The trip would take about 42 minutes—in an ideal model
In the familiar physics thought experiment, a frictionless tunnel through Earth delivers you to the opposite surface in roughly 42 minutes. That estimate assumes Earth has uniform density and ignores air resistance, heat, pressure, and the tunnel’s construction. It is a useful mathematical result, not a practical travel time.
Gravity speeds you up, then slows you down
At the entrance, gravity pulls you toward Earth’s center, so you accelerate as you fall. But gravity does not keep increasing all the way down: in the uniform-density model, the pull from the surrounding Earth partly cancels, leaving a net force that gets weaker as you approach the center. At the exact center, the pulls balance and gravity is zero.
You would be moving fastest there. After passing it, gravity points back toward the center, now slowing you as you climb toward the far side. You reach the opposite surface just as your speed falls to zero—then, with nothing to stop you, you would fall back again.
Why the timing is surprisingly simple
Inside a uniformly dense Earth, the inward pull is proportional to your distance from the center. That makes the motion a kind of back-and-forth oscillation, like a weight on a spring. The full cycle—from the starting point to the other side and back—takes about 84 minutes, so the one-way trip takes half that time.
Earth is not uniformly dense, and a real tunnel would face crushing pressure, extreme heat, and resistance from air. Those conditions change the practical problem; the 42-minute answer comes from the clean, frictionless model, where gravity alone carries you through.
