You’re strolling along on a hot summer's day, taking in the sights and not looking
where you’re going when OOOPPs! You’ve fallen… and you keep falling!
Holy Moly! You’re falling through the center of the Earth!
What will happen to you? Will you pop out the other side, and bounce back,
will gravity leave you stuck in the center, will you burst into flames? We’re about to find out!
I’m Stu, this is Debunked, and we’re here to sort the truths from the myths,
and the facts from the misconceptions.
Though it is a fairly common media trope, it’s pretty obvious to most people that the
idea of digging a hole through the Earth, often ending up in China, is a fanciful one indeed.
The deepest hole ever drilled by man is the Kola Superdeep Borehole,
which you can find out more about here, and despite its impressive
depth it still only got 0.3 percent of the way to the Earth’s core. Sad to say,
a true through-the-Earth tunnel is little more than a pipe-dream, pun very much intended.
Imagine for a moment, however, that such a feat were indeed possible…
imagine we did possess the technological capabilities to build a nice, stable
tunnel straight through the planet… what exactly would happen if you were to jump into the hole?
It should go without saying that the creation of a solid and sturdy tunnel
through the planet is ludicrously unfeasible for a number of reasons.
Even if we didn’t have to worry about trifling concerns like cost and where
exactly we’re going to put all the truly preposterous amounts of displaced earth,
our planet is not a solid lump of matter through which one can simply bore a hole. The Earth
has a number of internal layers that vary in density, ranging from solid to frankly gooey,
that do not behave in a single, uniform manner. These internal dynamics make the construction of
a simple 12,742 kilometer (or 7917 mile) long tunnel going from one side of the planet to
the other even more profoundly impossible than it already is.So, with the mere possibility of
creating such a hole already built on a variety of wild assumptions, what exactly would happen
to a person crazy-enough to jump into one of these hypothetical planet-piercing tunnels?
Well, without wanting to be too much of a buzzkill right out of the gate… they’d die.
Yep, sorry. They’re a goner for sure, for numerous fascinating reasons.
The first reason is the simple matter of heat. Work on the aforementioned
Kola Superdeep Borehole stopped in 1989 due to unexpectedly high temperatures
of up to 180 degrees celsius (or 356 degrees fahrenheit), and that’s only 12 kilometers down.
So unless you were wearing a very sophisticated and futuristic heat-resistant protective suit,
you’d already have burst into flames
before making it even 1 percent of your way to the center of the planet.
By the time you get to the Earth’s second layer, the mantle, temperatures rocket up
to 1,000 degrees celsius or over 1,800 degrees fahrenheit, and it only gets hotter from here.
The second principal concern to your immediate health is pressure -
the highest air pressure we experience on the surface of the Earth is a little under 16 psi,
or pounds per square inch. That’s with the full
weight of Earth’s atmosphere pressing down on top of you.
If the air pressure and temperature of the air in
the tunnel increased at the same rate as it does at the planet’s surface,
you’d only have to fall about 50 kilometres or 30miles before the pressure would exceed
15,000 psi, which is roughly equivalent to pressure found at the bottom of the ocean.
So your very sophisticated and futuristic heat-resistant
protective suit would also have to be very-well pressurized too.
But let’s make a few more far-fetched assumptions at this point and assert
that our wondrous hole-through-the-earth is not only stable, but temperature-controlled
and a sealed vacuum. That would allow us to circumvent being simultaneously burnt to a
crisp and crushed to a fine powder early on in our journey, which would be nice.
As long as you have a decent air-supply, you’re good to go, right?
Wrong!
Unfortunately, your problems don’t stop there.
Even ignoring the issues with heat and pressure, the very fact that the Earth is spinning presents
a serious threat to your successful descent, not to mention your survival.
In the same way that the outer edges of a spinning record (which are those big black
disc thingies that old people and hipsters use to play music) rotate faster than at
points closer to the centre, the surface of the Earth rotates faster than deeper sections do.
At sufficiently large scales, the consequences of this arise as the Coriolis Effect,
and mean that as the Earth rotates,
a perfectly vertical descent towards the planet’s core under only the force of gravity
will eventually move out of alignment with the tunnel itself.
This will cause you to smash into the interior walls of the tunnel at great speed. Not great.
To get around this problem, you could utilize some kind of propulsion system built into your
already very impressive suit to gently nudge you back on track as you fall through the Earth.
Alternatively, you can side-step this problem altogether by
boring the tunnel directly through the Earth’s axis of rotation,
which would require the hole to be built between the North and South pole.
So assuming you could build an impossibly stable, temperature-controlled and vacuum-sealed tunnel
directly through the Earth, as well as an incredibly advanced dive suit
to supply you with oxygen, you could in theory survive a fall into said hole.
That the tunnel is now a vacuum
also provides considerable benefits to the ease and comfort of your trip.
Traveling through air always incurs air resistance, which not only imparts
turbulence but also significantly slows you down. When the force of air
resistance on a falling object increases to equal that of the force of gravity,
said object has reached its “terminal velocity” and cannot fall any faster.
Given that the average human in a stable belly-down position has a terminal velocity
in freefall of about, 200 kilometers-per-hour (or about 120 miles-per-hour), it’s probably
going to take you well over a day of falling to reach the center of the Earth. And that’s
not even considering all the previously mentioned deadly issues with super hot and super dense air.
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Right, so let’s get back to falling through the Earth to said desired destination!
If we’re falling in a sealed vacuum, it will negate all the previously mentioned deadly issues
with super hot and super dense air, and it also means a sluggish descent is no longer a problem.
In the absence of air resistance, you’d be able to speed past terminal velocity in
a matter of seconds, and continue picking up speed at an alarming yet probably thrilling rate.
As you plummet towards the core, the resultant force being exerted on you
will be decreasing, this in turn slows the rate of your acceleration
as you approach your maximum velocity at the center of our planet.
So what sort of exhilarating speeds can you expect to hit at the equilibrium of your journey?
Well, for your futuristic dive suit let’s use your average NASA space suit as they come with
a Life Support Backpack and generally do pretty well in the vacuum of space…
Yes I’m aware space is not a true vacuum.
…one of these plus the mass of an average human is around 190kg.
Using our calculations, this means you would hit the center of the Earth at a
whopping 28,000 km/h, that’s over 17,000 miles per hour! And means,
this half of the journey would take a little over 21 minutes.
Fun fact alert! At the center of the planet, you’d also experience weightlessness akin to floating in
outer space. Unlike standing on the Earth’s surface with its mass entirely beneath you,
pulling you downwards, at the Earth’s center, the planet’s mass is all around you, pulling
you in all directions. As the Earth is near-enough spherical, these gravitational forces cancel each
other out, allowing you to merrily levitate like a scientist on the International Space Station.
Not that you’d really be there long enough to notice, given that in this situation when you
pass the Earth’s center you’d be traveling at roughly 22 times the speed of sound.
As soon as you shoot through the planet’s center, all the gravitational forces that
were acting upon you before will now begin acting upon you in the opposite direction.
The further and further you move away from the planet’s centrepoint,
the amount of the Earth that is behind you increases, progressively pulling against you.
This will slow you down considerably as you hurtle back towards the planet’s surface.
This motion your body is undergoing is referred to as Simple Harmonic Motion.
Think of it like being attached to an enormously long spring that stretches to a maximum length of
12,742,000 meters, nearly 42 million feet, which just so happens to be the diameter of our planet.
Once it reaches its maximum displacement on the other side of the planet you would come
to a complete stop at exactly the same distance from the Earth core
as the distance you fell to the Earth’s core when you jumped in.
As a result, the journey from the center of the Earth to the
other end of the tunnel will also take around 21 minutes,
for a total trip duration through the entire planet of just 42 minutes and 30 seconds.
With you now at a complete stop, your velocity will obviously be zero,
but the force exerted on you at surface level is at its maximum…
so unless you have someone there to catch you,
you’re just going to immediately start falling back down towards the center of the planet.
At this point, the process would start again, and, in the absence of anything to stop you,
you will simply oscillate through Earth indefinitely. This would
leave you oscillating sinusoidally between the opposite ends of the tunnel for all eternity,
appearing at each end every 42 minutes like some kind of haunting warning to
anyone else foolish enough to jump into a hole going through the center of the Earth.
Or you could just, y’know… grab onto the side or something.