "when" the first human perceived time as a when rather than linearly. Once you step out of time, it doesn't matter when you did it - you have access to all the whens, and linear time has no meaning. It could be in the past for us. It could be in the future for us. It could be yesterday, today, or tomorrow - only one person has to transcend time for all of us to transcend time. Once any human moves beyond that perception, all the whens are as accessible to that human as the wheres are accessible to us.

But, of course, the how doesn't then matter. The wall was transcended. The wall is transcended. The wall will be transcended. There is no wall.

Interstellar essentially says that we are fish, though we don't perceive ourselves that way.

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    You describe "when" and "where" as being comparable, however, I find this concept problematic. My perception of "where" is a location of matter relative to other matter. My perception of "when", however is very different: I perceive time not to be a dimension or "thing" to traverse at all; time is instead a measure or memory of a series of events. Subatomic particles move around, but their movement states don't exist as a trillion units of time, they just happen and there is nothing except for "now". – CuriousWebDeveloper Jan 17 '15 at 9:56
  • This doesn't really make so much sense to me. I may sound narrow-minded but I don't think you can just discuss away causality by that wall analogy and by equating wheres to whens. The idea of causality and the special behaviour of the temporal dimension compared to the spatial ones are concepts the movie is very well aware of and doesn't just ignore. The actions of the humans in the movie are pretty much bound to causality and don't just happen out of nowhen. I agree that it's unclear how the bulk beings did what they did but I don't think saying time is an irrelevant concept is a solution. – Napoleon Wilson Jan 20 '15 at 0:34

The movie gives us all the information to solve this paradox.

The movie revolves around the possibilities brought on by the intervention of the future 5-dimensional humanity, but there are key elements independent of said intervention namely:

  • The "Endurance" Starship
  • Cryo-sleep technology
  • Population bomb

Humanity was perfectly capable of sending a population bomb to kickstart a new colony the long way, using cryo-sleep to allow the crew members to survive the centuries-long trip to another star system. So we can assume that in the original timeline, humanity did just that, there was no Plan A, and all resources were spent in sending away the Colony ship, with the rest of humanity perishing back on Earth.

Then, in a distant future where humanity learns to transcend space and time, "they" decide to attempt and save the original human population of Earth (possibly as an attempt to reclaim their long lost origins).

Given that Coop's test flight crashing (at the start of the movie) and his reason for leaving NASA was due to interference from the future humans, it might even be that in the original timeline Cooper stayed with NASA and Murph was allowed to work as a scientist, making her prominent enough, from a historical point of view, for future humanity to target as the way to solve the gravity equation.

As for the problem of future humanity altering their past, I like to think that, being so far away into the future as they seem to be (and having transcended space and time, it seems), alterations as to the specific time (within an specific time frame), place and composition of the new human colony would have no practical effect on them, other than their cultural background being richer.

Alternatively, their original plan might account for the new version of humanity to understand they must execute the plan in their relative future to solve the issue, thus establishing the "loop".

In any case, I do agree that the intention of the filmmakers was probably to imply that the paradox exists because it does, I just see enough in the movie to justify an alternate solution.

I think that Napoleon Wilson's ansers says it all: it's a time paradox where the cause-effect relation seems to take an exception, so to speak.

I'm posting this answer only to remind that this kind of time paradox is not new to sci-fi movies. The other example I'm thinking of is the Terminator series, where humanity acquires the technology to build thinking machines from a microchip found exactly in one of those thinking machine arrived frome the future.

There may be other examples ....

  • Downvoters should be kind enough to explain the downvote. – Andrea Mori Nov 20 '14 at 1:50
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    I am not/was not a down-voter, but my guess is because you don't answer the question asked. Stack Exchange is not a discussion forum, it's a Q&A site. Ask a question and get an answer. You've not answered it. That would be my guess anyway. – CGCampbell Dec 9 '14 at 1:16

Here is a solution to the story ...

The humanity both survives and wipes out without any need of parallell universes or syclic timeloops. HOW?

There are not two ways of doing things. No non-determinism (splits into two ways at the same time) or no backtrackings (like a squirrell running branches of a tree of time back and forth). Done is done. Time is deterministic as we know it today. And as scientists has shown: particles can be teleported from one place to another - also from time to another - becuse time and space is the same. But the last said we do not yet know. Anyway...

Let the story start by the humanity rescuses by a wormhole travel in about say 55 seconds. They come into a new world without humans. Droids tell everyone of flesh was gone into that wormhole 3 years ago. It was because of some beliefe system based on logic and what seemed most positive for them. Because they existed that means they had to rescue humanity from a historical fact there had been a catastrophe at the same planet for about 5500 years ago. Life on earth in that time could not be possible. The catastrophe has now faded out but can still be measured by researchers. So they all offered their lifes for humanity, love and a possibility of eternal life in that timeloop.

Well the most of the droids and maybe you too is a bit confused then about how the humanity could come back? But an expert of timeholes among the droids, have all needed facts and a conclusion:

It is not a syclic timehole! There are no two ways of doing and yet it seems like that! No, in fact... It is more like a rubber-band. If shooting a stone 5500 mm with the rubber represents a timetravel in 5500 years (that felt like 55 seconds) that means if you looesn the rubber 3mm (that represents 3 years ago the humanity disappeared into the hole) then it must be that "they" came out 3 years too late! Three years after the humanity was rescuede by the wormhole! Ooooh nooo! They traveled past each other! They arrived direct into death while the others are here fully alive! Still those who are gone is born from those who have come.

So humanity booth was rescued and extinct? Isnt that a paradox? So where dit "they" come from if "we" are born into the future after our death? A droid come to answers the bewildered questions: Well - there are myths that tell some heroes sometimes fell out from the wormhole. The laws of physics seems not always be mathematically perfect. Or more correctly speaking - theories is too simple to describe the wormhole. Not you but they who are gone is born from them who fell out from that hole. Those who fell out are some of you. Those you believed not followed with you through the 55 second travel gave actually birth to a new civilisation.

And how did the wormhole come to existence? Who created it? That question the droids can not tell! Nobody actually does not know. The myths say that the people who fell out from the wormhole only knows that suddenly there was a wormhole in time. There was no other ways to escape than run into it. The fast increasing heat of the catastrophe was unbearable. Many died.

One of the characters in this story becomes angry and shoot at the wormhole. Bullets make visible holes which then slowly seals and disappears. The type of some leader or what gets an idéa. They put all their ammo into it. Yeah nice - but it repairs itself after a while. It needs more! Now the droids have to help - the people demanded. One of the more eager of the droids jumped into some kind of machine and there was a huge explosion and no wormhole anymore.

The people hurrayed. The type of leader tries to formulate something epic: Now it ended - long live the people. But a more clever droid answeres: Well - it was created now. It was my backwards time machine he started for first time.

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    WUT? Sorry, but I have a hard time getting what you're actually telling here. – Napoleon Wilson Dec 9 '14 at 9:33
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    WUT? Seriously, this was my genuine comment before reading the previous comment. – Viziionary Dec 9 '14 at 18:00
  • I tell an answer to a question, so try be creative with me Q: "How could the human race have gone back in time ..." A: A timehole was made by accident "... to save itself ..." A: I propose them not be saved a second time. I try to avoid a predictable stereotypic genre like "uh - that old timeloop thing again" Must it be interstellar and not on earth? Sorry I made you confused. To get it more "humanity saving itself": Exchange the droid firing time-machine to a human. – Pauli Sudarshan Terho Dec 10 '14 at 2:43
  • I propose a movie2: The "rubber band theory" shows to be proven wrong. Confusions changes to insights in the middle of the movie: They from future is discovering inside of a wormhole in 55 days, months or years whatever fits best. They find a bug causing holes in time and people drops out. They travel so far that it gives yet another alternative to Darwins theory. The are the first ones. Saving humanity in many aspects. Now cyclic ;) I want to see this movie - so use it or vote it down. Do both if you are that kind. – Pauli Sudarshan Terho Dec 10 '14 at 4:13
  • I think your answer probably makes sense. – Viziionary Dec 10 '14 at 6:21

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