This started as commentary regarding The Fall in the 2012 remake of Total Recall, an express transport via tunnel through the earth from the UK to Australia and back. The notion is completely preposterous due to reasons (and reasons…and reasons) but because this has been something of a thought experiment for so long, I find it actually refreshing that someone decided to give the hypothetical a nice home in a movie somewhere. Sadly, it probably won’t be remembered the way The Matrix serves as ubiquitous shorthand for simulated realities and the brains-in-jars that inhabit them, but in this case, it’s the effort that counts.
Granted, not much effort. Well, the kind of effort in design and production you expect in a mainstream feature film, and that’s a lot. But they really did fail to do their homework.
Thought experiments about holes through the Earth have been around for a while. Traditionally they’re holes to China. I think it’s more because China was a place everyone in Europe wanted to see, considering westerners hadn’t yet explored or settled the proper antipodes to China (e.g. Argentina, Chile, Uruguay, Brazil, Bolivia), and those who were already living in such places probably didn’t know about China or long to visit there.
Holes from the United States would dig you to the Indian Ocean or if you’re really precise, digging near Firstview Colorado, you can dig to Ile Saint-Paul. Or dig in a spot near Lamar to hit Ile Amsterdam. (Note, precision really is key, so map your dig project carefully before beginning or you’ll end up with a wet exit and a flooding problem.) Holes dug from France or Germany didn’t hit land either, surfacing in the South Pacific deep. Mid Spain might land you a nice exit port in New Zealand, though.
Now there are some HUGE logistics problems when it comes to digging a hole through the Earth. Some have thwarted efforts to do exactly that (though the missions of such projects were typically more humbly worded, e.g. dig as far as you can or dig until you hit oil.) The Kola Superdeep Borehole was the Soviet Union’s attempt to dig to the mantle, and while it is no longer the furthest dug (which has been exceeded by oil-seeking projects) but still retains the record for the deepest artificial point in the Earth. 12.3 kilometers down is pretty amazingly deep, but still, the Kola Borehole is a far cry from the 12,700 kilometers to penetrate to the opposite surface of the Earth. It’s even a ways from the 30 kilometers of mantle that the project was trying to pierce. The planet is big.
And, it’s just hard to dig deep, and the pressure of the Earth provides enough force to close up whatever hole you might have just opened. Pressure and vibration can cause an effect we call liquifaction in which solid or gaseous matter behave in accordance to fluid dynamics, rather than, well, like solids or gasses. This is what was happening when they stopped digging at the bottom of the Kola Superdeep. Probably just as well, given that liquefaction is foreshadowing for when we get to the Earth’s outer core, which actually is liquid. And hot.
And this is the beginning of the problems with The Fall. At the point you’re making a movie with a hole through the Earth, you might as well be making the movie about the hole through the Earth since it would be possibly the largest civil engineering project ever. Certainly larger than a space elevator. And possibly larger than a space-station the size of the Death Star.
Here are some of the problems that would have to be overcome during the project (pulled from a few other articles on holes through the Earth):
~ 12,700 kilometers times the width of the hole in displaced rubble. (More pedantically, 12,700 kilometers times the area of the hole’s shape.)
~ Monumental amounts of pressure trying to close the hole continuously. You’d need one super-amazing superstructure to keep it open.
~ Heat of the molten core (6000°K) which will be tricky to sink, given there’s an awful lot of Earth that wants to stay at that temperature. Maybe 12,700km of nuclear-reactor quality cooling system.
~ The inner core, which is still hot, but solid iron-nickel alloy. Some versions of The Fall sequence depict a graphic showing the tunnel circumvents the core. As I’m not a geologist, I have no idea how we’d cut through the inner core.
~ Interesting magnetic anomalies that will meddle with construction and the shuttle’s operation, and give geologists an endless topic on which to publish new papers.
~ Subterranean density anomalies that cause the gravity to vary. See interesting magnetic anomalies above. We’d have to compensate for these as well. Though we’re drilling a hole through The Earth. We’re clearly compensating for something.
In order to facilitate gravity driven transport (or at least gravity assisted transport), you’d have a few more issues:
~ Evacuating the entire tube to prevent problems with friction. Thankfully, this will also manage the problem of crushing air pressure near the center. Since our Total Recall heroes spent some time on the outside of the shuttle during transit neither suffocating nor getting blasted by insane wind forces, it’s not clear what solution was implemented on the Fall project.
~ 12,700 kilometers of magnetic mirrors to keep you from bouncing against the sides again and again and again. This is not just a problem with lateral micro-velocities, but also that pesky Earth’s rotation conspiring to smack you against the side. Science museums have big fancy pendulums to show how the Earth’s rotation messes with our minds. So too will it mess with our journey.
~ Speeds up to 29,000 Kilometers per hour and that’s before you do any additional acceleration. One way on a gravity-powered trip is 42 minutes. One way on The Fall takes only seventeen minutes, so it’s even faster, probably accelerated via the magnetic mirror array, above. But this makes our heroes’ extra-vehicular activities even more conspicuous. Also, unless you’re literally falling through space, I cannot imagine traveling at that speed, even being held in place by magnets, not suffering from some crazy vibrations. Another puzzle for the labcoats.
~ 42 minutes of free-fall for our passengers. Assuming a gravity-driven ride, the folks on the inside will be discovering what it’s like in orbit such as in the ISS. Many of them (me for instance) will be losing their lunch. Those lunches that don’t get diverted to a proper receptacle will bounce around the room for everyone’s entertainment. The Fall as it was portrayed in the movie had normal gravity until it approached mid-journey, at which point gravity turned off, everything turned upside-down and then the gs turned back on in the opposite direction.
The shuttle would accelerate and decelerate with gravity, but that would fling hats and loose objects to the ceiling for the duration. Our clever engineer team would compensate for this by starting and ending the journey in free fall during which they rotate the rooms upside-down (that is with heads towards the center of the Earth). That way, passengers experience acceleration / deceleration towards their feet.
That would have been cool. Maybe it’s what our movie producers intended, but the extra flips were cut for time, since The Fall was only incidental to the story.
Of course this all fails if they did as has been shown elsewhere and included a graphic showing that the journey circumvents the core by curving around it. The version of the movie I saw didn’t feature a progress map at all, so I assumed they shot straight through the inner core, which keeps gravitic forces fairly simple. These guys, however, saw the other version, and they explain the gravity of that (more sophisticated) scenario pretty well. Yet another task for the labcoats to make it easier on the passengers.
Image is of The Big Dig an art piece in the Xi’an International Horticultural Expo by the Topotek 1 Open Urban Space design team of Berlin, meant to celebrate centuries of hypothetical digging projects to China. The picture itself is used and re-used in many places on the internet, so there’s no clear ownership of it, but my (usual) gratitude to the person who took the photo.