PREFACE ⇡

Interstellar was promised to be scientific. Interstellar was promised to be a fantastic journey, an adventure never seen before. Interstellar was promised to be the intersection of Hollywood money and the fascinating world of physics and technology. Unfortunately, it is neither. It is a below average pseudo-science-fiction, a total logical nonsense with a higher than usual budget, and a shamefully missed opportunity. Let's see why.

Dude, fix your problem! ⇡

So we have a situation with crops. I would not claim to fully understand what they're saying, but what can cause crop failure on massive scale? Only some kind of germ, a virus or something, isn't it? It does not seem that hard to handle.

First, find it. You have electron microscopes. You have chemistry. Advanced analysis techniques, like mass spectrometers and others. You have all sort of things to employ when you are looking for a microbe. I mean, we have found HIV after a few years of search, and it was in 1981, and was hardly a devastating worldwide problem. You want to tell me that mankind watches the crops all fail one after the other, helpless? Or, as one character puts it, they train more and more ... farmers? Because you know, if we have less farm area every year, we need more farmers. Jeez! Not machines or scientists! No, farmers. They will surely be a great help!

Okay, let's suppose they don't find the cause. Why not try isolated indoor farming? Heat up the soil to kill all life, or use hydroponics. And then plant crops from seed banks. Are you telling me that by the time they discovered the problem, every single seed on the planet was infested, and there is absolutely no way to clean them?

Very well then. How about manufacturing nutrients? I get that it might be quite expensive, but surely better than dying in hunger. I mean, proteins, fats, vitamins ... it should not be all that hard to synthesize them.

But they don't do any of these. They come up with two plans, aptly named plan A and plan B. Plan A consists of finding a new planet, and migrating there. Excuse me, how does that help with the crops? I mean we probably still need to eat over there, so we need to bring seeds to plant. Do you think that whatever kills our food on Earth, will miraculously vanish if we move to another planet? Or do you hope to find edible vegetables there? Neither of these options seem to have any viability.

And there is plan B, populating the other planet with the astronauts, leaving everyone else to die on Earth. Now this solution might work a little better with an all female crew, don't you think? What if not Dr Hathaway, but one of the other members survives at the end alone? That much for plan B. Maybe something you should have considered. But it actually changes nothing, because you still didn't solve the main problem! What will they eat, damn it? Are we finished with all these nonsense that do not in any way address the actual problem at hand, namely the lack of food?

At the end of the movie, you can see mankind living happily on orbital stations. Risking being terribly boring, can I ask what kind of food you people were eating up there? Somehow the understanding of gravity also solved the crop problem? Or you just happened to find a solution meanwhile? But then, why not solve the situation down on Earth? Why did you go up to live in tubes? How about a plot that makes sense??

The Spaceship ⇡

Actually, nobody said the spaceship would be scientific. It was lightly implied, but that's all. But come on! It is a little too much to stomach here.

First of all. Why do we have separated compartments? Would not it be easier to have a sturdy structure, that, you know, can accelerate? Acceleration is pretty much the same thing as gravity (since the General Theory of Relativity, they are exactly the same). If you give the spacecraft one g acceleration, it is the same thing as putting it down on the ground, resting on its engines. The same kind of forces will appear, and attempt to tear the structure apart. Now does that spaceship look like a solid structure to you? That would withstand excessive forces acting upon it?

Second, the spinning. There are multiple problems associated with spinning a vehicle in space. If you want to steer a spinning mass, it will resist. I trust you remember that experiment involving a hanging bicycle wheel. It requires a whole lot of force to change the axis of the rotation. Therefore navigating a spinning object is a hassle. Another problem is the conservation of angular momentum. If you want to spin up an object, or spin it down, you will either need to use reactive forces, that is, rockets, which eject mass that you will never get back. Or you will need to store the angular momentum in a flywheel. But high mass high speed flywheels give you all sorts of engineering problems. In short, getting anything spinning in space is a serious undertaking, and you want to avoid it if at all possible. As a result, you probably want to spin only the parts humans live in, and let the cargo experience zero gravity, it does not mind. In our situation, since the crew went sleeping right away, spinning any part of the ship is a total waste of resources.

Wormhole woes ⇡

So the creators seem to have had discussions with an actual physicist who told them that wormholes don't look like discs, but spheres. The analogy would be that if you imagine two planes connected by a tube, the tube's connection to the plane is a circle, which is the 2D analogue of a sphere in 3D. A 3D wormhole is attached to our space through a 3D sphere, and extends into the 4th dimension. You can actually find animations about such a thing on the Internet. It is quite cool. Away from the hole, you see your own world. If you look right into the hole, you see the other world. And between the two, there is a region in which the two worlds are weirdly intertwined. This is due to the fact that such a geometry can not be, obviously, flat. You need to bend the space in order to form a connecting tube between two otherwise flat worlds. And as light always tries to travel as straight as it can, it goes along all sorts of spirals and circles on such a warped surface.

The creators seem to got only the fact that they need a sphere. Because how they implemented it in the movie, looks nothing like a realistic wormhole. More like a big sphere with another galaxy printed on the surface. And when they decide to hop in, some usual tunnel like special effects show up, right from the '80s. Lame! Give us an actual wormhole, damn it!

Orbital mechanics ⇡

The writers also don't seem to understand even the very basics of orbital mechanics. The spaceship does not have some super-futuristic propulsion technology, it is clear from the fact that they needed two full years to get to Saturn, which is only somewhat better than what we can do today. So they are bound by the limitations we understand very well. Or at least they should.

Our main enemy is the Tsiolkovsky rocket equation. Simply stated, it means that if you want to add more units of distance to travel, the required fuel multiplies. That is, having twice, four times, eight times as much fuel gives us only one, two or three additional chunks of distance covered. The easiest way to understand it is through a very simple thought experiment. Suppose we have a little rocket that can propel us, in some comfortable time, to a destination at a given distance. Let this be a million kilometers in one day of time. Also suppose that our cabin weights one ton, and the fuel needed to make this journey is also one ton. How much fuel we need if we want to travel another million kilometers in one more day? One way to do that is to take two more rockets, and put our first rocket with our cabin in the cargo bay. That is two tons of cargo for the two rockets. So we travel one million kilometers in one day, while using up all the two tons of fuel in the two rockets. Then we ditch the outer shell, and unpack the little spaceship in the cargo, and hop in it. Another day, another million kilometers. In total, we needed three tons of fuel. Similarly, we can travel one million kilometers more if we put our two stage rocket, totaling four tons, into a superspaceship with four engines, requiring seven tons of fuel in total. If we continue this, we get large numbers very fast. The next few numbers are 15, 31, 63 and 127. Now, this is a very rudimentary explanation, and largely lacks scientific rigor. But the actual math of the situation is not that far off from it. Alas, the result is that we need exponentially more fuel to travel larger distances.

Another concept to understand is gravity wells and delta-v. If you are in orbit around a mass, it is not easy to switch to another orbit, especially if you want to move closer or farther away from the mass. You can pretty much imagine it like a whole in the ground with sloped sides. It takes effort to climb out. The weird thing with gravity is that climbing down also needs effort. That is basically due to the law of energy conservation. As you orbit a mass, your potential energy (caused by the distance from the mass) and your kinetic energy (coming from movement) sums up to a constant, unless you do something about it. This something can be a swing around another mass, or burning a lot of rocket fuel. The change you make in your trajectory is measured by a quantity called delta-v. In the simplest case, linear acceleration, delta-v means what it sounds like: a difference between the starting and ending speeds. But in more complex situations it is more difficult than that. At any rate, it measures how much you worked on changing your movement, for example how much you climbed out of (or down) the pit. These gravity wells tend to be rather deep. For example in order to escape from the surface of the Earth and achieve a low orbit around it, you need approximately 10km/s delta-v. That is the same amount of effort as speeding up your spacecraft from a standing position to 10km/s in open space. That is some considerable speed, if you think about it. The Earth is 30km/s deep in the Sun's gravity well.

Now back to the so called science in the movie. There is basically no way with our technology to just run around in a solar (black-hole-ar?) system, and visit multiple planets within a reasonable timeframe, as we were shown. With the Tsiolkovsky equation in effect, the spaceship must have been carrying ginormous heaps of fuel. Essentially, the entire spaceship must be all fuel. Just for comparison, we launched a Delta-II rocket standing 40m tall, weighing 200 tons to get a little, one ton spacecraft in Earth orbit that was able to deliver the 185 kilogram Spirit rover to the surface of Mars. And it is the planet just next door. They didn't have neither the time nor the resources to manufacture, and put in Earth orbit, the many many billions of tons of fuel required for the journey depicted in the movie. Neither they seemed to have have huge fuel tanks.

And then, they descend to the gravity well of the black hole. How deep that gravity well might be? Just remember that the Earth's gravity well is basically one of the biggest problem we face in space exploration. How much deeper the well they had to descend into was? They actually gave us a hint: so deep the time dilation was a huge issue. According to the Theory of General Relativity, if you go down a gravity well, time slows down. It does not depend on the strength of the gravitational field, but your depth in the well. This effect is observable on Earth. That is why the GPS satellites have their clocks set differently. They are not as deep in the well as we are down here, so our clocks are a little slower. How much slower? 45 microseconds per day. That is microsecond, a millionth of a second. So the gravity well that gives us a huge headache causes a slowdown factor of 1.00000000052. It is not even noticeable if you don't have precision equipment. The well they descended into gave them a time dilation of seven years per hour. That is a factor of 61320. That is a gravity well so deep, words can't describe how deep. Our solar system is a shallow puddle compared to the steep chasm of that place. No energy or force ever created by mankind is able to put them down there, let alone get them out later. It just not going to happen.

Life Around the black hole ⇡

Planets orbiting a supermassive black hole is a good idea, because it looks good. No, seriously, this is the only reason. The problem is not what it seems to be at a glance. In fact, you can find stable orbits around a black hole, just you need to go far enough, and it is not very far at all. Also, black holes do radiate in visible light too, and thus can warm up planets and possibly feed their biosphere.

But unfortunately, black holes radiate a whole lot of gamma and x-rays. It might be all right for some kind of life. Life forms that evolved in such a hostile environment, and have some clever mechanisms to cope with the constant barrage of destructive radiation. But humans tend to react quite poorly to these bands of the electromagnetic spectra. So if you look for a new home, maybe try an actual star next time. The movie's science guy says in an interview that the idea was that it is not an accretion disk, but some unstable remnant of it, slowly cooling. I don't know who do you plan to fool with that, pal.

There is also a problem with the time dilation as presented in the movie. So we have this planet with time extremely slowed down. They find out that the person sent there possibly died minutes ago in her time, although it was decades ago for the outside world. And that is what misled them to think the planet would be habitable, as they received the signal almost to that date. Question. Should not you have realized that the radio transmission is actually a minute of content stretched out over months? How could you even receive such a slowed down signal? No doubt your radio is designed to receive a range of carrier signals. Can your radio pick up signals 60000 times below its designed frequency? And if it can, didn't you think that "Sooo faaaar iiiiiit iiiiiis fiiiiineeee" slowed down 60000 times is not a very reassuring message?

Also, a little side remark. The physics expert working for the movie is cited to say something along the lines of he was surprised how the simulations turned out. The equations were fed to a computer, but nobody expected such results. This gives you the impression that said simulations were done recently, maybe even for the movie. So we see a cutting edge scientific discovery, possibly even financed by the studio. In fact, very similar animations existed back in 1990. Granted, the results were surprising back then. But presenting it as anything new or related to the movie is just a gargantuan lie.

Every time travel plot ever ⇡

There are two possibilities. Either every time travel plot Hollywood comes up with has exactly the same problems. Or literally every time travel plot ever written has the same problems. Either way, it is advisable to follow time travel plot 101: if you want your plot not to suck, do not put time travel in it.

There are two major plot issues with all time travel stories. The first one is what they use it for. Time travel is an extremely potent capability to have. So extremely potent in fact, stories necessarily develop into a singularities if you want them to follow logic. In this movie, the guy went out of his way to communicate the coordinates of a NASA base. Why not go ahead a little bit, sneak peak into the solution for the gravity problem, and tell that instead? Or if we are at it, why not the solution to the crop problem? Or let's assume the guy was not able to travel to other places, only different times. At the end he is standing there in person, apparently somehow got out of the black hole. So here is an idea! Why not grab some relevant scientific data, and go back to the black hole once more, and tell the young girl about those? Or if you don't want to go in black holes anymore, just go to your house, dump the data on the floor, the other you can read it from the other side, and communicate to your young girl. In fact you can not fail, because if you do, you can repeat the process any number of times, you can continue to drop other people into the black hole, or present yourself any ideas in your house that you can dump on the little girl in the past.

Time travel also logically removes any sense of urgency. You have all the time in the universe to act, it does not matter when you go back in time, you can arrive at the same hour anyway. So why our heroes are so stressed? Why the hurry? Calm the f down, people, and get your act together. Of course, we understand very well why they need to act fast. It is because otherwise we had time to think the plot through, and that would ruin the experience. My bad. Please keep the pace up.

CONCLUSION ⇡

The good news is that we have a big budget movie with science in it. The bad news is science gets raped by the movie. This is the triumph of symbolism over realism. And I'm sad.