# Interstellar: A hard SF film that makes no sense

I hadn’t been to the movies in a while, but Christopher Nolan’s Interstellar was hyped up to be the best hard SF film since 2001: A Space Odyssey (and that film was religious philosophy in disguise to boot).

But the story makes no sense. The science makes no sense. Although the film makes generous use of Einstein’s special and general theories of relativity, what comes out makes no scientific sense.

I’m not the first to point out some of the things that are wrong with the science in Interstellar. Here’s some comments from Scientific American via Salon:

[Interstellar] paradoxically presents interstellar travel as both ridiculously easy yet impossibly hard.

This paradox stems from the film’s central plot device: a wormhole, a tunnel through spacetime that, if traversed, could allow for essentially instantaneous travel between far-distant points. Albert Einstein and his collaborator Nathan Rosen first popularized the idea in 1935, but wormholes have since found their greatest exposure in science fiction, since they in theory offer a way to shuttle fragile, corporeal characters around the cosmos at superluminal speeds. Place one end at, say, Saturn’s orbit, and another in the heart of the Andromeda Galaxy, and a chisel-cheeked hero like Matthew McConaughey can make an intergalactic crossing in a few moments that takes light itself—the fastest thing there is—a round trip of more than 5 million years. That’s the easy, appealing, compelling part.

The hard part is that outside of decidedly speculative equations there is no evidence whatsoever that wormholes actually exist, let alone that we could ever manipulate or traverse them if they did. Based on the theoretical work of Thorne and others, making a wormhole stable enough to use would require the existence and manipulation of another entirely hypothetical thing for which we have very little actual evidence: “exotic” matter—that is, matter that possesses negative mass and energy. So, to get to the stars, all we have to do is just rely on not one but two distinct entities, both of which we do not know how to create or manipulate and which in fact may be only mathematical mirages, like the impossible staircases in an M. C. Escher lithograph. All other schemes for faster-than-light travel—warp drives, hyperspace jumps, and the like—also have similar reality-challenging requirements.

Suffice to say that the task of traveling faster than light is in all likelihood even harder than making an interstellar voyage within the firm constraints of well-understood physical laws. If you put your faith in wormholes and warp drives to take us to the stars, you might as well rely on the intercessions of gods, ghosts, and demons as well—they’ll probably help just as much, which is not at all. Wormholes and other faster-than-light travel schemes won’t take us to the stars anytime soon, if ever.

That isn’t the biggest problem for me. The greatest problem is that on the greatest canvas of all – the Universe and the laws of astrophysics, the message is trivially and cloyingly naïve: the love of between a father and his daughter transcends everything including the gravity of supermassive black holes, wormholes and even the simultaneity paradox.

It’s not that I didn’t care about the characters. It’s that the story has more holes than a hyperdimensional sieve – meaning that I lost belief in the human predicament of the characters.

There are articles pointing out a few plot holes including an article in “The Business Insider” which points out three, as well as astrophysicist Neil deGrasse Tyson on Twitter who points out quite a few more.

And then there’s Bad Astronomer Phil Plait who gives it the full treatment. For example:

Cooper [played by Mat McConaughey] successfully pilots the ship through the wormhole (which was lovely and quite well-done, even down to the much-used explanation of how wormholes work borrowed from A Wrinkle in Time), and on the other side he and his crew find the three-planet system, which is inexplicably orbiting a black hole. I sighed audibly at this part. Where do the planets get heat and light? You kinda need a star for that. Heat couldn’t be from the black hole itself, because later (inevitably) Cooper has to go inside the black hole, and he doesn’t get fried. So the planets inexplicably are habitable despite no nearby source of warmth.

I sighed audibly at this part. Where do the planets get heat and light? You kinda need astar for that.

The Planet That Wasn’t There

It turns out that one of the three planets orbits very close to the black hole, so close there will be severe relativistic effects. Relative to a distant observer, time slows down near a black hole (true), so one hour on the planet will equal seven years elapsing back on Earth. Right away, this is a big problem. To get that kind of time dilation (a factor of about 60,000), you need to be just over the surface of the black hole, and I mean just over the surface, practically skimming it. But because of the way black holes twist up space, the minimum stable orbit around a black hole must be at leastthree times the size of the black hole itself. Clocks would run a bit more slowly at that distance than for someone on Earth, but only by about 20 percent.

and

Also, there’s the problem of tides. One side of the planet is much closer to the black hole than the other side. Gravity changes with distance; the farther you are from the source, the weaker the gravity you feel. The change in the force of the black hole’s gravity across a planet’s diameter is very large, creating a tidal force that stretches the planet. That close to a black hole, the tidal force is huge, mind-(and planet-)bendingly huge. So huge, the planet would be torn to shreds, vaporized.

So if the planet doesn’t fall in, it’s crushed to literally vapor. Either way, there’s no planet.

and

The explorers go down and find it covered in water as well as suffering through periodic ginormous tidal waves sweeping around it. These are unexplained, and I assumed they were caused by tides from the black hole … but that doesn’t work either. That close to the black hole, this inexplicably unvaporized planet would be tidally locked, always showing one face toward the hole. There would be huge tidal bulges pointing toward and away from the hole, but they wouldn’t move relative to the surface of the planet. No waves.

and

OK, fine, let me give just one more: the ultimate black hole. For the climax of the movie, Cooper has to fall into it. We see a ring of material around the black hole, presumably the accretion disk: a flat, swirling disk of material that is about to fall into the hole. Because of the incredible forces involved, accretion disks are extremely hot, like millions of degrees hot. They are so brilliant, they can be seen millions of light-years away and blast out enough radiation to completely destroy any normal material.

Yet Cooper flies over one like he’s flying over Saturn’s rings (literally; it was a visual callback to an earlier scene in the movie when they actually fly past Saturn’s rings). In reality, his ship would be flash-heated to a bazillion degrees and he would be nothing more than a thin and very flat stream of subatomic particles. All right all right all right?

Also, for some reason, we don’t see the accretion disk moving; it’s static, frozen, when in reality it would be whirling madly around the black hole. And, due to the tides I mentioned earlier, as Cooper fell in he would’ve been torn apart.

I don’t know about you but the hull of the spaceship (whose constituent parts can inexplicably land and take-off multiple times from alien planets but need an enormous chemically fired, multi-stage rocket to get to orbit from Earth) was clearly made of unobtanium.

But this is a film which heavily used ideas on black holes by theoretical physicist Kip Thorne, but I found myself thinking other heretical thoughts:

• Are wormholes so massless that they can appear near Saturn and not have any measurable effect on the planet, its rings or it’s numerous moons?
• The film’s central paradox is that the black hole/wormhole construction was revealed in the film to be caused by future humans – so where did they get the technology to do this from? Other future humans? It’s worse than the chicken-and-egg paradox, isn’t it?
• How did a black hole and up having three Earth-like planets in the habitable zone? Does a black hole have a habitable zone?
• If the character Cooper falls into a black hole, won’t he take an infinite amount of time as seen by Brand [Ann Hathaway] to cross the event horizon? I know that sometimes people can wait for love, but not literally forever.

The name of the black hole, Gargantua, is clearly from Kip Thorne’s book “Black Holes and Time Warps: Einstein’s outrageous legacy”, where the supermassive black hole that Thorne discusses is also called Gargantua (weighing in at 15 trillion  solar masses).

But then I formed an even more heretical thought:

• What if black holes don’t exist?

I mean, although compact massive objects (much more massive than any neutron star) have definitely been described (including one at the centre of our own Milky Way galaxy), none of the other predictions of black hole theory have ever been observed – an event horizon, or the effects of the extreme frame-dragging of spacetime by a rotating black hole, for example.

I find myself looking at Schwarzschild’s solution for a spherically symmetric mass

${d \tau}^{2}=\left(1 - \frac{2M}{r} \right) dt^2 - \left(1-\frac{2M}{r}\right)^{-1} dr^2 - r^2 \left(d\theta^2 + \sin^2\theta \, d\varphi^2\right)$

and I wonder whether we’ve missed something…