Journey to the Center of the Earth

Okay, this is probably a lame question, so I’ll apologize beforehand. Nevertheless, I posted a comment to someone in the Pit that he was digging a hole so deep that he was nearing China. That got me to thinking about this question:

If we were able to dig a hole through the center of the Earth to the other side, at what point would the dirt be above us instead of below? Exactly in the middle? Would gravity pull the dirt down into the hole at that point? If we were in a hole exactly in the center of the Earth, which way would gravity pull us?

Does anyone know?

Well, you would only have to go down a few feet before the dirt was above you. “Dirt” is only a thin scrum on top of all the rocks.

If you were right at the center you would be weightless, as the mass/attraction on any side of you would balance off the mass/attracation from any other side.

I should have said, “how long before you would be digging up instead of down?”
Thank you for your answer.

If you were digging to China, you would start by diggin a slanted hole going west (from the continental US, that is).

As you proceeded you would dig slightly “up” as your gravity sense told you.

About the point that you feel that you’re diggin a horizontal tunnel, you’d be under the International Date Line.

The rest of the digging would be “uphill”, until you came out in China.

E.g., digging from LA to Shanghai, your tunnel would start going west at a 60[sup]o[/sup] slope (2 meters depth per 1 meter westward. It would emerge in China mirrored, coming from the east at 60[sup]o[/sup].

At the halfway point, you’d be about 3200 km below the surface.

Well, the depends on how we define “middle”. Geometry (as in, “the earth is not a perfect sphere”) alone won’t cut it. You also need to consider the mass of the earth, which is not equally distributed, neither on the surface, nor deep underground.

As you dig down, more eather will be above you than below, which will counteract the gravty pulling from below. When you are at a point where the mass is equally distributed in all directions, you will be weightless. Keep going a bit further in the same direction, and you’ll find that now that direction is called “up”.

As you continue digging up, gravity will become stronger. Eventually, depending on various factors such as the width of this tunnel, there may indeed be a danger of a cave-in. Of course, we are conveniently ignoring the fact that this tunnel would be “dug” through molten rock for most of its length!

You wouldn’t want to dig straight down. You’d emerge at the bottom of the Indian Ocean about 1600 km from Madagascar.

DrFidelius: you’ve now got a fan in me for your apt description of dirt… “scum”, indeed!

Anyway, say you could dig all the way through the lithosphere… the ductile asthenosphere would continuously close up your hole and thwart your progress, anyway!

But assuming the Earth was made of dirt (shudder!)… I dunno. I’d say “halfway”.

Isaac Asimov pointed out in an essay that the reason we’ll never have tunnels through the center of the earth, aside from the molten core, is that no major city is even near to diametrically opposed on the globe to any other.

Never attribute to an -ism anything more easily explained by common, human stupidity.

Something like 98% of the land mass is antipodal to water, but Santiago Chile is antipodal to the interior of China, I believe.

There’s an interesting quirk of the density profile of the earth–if you were to dig down, the force of gravity wouldn’t steadily decrease as you go deeper. In fact, it stays pretty much constant all the way to the earth’s core, where there is a slight maximum.

The force of gravity is the same for the earth reguardless of your location. The center of a mass might not be the same as the point where the pull of gravity is equal all around you.

Since gravity is the attraction a mass has on another mass. In the center of a homoginous mass, it still has the same gravity, but it’s pulling you equally in all directions. You could be ripped to pieces in the center of a large gravity field just because your five to six feet tall. Every point on your body not exactly in the center being pulled at with different amounts of force. Only the exact center point of the gravity field would be balanced.

1)I went to and looked up my Zip Code, 90013 and got the Lat/Lon coordinates: 34.0451 by -118.2418 .

2)Next, I went back to the Home Page and clicked on “Map” and used the pull-down menu to select “Latitude/Longitude”.

3)In the spaces, I entered the same numbersas above, but with OPPOSITE values, to get a SOUTH latitude and an EAST Longitude. Then I clicked the “Show Map” button.

Where did I end up? Roughly 200 miles southeast of Perth, Australia.

Enter your own Zip Code, follow the steps and you’ll find out exactly where the other side of the world is, assuming the MapBlast software is working properly. :wink:


I’m over 2,000 miles away from ANY land mass at my own personal Bizarro world.

Guess I better stop digging that hole…

Yer pal,

Wait a minute, jab1, does that really work? I’d think it would work for north/south, but east/west is calculated on distance from the Prime Meridian. 1 degree East is right next to 1 degree West; 179 degrees East is right next to 179 degrees West. At least, I think I’ve got that right.

I don’t want to make people think like me, I want them to think like me of their own free will.

Boris B, I think you’re right.

Let’s re-number longitude from 0 to 360 and say that L.A. is at 118. The opposite of that would be 298 (180 + 118), which would correspond to 62 East on the system actually in use. (180 - 118).

So the opposite of 34 North and 118 West would be 34 South and 62 East. this would be in the Indian Ocean, 1000 miles, roughly, southwest of Madagascar, which is what AWB noted above us.