The Science of Interstellar

The intersection — maybe the union! — of science and sci-fi geekdom is overcome with excitement about the upcoming movie Interstellar, which opens November 7. It’s a collaboration between director Christopher Nolan and physicist Kip Thorne, both heroes within their respective communities. I haven’t seen it yet myself, nor do I know any secret scoop, but there’s good reason to believe that this film will have some of the most realistic physics of any recent blockbuster we’ve seen. If it’s a success, perhaps other filmmakers will take the hint?

Kip, who is my colleague at Caltech (and a former guest-blogger), got into the science-fiction game quite a while back. He helped Carl Sagan with some science advice for his book Contact, later turned into a movie starring Jodie Foster. In particular, Sagan wanted to have some way for his characters to traverse great distances at speeds faster than light, by taking a shortcut through spacetime. Kip recognized that a wormhole was what was called for, but also realized that any form of faster-than-light travel had the possibility of leading to travel backwards in time. Thus was the entire field of wormhole time travel born.

As good as the movie version of Contact was, it still strayed from Sagan’s original vision, as his own complaints show. (“Ellie disgracefully waffles in the face of lightweight theological objections to rationalism…”) Making a big-budget Hollywood film is necessarily a highly collaborative endeavor, and generally turns into a long series of forced compromises. Kip has long been friends with Lynda Obst, an executive producer on Contact, and for years they batted around ideas for a movie that would really get the science right.

Long story short, Lynda and Kip teamed with screenwriter Jonathan Nolan (brother of Christopher), who wrote a draft of a screenplay, and Christopher eventually agreed to direct. I know that Kip has been very closely involved with the script as the film has developed, and he’s done his darnedest to make sure the science is right, or at least plausible. (We don’t actually whether wormholes are allowed by the laws of physics, but we don’t know that they’re not allowed.) But it’s a long journey, and making the best movie possible is the primary goal. Meanwhile, Adam Rogers at Wired has an in-depth look at the science behind the movie, including the (unsurprising, in retrospect) discovery that the super-accurate visualization software available to the Hollywood special-effects team enable the physicists to see things they hadn’t anticipated. Kip predicts that at least a couple of technical papers will come out of their work.

And that’s not all! Kip has a book coming out on the science behind the movie, which I’m sure will be fantastic. And there is also a documentary on “The Science of Interstellar” that will be shown on TV, in which I play a tiny part. Here is the broadcast schedule for that, as I understand it:

Wednesday, October 29, at 10pm PDT/9c

AHC (American Heroes Channel)
Sunday, November, 2 at 4pm PST/3c (with a repeat on Monday, November 3 at 4am PST/3c)

Thursday, November 6, at 11pm PST/10c

Of course, all the accurate science in the world doesn’t help if you’re not telling an interesting story. But with such talented people working together, I think some optimism is justified. Let’s show the world that science and cinema are partners, not antagonists.

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47 Responses to The Science of Interstellar

  1. Adam says:

    I was thrilled to meet Kip whilst a SURF intern at Caltech during the summer of 2013. I walked in the first day to find the great man had taken what was supposed to be my seat! I would have let him sit there but one of the astro department admins wouldn’t have it…so he just stood up, shook my hand, asked me my name, and when I gave it simply said “Hi Adam, I’m Kip. Good luck this summer!” and went on his way. I’ve never met a living legend who was so personable and good-humored, but then again I never ran across Sean. Really looking forward to “Interstellar”.

  2. Ray Gunn says:

    I’m more interested in the logic to the premise of saving humankind by finding/traveling to a newly discovered planet. If the problem is global warming, then it should be easier to fix (re-terraform) the Earth than find a planet with just the right properties and conditions — for example atmospheric composition and pressure — to support human life. If the premise is a plague that kills humans or foodstock, then why can’t we prevent it from spreading on Earth but we can keep it from accompanying us to another planet. A cosmic catastrophe? The chance of this happening at the same point in time when we’ve just discovered a wormhole and have the technology to travel to it is extremely small.

    In terms of a logical premise, this could be another “Loopers.”

  3. Kasuha says:

    Hollywood becoming aware of science and trying to present its ideas in scientifically correct way is definitely good news but these things have been done long ago and I don’t see anything new – except the ring aroung the hole appears very Hollywood-ish to me.
    Here are some scientifically accurate animations of descent into a black hole from 2006 or so, including visualization of ring of material surrounding the black hole that came from a simulation of material accretion around a black hole:

  4. Re. the realism of the movie black hole – and whether anything was ‘discovered’ in the process of its creation – the remarks by Jean-Pierre Luminet in this discussion on FB are … illuminating.

  5. Shmi Nux says:

    > Kip recognized that a wormhole was what was called for, but also realized that any form of faster-than-light travel had the possibility of leading to travel backwards in time.

    Sean, as a GR expert, you ought to know that the metric tensor is unique at each point in spacetime (up to diffeomorphisms, of course), which makes the stress-energy tensor also unique, thus precluding any meaningful back-in-time travel in classical GR, even if the stress-energy tensor in question violates the dominant or the weak energy conditions.

    The best you can get is some matter stuck in a CTC, like in the Godel universe. What you cannot possibly get is the grandfather paradox-type stuff, no matter what matter sources you use.

    The standard time travel lore is due to the fallacious background-spacetime thinking, where one erroneously assumes that multiple different matter configurations are compatible with the same spacetime.

    I hope that the movie does not perpetuate this fallacy.

  6. Shmi Nux says:


    Indeed, JP Luminet’s , and later AC Fabian’s, accretion disk ray-tracing papers are the classic references, and now every black-hole ray-tracing code reproduces their results as a matter of course. We’ll have to see what new effects Thorne finds in this well-traveled field.

  7. It’ll be nice if the science of the story comes out right, or even mostly right, in Interstellar. I’m just as concerned about the sense of the story, though. The trailer currently showing on the film’s IMDB page suggests that a determined pilot-hero ventures into the cosmos in order to find his family a new home, though he adds in passing that he’s also doing it for a bunch of other families. Aw—he’s going to all that trouble for his family! Such a motivation isn’t inconceivable for a real person, but it’s not a very ringing ambition, and it sounds just like what we find in scores of other American movies.

  8. vmarko says:

    Having accurate science in a movie is always a step in the right direction, and is commendable.

    That said, I am afraid that the scientific accuracy in this movie might turn out to be a dissapointment. Aside from the rendering of the black hole (and also here Doppler effects have been grossly neglected, as Kip admitted, for better visual appearence), I have a sinking feeling that not much of anything else will be scientifically accurate.

    To begin with, if the wormhole is the actual Einstein-Rosen solution of GR, then both “ends” of the wormhole are within the respective event horizons. This means that the only way to traverse it is to step through the horizon, which means that — once you reach the other end of the wormhole — you remain trapped inside the horizon of the remote black hole. I don’t think that there is a way to make the wormhole traversable for a spaceship which could then exit into some solar system on the other end, at least not in ordinary GR. This is a rather obvious feature of the ER solution, which non-experts seem to misunderstand more often than not.

    Next, what about the tentative position of the BH in our solar system? How much time (let alone fuel) is needed for a spaceship to reach it from Earth? Note that the Discovery ship from Clarke’s 2001 took 18 months only to reach Jupiter. If the BH is on the outskirts of the solar system, it would take at least several years for a human-occupied spaceship to reach it. How much food, air and other resources would the crew need for such a voyage? Or do they have some powerful new fuel to speed up the ship? Note that human body cannot tolerate more than cca 10 G’s of acceleration. Is this going to be realistic in the movie?

    I won’t even attempt to discuss the landing and takeoff fuel issues once a remote-found planet has been reached.

    So, I hope to see some nice-looking pictures of a black hole (which still fail to be accurate), but unfortunately I don’t expect any scientific accuracy beyond the pictures themselves.

    Best, 🙂

  9. Shmi Nux says:


    > I don’t think that there is a way to make the wormhole traversable for a spaceship which could then exit into some solar system on the other end, at least not in ordinary GR. This is a rather obvious feature of the ER solution, which non-experts seem to misunderstand more often than not.

    Einstein-Rosen (vacuum) bridge is not timelike, so it is not a traversable wormhole unless you go FTL.

    As Kip Thorne and others showed way back in the 80s, you can construct a traversable wormhole with exotic (negative-density) matter. Matt Visser showed later than the actual amount of it can be arbitrarily small.

    The real issue with potential wormholes is their instability, which is due to Quantum mechanics and QFT, but that’s a separate issue.

  10. vmarko says:

    Shmi Nux,

    Sure, I agree that the Morris-Thorne solution is a traversable wormhole, provided exotic matter. However, this solution does not have an event horizon, or a large central massive object with an accretion disc, or any such thing. IOW, there is no black hole involved in any way.

    However, a black hole seems to be prominent in the movie. So what is going to have happened in the movie? Did they find a traversable wormhole or a black hole?

    The Schwarzschild solution cannot be used for a traversable wormhole, while the Morris-Thorne solution has nothing to do with a black hole. That’s the problem I’m having with this scenario.

    I am afraid that the scientific input of Kip Thorne was limited to how a realistic black hole would look to a camera, and nothing beyond that. I anticipate that the rest of the movie is as unscientific as it usually gets in a Hollywood production.

  11. bostontola says:

    Movies are art. If the art can be done with good science, all the better, but correct science isn’t the priority, art is (as long as it isn’t a science documentary).

  12. Shmi Nux says:


    I agree that scientific realism is a bit too much to expect from a Hollywood movie, but we’ll have to see.

    As for the Morris-Thorne-type solution, my recollection is that you can make it look like a black hole, if you line it up with just enough exotic matter inside the throat. The mass function could be something like m(r) = Mr/R0 for |r|<R0. This patches smoothly to the vacuum Schwarzschild solution for some R0<2M.

    The other throat would likely behave as a white hole for the matter leaving the wormhole, so the matter can exit through the horizon freely. Admittedly, this is not the original horizon-free M-T solution, but is based on the same idea. It can even be made bidirectional if the white hole is also a black hole, and it does not have to open to the same place as the original wormhole entrance.

  13. Ray Gunn says:

    Orbital Mechanics 101: Not only do you need a fast ship to reach the wormhole; you also need a lot of fuel to match its velocity and trajectory. New Horizons requires 10 years to reach Pluto, but it’s going to shoot by at a large relative velocity; it’s not going to stop there. Problem is, the mass of the extra fuel you need to slow down at your destination requires still more fuel to accelerate your now heavier ship at the start of your journey. Somehow I doubt this problem will be discussed in the movie.

  14. Shmi Nux says:

    Ray Gunn,

    A wormhole made with exotic matter can have arbitrarily low mass or no mass at all, and orbit the Sun or something else, like the Earth (though this is not the choice made in the movie, given how the wormhole has an accretion disk). And you do not need to slow down, just aim at it and go right through. David Weber’s “warp points” in his Starfire series describe these wormholes reasonably well… for a scifi story.

  15. Navneeth says:

    The comments section of this post ought to get the award for the ‘Nerdiest Discussion of an As-of-yet Unreleased Movie not seen by the Commentors’*.

    P.S. Enjoyed it a lot, BTW.

    *Either that or perhaps I don’t hang around comic book nerds/fora.

  16. Ray Gunn says:

    Shmi Nux,

    Good point on my previous comment!

    I’ll probably be wrong, but I’m speculating that the movie’s wormhole is actually the small sphere (seen left of center in the movie image), and the large sphere with accretion disk and gravitational bending of light is a separate black hole which is forming/powering/stabilizing the worm hole.

    Now I do want to see the movie.

  17. Ray Gunn says:

    Hi Sean. I saw your cameo last night on the the network once known as The Science Channel. Surprised they actually aired a program that wasn’t about Alien Conspiracies.

    Side note: I’m betting the next step for the former Science Channel will be to replace its Firefly mini-marathons with episodes of Stargate SG1.

  18. Gary Godfrey says:

    “Interstellar” needs the speculative notion of a wormhole kept open with negative energy to tell a human interest story where the travelers can return to their families and the rest of humanity. However, the real story of a journey to the stars would be a much lonelier one, unless all the people you need for a satisfying life came along too. Once launched, this true journey would no longer involve the Earth unless it was many human generations in the future … perhaps beyond the tenure of man.
    Strangely, our lifespan and acceleration tolerance is a perfect fit for a trip to the edge of the Universe. We would accelerate at a constant 1 gravity for 20 years, and then decelerate at 1 gravity for 20 years. An acceleration of 1 gravity for 1 year happens to give a Lorentz boost parameter of 1.0, and since collinear Lorentz boost parameters are additive, the half way boost of our spaceship relative to Earth would be 20 after 20 years. If we paused our acceleration for 1 year, our traveler’s clock would record 1 year of time passage, but Earth would record cosh(20)=2.4 E+8 years had passed. Earth would see us receding very close to the speed of light (v/c=tanh(20)), and therefore during our 1 year measure we had travelled 2.4 E+8 Lyrs.
    If we decided to return to Earth with a second 40 year trip, no one would greet us. Approximately 1 billon years would have passed on Earth since our departure. This trip is an extreme example of the Twin Paradox.
    Of course, there is the overwhelming engineering question of how to accumulate and use the enormous quantity of anti-matter for the propulsion of our rocket, but this trip is allowed by well proven physics. Perhaps Hollywood will one day weave the human drama of this story.
    As an a side, Star Trek Gene Roddenberry’s warp number has the correct magnitude to be the Lorentz boost parameter. Typical Enterprise trips within the galaxy were at warp 8, a perfectly reasonable half way Lorentz boost parameter for a few thousand Lyr trip. In one episode some aliens modified the Enterprise’s engines to give warp 12 for a trip to our neighboring Andromeda galaxy, once again a reasonable half way Lorentz boost parameter for a million Lyr trip. As a synonym for “Lorentz Boost Parameter”, “Warp” is much easier to say.

  19. John Barrett says:

    The irony of it all will be that they changed the physics of what a black hole looks like that people are used to seeing, so everyone will then think that it is just that more fake, especially if they are having to rewrite the physics on this one from working on it.

    The biggest problem I see in all movies and media is that it is like they are always driving a car in space. The top speed of a space craft would be the terminal velocity of a ship through space with a density of about 1 atom per cubic meter with a certain force of acceleration from the engines. That would be nothing like topping out driving a car.

    Say Bob and Jim are flying through space. They accelerate to 150,000 km/s faster than they started. Assuming there is no friction at all in space, they cut the engines and continue to coast at that speed. They measure the speed of light, and it is 300,000 km/s. They figure the engines must have not been working (they seem to be at rest), so they shut them down and fire them back up. They fire up the engines again to accelerate to 150,000 km/s faster. They cut the engines again and measure the speed of light. It is still 300,000 km/s. Jim tells Bob, that the engines where actually working both times. Bob tells Jim, “That is impossible, because then they would be going the speed of light. Get back to work on those engines!”.

  20. Bostontola:

    Though I agree that art is the highest priority in any fiction movie, the distinction between the genres of Sci-Fi and Fantasy is their respective degrees of realism and plausibility. This is thoughtfully discussed in an essay by the physicist, Daniel Kennefick: A Few Beasts Hissed: Buzz Lightyear and the Refusal to Believe.

    Concerning the difference between a black hole and a wormhole, Morris and Thorne’s 1987 paper is to be recommended:

    Concerning the existence of black holes, it is good to remember the warning of Einstein’s colleague, Peter G. Bergmann, who, in 1979 said:

    “A theory that involves singularities and involves them unavoidably, moreover, carries within itself the seeds of its own destruction. . . . The whole situation looks like one in which a completely new idea is required.”

    Both wormholes and black holes require “deeply troublesome” (i.e., “exotic”) states of matter. Strictly speaking, they are geometrical objects, not physical objects. Therefore, it is ironic that scientists have so far neglected to explore a patently accessible physical regime and state of matter pondered by Galileo in 1632. Galileo wondered what would happen when a test object falls into an ordinary hole through the center of an ordinary body of matter.

    For this circumstance physicists relinquish their empirical ideals and pretend to know, without evidence, the result of the experiment. It is sadly rare to find a physicist who would acknowledge the value of doing Galileo’s humble experiment. One exception is Kennefick, who wrote:

    “An experiment is worth doing even when physicists are sure they know what the result will be [because] the reward from one experiment that confounds all expectations is likely to be enormous.”

    The monetary cost of doing Galileo’s experiment dwarfs the cost of many experiments and Hollywood movies designed, proposed, or fantasized to explore various extreme states of matter.

    The Father of Modern Science, in this regard, gets no respect.

    That’s $how Biz!

  21. Latverian Diplomat says:

    I don’t know what role time travel plays in the movie, or if so, what mechanism is used to explain it. But, IIRC, in one of his books for a lay audience,

    Black Holes and Time Warps: Einstein’s Outrageous Legacy

    Kip Thorne gives a recipe for using a wormhole to make a time machine. Basically, apply the twin “paradox” to the ends of the wormhole, so that one end is the “young twin” and one the “old twin”. Traversing the wormhole now gives a fixed displacement in time to the future or the past depending on which way you traverse the wormhole. One is, of course, limited to travelling to times when the wormhole exists.

    To a time travel skeptic like me, this is an argument against the existence of wormholes, but YMMV.

    Obviously, this is a half-remembered summary of a simplified description from a popularization, so please, be kind.

  22. Robin Herbert says:

    Of course that union or intersection of science with sci-fi geekdom was first overcome with the film “Frau Im Mond”, by sci fi fan Fritz Lang (of Metropolis fame) which had Hermann Oberth as a technical consultant. It was reputedly withdrawn from screens because the rocket science was too realistic (although not the Cosmology) and might have given away technical secrets to other governments.

    On the other hand the breathable atmosphere on part of the Moon was probably more suited to the aesthetics of the film than to any realistic theory at the time.

  23. daniel says:

    Typo: “We don’t actually *know* whether wormholes”
    Good read otherwise. I am always wary of sci-fi films that try to be realistic. I prefer it to not worry and to be internally consistent rather than has up both aspects.

    But I think science needs to get better at educating the public through a medium they actually engage with!

  24. Jesse M. says:

    Shmi Nux:
    “The best you can get is some matter stuck in a CTC, like in the Godel universe. What you cannot possibly get is the grandfather paradox-type stuff, no matter what matter sources you use. The standard time travel lore is due to the fallacious background-spacetime thinking, where one erroneously assumes that multiple different matter configurations are compatible with the same spacetime.”

    You may known your physics, but you need to expand your horizons when it comes to time travel stories! There are any number of classic stories that operate under the assumption that anything the time traveler does was always a part of history so that nothing can be “changed” and everything is guaranteed to work out self-consistently, from Heinlein’s “By His Bootstraps” (where the whole point was to play around with the strangeness of these sorts of self-consistent loops) to “Bill and Ted’s Excellent Adventure” (note for example the father’s missing keys at the beginning of that movie and the later explanation for what happened to them, not to mention Bill & Ted’s conversation with themselves).

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