## Interstellar’s dangling wormholes

Update (Nov. 15): A third of my confusions addressed by reading Kip Thorne’s book! Details at the bottom of this post.

On Saturday Dana and I saw Interstellar, the sci-fi blockbuster co-produced by the famous theoretical physicist Kip Thorne (who told me about his work on this movie when I met him eight years ago).  We had the rare privilege of seeing the movie on the same day that we got to hang out with a real astronaut, Dan Barry, who flew three shuttle missions and did four spacewalks in the 1990s.  (As the end result of a project that Dan’s roboticist daughter, Jenny Barry, did for my graduate course on quantum complexity theory, I’m now the coauthor with both Barrys on a paper in Physical Review A, about uncomputability in quantum partially-observable Markov decision processes.)

Before talking about the movie, let me say a little about the astronaut.  Besides being an inspirational example of someone who’s achieved more dreams in life than most of us—seeing the curvature of the earth while floating in orbit around it, appearing on Survivor, and publishing a Phys. Rev. A paper—Dan is also a passionate advocate of humanity’s colonizing other worlds.  When I asked him whether there was any future for humans in space, he answered firmly that the only future for humans was in space, and then proceeded to tell me about the technical viability of getting humans to Mars with limited radiation exposure, the abundant water there, the romantic appeal that would inspire people to sign up for the one-way trip, and the extinction risk for any species confined to a single planet.  Hearing all this from someone who’d actually been to space gave Interstellar, with its theme of humans needing to leave Earth to survive (and its subsidiary theme of the death of NASA’s manned space program meaning the death of humanity), a special vividness for me.  Granted, I remain skeptical about several points: the feasibility of a human colony on Mars in the foreseeable future (a self-sufficient human colony on Antarctica, or under the ocean, strike me as plenty hard enough for the next few centuries); whether a space colony, even if feasible, cracks the list of the top twenty things we ought to be doing to mitigate the risk of human extinction; and whether there’s anything more to be learned, at this point in history, by sending humans to space that couldn’t be learned a hundred times more cheaply by sending robots.  On the other hand, if there is a case for continuing to send humans to space, then I’d say it’s certainly the case that Dan Barry makes.

OK, but enough about the real-life space traveler: what did I think about the movie?  Interstellar is a work of staggering ambition, grappling with some of the grandest themes of which sci-fi is capable: the deterioration of the earth’s climate; the future of life in the universe; the emotional consequences of extreme relativistic time dilation; whether “our” survival would be ensured by hatching human embryos in a faraway world, while sacrificing almost all the humans currently alive; to what extent humans can place the good of the species above family and self; the malleability of space and time; the paradoxes of time travel.  It’s also an imperfect movie, one with many “dangling wormholes” and unbalanced parentheses that are still generating compile-time errors in my brain.  And it’s full of stilted dialogue that made me giggle—particularly when the characters discussed jumping into a black hole to retrieve its “quantum data.”  Also, despite Kip Thorne’s involvement, I didn’t find the movie’s science spectacularly plausible or coherent (more about that below).  On the other hand, if you just wanted a movie that scrupulously obeyed the laws of physics, rather than intelligently probing their implications and limits, you could watch any romantic comedy.  So sure, Interstellar might make you cringe, but if you like science fiction at all, then it will also make you ponder, stare awestruck, and argue with friends for days afterward—and enough of the latter to make it more than worth your while.  Just one tip: if you’re prone to headaches, do not sit near the front of the theater, especially if you’re seeing it in IMAX.

For other science bloggers’ takes, see John Preskill (who was at a meeting with Steven Spielberg to brainstorm the movie in 2006), Sean Carroll, Clifford Johnson, and Peter Woit.

In the rest of this post, I’m going to list the questions about Interstellar that I still don’t understand the answers to (yes, the ones still not answered by the Interstellar FAQ).  No doubt some of these are answered by Thorne’s book The Science of Interstellar, which I’ve ordered (it hasn’t arrived yet), but since my confusions are more about plot than science, I’m guessing that others are not.

SPOILER ALERT: My questions give away basically the entire plot—so if you’re planning to see the movie, please don’t read any further.  After you’ve seen it, though, come back and see if you can help with any of my questions.

1. What’s causing the blight, and the poisoning of the earth’s atmosphere?  The movie is never clear about this.  Is it a freak occurrence, or is it human-caused climate change?  If the latter, then wouldn’t it be worth some effort to try to reverse the damage and salvage the earth, rather than escaping through a wormhole to another galaxy?

2. What’s with the drone?  Who sent it?  Why are Cooper and Murph able to control it with their laptop?  Most important of all, what does it have to do with the rest of the movie?

3. If NASA wanted Cooper that badly—if he was the best pilot they’d ever had and NASA knew it—then why couldn’t they just call him up?  Why did they have to wait for beings from the fifth dimension to send a coded message to his daughter revealing their coordinates?  Once he did show up, did they just kind of decide opportunistically that it would be a good idea to recruit him?

4. What was with Cooper’s crash in his previous NASA career?  If he was their best pilot, how and why did the crash happen?  If this was such a defining, traumatic incident in his life, why is it never brought up for the rest of the movie?

5. How is NASA funded in this dystopian future?  If official ideology holds that the Apollo missions were faked, and that growing crops is the only thing that matters, then why have the craven politicians been secretly funneling what must be trillions of dollars to a shadow-NASA, over a period of fifty years?

6. Why couldn’t NASA have reconnoitered the planets using robots—especially since this is a future where very impressive robots exist?  Yes, yes, I know, Matt Damon explains in the movie that humans remain more versatile than robots, because of their “survival instinct.”  But the crew arrives at the planets missing extremely basic information about them, like whether they’re inhospitable to human life because of freezing temperatures or mile-high tidal waves.  This is information that robotic probes, even of the sort we have today, could have easily provided.

7. Why are the people who scouted out the 12 planets so limited in the data they can send back?  If they can send anything, then why not data that would make Cooper’s mission completely redundant (excepting, of course, the case of the lying Dr. Mann)?  Does the wormhole limit their transmissions to 1 bit per decade or something?

8. Rather than wasting precious decades waiting for Cooper’s mission to return, while (presumably) billions of people die of starvation on a fading earth, wouldn’t it make more sense for NASA to start colonizing the planets now?  They could simply start trial colonies on all the planets, even if they think most of the colonies will fail.  Yes, this plan involves sacrificing individuals for the greater good of humanity, but NASA is already doing that anyway, with its slower, riskier, stupider reconnaissance plan.  The point becomes even stronger when we remember that, in Professor Brand’s mind, the only feasible plan is “Plan B” (the one involving the frozen human embryos).  Frozen embryos are (relatively) cheap: why not just spray them all over the place?  And why wait for “Plan A” to fail before starting that?

9. The movie involves a planet, Miller, that’s so close to the black hole Gargantua, that every hour spent there corresponds to seven years on earth.  There was an amusing exchange on Slate, where Phil Plait made the commonsense point that a planet that deep in a black hole’s gravity well would presumably get ripped apart by tidal forces.  Plait later had to issue an apology, since, in conceiving this movie, Kip Thorne had made sure that Gargantua was a rapidly rotating black hole—and it turns out that the physics of rotating black holes are sufficiently different from those of non-rotating ones to allow such a planet in principle.  Alas, this clever explanation still leaves me unsatisfied.  Physicists, please help: even if such a planet existed, wouldn’t safely landing a spacecraft on it, and getting it out again, require a staggering amount of energy—well beyond what the humans shown in the movie can produce?  (If they could produce that much acceleration and deceleration, then why couldn’t they have traveled from Earth to Saturn in days rather than years?)  If one could land on Miller and then get off of it using the relatively conventional spacecraft shown in the movie, then the amusing thought suggests itself that one could get factor-of-60,000 computational speedups, “free of charge,” by simply leaving one’s computer in space while one spent some time on the planet.  (And indeed, something like that happens in the movie: after Cooper and Anne Hathaway return from Miller, Romilly—the character who stayed behind—has had 23 years to think about physics.)

10. Why does Cooper decide to go into the black hole?  Surely he could jettison enough weight to escape the black hole’s gravity by sending his capsule into the hole, while he himself shared Anne Hathaway’s capsule?

11. Speaking of which, does Cooper go into the black hole?  I.e., is the “tesseract” something he encounters before or after he crosses the event horizon?  (Or maybe it should be thought of as at the event horizon—like a friendlier version of the AMPS firewall?)

12. Why is Cooper able to send messages back in time—but only by jostling books around, moving the hands of a watch, and creating patterns of dust in one particular room of one particular house?  (Does this have something to do with love and gravity being the only two forces in the universe that transcend space and time?)

13. Why does Cooper desperately send the message “STAY” to his former self?  By this point in the movie, isn’t it clear that staying on Earth means the death of all humans, including Murph?  If Cooper thought that a message could get through at all, then why not a message like: “go, and go directly to Edmunds’ planet, since that’s the best one”?  Also, given that Cooper now exists outside of time, why does he feel such desperate urgency?  Doesn’t he get, like, infinitely many chances?

14. Why is Cooper only able to send “quantum data” that saves the world to the older Murph—the one who lives when (presumably) billions of people are already dying of starvation?  Why can’t he send the “quantum data” back to the 10-year-old Murph, for example?  Even if she can’t yet understand it, surely she could hand it over to Professor Brand.  And even if this plan would be unlikely to succeed: again, Cooper now exists outside of time.  So can’t he just keep going back to the 10-year-old Murph, rattling those books over and over until the message gets through?

15. What exactly is the “quantum data” needed for, anyway?  I gather it has something to do with building a propulsion system that can get the entire human population out of the earth’s gravity well at a reasonable cost?  (Incidentally, what about all the animals?  If the writers of the Old Testament noticed that issue, surely the writers of Interstellar could.)

16. How does Cooper ever make it out of the black hole?  (Maybe it was explained and I missed it: once he entered the black hole, things got extremely confusing.)  Do the fifth-dimensional beings create a new copy of Cooper outside the black hole?  Do they postselect on a branch of the wavefunction where he never entered the black hole in the first place?  Does Murph use the “quantum data” to get him out?

17. At his tearful reunion with the elderly Murph, why is Cooper totally uninterested in meeting his grandchildren and great-grandchildren, who are in the same room?  And why are they uninterested in meeting him?  I mean, seeing Murph again has been Cooper’s overriding motivation during his journey across the universe, and has repeatedly been weighed against the survival of the entire human race, including Murph herself.  But seeing Murph’s kids—his grandkids—isn’t even worth five minutes?

18. Speaking of which, when did Murph ever find time to get married and have kids?  Since she’s such a major character, why don’t we learn anything about this?

19. Also, why is Murph an old woman by the time Cooper gets back?  Yes, Cooper lost a few decades because of the time dilation on Miller’s planet.  I guess he lost the additional decades while entering and leaving Gargantua?  If the five-dimensional beings were able to use their time-travel / causality-warping powers to get Cooper out of the black hole, couldn’t they have re-synced his clock with Murph’s while they were at it?

20. Why does Cooper need to steal a spaceship to get to Anne Hathaway’s planet?  Isn’t Murph, like, the one in charge?  Can’t she order that a spaceship be provided for Cooper?

Anyway, rather than ending on that note of cosmic pessimism, I guess I could rejoice that we’re living through what must be the single biggest month in the history of nerd cinema—what with a sci-fi film co-produced by a great theoretical physicist, a Stephen Hawking biopic, and the Alan Turing movie coming out in a few weeks.  I haven’t yet seen the latter two.  But it looks like the time might be ripe to pitch my own decades-old film ideas, like “Radical: The Story of Évariste Galois.”

Update (Nov. 15): I just finished reading Kip Thorne’s interesting book The Science of Interstellar.  I’d say that it addresses (doesn’t always clear up, but at least addresses) 7 of my 21 confusions: 1, 4, 9, 10, 11, 15, and 19.  Briefly:

1. Thorne correctly notes that the movie is vague about what’s causing the blight and the change to the earth’s atmosphere, but he discusses a bunch of possibilities, which are more in the “freak disaster” than the “manmade” category.

4. Cooper’s crash was supposed to have been caused by a gravitational anomaly, as the bulk beings of the far future were figuring out how to communicate with 21st-century humans.  It was another foreshadowing of those bulk beings.

9. Thorne notices the problem of the astronomical amount of energy needed to safely land on Miller’s planet and then get off of it—given that this planet is deep inside the gravity well of the black hole Gargantua, and orbiting Gargantua at a large fraction of the speed of light.  Thorne offers a solution that can only be called creative: namely, while nothing about this was said in the movie (since Christopher Nolan thought it would confuse people), it turns out that the crew accelerated to relativistic speed and then decelerated using a gravitational slingshot around a second, intermediate-mass black hole, which just happened to be in the vicinity of Gargantua at precisely the right times for this.  Thorne again appeals to slingshots around unmentioned but strategically-placed intermediate-mass black holes several more times in the book, to explain other implausible accelerations and decelerations that I hadn’t even noticed.

10. Thorne acknowledges that Cooper didn’t really need to jump into Gargantua in order to jettison the mass of his body (which is trivial compared to the mass of the spacecraft).  Cooper’s real reason for jumping, he says, was the desperate hope that he could somehow find the quantum data there needed to save the humans on Earth, and then somehow get it out of the black hole and back to the humans.  (This being a movie, it of course turns out that Cooper was right.)

11. Yes, Cooper encounters the tesseract while inside the black hole.  Indeed, he hits it while flying into a singularity that’s behind the event horizon, but that isn’t the black hole’s “main” singularity—it’s a different, milder singularity.

15. While this wasn’t made clear in the movie, the purpose of the quantum data was indeed to learn how to manipulate the gravitational anomalies in order to decrease Newton’s constant G in the vicinity of the earth—destroying the earth but also allowing all the humans to escape its gravity with the rocket fuel that’s available.  (Again, nothing said about the poor animals.)

19. Yes, Cooper lost the additional decades while entering Gargantua.  (Furthermore, while Thorne doesn’t discuss this, I guess he must have lost them only when he was still with Anne Hathaway, not after he separates from her.  For otherwise, Anne Hathaway would also be an old woman by the time Cooper reaches her on Edmunds’ planet, contrary to what’s shown in the movie.)

### 123 Responses to “Interstellar’s dangling wormholes”

1. Show Runner Says:

Great story Scott.

http://en.wikipedia.org/wiki/%C3%89variste_Galois

The screen writes itself.

2. Chris Roberts Says:

I share many of your questions, but think others have answers. My speculations:

1. I think war is the implied cause. There were a few references to war – the Indian drone, Cooper’s crash (which I thought was military in nature), professor Brand’s refusing to drop bombs on civilians – and I assumed the war triggered the climate crisis.

2. I think I caught them saying the drone had been from the Indian military and was still flying around autonomously on solar power. I thought it odd that they would interact with the drone without concern if my assumption was right that it was in fact leftover from a catastrophic war.

8. I think this was explained by the missing data. They couldn’t send large colonies to the other planets until they had the data professor Brand thought was unobtainable.

13. I think we see quickly shifting emotions. At that point he assumed there was no way to communicate the data, making his time away from his family all for nothing. Moments later, he figures out how to communicate the data. What I thought bizarre is how such complex data could be communicated entirely over morse code.

18. We see her as an adult, but only during one slice of adulthood and we do see her kiss a fellow when she’s interpreted the “quantum data”. May or may not have implied a future relationship.

21. Perhaps afraid of the butterfly effect?

3. Greg Egan Says:

On point 9, Chandrasekhar’s The Mathematical Theory of Black Holes, section 61, equation 117 gives the specific energy for a body in circular orbits around an arbitrary hole.

I estimated the radius of the orbit here from the time dilation effects (I hope I got it right on the second try), as:

r ≈ 2.000025339 M

If that’s correct, for an extremal black hole (rotating at the maximum possible rate), Chandrasekhar’s formula for the specific energy gives:

E ≈ 0.777

In other words, to enter and leave this orbit from infinity involves energies of the order of 22% of your rest mass.

[I haven’t seen the movie yet myself.]

4. anup Says:

I didn’t understand one more thing. Since the blight was troubling the entire world, why on every planet do we see the American flag. Agreed that NASA is saving all of us but are we in a space race in the moment of a calamity?

5. Scott Says:

Chris #2: Thanks!

1. I think war is the implied cause. There were a few references to war – the Indian drone, Cooper’s crash (which I thought was military in nature), professor Brand’s refusing to drop bombs on civilians – and I assumed the war triggered the climate crisis.

Huh? You’re referring to things that I don’t remember at all from the movie. Probably I wasn’t paying attention? (Or could there be any truth to the claim, which I read somewhere, that certain scenes left in the international edition were cut from the US one?)

8. I think this was explained by the missing data. They couldn’t send large colonies to the other planets until they had the data professor Brand thought was unobtainable.

OK, but then why not small colonies? I.e., why not try to initiate “Plan B” on all 12 of the planets, even while waiting for the “quantum data”?

21. Perhaps afraid of the butterfly effect?

In that case, they shouldn’t have done anything. The whole point of the butterfly effect is that it can get triggered by even the tiniest change to the past state, not just by a large change.

6. Scott Says:

Greg #3:

In other words, to enter and leave this orbit from infinity involves energies of the order of 22% of your rest mass.

Thanks!! If I remember the relevant equation correctly (e=mc2 or something?), that does indeed sound like an improbably enormous amount of energy.

7. Joe Yoon Says:

I second anup, the movie was very USA-centric. No Europeans or Asians even though they have advanced space programs.

1. If the landing craft can take of from a planet with 1.3 times Earth’s gravity, why did it need a huge rocket with multiple stages to get off Earth?

2. Maybe an expert in wave mechanics can answer if it’s possible to have such huge waves in water that’s only a couple of feet deep. Phil Plait has already said that such waves are impossible on a tidally locked planet.

3. What is the power source for the spacecraft. Are the engines chemically powered? If so, there’s no way they had enough volume in the craft. Nuclear? And how did the craft survive 20+ years in space without maintenance? There’s no complex machine ever made that would last that long.

4. If there was a blight, one would think corn would be one of the first crops to go, not the last. The movie only showed one meal but couldn’t tell what they were eating. Can you survive on the diet of only corn?

5. The whole Mann docking scene was just contrived.

The best part of the movie were the robots. They were more humorous, more intelligent, more physically capable, their dialogue more interesting and their interactions more “human” than the purported actual humans. They should have been the stars of the film.

I really wanted to like this movie, it was beautiful to look at but the story and the technical “bugs” just ruined it. 2001 and Blade Runners have nothing to worry about in the sic-fi pantheon. Hollywood seems incapable of making a coherent movie anymore, I’m looking at you J. J. Abrams.

8. Joe Yoon Says:

To clarify the Mann docking scene, if he didn’t have authorization to override the automatic docking lockout, why couldn’t the others just take over control of his ship or at least make it more difficult for him by moving the Endurance?

And is the pressure that great that opening the airlock would cause an explosion?

Even if Mann did get inside, he didn’t have authorization to override the others’ commands.

9. hull Says:

Another question on the line of your #21 is why future super-humans placed the wormhole so far from heart, forcing humans to engage in a suicide trip and increasing difficulty of the entire mission exponentially; why not place it somewhere around the heart, reachable in a couple of weeks..

10. Scott Says:

hull #9: Yeah, I had a similar question (I assume you meant “earth” rather than “heart”), though I figured it was superseded by question 21. If they just wanted the wormhole mouth to be an interesting challenge to get to, they could’ve put it in Ithaca, NY, rather than Saturn.

11. Clément C Says:

An other question, maybe only due to my lack of understanding of black holes: why is the time going so slowly on the “water planet”, compared to the time in the rest of the spaceship which is in orbit around it?
Is there some sort of weird limit between the surface and the orbit where things change abruptly? And even so, if the time is going so slowly on the planet, doesn’t it mean that either the gravity should be insanely strong on it (not a mere 33% more than on Earth), or that its speed should be really high (in which case the orbiting spaceship should also go quite fast)?

12. Scott Says:

Clément #11: Oh, I assumed the spaceship wasn’t in orbit around the water planet, but was someplace further away. If I’m wrong, then yes, that would be a major issue.

13. Shmi Nux Says:

Haven’t seen the movie, but it is not inconceivable to get a “free” ride out of the Kerr black hole ergosphere (where presumably the planets are, given their proximity to the marginally outer trapped surface, commonly confused with the event horizon). This can theoretically be done classically using super-radiance (though there are issues with fermions) or even with the Banados-Silk-West effect. Both use the black hole’s rotational energy to catapult matter out.

14. Scott Says:

Shmi #13: Thanks! Let me see if I understand correctly: you agree with Greg Egan #3 that an enormous amount of energy is needed (22% of your rest mass) to decelerate from infinity and then accelerate away, but claim that that energy can be obtained by exploiting the black hole’s own rotation?

(If so, the question would still remain: is this remotely plausible given the level of spacecraft technology portrayed in the movie, which isn’t that far beyond what we have today?)

15. Scott Says:

anup #4 and Joe #7: I agree with the observation about how US-centric the movie was. They could’ve at least had a few montage scenes about what was happening in other parts of the world, like Independence Day did. (Then again, the entire notion of space as simply the next frontier to be settled is, for better and worse, an extremely American one. A central challenge for that notion has always been that at least the Wild West had an oxygenated atmosphere.)

16. Aaron Sheldon Says:

From my perspective the movie was inadvertently profoundly insightful, although I doubt many in the audience would have had nearly close to the same intellectual experience I had. Setting aside the healthy suspension of disbelief one needs (but then again that is why we watch movies isn’t it), the authors, I think completely by accident, managed to nail a few of the philosophical problems facing, mathematics, physics, and humankind.

First, the narrative is itself an argument that nothing short of a miracle will save the human race from inevitable extinction. While the authors may have been trying to express hope in the ingenuity and tenacity of the human will to survive, the plot required a miracle to save the human race. The point is particularly poignant when placed into the context of considering the thermodynamic limits on chemical life in any stellar system. It is not evolution or love that pushes us forward, it is plain old simple thermodynamics (I’m sorry if that is nearly a tautology, even if it is useful). One can reasonably conjecture that if our thermodynamic role is to be anything more than enzymes reducing the elevated chemical potential stored fossil fuels, then that future civilization is quite possibly upper bound by Dyson sphere civilization, extracting solar entropy from the Dyson optimal orbit.

The second nod that was rather acute, and I hope directly attributively to Dr. Thorne, was the short soliloquy on the difficulty of solving Einstein’s field equations, because of recursion. Specifically that for a given metric the Einstein’s field equation computes the stress-energy; but the metric also defines the geodesics, which in turn define the motion of matter. The difficulty is in finding a metric such that the motion of the matter on the geodesics matches the stress-energy, not to mention finding an infinite orthogonal family of such solutions over which to build annihilation and creation operators for a QFT.

The third subtle reference, again hopefully due to Dr. Thorne, was to the possible resolutions of the black hole information paradox. The whole film could be viewed as a philosophical treatise on the topic, from the perspective of what happens to the knowledge of a man when he falls into a black hole. I’m going to take and guess and say the film is purposing that information specifically about the black hole can only come out in the gravitational field, which would imply that both the hero’s and the robot’s memories of the time inside of the black hole would have been completely erased after being higher dimensionally spit into the wormhole.

The fourth theoretical observation the film made, that was interesting, was in justifying the hero’s presence in the tesseract as being because the higher dimensional being could not sort through all the mutli-dimensional data. I’m again hoping this was, at least, an inadvertent nod to the O(nlogn) bounds on constructing indexes on any information. Presumably the higher dimensional beings have the same problem, having to index the whole of the universe in O(nlogn) somethings (operations? time? complexity? I’m not quite sure about that one).

The final contemporary topic addressed by the film is the current limitations facing theoretical physics. By hinging the plot on the need for more observations to solve the theoretical models the filmy amicably summed up the current state of affairs. Humanity faces a real observational crunch at the extreme scales. For certain we will not be probing energy scales much higher than the LHC anytime soon, although we may be able to make broader and more detailed observations of the cosmos for some time to come.

The only glaring philosophical shortcoming was the lack of any reference at all to Godel’s theorems. After all if we could formulate a theory that explained the universe, that is we could determine as true or false any statement about the universe, then presumably that would include any statements made in any axiomatic systems formulated in the universe. This would contradict Godel’s theorems. Q.E.D there will never be one final theory of the universe, only an infinite sequence of refinements.

P.S. my only moment of feeling really let down was when Murph started writing down the climax solutions. I would have hoped these would have been formulated as exponential’s of Haar measures of generators of a symmetry group. Instead they had her writing yet more tensor equations. But that speaks more to my own theoretical inclinations, and direction of investigation, than to anything attributively to the film.

17. Hush in vain Says:

Here is my film idea- Puzzle: The Story of Ettore Majorana.

By the way, I think I saw MTW’s textbook on Gravitation on Brand’s desk during one of the scenes. And here’s another question that remains unanswered:

Since Cooper and Brand’s detour around Gargantua causes them to spend 68 more years in Earth’s time, why is that Murph is still the same age (i.e. thirty five years, I think) during Cooper’s confinement in the tesseract (as gathered from both the scenes running in parallel)? Shouldn’t she be, like, 103 and possibly dead?

And this is tied to another question very closely: How is it that Cooper was stuck in the tesseract (which as Scott says is inexplicably linked to Murph’s bookshelf) before venturing out into space and therefore, before getting stuck in the tesseract? I don’t understand this at all. 🙁

Also, how is solving the problem of Quantum Gravity supposed to help transport people from this planet to others? But this one’s just a nitpick.

18. Scott Says:

Aaron Sheldon #16:

“…although I doubt many in the audience would have had nearly close to the same intellectual experience I had.”

After reading your interesting and provocative comment, I think that’s an accurate assessment! I wonder, can you also extract what the movie was saying about derandomizing polynomial identity testing, or about the Scottish independence referendum? 😉

19. Shmi Nux Says:

Scott #14: I suspect the amount of energy needed is worse than that. I have not done the calculation, but it can be close to the rest mass (see e.g. Introduction to Black Hole Physics by Valeri P. Frolov, Andrei Zelnikov, section 8.3.3). Your buddy Sean Carroll probably remembers the equations and numbers by heart.

I don’t know what tech the spacecraft uses in the movie, but it would seem very reasonable to aim your exhaust such that it maximally slows down the black hole while giving you some extra boost. Probably doable with the regular chemical/nuclear fuel, as well. Again, I am not sure off hand how much extra boost this gives you compared to the usual thrust, but it’s no more than about double, so you still have to spend in a lot of energy to get out. I suspect that nuclear fusion would not cut it. On the other hand, there is a lot of energy waiting to be used in the accretion disk (if you survive the hard gamma radiation to get there), so maybe it can be used for propulsion instead.

Or even ride the mysterious astrophysical jets out along the rotation axis. No energy expenditures required, just go with the flow, like Nemo’s dad in Gulfstream.

20. Shmi Nux Says:

Oh, and my biggest beef with this movie supposedly being scientific is their use of the back-in-time plot device. There is no deliberate back-in-time travel in GR, sorry. I mentioned it on Sean’s blog before: http://www.preposterousuniverse.com/blog/2014/10/29/the-science-of-interstellar/#comment-7295910552604300094

21. aviti Says:

“the world doesn’t need any more engineers,” now here i take ‘offense’ .:. personally. OTOH, No.5 above hits home, I was once led into thinking that lunar landings were faked and almost believed the lies, because I had the authority bias with me. When I had shaken that up, I dug on my own and realized how lame I was for being so misled. I’d rather say that it is a good movie and will watch it several times to answer my questions. IMHO, a movie about Evariste Galois is something I have been searching for.

22. Scott Says:

Shmi #20: I’m not sure I follow your argument for why CTCs are impossible in classical GR. Maybe you could clarify? The argument I knew was simply that, to maintain a wormhole, you’d need negative-energy regions (which of course don’t seem to be classically possible, and would have all sorts of weird consequences if they were). However, assuming that the null or weak energy conditions fail, do you agree with Morris, Thorne, and Yurtsever that wormholes would be classically allowed? And that once you have wormholes, you also have CTCs, since you could always accelerate one mouth of the wormhole to relativistic speed while leaving the other stationary?

The fact that the grandfather paradox would then arise—i.e., that just locally following the equations, while ignoring the global topology, would yield a ‘non-unique prediction’ for the stress-energy configuration inside the CTC—is not, of course, an argument that there can’t possibly be any issue here. It’s just a restatement of the issue.

Is your argument that the stress-energy configuration determines the spacetime geometry, and that a different stress-energy configuration would produce a different geometry with no CTC? If so, then my knowledge of GR will very quickly hit a limit … but why don’t we simply get a more sophisticated variant of the grandfather paradox? I.e., the equations predicted a CTC, which therefore, if we trace through, implies a different spacetime configuration with no CTC. But surely we could arrange things so that, in the configuration with no CTC, we go on to create a wormhole, so that there is a CTC after all?

(FWIW, my own guess is that CTCs aren’t possible, but that fully explaining why will require quantum gravity.)

23. Greg Egan Says:

FWIW, I think I was wrong to revise my estimate of the orbital radius for Miller’s world from r ≈ 1.00003766 M to r ≈ 2.000025339 M. I tried a third method and got the first result, not the second. [This is all based on the time dilation factor of 61,320, or one hour to seven years, mentioned in the movie.]

Anyway, if that’s the case the energy demands become even steeper; the specific energy of matter in the orbit becomes 0.57736, so the difference from the rest mass at infinity is about 42%. (There’s actually a limiting case here of 1/√3 for the specific energy as r goes to M, which is both the radius of the event horizon and of the smallest stable orbit, for a maximally rotating Kerr hole.)

24. Garvit Says:

1. What’s causing the blight, and the poisoning of the earth’s atmosphere? The movie is never clear about this. Is it a freak occurrence, or is it human-caused climate change? If the latter, then wouldn’t it be worth some effort to try to reverse the damage and salvage the earth, rather than escaping through a wormhole to another galaxy?

I don’t think the movie needs to be entirely clear about this and they can be afforded some cinematic leeway. They do allude to nature being ‘evil’ which sides with some ideologies of the earth fighting back through climate change. Humans do try to reverse the damage by becoming more agrarian and highly limiting higher education.

2. What’s with the drone? Who sent it? Why are Cooper and Murph able to control it with their laptop? Most important of all, what does it have to do with the rest of the movie?

It serves purposes to enlighten viewers of a. The level of technological advancement because the drone is old technologically b. Show Cooper’s inclination to science. He’s not just another cowboy farmer c. Depict the unstable nature of the world we live in, that in addition to all the climate crop issues, there are drones from past conflicts flying around d. Highlight the common interests of the father daughter relationship

3. If NASA wanted Cooper that badly—if he was the best pilot they’d ever had and NASA knew it—then why couldn’t they just call him up? Why did they have to wait for beings from the fifth dimension to send a coded message to his daughter revealing their coordinates? Once he did show up, did they just kind of decide opportunistically that it would be a good idea to recruit him?

We don’t know what soured in the past relationship between Cooper and NASA. Maybe Cooper left them and they respected that, or possibly protocol didn’t allow them to contact Cooper. Once he arrived, yes it was opportunistic.

4. What was with Cooper’s crash in his previous NASA career? If he was their best pilot, how and why did the crash happen? If this was such a defining, traumatic incident in his life, why is it never brought up for the rest of the movie?

Three hours is long enough and they leave you with just the right amount to imagine and fill in your own blanks. Immaterial in the larger scheme of things.

5. How is NASA funded in this dystopian future? If official ideology holds that the Apollo missions were faked, and that growing crops is the only thing that matters, then why have the craven politicians been secretly funneling what must be trillions of dollars to a shadow-NASA, over a period of fifty years?

NASA was going to be shut down because the government wanted resources set to food production. It’s the appearance of the wormhole that gave them a chance to prove their utility, yet it was hush hush for obvious reason. Would not go well with the public.

6. Why couldn’t NASA have reconnoitered the planets using robots—especially since this is a future where very impressive robots exist? Yes, yes, I know, Matt Damon explains in the movie that humans remain more versatile than robots, because of their “survival instinct.” But the crew arrives at the planets missing extremely basic information about them, like whether they’re inhospitable to human life because of freezing temperatures or mile-high tidal waves. This is information that robotic probes, even of the sort we have today, could have easily provided.

They did send robots on all the missions. Just with a human. If you’re going to go on a journey never experienced before how do you program a robot effectively (and also the reason you cited)

7. Why are the people who scouted out the 12 planets so limited in the data they can send back? If they can send anything, then why not data that would make Cooper’s mission completely redundant (excepting, of course, the case of the lying Dr. Mann)? Does the wormhole limit their transmissions to 1 bit per decade or something?

Yes. Transmitting through a wormhole is not simplistic.

8. Rather than wasting precious decades waiting for Cooper’s mission to return, while (presumably) billions of people die of starvation on a fading earth, wouldn’t it make more sense for NASA to start colonizing the planets now? They could simply start trial colonies on all the planets, even if they think most of the colonies will fail. Yes, this plan involves sacrificing individuals for the greater good of humanity, but NASA is already doing that anyway, with its slower, riskier, stupider reconnaissance plan. The point becomes even stronger when we remember that, in Professor Brand’s mind, the only feasible plan is “Plan B” (the one involving the frozen human embryos). Frozen embryos are (relatively) cheap: why not just spray them all over the place? And why wait for “Plan A” to fail before starting that?

The planets in our solar system are not inhabitable. To create sustainable satellites need huge energy resources that the present technology does not have. That’s the missing data in Brand’s equation which is transmitted later.

9. The movie involves a planet, Miller, that’s so close to the black hole Gargantua, that every hour spent there corresponds to seven years on earth. There was an amusing exchange on Slate, where Phil Plait made the commonsense point that a planet that deep in a black hole’s gravity well would presumably get ripped apart by tidal forces. Plait later had to issue an apology, since, in conceiving this movie, Kip Thorne had made sure that Gargantua was a rapidly rotating black hole—and it turns out that the physics of rotating black holes are sufficiently different from those of non-rotating ones to allow such a planet in principle. Alas, this clever explanation still leaves me unsatisfied. Physicists, please help: even if such a planet existed, wouldn’t safely landing a spacecraft on it, and getting it out again, require a staggering amount of energy—well beyond what the humans shown in the movie can produce? (If they could produce that much acceleration and deceleration, then why couldn’t they have traveled from Earth to Saturn in days rather than years?) If one could land on Miller and then get off of it using the relatively conventional spacecraft shown in the movie, then the amusing thought suggests itself that one could get factor-of-60,000 computational speedups, “free of charge,” by simply leaving one’s computer in space while one spent some time on the planet. (And indeed, something like that happens in the movie: after Cooper and Anne Hathaway return from Miller, Romilly—the character who stayed behind—has had 23 years to think about physics.)

It is a spinning black hole so you don’t get sucked in that way. The g force is 130% I recall. That’s all that matters to escape the planet. The payload of the docking ship is far greater than their little pod.

10. Why does Cooper decide to go into the black hole? Surely he could jettison enough weight to escape the black hole’s gravity by sending his capsule into the hole, while he himself shared Anne Hathaway’s capsule?

I guess not then. Also it’s about human resources he would use up. Also he wanted to send the singularity data to earth and he just gave himself a chance. He wasn’t keen on the new planet. He wanted to save earth and just maybe get back. Ludicrous as this sounds, it is central to the plot, because his very survival and the tesseract were placed their by Anne and the plan B ers, who knew his coordinates. A part of the big paradox, which is actually permitted by science as we know it.

11. Speaking of which, does Cooper go into the black hole? I.e., is the “tesseract” something he encounters before or after he crosses the event horizon? (Or maybe it should be thought of as at the event horizon—like a friendlier version of the AMPS firewall?)

It’s after the event horizon, though I believe in case of rotating black holes it’s called the ergo sphere. That’s why he’s not sucked in.

12. Why is Cooper able to send messages back in time—but only by jostling books around, moving the hands of a watch, and creating patterns of dust in one particular room of one particular house? (Does this have something to do with love and gravity being the only two forces in the universe that transcend space and time?)

He can send information only through gravity. The particular room and person was chosen by Anne when she made the tesseract blueprint as it was the best chance. Love was to add some spice.

13. Why does Cooper desperately send the message “STAY” to his former self? By this point in the movie, isn’t it clear that staying on Earth means the death of all humans, including Murph? If Cooper thought that a message could get through at all, then why not a message like: “go, and go directly to Edmunds’ planet, since that’s the best one”? Also, given that Cooper now exists outside of time, why does he feel such desperate urgency? Doesn’t he get, like, infinitely many chances?

The stay message is because he gets caught up emotionally reliving that instance. But on a grander scheme of things he cannot change the past as it would violate the Novikov principle and science as we know it. Only closed time curves, or consistent paradoxes are allowed.

14. Why is Cooper only able to send “quantum data” that saves the world to the older Murph—the one who lives when (presumably) billions of people are already dying of starvation? Why can’t he send the “quantum data” back to the 10-year-old Murph, for example? Even if she can’t yet understand it, surely she could hand it over to Professor Brand. And even if this plan would be unlikely to succeed: again, Cooper now exists outside of time. So can’t he just keep going back to the 10-year-old Murph, rattling those books over and over until the message gets through?

The 10 year old Murph wouldn’t know what to do with it. Also she doesn’t enter the room for years after because of the memories. Her brother and his wife preserve it for her.

16. How does Cooper ever make it out of the black hole? (Maybe it was explained and I missed it: once he entered the black hole, things got extremely confusing.) Do the fifth-dimensional beings create a new copy of Cooper outside the black hole? Do they postselect on a branch of the wavefunction where he never entered the black hole in the first place? Does Murph use the “quantum data” to get him out?

The wormhole is a construction requiring massive amounts of energy. It was never meant to be there forever. Eventually it closes, after a predetermined longevity, decided by its designer, Anne, based on a sufficient duration which should hopefully solve it’s purpose. Cooper gets spat out on the side of our solar system.

18. Speaking of which, when did Murph ever find time to get married and have kids? Since she’s such a major character, why don’t we learn anything about this?

Three hours is long enough for a movie.

….more later

25. Scott Says:

Garvit #24: Thank you for that Talmudic exegesis of the movie! And I really do mean “Talmudic”: that is, an analysis that starts from the premise that the source material is perfect and infallible, and that anything we perceive as a plot hole or inconsistency merely reflects our own limitations — and which is allowed to expend arbitrary creativity in justifying that premise. Such analyses are not exactly my taste, but they do have some value and interest.

26. Garvit Says:

19. Also, why is Murph an old woman by the time Cooper gets back? Yes, Cooper lost a few decades because of the time dilation on Miller’s planet. I guess he lost the additional decades while entering and leaving Gargantua? If the five-dimensional beings were able to use their time-travel / causality-warping powers to get Cooper out of the black hole, couldn’t they have re-synced his clock with Murph’s while they were at it?

They don’t have causality warping powers. They warp space time. Nobody time travels in the movie. Only information through gravity is sent, and that too only to create consistent closed time loops. This is science as we know it. Causality is not destroyed in any aspect of the movie and neither is any history changed. This isn’t back to the future.

20. Why does Cooper need to steal a spaceship to get to Anne Hathaway’s planet? Isn’t Murph, like, the one in charge? Can’t she order that a spaceship be provided for Cooper?

While for cinematic purposes it’s a somewhat cool way to end alluding to his never say die spirit, in all probability he is just trying out the new technology. I’m pretty sure you can’t steal a ship which would have a tone of override capabilities from the base. And go where? The wormhole is closed. He’d have to make the long journey to Edmunds, which is millions or billions of light years away. It’s not like jumping in your car to buy some smokes from the mall. There is no indication if earthlings have the technology for that. It’s just an ending.

The core struggle here arises because we 3d beings can only perceive time as linear moving forward. This story is a closed time curve ( and consistent, no grandfather paradoxes). There is only one reality. 5 d beings CANNOT mould their past. They can warp space time to communicate with the past and only effect changes that are consistent. That’s why Cooper can’t stop himself a second time by telling himself to stay, that would violate the Novikov principle. You can however make consistent changes such that nobody’s reality is questioned and causation is not broken. On wiki an example given is if you are a time traveller on the titanic you can replace bodies with dummy replicas and thus save people, but for purposes and consequences everyone’s reality will be that those passengers died. Again this is not a good example because this movie does not make any claims about physical time travel into the past, only the future. Anne’s character even states it, and their is no present known physics that supports it.

Now coming back to the movie, and your question, of which all parts should have a unifying answer, this is in my humble opinion the only plausible and satisfying answer.
After Cooper and Tars disengage into the black hole, Anne goes on and establishes a human settlement at Edmunds. She also develops blueprints for the wormhole and for the tesseract. Also note she is the only one who knows the coordinates of where the tesseract should be in space time for Cooper to have a chance. After thousands of years or so when the humans at Edmunds have evolved enough (into what is a type 3 civilization), they follow her blueprint and create the wormhole and tesseract as per her instructions. They probably don’t have a clue of what or why they are doing it, but it’s coded in their law if you may, she’s probably considered a God on their planet ( not unlike theories suggesting advanced humans landed on earth and colonized it). Sorry, I digress.
Coming back, it’s a necessary condition that Edmundians have no information of Earth, which they can’t because they are millions of light years away and no information has reached them. They are thus not altering history in any inconsistent way and not creating multiple realities. There is only one consistent reality in this movie. If Edmund was say only 15 light years away and humans their saw the end of earth they could not do anything to save it, just like Cooper can’t get himself to stay, because it’s happened and is a known reality.
Most of your other queries resonate about changing established realities, like preventing the blight – you can’t change that because it’s happened, go straight to Edmunds – can’t already didn’t.
So yes, there is a touch of paradoxical dissatisfaction, but it is scientifically legitimate. An illegitimate paradox would be saying something like, blithe survivors made the wormhole – which is akin to staring at the Eiffel Tower and telling somebody, my grandson is going to build that; a clear violation of causality. Other solutions like a random wormhole cropped up are akin to staring at the Eiffel Tower and saying it got built by random permutations of nature – garbage. Solutions relying on externalities like aliens and space wizards are completely dissatisfying partly because there is no indication to lead us there and it’s like constructing a highway and building a dam to save an anthill – will never happen.

A note about the end. A lot of people think there is something more to do. Not really and no indication either.
Do note that the wormhole is closed (that’s the tesseract breaking down, and that’s why Cooper is out of the black hole). There is no communication between Edmund and Earthlings. Earthlings are happily settled on various man modified satellites in our own solar system. This was achieved by completing the formula which allowed them to harness the levels of energy they needed for such an endeavour. Edmundians are fine by themselves. Everyone’s happy and getting along. While they are connected, both Plan A and Plan B worked out independent of each other.

27. Aaron Sheldon Says:

Scott #18

Hahahaha now that is funny,

For Scottish independence the film is very clear on the topic. The movement is completely superfluous as the Scotts will inherent the Earth, because their chief forms of sustenance are sheep, whiskey, and headbutts (do not ever under any circumstances agree to a Scottish handshake!).

For polynomial identity testing, well that was the whole point of the scene where the Indian drone gets hacked. Presumably the drone is equipped with some form of fail safe SSH-ish host. The fact that the drone could be hacked with a laptop implies some great advances have been made in discrete polynomial logarithms.

Scott #22

I’m not sure there is anything specifically in GR itself that prevents CTC. However if one requires the geodesics be infinitesimally generated by continuous paths in the algebra of the Lorentz group, which is not simply connected, then those paths cannot travel backwards because the largest normal sub-group of the algebra does not include generators of time reversed boosts.

28. Aaron Sheldon Says:

Gravit #26

The movie almost found the loophole, so to speak, in their laws of physics. Except, by your explanation, the Edmundians caused themselves to come into existence, by creating the wormhole that caused their progenitors existence. Which unfortunately returns right back to the grandfather paradox.

I think at some point it must be conceded that the movie was not meant to be a demonstration of the precision and accuracy of our understanding of the laws of physics, but rather as an imaginative and emotional exploration of the philosophical questions around the purpose and limits of life.

29. Steven Says:

If it helps:

#4 IIRC, his crash was caused by a previously unexplained ‘gravitational anomaly’, presumably induced by 5th dimensional beings. We learn this when Cooper meets the rest of the crew for the first time in the NASA conference room. I remember him muttering something silly like ‘it tripped my fly-by-wire’.

#10 I seem to recall Cooper saying to Brand as he explained his slingshot-around-the-blackhole plan that the lander was damaged and had to be piloted manually. This implies that it couldn’t be jettisoned from outside the lander, and so he must go with it.

#13 I think this is a simple as Cooper was acting like an emotional human often does. He’s just figuring out what’s going on as it’s happening, and seeing him leaving his daughter right in front of him has got to be terribly heart wrenching.

Over all, even though #3 was hard to get past, and while I was somehow able to squelch the loud voices in my head shouting ‘but the radiation!’, ‘the sheer amount of energy!’, and ‘spaghettification!!’, I think #17 bothered me the most out of all the internal inconsistencies.

Thanks for your write-up, you presented a number of things I didn’t even think about after the movie.

30. Pete Says:

I have more qualms about the pings. 1) The transmission bandwidth (1 bit per year or decade or whatever) does not seem to vary depending on which side of the wormhole one is on. It’s not like the explorers got HD video of Dr. Mann once they entered the wormhole. So there is really no explanation for not sending more data. 2) They would not have gotten 10 years of pings from the Gargantua planet – they would have known about the time dilation, so they would know they only had a few minutes of data, compared to years of data for the other candidate planets. This would have made it a poor choice to visit.

31. NKV Says:

Sometimes I think that physicists pay insufficient attention to biology. E O Wilson says that any intelligent alien would stay away from Earth because of microbes. If we need an extensive network of microbes and other biological organisms to exist, most of which we don’t even know about, how can we transport the true Noah’s Ark to set up shop in other planets?

32. Garvit Says:

Aaron #28:
That’s not a grandfather paradox. A grandfather paradox is irrational; its going back in time and killing your grandfather or preventing him from meeting your grandmother or something like that. The time traveller here knows he exists, he cannot change that reality. The grandfather paradox is basically back to the future type of stuff. That’s not possible.
A Self consistent paradox, or sometimes I believe called a Bootstrap paradox, is what is in this movie, is actually permitted by the science of today (meaning science tomorrow may not allow it, Stephen Hawking has a term for this). And yes, the Edmundians did cause their own existence, which completes the loop, but its a consistent loop. There are no multiple realities.

33. Shmi Nux Says:

Scott #22: sorry for being unclear. Spacetimes which admit CTCs are very much possible in GR, in fact they are a consequence of the Einstein’s original covariant formulation of it, the Godel universe and the Kerr metric (where there are CTCs around the ring singularity), as well as the Morris-Thorne-Yurtsever wormholes being some of the standard examples. Or you can just take a flat spacetime and replace the usual R timelike fiber with S^1, i.e. “wrap the time around”, and get CTCs that way, no fancy GR required.

The initial value formulation of GR, such as the ADM formalism, is less clear on the subject, although Amos Ori a decade or so ago constructed a reasonable-ish setup whose evolution results in a Cauchy horizon.

What I objected to is the inference that

“Spacetime X admits CTCs => One can use X to travel back in time.”
The reason is that you cannot enter or exit a CTC, you *are* the CTC. In a more comp-sci speak, there are no joins of past-you with looped-you, and no forks of future you-from looped-you. Joins and forks are local events. Changing a local matter content is equivalent to consuming/releasing E=delta-m*c^2 amount of energy from/to the environment. Thus a join would have to dissipate mc^2 amount of energy in a form of some matter/radiation leaving the area, which would be rather spectacular. This is the GR version of the Gauss law. Similarly, a fork would require consuming mc^2 worth of energy from the environment, in a form of matter and radiation miraculously converging from everywhere to form a person.

Other, join/fork-free, setups for time travel, like in Back To The Future or Harry Potter, also fail for similar reasons.

So, unless you are willing to globally split the whole universe in some way, so that your first and second pass through apparently the same events are in fact different branches, you are not going to be able to make use of CTCs. This same logic also constrains CTC-based computation circuits, or at least the way they look classically.

And if you are happy with branching the universe globally in some Everettian fashion, I would love to see some more details of this mechanism and how it is compatible with relativity. But that’s a different topic.

34. Dave R Says:

What happens if they fly too close to a plothole?

35. Scott Says:

Pete #30: Both excellent points—thanks!

I was also wondering what could possibly cause them to visit Miller first (besides plot reasons)—given that they knew the time dilation would waste precious years while the entire human race was suffering and starving back on earth. And I hadn’t even considered the point you raised, that they’d only have a few hours’ worth of advance data from Miller. That makes it particularly puzzling what happened to Miller herself a few hours prior—I guess she was swept away by a tidal wave?

Incidentally, Kip Thorne’s The Science of Interstellar arrived, and I just started reading it. I’ll post an update about how many of my 21 questions it answers. 🙂

36. Scott Says:

Shmi #33: OK, thanks very much for clarifying! So, you say that CTCs can exist in GR, but that they’re necessarily “pinched off” from the causality-respecting region of the spacetime, so that the two can’t interact with each other. And you give an argument for that, which involves the two regions being unable to exchange matter or energy. The trouble is, I’m still not convinced that the two regions would be unable to exchange information. And an exchange of information is all we would need, for an observer in the causality-respecting region to (for example) set up a CTC computer to solve a PSPACE-complete problem in polynomial time, and then observe the answer to the problem, all without ever entering the CTC herself.

Here I should clarify that, at a formal level, most of what I know about CTCs comes from David Deutsch’s model of quantum computing with CTCs, which also has a classical probabilistic analogue. In that model, there are two regions of spacetime: a CTC region as well as an ordinary causality-respecting region. You get to specify a computational transformation (say, a quantum circuit) that acts on both regions. Then, whatever superoperator is induced by your transformation on the CTC region alone, Nature is forced to find a fixed-point of that superoperator. (It can be shown that at least one fixed-point always exists; if there’s more than one, Nature gets to choose one arbitrarily.) And crucially, the fixed-point that’s stuck in the CTC region can then affect what an observer measures even in the causality-respecting region—this is how the observer can use the CTC as a computational resource. For more details, see, e.g., my paper with Watrous.

So, if GR is consistent with any exchange of information between the CTC and causality-respecting regions, that’s pretty much all I’d need from it to get observable computational superpowers—not an exchange of energy.

OK, but suppose that even an exchange of information between the CTC and the causality-respecting region were disallowed by GR. Even then, one could argue that, philosophically, giving a complete accounting of the contents of spacetime requires dealing with whatever is inside the CTC—and that, in turn, requires dealing with the issue of causal consistency (i.e., grandfather paradoxes). After all, can we be certain that we’re not in one of the CTC regions?

The situation would be a little analogous to that regarding the interiors of black holes: we can give a complete accounting of what observers outside the region (presumably including ourselves) will experience, but it still doesn’t feel like physics is done, since there’s a region that our theory describes but that we left out. (A difference, of course, is that with black holes, you can at least take a one-way trip to the interior—like dying and going to heaven or hell! Whereas with CTCs, if information exchange were prohibited at all, it would presumably be prohibited in both directions.)

37. Michael Says:

How could cooper program an analogue watch to tick in a certain looped pattern using just gravity?

38. Shmi Nux Says:

Scott #36:

First, I greatly appreciate you engaging my arguments seriously, as my area is just (a small subset of) classical GR, and I have not been able to make sense of the CTC-based quantum computing.

> So, you say that CTCs can exist in GR, but that they’re necessarily “pinched off” from the causality-respecting region of the spacetime, so that the two can’t interact with each other.

I guess this is a good summary. Certainly more accessible than what I wrote 🙂

> an exchange of information is all we would need, for an observer in the causality-respecting region to (for example) set up a CTC computer to solve a PSPACE-complete problem in polynomial time, and then observe the answer to the problem, all without ever entering the CTC herself.

Well, first, in classical GR you don’t get to construct a CTC region (since it does not have a past to construct it from)

Second, my understanding of Deutsch’s approach is not much better than what the wiki article describes: http://en.wikipedia.org/wiki/Quantum_mechanics_of_time_travel
where the quantum state in a CTC is a (not the) fixed point compatible with the quantum state outside of the CTC, and you investigated the case where such a fixed-point quantum state happened to solve a PSPACE-complete problem (sorry if I am butchering the terminology).

Now we are quite far from the events of the movie, I imagine, but whatever. We are on a dicey surface of doing QM on a curved spacetime background, with all kinds of weird firewall-like things popping up from the calculations. But hey, internal inconsistency never stopped a determined physicist. Just ask Feynman.

So we have a macroscopically invisible and undetectable CTC computer: it is not located any place we can point to from the “outside”. How did we find a CTC anyway, since we cannot construct one? Deutsch’s calculation only shows that, given a spacetime with a CTC region, it is possible to find a consistent compatible quantum state on this spacetime background, without considering any backreaction. Not that we can manipulate quantum fields to magically produce a CTC. Unless I misunderstand something major in his or your argument.

Eh, I interrupt this stream of consciousness until I get a chance to reread this old paper again: http://thelifeofpsi.com/wp-content/uploads/2014/09/Friedman-et-al.-1990.pdf as it claims that some CTCs do not violate the Gauss law, in contradiction to what I said earlier.

39. Scott Says:

Shmi #38:

Deutsch’s calculation only shows that, given a spacetime with a CTC region, it is possible to find a consistent compatible quantum state on this spacetime background, without considering any backreaction. Not that we can manipulate quantum fields to magically produce a CTC. Unless I misunderstand something major in his or your argument.

Yes, that’s exactly right.

My question about classical GR was just whether it permits the kind of interaction between CTC and causality-respecting regions that’s assumed in Deutsch’s model. Even if the answer was yes, there would still remain the question of how to manipulate fields to create the CTC, and then of course there would remain the further question of whether whatever you had done survived in quantum gravity.

40. nick Says:

In answer to #21 on why “THEY” chose the specific message by Cooper to age 10 Murph.

Its possible that LOVE had a big play along with GRAVITY to be able get anything across the ocean of space-time.

It HAD TO BE cooper and murph. They had to have deep yet quantifiable connection, that “THEY” could calculate she would never give up believing that her father also hadn’t given up. She tossed THE WATCH for 20 years in a box which she had a connection to also.

I think im onto something….? wait now im getting confused again.

41. Paulus Says:

The movie should have been split in 2 or 3 parts. It was just too much for a single one, and by doing so some minor details could have been work out a little better. If Dr. Mann argued about not sending AI’s because of their lack of survival instinct, then why not send an avatar of himself? I guess we can all agree that this cheesy option doesn’t make sense for cinematographic reasons.

42. Scott Says:

Paulus #41: Well, because of the speed-of-light barrier, sending an avatar would still require Mann himself to get very close to the planet.

As I said, if humanity really is facing imminent extinction, then they should just send out fleets of colonization crafts immediately, despite the likelihood that most of the colonists will die—since the colonists were going to die anyway. Alternatively, if there’s enough time, then they should first reconnoiter the planets using robots. In neither case does their actual plan (sending one human scout to each planet, and then relying on those humans’ cryptic, low-bandwidth, possibly-falsified reports) make the slightest bit of sense to me—particularly since, as it happened, the intelligence they got from that plan was so crummy. (I do realize, of course, that the scriptwriters relied on the plan’s crumminess to drive the plot.)

43. Trent Knebel Says:

I’d love to see a Galois film. Until then however, there’s always this Galois mini-documentary: http://www.youtube.com/watch?v=J6dsanpnpt0 .

44. david Says:

I think most questions can be answered with a “we can’t understand because our understanding of those things are too limited”. For example, how did he get out of the blackhole? Of course according to current knowledge of blackholes we could say that it’s nonsense because nothing can get out of a blackhole, even light. But maybe the blackhole is something that “we” created in the future and that we can control as much as we want, etc…

Also. I have a question that I haven’t seen answered: why are the machines going back to his house at the beginning of the movie?

45. Paulus Says:

And like you said in point 6 the physical presence of a probe in the planet’s surface might as well be unnecessary because we can study some of the biochemical properties from a distance, possibly eluding this time dilation problem.

46. Greg Egan Says:

I finally saw the movie, and I think there was a blink-and-you’ll-miss-it diagram putting Miller’s world almost on the event horizon, which would confirm that r ≈ 1.00003766 M is the orbital radius needed to get the quoted time dilation.

That implies some pretty scary tidal forces, of the order of one gee per thousand kilometres from the planet’s centre. It’s a shame they didn’t really make anything of this; assuming such a world could exist at all, there’d be much more interesting things going on than, er, monster waves that nobody seemed to anticipate, let alone spot from orbit. “Is that a mountain?”

I was left none the wiser as to how they moved between all these orbits around Gargantua, when the energy differences amounted to having about a ship’s worth of antimatter to play with. I doubt it was through any tricks for extracting energy from the hole’s rotation, since they rely on being able to emit substantial mass at a relativistic speed. If you’re in a co-rotating orbit in the ergosphere, any object you eject into the (unstable) counter-rotating orbit at the same radius will have negative energy when measured at infinity, and Penrose devised a scheme to “mine” energy from rotating holes this way. But the difference between co- and counter-rotating orbits is relativistic; merely firing normal rocket engines won’t work magic just because you’re in the ergosphere.

Anyway, I thought the movie had a few brief moments of poignancy, audacity and spectacle, but mostly it was a clunky mess and a wasted opportunity. I wish someone would take all of Christopher Nolan’s money away until he comes up with something as taut and ingenious as Memento again.

47. Scott Says:

david #44:

Also. I have a question that I haven’t seen answered: why are the machines going back to his house at the beginning of the movie?

Obviously, the correct answer is: “we can’t understand because our understanding is too limited.” 😉

48. Scott Says:

Greg Egan #46:

I wish someone would take all of Christopher Nolan’s money away until he comes up with something as taut and ingenious as Memento again.

Yeah, I found myself wondering whether the movie would be more coherent had Steven Spielberg had gone through with his original plan to direct it. The only other Christopher Nolan movie I saw was The Dark Knight (and maybe the sequel—I don’t remember!), and that one also confused me. (Here’s a wonderful Key of Awesome parody, where Batman and the Joker themselves get stumped by the movie’s plot holes.)

49. Paul Says:

As to the central paradox – how can future humans create a wormhole that must exist in order for them to have evolved in the first place – I can’t reconcile that in my mind without going to the multiverse theory. If there are infinite parallel universes there will be some where humanity survives on its own – no blight, they cure the blight, they escape Earth with technology they invent on their own, aliens save them, etc. Humans in some of those universes could evolve into 5D beings and learn to move between the universes. They could then cross over into the universe portrayed in the film to help the doomed humans in this universe by creating the wormhole etc.

Is there anything in scientific theory that would preclude this possibility?

50. Scott Says:

Paul #49:

Is there anything in scientific theory that would preclude this possibility?

Well, other than

(1) the nonexistence (as far as anyone knows) of closed timelike curves,

(2) the linearity of quantum mechanics, which precludes communication between parallel universes, at least in a world without closed timelike curves, and

(3) the nonexistence (again, as far as anyone knows) of a fifth large dimension into which humans could evolve,

no, I can’t think of a thing! 😉

Or to put it another way: given that we’re already entertaining closed timelike curves and the like, your idea involving multiple universes seems perfectly reasonable to me—and indeed, like the most reasonable way to resolve the paradox of the movie. (Alas, I can’t remember anything like this being hinted at in the dialogue.)

51. Chris Says:

I just want to know why a person in nothing but a flimsy spacesuit isn’t crushed to death by the gravity of a Black Hole. I agree with all the other flaws, but this one annoyed me the most. Cooper would have melted or something.

52. Scott Says:

Chris #51: I think that again has to do with its being a rapidly-rotating black hole.

53. Chris Bowen Says:

Or maybe the recent Phys Rev X paper published on many interacting worlds is correct and Paul’s benevolent humans in a good universe have learned to manipulate matter in the doomed universe via the interworld interaction potential to come to their rescue ;).

http://journals.aps.org/prx/abstract/10.1103/PhysRevX.4.041013

54. Joshua Zelinsky Says:

Scott, can you expand on how linearity precludes interaction between parallel universes? That’s not obvious to me.

Also, when are you go to do your next let us ask you anything thing?

55. Garvit Says:

Paul @ 49:

The central paradox is a consistent paradox and the physics of today does allow it (though heavily debated). The time loop is closed and consistent and does not defy the principle of causality.
This is as opposed to saying that descendants of blithe survivors on earth made the wormhole and sent it in the past. That is inconsistent and defies causality and is not allowed by physics. Essentially it means that the descendent of somebody on earth is going to make the wormhole. So the cause of somebody procreating will effect the building of the wormhole. But the wormhole is already there so the effect preceded the cause and thus physics does not allow it. Also it would mean that the blithe did take place, a fact recorded in history. The descendants cannot change something that happened. It would create multiple realities in the the same space time and thus violate Novikov’s theorem, or create a grandfather paradox, which our physics does not allow. Remember the scene where Cooper tries to get himself to stay. He can’t. It’s like 12 monkeys, Bruce Willis cannot change what happened and will live that loop ad infinitum.
The way, I guess, to think about it is that the story, or the loop, is prewritten. What happens on the other side of the wormhole is not time sequentially related to what happens on this side. To think of time linearity between those systems is an incorrect assumption.

56. Shmi Nux Says:

Greg Egan #46:

Strictly speaking, a photon rocket can use the Penrose effect, but without an antimatter drive or similar it will not get enough extra thrust.

Re tides, the square root of the Kretschmann scalar should be a good approximation of it. This link shows the calculation: http://iopscience.iop.org/0004-637X/535/1/350/fulltext/40794.text.html . Note that for equatorial orbits the contribution from the angular momentum disappears, so you basically get Schwarzschild tides. (I have not checked the calculation.) For a 10 million solar masses black hole this works out to about 10,000 gee per meter near the horizon, falling off as 1/R^3. Not a chance for a planet to keep its shape there.

57. Sasho Says:

That Galois biopic idea (and the title) is golden! I say you take a sabbatical to write the screenplay and start showing it to the right people.

58. fredo Says:

Interstellar sounds similar to Inception and Memento. At first glance it kind of makes sense, but when you think about it it really doesn’t make any sense at all.

I like Will Self’s quote: “Inception wasn’t the last word in SF meta-sophistication, but rather a stupid person’s idea of what an intelligent film is like.”

59. John Sidles Says:

The STEAM community can be *very* welcoming and appreciative of a recent film that:

• addresses a broad spectrum of STEAM concerns with the utmost seriousness, maturity, and professional fidelity, and

• creates a sense of wonder, and advances both the art of cinematography and our appreciation of the STEAM enterprise, even by the seamless technology of its making, and

• is contending seriously for Academy Awards in the major categories of Best Picture, Best Director, Best Actor, Best Actress, Best Supporting Actor, Best Supporting Actress, Best Original Screenplay, and Best Cinematography.

Caveat:  The name of this outstanding STEAM-relevant film isn’t Interstellar … it’s Birdman.

Falsifiable Prediction:  In none of the above eight Academy Award categories will Interstellar surpass Birdman.

It helps … in viewing both Birdman and Interstellar, to watch for the transdisciplinary themes of contemporary STEAM-centric works like Yannick Grannec’s The Goddess of Small Victories and Francis Spufford’s Red Plenty and Unapologetic.

———

The World Wonders  Why do the blackboard equations in Interstellar eschew modern mathematical notations and frameworks$$\$$— commutative diagrams and exact sequences for example$$\$$— in favor of old-fashioned tensor-index/bra-ket equations?

No wonder the capabilities of Interstellar’s earth-bound STEAM community evolve so fatally slowly!

60. Anon Says:

Great your knowledge and hanging out with a real astronaut: your are very lucky and I think working at MIT helps in meeting certain people!

Concerning Interstellar: typical low-level american-hollywood movie with poor and superficial analysis of supposedly big problems. All sounds and images and childish conversations. For sure a blockbuster for everyone but great movies are something else, even in the sci-fi realm..

61. Brian Swingle Says:

My favorite part was the tensor network behind the horizon! At least that’s what the network of bookshelves looked like to me. In particular, it really tickled me how well the idea of an array of possible moments behind the horizon accorded with recent ideas of Susskind and friends, e.g. http://arxiv.org/abs/1411.0690.

62. Greg Egan Says:

Shmi Nux #56:

For a 10 million solar masses black hole this works out to about 10,000 gee per meter near the horizon.

You’ve used a tenfold smaller mass than the hole in the movie … but I think you’ve also slipped a few decimal places somewhere. 10,000 gee per meter? I think Kip Thorne would have picketed the premiere if they’d really got it that wrong.

I worked out the tidal accelerations exactly; the results are here. I believe we essentially agree on the formulas, which give tides of order M^{-2} near the horizon (i.e. M / r^3 with rM), but Gargantua is described as being 100 million solar masses, which is about 1.5 × 10^{11} metres in geometrical units. That means the tidal acceleration in geometrical units is of the order of 4.4 × 10^{-23} per metre. One gee, or 9.8 metres per second squared, corresponds to 9.8/c^2, or about 1.1 × 10^{-16} in geometrical units.

So the tidal accelerations are of the order of 4 × 10^{-7} gees per metre, or 0.4 gees per thousand kilometres.

63. Raoul Ohio Says:

STEM experts analyzing “Interstellar” reminds me of some creative writing grad student pals (back in the day) who would debate stylistic issues of “The Phantom” at great length. It was a lot of fun.

I don’t see a lot of movies, but I have noticed that:

(1) I generally love movies that are serious stories and do a good job of getting every detail right, so my thought process is not interrupted by thinking “could not happen”. Excellent examples: “Atonement”, “The English Patient”, and “Nowhere in Africa”. These are all so intense that the theater was silent from start to finish. NIA is a true story, written by the adult version of the girl in the movie. Check them out if you get a chance.

(2) I often enjoy movies that are obviously adult cartoons, such as “Pulp Fiction”, “Ronin”, and “No Country for Old Men”. You don’t have to think about logic, evil, etc., because your brain is in cartoon mode.

(3) I tend to get P.O.’ed by movies presented as serious but where insufficient effort was put into writing a plausible plot or getting historical detail right. I feel like I have been tricked into wasting time watching an unfinished product.

(4) Science Fiction movies fit into the cartoon category. Once you understand what is possible and what is not, there is not much room to develop SF plots. To enjoy a SF movie, I suggest disabling your logic coprocessor.

If Murphy has found a way to harness gravity, and tje technology is already that good to be able to terraform a barren looking planet like Edmund, then why they cant just fixing the earth? Or at least build cities inside a giant glass house? Where they can safe from dust strom? Also creating oxygen they need?

65. Scott Says:

Joshua #54: Sorry for the delay!

can you expand on how linearity precludes interaction between parallel universes? That’s not obvious to me.

On reflection, it would be better to say: the linearity of classical probability theory, together with decoherence, is what precludes interaction between parallel universes in QM. More concretely (and let me use the Many-Worlds view for convenience), suppose the state of the universe consists of a superposition of two macroscopically-distinct configurations, W1 and W2:

α|W1> + β|W2>.

An observer will find themselves in W1 with probability |α|2, and in W2 with probability |β|2.

Now suppose a unitary transformation U is applied. Then by linearity, the new state is

U[α|W1> + β|W2>] = αU|W1> + βU|W2>.

By the assumption that W1 and W2 are macroscopically distinct (and hence, that there’s no interference between them), the observer now finds themselves in U|W1> with probability |α|2, and in U|W2> with probability |β|2. Indeed, conditioned on being in W1, we’ve simply applied U; the fact that there was also a W2 branch is now empirically irrelevant. Likewise, conditioned on being in W2, the fact that there was a W1 branch is also empirically irrelevant. This is the sense in which linearity (plus decoherence) precludes communication between parallel worlds.

Also, when are you go to do your next let us ask you anything thing?

Yeah, I’ve been thinking about it, but life has been too hectic for the last couple months. Maybe once the semester is over?

66. Shmi Nux Says:

Greg Egan #62:

Serves me right for not double-checking my numbers before posting on a public forum. Tidal acceleration per unit distance is indeed (c/R)^2, Sun’s Schwarzschild radius is about 1km, so for a 10^8 solar mass BH it is 10^-5 s^-2, or about 1 gee per 1000km, which matches what you wrote. This is right about the Roche limit (where tidal gravity is equal to self-gravity) for an Earth-like planet.

67. Joshua Zelinsky Says:

Scott at 65,

Thanks, that clarifies that pretty well.

68. Aaron Sheldon Says:

I apologize, one last comment.

The discussion of the physical plausibility of the movie has overshadowed its interpretation within the context of epic narratives such as the Argonautica, and the Iliad/Odyssey.

I thought the film did an amicable job of illustrating the universal human dialectal tensions between the desire to explore, and the desire to return, between longing for adventure, and longing for home. All in a story that was no more or less implausible than any of the Greek epics; swapping gods for exotic physics.

69. Aaron Sheldon Says:

Ah jeez I really have to stop this…

The film carries on the literature tradition of arguing that true sadness comes not from despair over unavoidable events, but rather from the tension of knowing that not all that one desires can be so; that we all must make difficulty choices between equally worthy paths.

Is the hero saddened by the apparent inevitable extinction of the human race, or the seemingly insurmountable obstacles of interstellar travel? No! He is saddened when faced with choosing between his desire to change the fate of the human race, and his desire to be with his family.

I think this points to why the ending of the film felt hollow, because it failed to recognize the tragedy in those choices. With both the safety of the human race assured, and the last of the hero’s emotionally close family members dying, we are left with a “twiddle the thumbs” sense of “ho hum what do we do know?”. The poignancy of the movie is lost when it fails to acknowledge tragedy.

Maybe I watch too much French cinema?

70. Scott Says:

Aaron Sheldon #68: Well, the movie was explicitly promoted as being “rooted in real science”; I think that fact makes it legitimate for people to ask to what extent it is (and even if not, you know nerds are going to do it anyway 🙂 ). Even then, however, notice that my questions were mostly not about the science, but rather about the logic of the plot.

71. Robert Says:

I read a comment here that the worm hole collapsed at the end .. was this said in the movie?? I thought that it was very much implied that coop was going to return to ann at the end.

coops (now old) daughter says that ann is now just landed and doing her thing on edmunds. i thought that becuase she knew this and that because it seemed to me coop was returning to her at the end that there was still access to the wormhole. Did i miss something? (after 3 hours very likely)

72. Pete Says:

Just saw the movie a second time. Indeed, as far as question (19), after the slingshot, while Cooper and Brand are still together with the endurance, Cooper says something like “that maneuver just cost us 51 years”.

73. Howard Says:

Appreciate all the commentary and naturally agree with the paradox dilemma, but have a very basic question. If Murph solved the equation to achieve Plan A, where did the people go? Did they go to another planet?

74. Scott Says:

Howard #73: My understanding is that the people all head to Edmunds’ planet—that’s what Anne Hathaway is there preparing for. (Though the mind boggles at the details of those preparations: does she need to make 7 billion beds?)

75. Howard Says:

Scott #74. Thanks for the answer. But how big could this Plan A space Station possibly be to move the earth’s population? Or does Murph’s formula allow it to exist outside the limits of 3 dimensional space so that you can fit an infinite number of people inside, like a clown car that is deceptively larger than it looks?

AND.. if the are heading to Edmunds planet via some quantum “leap”, shouldn’t they already be there? You would think they would travel faster than in a conventional space ship.

76. Scott Says:

Howard #75: It feels weird to be the one explaining this, but:

(1) I believe they have a whole network of space stations, which are the way-stations on the way to Edmunds’ planet. Cooper just visits one of them. (Now, do the remaining space stations actually hold the entire human population? All at once? And if they do, is there really an urgent need to settle a new planet? These questions are left as exercises for the reader.)

(2) No, they’re going to Edmunds’ planet in conventional spaceships, albeit spaceships that go through the same wormhole that Cooper went through before. As for why they can’t just go now to Edmunds’ planet, but have to wait around in space stations—and why, if the space stations are so nice and comfortable, they can’t just stay in the space stations—again, I remain befuddled about those points.

77. Darrell Burgan Says:

Finally saw the movie. Scott I can’t have much comment on your science questions, but many of your plot questions I think can be ascribed to a bad edit. My sense is that this movie needed to be even longer than it was to close many of the narrative gaps. I’m hoping a director’s cut happens some day.

One science question I had, which I haven’t seen anyone comment on, regards the wormhole. Wouldn’t such a massive object in relatively close proximity to Saturn cause severe orbital issues for Saturn itself, certainly its moons? Wouldn’t that black hole in orbit around the sun itself threaten humanity?

78. John Murphy Says:

OK I haven’t seen this one mentioned. Anne Hathaway’s character mentions that “they” put 12 possible planets within our reach on the other side of the wormhole, three in one system, which they visit in the movie. This implies the other 9 are in different systems on the other side of the wormhole. If the trip to Saturn takes two years, how are these other 9 systems within our reach if they are at interstellar distances on the other side of the wormhole. Stars would still be lightyears apart even in a very tight globular cluster. The other 9 Lazarus missions would take thousands of years to reach their destinations. Might as well stay in our galaxy.

79. Scott Says:

John #78: Good point! But I think I know the answer: those other systems could be reached in a few years using gravitational slingshots around yet more intermediate-mass black holes, which happen to be lying around conveniently on the other side of the wormhole.

80. mark Says:

It was obvious that Cooper should send data about quantum nature off Black holes., if he would like to ‘save the world’.

81. Greg Schaben Says:

And why would “they” put the other “end” of the wormhole in such a ridiculously dangerous, indeed almost useless place? Even the planet where Brand ends up and starts executing plan B doesn’t exactly look welcoming. Are we meant to believe there are no other earth-like planets in the entire universe that advanced 5-D beings could find?

82. ravi Says:

One question I had in mind which is related to #7 in the original list of questions is regarding communication. I think it’s not answered properly yet in the posts (I’m sorry if I have missed anything….)

It seemed that only one-way communication was possible (from Earth to Endurance) but not the other way round. But then wasn’t endurance equipped with the same technology that allowed those 12 Lazarus missions to send some basic data back to Earth? Why was Endurance not able to send anything back to Earth at all? Ideally it should have been able to send at least a ‘Thumbs Up’ every now and then so that NASA and people like Cooper’s family would know that he’s fine. Surprisingly, from the other side they are able to send their home videos!

Exactly how does communication take place in long distance space missions? I assume from Earth they direct all their communication towards the worm hole and but from the ‘other’ side is it sending data in all possible directions which makes the possibility of the data reaching the Earth infinitesimally small? On the other hand, wouldn’t there be an identical worm hole on the ‘other side’ through which they ‘come out’ after their interstellar journey? So, from the other side, communication should be equally easy or difficult.

Someone please explain. I’m not a scientist and know only the basic science facts. Apologies if I have missed anything obvious.

83. An Says:

#1: The movie includes excerpts of the PBS documentary ‘The Dust Bowl’ (http://www.pbs.org/kenburns/dustbowl/) which was a man-made disaster. The older people giving accounts of that time have actually lived through it and were also featured in the PBS documentary.
With that much reference, I conclued that the dust disaster in Interstellar was also man made.

84. Arko Bose Says:

I find Thorne’s explanation to why the quantum data was required to be a bit dissatisfying. The Newton’s constant G is a universal constant: you don’t get to pick and choose where you can reduce it and where you can leave it as it is!

Unless Thorne’s implication is that the quantum data allows Murph to learn how to achieve precisely that?

85. Shivam babel Says:

I am not an expert but why was cooper of the future trying to make his past self “stay” knowing full well that he wouldn’t have reached the black hole if his past self wouldn’t leave the earth.

86. Rick Says:

Can you address the wave planet issue? I don’t see how a mega-tsunami sized wave could be coming at them without sucking the underlying water out from under the astronauts and leaving them high and dry. Even regular ocean waves create troughs, or suck out from the beach before coming back in. That very shallow water seemed to just sit there and then they got hit by that enormous wave. Even the way they rode it seemed ridiculous, given how low they were to the wave’s crest. Surfers drop in from the point where the waves break and have to get over the lip. Not sure any of that made sense.

87. Scott Says:

Rick #86: Yes, I think I’ve now learned the rules of Interstellar well enough to answer your question. The key is that there were yet more intermediate-mass black holes, which happened to be in the right place at the right time to drag some more water under the crew’s feet, thereby cancelling the effect you mention. 😀

88. Rick Says:

Scott,

Thanks, but you’re saying that water is being sucked up into that big wave, but somehow being replaced, from the direction that the wave is coming, so that the crew can walk around without any current pulling in any direction due to intermediate, perfectly-placed black holes. I can not “fathom” how that that theory holds any water. Liquid is being sucked away from them into the wave to create the wave. If there was an equal, counteractive, force of water to create a stasis- no change in water depth or current – how could their be a wave?

89. KWillets Says:

The first objectionable plot hole for me was that they didn’t even notice that the time dilation on the time-dilated planet would affect the reporting period and the communications they received.

They later rationalize it by saying that the multiple pings they received were the same ping echoing somehow, as if all their other nonsensical decision-making does not require explanation.

90. Navneeth Says:

The reconaissance missions were sent a decade before ‘the present’ in the movie. So, Damon’s character would have taken about 2-3 years to enter the wormhole near Saturn. Once in, he goes near Gargantua, an hour spent in the vicinity of which translates to roughly 7 years in Earth time. Essentially this means that he’s spent a little over an hour on his planet — not enough time for one man to even look around at set up camp, let alone trek, collect samples and analyse them and then spend enough time to feel depressed and hibernate.

Does Prof Thorne address this issue in his book?

91. Hello Kitty Says:

Lol… Blackholes explain the tidal waves… I guess blackplotholes pretty much explain everything.

I’m just wondering what happens when Cooper goes through the wormhole to get Brand who is busily… Doing what… Planting the frozen (American… USA!) embryos into the ground? Or does she need to birth them one at a time? Oh, never mind… There are 300 surrogate black holes to help with that.

Anyway, so he gets there, and depending on how long he was in the hospital, shows up and says “Hey, thanks for planting all these eggs, but Plan A worked so nevermind.”

Wait, what was plan A, again? To send everyone to a new planet? So why was Brand all alone? How did Murph know she was? They had those ships and no one had bothered to fly to where she was and get her already? Did the space station already go through the worm hole or did it show us Saturn again (I can’t remember… I thought he was floating by Saturn). It seems to me that the wormhole had to still be there for him to just take a small ship. It also doesn’t make sense that a space station would undergo…. Wait for it… Interstellar travel the regular way. I doubt it was going the speed of light or it would have just zipped by cooper and not seen him. So it seems like it was just hovering… Were they waiting outside the wormhole to get confirmation of the best planet to go to since coms from the expedition went dead? Again, how on earth did Murph know that Brand was all alone since no one knew what happened during the mission? Oh, right, the black holes told her. Got it.

But the end still doesn’t make sense if Brand’s blackhole birthed egg humans were the 5th dimension beings. Where the hell was cooper going on that little ship if the wormhole was gone? If they lost another 51 years on the blackhole sling shot, Brand just got there. If he went and got her through the wormhole, what would happen to the eggs? Then who were the 5th dimension beings that knew about his connection with Murph? That is the part that puzzled me the most:

If the wormhole was still there, why did Cooper even have to get Brand? Why wouldn’t they have gotten her already?

Also, I got that the older Murph’s memory of the 10 year old Murph was overlapping with Cooper’s Tesseract interactions, not that he was communicating to older Murph, too. 10 year old Murph didn’t notice the second hand programming because she was too angry. Older Murph was reconstructing the ghost events and finally noticed the second hand. It had been there all those years. And so many people had died that the space station didn’t have to hold 7 billion. At least we know they saved the doctors, baseball players and pilots.

92. Scott Says:

Navneeth #90:

Does Prof Thorne address this issue in his book?

Yes. He says that Matt Damon’s planet is on a highly elliptical orbit around Gargantua, and is far away from Gargantua when they get there, so it’s not undergoing significant time dilation relative to earth.

93. Navneeth Says:

Thanks for the reply. Looks like the book is rather well-thought out, anticipating all sorts of questions that keen movie-goers are likely to raise. It’s already on my to-read list.

94. James Gallagher Says:

I loved the movie, despite the inaudible dialgue at crucial points. 🙂

I don’t understand Kip Thorne’s extravagant solution to point 9: – doesn’t the wormhole do all the effort of placing the endurance at a safe distance from Gargantua so that when the shuttle travels to Miller’s planet it gains sufficient kinetic energy (huge)? The only effort the shuttle rockets have to do is overcome the 1.3G to escape from the planet’s gravity.

I guess he’s worried that Cooper couldn’t control the HUGE deceleration required for the landing – ok, but they make a HUGE deal about the manoeuvre (“We’re supposed to get there in one piece”) – and Cooper is practically a superhero, The One, in the movie – or even, we can assume the future humans assist him here (as well as in the Tesseract via TARS)

95. Daniel Gilbert Says:

*edit*
1) I agree with other commentors that the likely cause of the blight was war. There is clearly a post-apocalyptic vibe: the Granddad mentions how there used to be 6 billion people, and how much simpler things are now. The drone is said to belong to India and according to Cooper “their satellites went down same time as ours.” So clearly there was some war going on. I think environmental damage associated with development would also be included.

2) The drone belongs to India, it’s been roaming aimlessly with no job to do since the satellites went down (apparently 10 years ago). They’ve developed computer programs to hack the drones and bring them under control. They can then use the drone computers to power massive machine equipment which is needed to take care of the massive amount of corn that is needed to compensate for the lack of any other crops.

This scene is also important in establishing the humanization of robots that exists among many people, like Murphy (and later on, Brand). It introduces Cooper’s initial lack of the empathy. I would argue we see that change over the course of the movie, especially in regards to one of the last scenes where Cooper is fixing TARS (but that’s merely my own conjecture)

96. Claudio (l'altro) Says:

Interesting review on some confusing points of the plot.
You all are arguing that at the end of the movie the wormhole is closed, but I do not remember when it is said in the movie. Is the tesseract actually the wormhole or is it another and different “structure” created by the 5D beings?
I supposed the wormhole still existed, otherwise Cooper would not have left the space colony. Notice that the fact that Cooper actually stole the spacecraft is cleared only by the following scene with the puzzled ‘guardian’: without this scene the departure of Cooper could be seen as permitted. Some script writer thought that stealing a spacecraft was more ‘cool’.

Apart Interstellar, I would like to inform you that at least one old movie about Galois already exist: its “Non ho tempo” [“I have no time”], a 1973 B/W Italian movie by the director Giannarelli, based on the book “Whom the Gods Love: The Story of Evariste Galois” by Leopold Infeld.
Indeed, the movie is very old and it is difficult to find a copy even in Italy.

Here the page on IMDB:
http://www.imdb.com/title/tt0198841/

And here the wiki page (in Italian, sorry):
http://it.wikipedia.org/wiki/Non_ho_tempo

97. Tivep Says:

Awesome stuff from Nolan, however these plot holes are hard to ignore:

http://digestivepyrotechnics.blogspot.com/2014/11/interstellar-plot-holes-explained.html

98. E.P. Says:

From the multiple fishy orbital-mechanics manoeuvres in the film, one of them really stuck out for me, and I don’t think it’s been addressed.

When TARS, and later Cooper’s ship, separate from Endurance right after the rocket burn near Gargantua, they seem to just plunk straight down into the hole. If you separate during orbit in classical gravity, what happens is… nothing. You just slowly drift apart. Is this plunking down meant to be due to tidal forces? If so, how on Earth (heh) did the damaged Endurance manage to endure those forces?

Similarly, and expanding on q. 10, why does Cooper feel he needs to jettison any mass at all? Since they’ve done the burn already, everything that was connected to the Endurance during the burn would follow pretty similar orbits. To achieve Cooper’s aims and maximize fuel efficiency, the sequence should really be (1) drop TARS, (2) burn the engines on Cooper’s ship, (3) drop Cooper, and (4) burn all the other engines. That way no fuel is spent on accelerating TARS, and as little fuel as possible is spent on accelerating Cooper’s ship.

(But then the plot looks quite different. It’s not Cooper plunking down into Gargantua, it’s Brand rocket-burning away from him.)

99. Kaitain Says:

Re: #21.
“Astute readers will note that I haven’t yet said anything about the movie’s central paradox, the one that dwarfs all the others.”

Predestination “paradoxes” are not true paradoxes. They only seem paradoxical to us, i.e. agents who assume that information can only travel forward in time. In the narrative universe of Interstellar we know that this is not the case. Note that Cooper doesn’t change the past; he becomes the agent who puts the information in the past where it has always been (and taking it from a place where it always was). This conception of our 3D spacetime as a static hypercube is what astrophysicists (and philosophers dealing with time) refer to as the B-theory of time. It is not intuitive to most humans, but it is a coherent logical idea.

From a certain point of view, the bland answer to any question that asks “…but why didn’t A do X rather than Y in this story..?” is simply: because A did Y. It is essentially written into the fabric of history: it’s a part of the static hypercube. All of history exists simultaneously, and the passage of time is to all intents and purposes the subjective experience of beings operating in three dimensions (plus time).

13. Why does Cooper desperately send the message “STAY” to his former self?

Because to begin with, he’s panicking. A little later, he calms down and realizes what he has to do.

100. Rob Says:

I think you missed a couple of things Kip addressed in the book when you updated your initial post (12, 14, 16, and somewhat 21). Also a couple of things I noted in the movie.

I’ll number these by your scheme, ignoring points you updated.

2. Unless I imagined this, they said the drone was observing crop densities for the Indians. Presumably to observe in order to increase their food levels if they invaded the USA. They said after the Indian govt/military fell apart, it kept hovering on mission for 10 years, observing the USA’s crop levels. They probably controlled it in the same way Iran took down a secret drone recently. Spoof its GPS location signals, and make it land by providing false data. I found this quite fascinating when watching

5. In the movie as mentioned earlier, they did say NASA was secretly funded to some level because of the wormhole AFAIK Realistically, I seriously doubt they’d get that much funding… but hey, artistic license right?

12. Addressed in Kip’s book. The cube tesseract face Cooper was in was big enough to dock to the side of a single room. Why? Not explained. Maybe an energy thing. So what room? His daughters. He altered things by whacking the worldlines of the particles in the books/watch with minor gravity waves.

As to why her room and not say Brand’s: It’s another paradox. The signals sent to the past conditioned her to receive the data that was sent to the past. They might not have been understood by anyone else. Paradoxus ex Machina.

13. Because, PANIC!!! But later he sends other stuff, since of course he does have other chances.

14. Addressed in Kip’s book. He does. The tesseract stores his data and repeats it all through time until 40 year old Murph gets the message. See chapter 30

16. Addressed in Kip’s book. The bulk beings put him in the cube face of a tesseract before he hit the singularity, and ripped it out of the black hole and right out of our universe into the bulk. They then moved it to earth over a period of a few minutes, and docked it against his house, then moved it back to saturn and regurgitated him back out the tesseract face near the wormhole when they collapsed it.

20. I don’t think she was in charge. Just the equivalent of a Nobel winner. No real power.

21. You may have missed the part where Murph says nobody believed her about how she solved quantum gravity. They just considered her a super-genius. So part of the design probably WAS to not influence humans too much. After all even though Cooper ended up back there, he immediately left again without explaining anything, therefore leaving things with the original narrative of supergenius Murph.

Then again, according to Kip, the last time they interacted with Cooper, they accidentally crashed his ranger on a test flight and gave him PTSD.

101. Claudio (l'altro) Says:

Re: #98
“Similarly, and expanding on q. 10, why does Cooper feel he needs to jettison any mass at all?[…]”

Nice point. I assume that this way the sequence is more “dramatic”. The correct sequence would not have been understood by the 90% of the people who do not know “rocket science” (but they are buying the tickets for the movie).
If the sequence was performed in the correct way, the scriptwriter had to explain it to the spectators (I assume, to the 90% of the spectators), and it is difficult to put such a talk in that scene. The easiest way was to write the wrong sequence, and let the 10% of the spectators complain about it 🙂

It is funny to realize (see comment #99 by Kaitain) that it was easier to write correctly the scenes involving frontiers of physics and philosophy, than the scenes involving old classic gravitational physics.

102. Mike Musson Says:

I am confused about two points.

0. I guess I have always understood a theory of quantum gravity as filling in details at extremely small and/or high energy regimes. I am confused how this understanding is related to the problem of getting the surviving humans off the Earth. There is no mention of animals but I don’t remember seeing any animals at any point during the film.

1. I have heard many times, crossing the event horizon of a sufficiently large black hole as being something so gentle you may not even notice. I don’t see how this would be the case because even without strong tidal forces you still have the one way nature of the crossing. My limited understanding is that the event horizon is vibrating in complicated ways. While an object is passing the horizon with part inside and part outside wouldn’t the fluctuating event horizon still act as a mini-tidal force ripping slices off the object as the horizon ebbs and flows.

103. Shmi Nux Says:

Mike #102:

Re 1: Yes, you have the one-way nature of the crossing. But you don’t know it when you cross until, you try to escape and after a while realize that you are not making any progress, just the opposite. As opposed to doing the same just outside the horizon and eventually getting further away, if slowly at first.

The horizon most emphatically does not “act as a mini-tidal force”. Re being ripped apart because you are in part inside and in part outside, that would only happen if you are gently lowered toward the horizon on a very long tether, not just let go. And you are ripped apart by the force the tether which lowers you exerts on you to keep you from falling freely. Because this force becomes infinitely large at the horizon.

If you are simply let go, you feel more tidal forces as you fall, but there is no spike in it at the horizon.

104. ecomostro Says:

Re: #96.

“But the one thing you know about wormholes is, they’re not real. Wormholes don’t exist because the only way they would exist is if they were seeded with exotic material created by an intelligence far beyond our own. Something would have to make one. So the idea with the film was that it was a wormhole that leads us to a place that creates an opportunity for us and then disappears. By the end of Cooper’s journey, the wormhole is gone. It’s up to us now to undertake the massive journey of spreading out across the face of our galaxy. Brand is still somewhere out there on the far side of the wormhole. The wormhole has disappeared entirely. It’s gone.” – Jonathan Nolan on his post-release interview with IGN

105. James Gallagher Says:

#104

Jonathan Nolan’s earlier draft script was rewritten by Chris Nolan, in particular, after they leave Earth it’s Chris Nolan ideas, so you can safely assume Jonathan misunderstands what happens to the wormhole.

http://www.slashfilm.com/jonathan-nolan-interstellar-interview/2/

The rangers are being prepared to go to Brand’s planet at the end (Cooper steals one to get a head start I guess) – that wouldn’t make sense if the wormhole had gone.

I saw the movie for a second time and, as someone posted above, Cooper does indeed suggest an orbital manoeuvre around a nearby Neutron star to get to Miller’s planet – I guess Nolan decided, having made the point that he was aware of the physics issues, to use artistic licence and have Cooper do an impossible but thrilling aerobraking landing – “Very graceful” is my favourite sarcastic line from Amelia in the movie.

106. Shmi Nux Says:

ecomostro #103:

Still haven’t watched the movie, but, given the oft mentioned tesseract, it is safe to assume that there are at least 4 space dimensions, and a three-dimensional slice of a four-dimensional space may look like it’s full of exotic matter, even if there is none in 4 dimensions.

107. evelyn jonna Says:

http://moviepilot.com/posts/2014/11/22/got-5-minutes-all-your-interstellar-doubts-explained-here-huge-spoilers-2453531?lt_source=external,manual,manual

108. ecomostro Says:

Re: 104.

the wormhole is not shown in any frame of film during Cooper’s final flight. We can’t assume for sure if is still there or not. Not only that, but no character refers to the wormhole being extant at that point. If the wormhole has been there for about 70 years after Cooper sent the solution to the gravity equation, why is Cooper’s flight to Edmunds’ planet the first one in all of those years? What is mankind waiting for? Well, with no more wormholes out there, human hesitation makes more sense, as for the terrestrial space stations wide spread in the solar system; although, with this solution, Cooper’s final flight looks totally senseless. It’s a cul-de-sac.

109. James Gallagher Says:

#108 ecomostro

NASA sent 12 people through the wormhole who never returned. Those people went through the wormhole because the survival of humans was at stake.

Now that the survival of humans is not at stake why would anyone volunteer to go through the wormhole?

Yeah, they can send probes, but hardly any communication gets back through the wormhole.

Cooper’s flight may or may not be the first one back to Edmunds’ planet, but you can bet he “steals” the ranger knowing he can beat all the others there.

110. Doug B Says:

how does Cooper expect to reach Hathaway planet with the wormhole closed (as Nolan himself has said)? please don’t tell me it’s a “love finds a way thing”.

111. James Gallagher Says:

Doug B #110

Either the new rangers have warp capabilities or the wormhole isn’t closed. You decide.

Note: just before Cooper is shown his new “home” on Cooper Station (purposely unbearable, courtesy of his daughter) he sees the rangers being prepared for transport, and the agent says “oh yeah, Brand” – EVERYONE is going to find Brand

112. ZJ Says:

@Aaron Sheldon #16, I just want to propose that there WERE a few references to Godel’s incompleteness theorems. Coop’s discussions with TARS about his “truth parameter” were subtly hilarious – (paraphrasing here): “Truth parameter set to 90%, sir.” Also, “I have a cue light for jokes, would you like me to use it?” “I am definitely not joking” [cue light indicating joke comes on]. I realize the liar paradox isn’t the incompleteness theorems, but it’s close enough.

I’m not sure I agree with you about the implications for the incompleteness theorems on some final grand unified theory for physics, although I feel that Godel himself probably would have agreed with you, so maybe I’m just wrong.

Also here’s my favorite rap band that uses the liar paradox as a chorus: https://www.youtube.com/watch?v=LliTqJNKJrM

113. Eric Says:

I only read #19, but yes the problem was the time that he spent via Miller’s and the time dilation of him falling into a black hole. The 5th dimensional beings were not actually able to time travel, they could simply perceive time as something that isn’t linear. One thing that was made very clear was that the only thing that can travel between dimensions was gravity (And love apparently, but not gonna get into it). A 3 dimensional being could not travel in the 4th dimension, therefore there was no way for him to “Sync” his clock.

114. Arvind Says:

I’m not sure if this was mentioned, but if they ran out of food then how are they able to continue feeding all the people on the space station? Are they just growing food on the station?

Also, is the Earth becoming uninhabitable because of food running out or are there other factors? Are the dust storms temporary or has the climate permanently changed?

115. Uzi Awret Says:

What about the next scenario: Consider a computer made up of two similar interacting parts A ad B. They have an energy source that can be both used to send them flying apart and for computing. As they accelerate away from each other both are given the same task, say discovering a couple of new primes. At some stage both A and B are convinced that their counterpart has already solved the problem that they have just began to work on. What happens when they ‘put on the breaks’ and reverse course, now heading towards each other at relativistic velocities. Does the other part lose its knowledge, forgetting the primes it had discovered? Assuming that they reunite, anything else would result in a contradiction.

116. Robert Müller Says:

One other unsolved question:

How is it possible that Romilly (the guy who stayed in the Endurance) aged 23 years while the others were visiting Miller’s planet? Cooper said something about not parking the Endurance in orbit around the planet, but in a parallel orbit around the black hole to avoid time dilation. But anyway, the Endurance must have been near enough to Miller’s planet to reach the planet with the lander within reasonable time.

I am certainly not a master in general relativity, but I would have thought that the time dilation of a black hole (even if it is rotating black hole) declines only very slowly while you move away from the black hole with non-relativistic speed. I simpy cannot imagine that there is a time dilation of 1 hour = 7 years on Miller’s planet, but there is almost no time dilation at all at a distance that can be reached within a few hours of lander travel.

117. Bob Muller Says:

I saw Interstellar last night. I teach CS, coding in particular and am known to be fairly recursion-crazed. Recursion is the first repetition idiom that my students learn. (They don’t see while-loops until week 10.) So I was a little shocked when Cooper said that Prof. Brand’s model was recursive and made no sense. I googled around and found something that appears to be the script. No recursion. And now reading your blog, I am still adrift, why was recursion in there at all other than to add something that sounds complicated?

118. Freewhird Says:

Thank you for putting up this post on your thoughts on the film. It was practically flawless as far as I am concerned (after 2 viewings). As far as depicting complex concepts in easy to understand illustrations, such as quantum existence, for mass viewing and entertainment – it was excellent imho. The actors could have showboated, but they let the story be the star. I rarely watch movies because I find them boring and predictable. This was a treat among some real compost ready films I’ve spent irrecoverable hours viewing.

119. CForne Says:

These planets are orbiting a black hole… Is its halo of light powerful enough to enlighten them as a sun would do ?

120. AnaRiley Says:

The scene where Anne said that Time could be in four dimensions there, I just shocked that what’s the science on which she is trying to let our attention? Celebsclothing

121. MarkjOwen Says:

My main “headscratcher” is…if they needed the landing vehicles to land on a planet, and they jettisoned both of the landers, how was Hathaway’s character expected to land on the planet she was heading for.

122. fred Says:

An interesting paper about the accuracy of the movie’s black hole rendering:
http://iopscience.iop.org/0264-9381/32/6/065001/pdf/0264-9381_32_6_065001.pdf

123. Links for November 2014 – foreXiv Says:

[…] Scott Aaronson lists some peculiarities of the plot of Intertellar. […]