If you could hypothetically drill a perfect, airless, frictionless tunnel straight through the Earth's center and jump in, you wouldn't just fall to the middle and stop. You would experience a unique journey dictated by gravity, passing through the center and oscillating back and forth.
The Journey Begins
Upon jumping into the hole, you would immediately begin to accelerate towards the Earth's core due to gravity. Initially, the pull would be strong, similar to gravity on the surface.
Approaching the Center
As you descend deeper into the Earth, a fascinating effect of gravity comes into play. As explained in a video discussing digging a hole through the Earth, "as you get toward the center there's less Mass pulling you down." This is because a significant portion of the Earth's mass is now above you, pulling you upwards, which counteracts the mass below you pulling you downwards. The net gravitational pull pulling you towards the center decreases as you get closer to it. Despite the decreasing pull, you continue to accelerate because there's still a net force towards the center.
Reaching the Core
Your speed would be greatest when you reach the Earth's geometric center. At this point, the gravitational pull from all directions would be balanced. As the reference states, "when you reach the center... the Earth is going to be pulling you equally in all directions." This means the net gravitational force on you at the very center is zero. According to the video reference, reaching the center would take "about 21 minutes."
Passing Through
Because you reach maximum speed at the center, you wouldn't stop there. You would shoot right past it. As you move beyond the center towards the other side of the Earth, gravity, which is always pulling towards the center, would now be pulling against your direction of motion. This would cause you to start decelerating.
The Other Side and the Oscillating Fall
If the tunnel extended perfectly to the exact opposite side of the Earth (the antipode), and assuming no friction or other forces, you would theoretically decelerate until you reached a speed of zero just as you arrived at the surface on the other side. Gravity would then immediately pull you back towards the center, and the process would repeat. You would fall back through the Earth, reach the center, pass through it, and return to your starting point, oscillating back and forth indefinitely like a pendulum or a mass on a spring.
Hypothetical Journey Summary
Here's a simplified look at the key points:
| Stage | Gravitational Pull | Speed | Approximate Time to Center |
|---|---|---|---|
| Beginning of Fall | Strongest net pull towards center | Starts at zero | - |
| Approaching Center | Decreases as you get closer to center | Increases | - |
| At the Center | Net pull is zero (equal pull in all directions) | Maximum speed | ~21 minutes |
| Beyond Center | Net pull is towards center (opposite your motion) | Decreases | - |
| Other Side | Strongest net pull back towards center | Reaches zero | ~42 minutes total (approx) |
Reality Check
It's important to remember that this is a highly simplified scenario based on physics. In reality, drilling such a hole and surviving the fall would be impossible due to:
- Extreme Heat and Pressure: The Earth's core is incredibly hot and under immense pressure.
- Air Resistance: Even if the hole were initially empty, air or other gasses would fill it, creating significant drag.
- Coriolis Effect: The rotation of the Earth would cause you to hit the sides of the tunnel almost immediately unless the hole were drilled along the axis of rotation.
Therefore, in a real-world scenario, you would likely be burned, crushed, or slowed to a stop by air resistance long before reaching the center. The hypothetical scenario assumes a perfect, empty tunnel through a non-rotating Earth.
