Could You Dig a Tunnel Straight Through the Earth's Core?

If you truly want to escape everything, the farthest point you can travel from home (and still stay on Earth) is about 7,900 miles (12,700 kilometers) straight down. But to reach that depth, you'd have to take the long way around: 12,450 miles (20,036 kilometers) over land and sea.

Why not take a more direct route and go straight down? It would take you around 42 minutes—a quick enough trip for a long lunch, provided you steer clear of Mole Men, prehistoric reptiles, and other underworld creatures. Of course, most Americans would find themselves in the Indian Ocean, but Chileans could enjoy authentic Chinese cuisine, and Kiwis could savor Spanish tapas for dinner [sources: NOVA; Shegelski].

Naturally, this would be quite the challenging journey. First, you'd need to make your way through 22-44 miles (35-70 kilometers) of continental crust (3-6 miles/5-10 kilometers on the ocean floor), followed by a staggering 1,800 miles (2,900 kilometers) of mantle. Then, you'd traverse an outer core made of liquid iron, as hot as the sun's surface (10,000 degrees F, or 5,500 degrees C), followed by a solid, moon-sized inner core, and, according to some studies, a liquid innermost core [sources: Angier; Locke; NOVA].

For the sake of this thought experiment (and your survival), let’s assume Earth is a cold, uniform sphere of rock. And while we’re at it, let’s conveniently ignore air resistance.

At the surface of Earth, gravity pulls us at a rate of 32 feet (9.8 meters) per second squared. This means that every second you fall, you accelerate by 32 feet per second—at least near the surface. Gravity is a function of mass, and mass is a characteristic of matter. On the surface, all of Earth’s mass is below you, but as you fall, more and more of it surrounds you, exerting its own gravitational pull. These horizontal forces cancel each other out, but as the mass above you increases, the force it exerts grows stronger, while the mass below you decreases, slowing your acceleration as you get closer to the core. At the center of the planet, gravity reaches zero—you’re weightless as Earth’s mass surrounds you [sources: Locke; Singh].

However, you’ll still be moving at an impressive speed, so don’t expect to stop there. Halfway to the center, you’ll be traveling at 15,000 mph (24,000 kph). Just 21 minutes after jumping in, you’ll zoom past the center at 18,000 mph (29,000 kph). Another 21 minutes later, with gravity slowing you down, you’ll reach the other side and briefly float in midair. Unless someone catches you, you'll reverse direction and begin the journey again. In our idealized scenario, this process will continue indefinitely, like a pendulum or spring, in a phenomenon known as harmonic motion [sources: Plait; Shegelski; UCSB].

Of course, reality has a way of interfering with even the most imaginative thought experiments.

When Reality Crashes into Earth

Now that we've imagined a perfect rock sphere, it's time to bring things back to reality.

Under immense pressure: Digging a tunnel through the Earth would require overcoming the overwhelming pressure created by 6.6 sextillion tons of rock pressing inward—equivalent to about 3 million times the pressure at sea level [sources: Locke; Plait; UCSB].

Heavy lifting: A tunnel with a diameter of 25 feet (7.6 meters) would displace a massive 20 billion cubic feet (578 million cubic meters) of rock. That's a huge amount of material.

It's scorching down there: The Earth's interior is intensely hot due to factors like kinetic energy from early impacts, gravitational compression, internal friction, and radioactive decay [source: Plait]. In fact, the crust alone is too hot for current tunneling technology: The deepest hole ever drilled, the Kola Superdeep Borehole in Russia, reached 40,230 feet (12,262 meters)—just a small portion of the crust—before it was halted by extreme temperatures. However, scientists have managed to drill closer to the mantle on the ocean floor [sources: Fisher; Levitt; Santoski; UCSB].

Mass effect: Variations in crustal mass, caused by mountains and oceanic trenches, are insignificant when compared to the varying densities of Earth's interior, which increase as you approach the core. This results in your acceleration fluctuating more than we've previously described [sources: Reich; Singh; UCSB].

Fatal attraction: Thanks to the Coriolis effect and angular momentum, your sideways movement will inevitably propel you into a wall before you descend very far into the shaft.

To understand why, picture a hole drilled from the equator. Whether you're standing on Earth's surface or near the core, you complete a full revolution every 24 hours, but the distance traveled is different: on the surface, you cover 24,900 miles (40,000 kilometers), whereas halfway to the core, it's only half that. As you fall, you'll keep your 1,000 mph (1,600 kph) eastward speed, while the surrounding walls move slower eastward, causing you to crash into them.

To avoid a painful fall, you could drill from pole to pole, where the Coriolis effect is absent. But eventually, solar and lunar gravity, which also influence orbiting satellites, would draw you toward the tunnel wall regardless [source: Darling].

Strike a chord: Fun fact: A straight path from any point to another through the Earth would take the same amount of time as a journey through a tunnel to the planet's center. Even though the tunnel would be shorter, gravity would exert less pull, making the journey longer [sources: Plait; Shegelski].

On the bright side, if you were to turn the journey into a tourist destination or a really extended subway ride, the fuel expenses would be practically nonexistent.