My Little Brother The Physicist Explains 2003’s The Core

corePreviously: My brother the physicist explains Futurama and Animorphs.

Hey, John Boy. I made you watch The Core with me this week and you were a pretty good sport about it. It’s a pretty ridiculous movie — the basic premise is that the earth’s core stops rotating, dissolving the magnetic field surrounding the atmosphere, and a group of astronauts/scientists/Stanley Tucci have to set off nuclear bombs at the center of the earth to get things started again. Before we really get into things, would you mind giving us some background on the earth’s core in real life?

Short answer: SCIENCE. And lots of it.

Long answer: The earth’s core is the source of the magnetic field that surrounds Earth. Although it’s useful for navigation (compasses), its most important role is protecting earth from the sun’s “solar wind” (stream of plasma that could strip away our atmosphere). There’s some debate about this, but the conventional belief is that we wouldn’t exist without the magnetic field’s protective bubble.

The exact details of how the core generates a magnetic field aren’t well understand, but the basic concept is that the liquid iron in the core of the earth circulates electric charges as it spins, which “induces” a magnetic field.

Great, so far, so good. Everything’s checking out, science-wise.

Would it really be possible for human activity — even shadowy, government-induced EMP-weapon activity — to affect the core’s rotation? I think they described the EMP weapon of Project Destiny as “a wrench in the engine” of the earth’s core. But the earth’s core is a massive ball of iron and nickel almost 3000km below the earth’s crust! That’s one far-traveling wrench.

IF that were possible, and if the core DID stop rotating, would the earth’s magnetic field really start breaking down right away? Are there any other effects we would start to notice? Would pigeons really drop out of the sky like in this scene?

In the movie, they describe how something as small as a human EMP device could stop the earth’s core from rotating by saying how something as small as a wrench can stop an engine. But this is a horrible analogy – it’d be more accurate for them to say it’s like how a small fan can dissolve a thunderstorm. Which it can’t – kinda like how an EMP device can’t stop the earth’s magnetic field.

If the earth’s core did stop moving (or it all moved uniformly in the same direction as the earth’s crust), the magnetic field would disappear instantly. There could be aurora borealis in low latitudes (which actually did happen in the movie). Pigeons would not really drop out of the sky. They use the magnetic field to help with migration, but they can still fly without it.

Like remember that one time we went to Maine, and Mom said it felt really weird that the ocean was to the east, but she didn’t start uncontrollably heaving herself into large objects? It’d be like that.

In the movie, there were two things that struck me about the initial journey of the Virgil. One was that they decided to enter the earth’s crust through the Marianas Trench — is there any advantage to doing that rather than just starting from the ground?

The other, of course, was the premise that even thousands of miles below the earth’s surface, the crew was able to send and receive messages from the ground crew with absolutely zero delay. They even managed to send secret text messages to Rat when the ground crew wasn’t able to give them enough time to set off the bombs. Is there any way that could be possible?

Other than getting to see an MRI of those whales, no. In the 4,000 mile journey from the surface to the core, it’s a 7-mile head start. And with all the time they’d have to waste getting their ship to the Western Pacific?

No, not even close. Any signal that could go through 4000 miles of rock would also go through any antennae you used to receive it at the surface. Imagine you’re in a crowded gym with no cell service, and you need to get a message to your friend who’s all the way on the other side (and you can’t play “telephone” with the people cause they represent rocks in this analogy). Anything you send the message on that’s going to get through all those people – say, a bullet – is also going to go through your friend.

There’s a scene where the magnetic field falls apart over San Francisco and (I think?) microwave radiation destroys the Golden Gate Bridge. It melts through the steel of the bridge, but people in their cars remain perfectly safe unless they roll down their windows, in which case they are immediately burned alive. That could happen, right?

Oh man – so many things wrong with that scene. First of all, a magnetic field is structured more like a whirlpool than a bubble around the earth, so it can’t just get one “hole” in it. Also, a magnetic field can’t stop microwave radiation in the same way water can’t stop waves. Now there would be some crazy high energy ions coming through if this magic hole could exist, but they would mostly just interact with the upper atmosphere (and make pretty colors).

Even granting the movie some magic, the metal in the Golden Gate Bridge would last way longer than the dinky roof of your car. BUT while the roof of your car stayed intact (not long at the intensity they showed) it would protect you.

The magnetic field periodically reverses itself in real life, apparently. Does anything weird happen when that happens?

Actually yes. The magnetic field never “turns off” at any point in this process, but it goes from being strong and organized to weaker and more chaotic (there can be several “north poles” while this happens). More “solar wind” gets in though, and knocks some of earth’s atmosphere into space. There’s some evidence to suggest this drop in oxygen may have had a role in some mass extinctions. This would be gradual though, so it’d make for a boring movie.

Thousands of miles below the earth’s surface — like, in the mantle, the Virgil’s crew enters a geode full of amethyst crystals. Could that exist?

No – this was the dumbest part of the movie in my opinion. I’d liken this to a hollow eggshell staying intact with a rhino laying on it.

During their sojourn in the geode, the crew manages to walk around outside while wearing light, flexible suits comparable to what an astronaut wears. Would a uniform made of fabric — even threaded with Unobtanium — really protect the human body against the kind of heat and pressure found in the earth’s mantle?

No. To put this in perspective, have you ever felt the pressure change when traveling in a plane or up and down mountains? That’s about a 25% change in pressure. The pressure at the earth’s core is 330,000,000% stronger than at the surface.

The surviving terranauts manage to outrun the ultimate nuclear blast because the ship’s hull can convert heat into energy. Can you convert heat into energy?

No – that’s the whole “2nd law of thermodynamics” thing. You can turn a heat gradient into energy (hot air inside a piston in an engine pushes against cold air outside to move a car), but grabbing heat out of the surrounding environment to move a ship is straight-up magic.

Are there really nukes powerful enough to move the earth’s core? Are there any possible negative side effect of nuking the center of the Earth? Wouldn’t the crust eventually become contaminated with radiation?

A nuclear bomb in the earth’s liquid core would definitely move some stuff around. But moving the liquid iron around randomly wouldn’t restore the magnetic field – the mechanism is more complicated than that and involves some positive feedback with moving charges and induction and the coriolis effect and stuff.

Given the 3.3 GPa of pressure down there, I don’t think there’d be many negative side effects. It’d contain the explosion pretty well, and the dense radioactive elements would probably be content to hang out in the center of the earth as long as possible.

johnnyThis movie had a hacker in it named Rat. At one point he asked a four-star general “So you want me to hack…the planet?” and then asked for “a lot” of Hot Pockets. I don’t have a question, I just wondered if you wanted to comment on that.

Yeah, what the heck was with that guy? They had him in the beginning like he had a huge role, and then disappeared until the end when they had him do something completely unrelated to what his role was supposed to be. It’s like someone in the production had a really cool idea for a character after the movie was written, and they wanted to be nice so they just threw him in during the filming. And the casting director owed the make-up guy a favor so he let his nephew with no acting experience play the part.

Any other physics things you’d like to add?

Physics things – you know there’s the one part towards the end, when two of the brightest minds in physics are trying to figure out how to adjust the nuclear bomb placement in the earth’s core with the new information they have about its density, and I distinctly remember Aaron Eckhart’s character saying “Okay, torque equals r cross F, but you have to integrate over volume. What’s the bulk modulus of liquid iron?” Like they just had him say barely relevant physics things.

You were an English major, so let’s say you and a colleague found a collection of undiscovered Shakespeare plays/sonnets/whatever in a treasure chest somewhere (cue Zelda “found item” sound) and had to go through them and try to connect details about his personal life and why they were never released in his time. Then you say, “Okay, so rhyme scheme is the pattern of rhyming for a poem, but each poem has different words. What’s literary allusion again?”

That’s really funny to imagine. Thank you for your time. Do you want to play Majora’s Mask for a while? 

Yes.

John(ny) Ortberg is a physicist who works at someplace that’s “like Google Maps, but for ships, and instead of traffic we measure storms and piracy.” He’s not on Twitter or anything.

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