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Coop is able to communicate with his past self. So why does he not provide the correct data about which planet is the viable one, saving lives and resources?

Valorum
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Yaroslav Kornachevskyi
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    Because everything needed to play out as it had played out before – Valorum Dec 16 '21 at 23:30
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    @Valorum that looks like infinite loop without start point. Someone must bring data in, to start the loop. – Yaroslav Kornachevskyi Dec 17 '21 at 00:01
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    That's a very four-dimensional way of thinking. When you have a recursive loop, you don't need a first mover. – Valorum Dec 17 '21 at 00:03
  • @Valorum so it means that our descendants just watched us played the right way, and that way occurred to be the best one to transfer data and thus maintain the loop? – Yaroslav Kornachevskyi Dec 17 '21 at 00:11
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    “Someone must bring data in, to start the loop” — really? Is that how time-travel works in the real world? Cool! Please explain further. – Paul D. Waite Dec 17 '21 at 18:45
  • @PaulD.Waite It depends on the time model selected by the author. In the Interstellar in does not need someone to bring data in. – Yaroslav Kornachevskyi Dec 17 '21 at 22:08
  • Also, he didn't need to, Plan B worked just fine (as he realised it was far advanced humans who built the Tesseract), his hope and mission was the people of Earth (Plan[et] A) – Möoz Mar 06 '23 at 00:56

2 Answers2

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Cooper cannot change the past.

Once his future self, who entered the tesseract from the black hole, accepts that he can't change the past, he then understands that he can make sure that the lives and resources were not sacrificed in vain and so moves on to hatching his plan to save mankind.

This is explained in the discussion with Coop and TARS:

TARS: Cooper, they didn't bring us here to change the past.
Cooper: Say that again.
TARS: They didn't bring us here to change the past.
Cooper: But they didn't bring us here at all. We brought ourselves. TARS, give me the coordinates for NASA, in binary.
TARS: In binary, roger, feeding data. [Cooper creates the binary lines in the dust on Murphy's bedroom floor]
Murph: It's not a ghost... it's gravity.
Cooper: Don't you get it yet, TARS? I brought myself here! We're here to communicate with the three-dimensional world! We're the bridge! I thought they chose me. But they didn't choose me, they chose her!

Mark Rogers
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Silly but True
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    But while in tesseract he can just do nothing and thus change the past. Or do something different (not just what he did). – Yaroslav Kornachevskyi Dec 17 '21 at 00:05
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    So, in other words, "our descendants just watched us played the right way, and that way occurred to be the best one to transfer the data and thus maintain the loop?" – Yaroslav Kornachevskyi Dec 17 '21 at 00:15
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    @YaroslavKornachevskyi I don’t disagree, but it’d then be a completely different movie and discussion from this one. – Silly but True Dec 17 '21 at 00:16
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    @YaroslavKornachevskyi You're still assuming it's possible to change the past. Stable closed time-loops imply a universe that already is the way it is, and cannot be changed in any way (in the past or the future). Of course, both approaches (and many others) are plentiful in sci-fi, and real world science also has some support for many approaches to time travel. But this movie definitely shows a spacetime that doesn't change - we just observe its evolution over a time axis. Unlike, say, Terminator, which doesn't have stable loops. – Luaan Dec 17 '21 at 09:00
  • @Luaan ok, it is about defining which time logic applies in that case. And so my question was actually about that definition) – Yaroslav Kornachevskyi Dec 17 '21 at 09:08
  • @YaroslavKornachevskyi But can he actually do anything else? That's a question about free will, that many scientists believe does not exist in this sense. See e.g. Hawking in A Brief History of Time: if memory serves, there is a statement like "Is everything determined? I believe it is." – comodoro Dec 17 '21 at 09:41
  • @comodoro I hope we still have some quantum oscillations in our neurons that are never the same) – Yaroslav Kornachevskyi Dec 17 '21 at 10:22
  • @YaroslavKornachevskyi That's utterly irrelevant to the question of free will or determinism, though. But even if it were relevant, it would mean that the causal loop wouldn't be stable, and would not form a consistent future. Quantum uncertainty doesn't imply the world is non-deterministic in quite this manner. – Luaan Dec 17 '21 at 13:04
  • They may never be the same, but if you lived within the Intersteller film, those individually unique sequences of neurons would be predestined. – Silly but True Dec 17 '21 at 13:08
  • Or they could just bounce around some minima point, always returning back. – Yaroslav Kornachevskyi Dec 17 '21 at 13:22
  • @YaroslavKornachevskyi If Cooper did nothing while in the tesseract, he would fade out of existence after he died (having then run out of time to send the coordinates to Murphy) and humanity would be doomed, due to him breaking the loop. While a viable outcome, it would probably be a less enjoyable movie ending. – TylerH Dec 17 '21 at 15:08
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    @TylerH But would it? If script writer wrote a different outcome, and the director filmed it, then whatever that was would most likely be the movie outcome; unless the film Intersteller Stack Exchange comments discussion itself meta-existed in our real world as a closed-time-loop and that’s the ending that has to happen regardless of what got scripted and filmed. – Silly but True Dec 17 '21 at 15:28
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    I'll drink for that too! – Yaroslav Kornachevskyi Dec 17 '21 at 15:39
  • @SillybutTrue Would it what? Be less enjoyable? Absolutely; most movies have happy endings for a reason. – TylerH Dec 17 '21 at 15:55
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    @YaroslavKornachevskyi But while in tesseract he can just do nothing and thus change the past. Not if you go by the Novikov self-consistency principle which the movie's science consultant, physicist Kip Thorne, is assuming (Thorne is actually the one who discovered the theoretical possibility in relativity of traversable wormholes allowing travel into the past). See my answer here for a thought-experiment that may help in thinking about self-consistent time travel. – Hypnosifl Dec 17 '21 at 19:13
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This is an example of a causal loop - where, for instance, a time traveller travels back in time to instigate a series of events, which may include events leading up to them going back in time to instigate the events.

In this case, future Cooper interacts with the dust in order to send Murph the coordinates for NASA, thus leading up to the events of the movie. In a hypothetical scenario, had he not done this, Cooper would not have joined the mission and he would not be able to travel back in time to do this in the first place. You could say that he has to do this - someone has to manipulate the dust from the future to send Cooper on his mission, otherwise all the events we've seen wouldn't happen. And we know that they have to happen because they did happen, so they can't not happen.

As to why Cooper doesn't just send the location of the correct planet etc. - same reason. Events have already played out in the past. There is only one past - Cooper can't change it and cheat.

user25730
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