How Long Would It Take to Fall Through the Earth?

As children growing up in the US, we often made attempts to “dig to China.” If we could just have a little more time on the playground or out in the backyard, maybe, just maybe, we could dig a hole deep enough that it would take us all the way to the other side of the Earth. We always hoped there were Chinese children on the other side digging to get to us, and we didn’t want to let them down. 

If my childhood self had known what I know now, I wouldn't have gotten my hopes up. Now I know the deepest hole ever dug is the Kola Superdeep Borehole at 7.5 miles underground—less than 0.2 percent of the Earth’s radius. And it took a hugely impressive feat of engineering to get there. Another big snag in the grand Dig-to-China plan is that the antipode of the US—that’s the spot directly opposite us on the globe—was actually somewhere in the Indian Ocean off the southeastern coast of Africa.

As children growing up in the US, we often made attempts to 'dig to China.' If my childhood self had known what I know now, I wouldn't have gotten my hopes up.

China and the US are often held up as cultural opposites, so it is possible the phrase “digging to China” was born less out of actual geography and more from a mix of ignorance and orientalism. The physical antipodes for China are better located in Chile and Argentina than anywhere in the northern hemisphere.

Want to know where your antipode is? Enter your location on this map.

But what if we had been able to make significant progress on our dig through to the other side of the Earth? I’m not sure what we were expecting. Some kind of slide? a chute all the way through? Well, it turns out physicists have thought about this problem.

What is a gravity train?

A tunnel stretching from one side of the Earth to the other, and passing through the center, is known as a gravity train. That's because you’d be letting gravity do the work of carrying you through it.

For the first half of the trip, the gravity of the Earth below pulls you down, converting all that potential energy you had standing at the surface of the Earth into kinetic energy or speed. Once you pass through the center, you gain enough speed to overcome the gravity that would otherwise pull you back down. Instead, you'd keep on moving toward the surface on the other side. It would be kind of like you were falling up.

When you get to the opposing surface, you’ll fall back down again, doomed to repeat your journey over and...

Keep reading on Quick and Dirty Tips