30 people in the same geographic area, all of whom have pacemakers, drop dead from an electromagnetic pulse. Thus begins The Core, an apocalypse movie in which a combination of science and rugged determination save the day. It’s hard to know where to begin with the badness in a movie that features the Space Shuttle landing in the L.A. River in the opening act (Can landing gear even do that?), so let’s start with the premise. The Earth’s magnetic field is being disrupted because the liquid outer core of the planet has stopped spinning. Since the fluid motion of the core is caused by convection, presumably this could happen when the outer core has cooled to the point that convection no longer occurs or when too much material has been deposited on the crust of the solid inner core. Precisely this is believed to have occurred inside Mars, causing Mars’s presumed magnetic field to collapse and its atmosphere to be largely eroded away by the solar wind (over millions and millions of years). The likelihood of this occurring on Earth is quite low, at least for another few billion years, but let’s go with it. We’ve got 3 months to restart the core before electromagnetic chaos (planes falling from the sky, dogs and cats living together) and a year before the solar wind fries the planet to a cinder.
The team of scientists assembles: Two-Face, the doctor who created Captain America, Captain Pike, and a two-time Academy Award winner join a cast of lesser-knowns to venture into the core. Thankfully one of the Red Shirts has invented an ultrasonic drill and a magic material that gets stronger as temperature and pressure increase. Convenient.
While they’re constructing the ship made of unobtainium, the plan to restart the core is revealed: detonate a thousand megatons of nukes which will start the core spinning again “like normal”. So wait, why did it stop again?
But seriously, there is a mass/yield ratio with nuclear weapons. The maximum theoretical yield for nuclear weapons is about 6 megatons per metric ton of fuel, assuming you need no casing for the weapon. (Note: you need a casing for the weapon.) So each of the five 200-megaton bombs inside the ship must contain at least 33 1/3 metric tons of fuel. Keep that in mind when, later in the film, one of these bombs, hanging from a small chain, falls onto a character’s shoulder. Guess they should’ve made the chain from unobtainium too.
Meanwhile, our hero has invented a way to see where they’re going underground: “It works like a CAT scan at the hospital”. As with dental X-rays, CAT scans work by emitting X-rays on one side of a thing (e.g., your head) and detecting them on the other side. Different materials absorb X-rays with different efficiencies (think amounts of transparency), and the detector obtains what is basically a shadow image. So if you’re aiming your X-rays into the Earth… how do you detect them?
Aside: apparently the filmmakers saw Independence Day and said, “Hey, you know that scene where the aliens blow up the White House? Give me some of that! And get us that same guy who played the president! Oh, he’s not available? Well get the closest thing.”
(Update: Embedded youtube clips seem to be broken. Here are links to the relevant Independence Day and The Core clips.)
When you have close to 3,000 km of crust and mantle to get through, why not cut off a few miles by starting at the Mariana Trench? Well for starters, it’s not the closest place to the Earth’s core. Since the earth is a prolate spheroid, bulging slightly at the equator, parts of the Arctic seafloor are 10-15 km closer to the core than the Mariana trench. If such a small difference matters, get the science right, people.
Once they’re inside the Earth, how are their communications getting back to the surface? All of our measurements from more than a couple miles down are from seismological studies. Hundreds of km of molten rock tend to absorb almost everything. Does the communicator work like a CAT scan too?
While on the way down, we see the ship maneuver in water and it has no problem with most of the materials in the crust and mantle, but it hits empty space and stalls. Then they get trapped in a giant geode, with a crystal stuck in the engine? Why can’t they just laser through it the same way they’ve been zapping through everything else?
As the team approaches the core, the inevitable happens: a hole opens up in the Earth’s magnetic field right above the Golden Gate bridge, allowing cosmic rays to vaporize it. What are the odds?
Physics 101: does just adding more plutonium make a nuclear explosion larger? Presumably they are using fusion bombs, right? Fusion bombs need a small fissile reaction to trigger the larger fusion reaction. What good is adding a little extra plu… Meh, just add a little extra. Couldn’t hurt.
Ok, here’s a question I’ll attempt to answer: what effect would a 200-megaton nuclear detonation have on the Earth’s core? 200 megatons is equivalent to the energy of a magnitude 8.75 earthquake, like Krakatoa in 1883, and 1000-megatons would be comparable to the tsunami-causing Indonesian earthquake of 2004. So the answer is… not much. Earthquakes don’t damage the Earth’s magnetic field. Even the impact that wiped out the dinosaurs didn’t disrupt the Earth’s magnetic field, and it was thought to have a power output around 10^8 megatons.
One last final comment. Towards the end of the film, the remaining heroes just shove a bundle of wires against the hot, energetic surface of the hull to generate electric power. Electrical systems don’t rely on any sort of particular regulated voltage, right? I’m sure most systems can just turn heat energy directly into electricity. I wonder if Tesla and/or Edison would have something to say about this.