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• Flying in a 747 from one side of the earth to the exact opposite side would take about

• 22 hoursand while I know there's a bit of rock in the way, that's really going the

• long way round.

• So what if we did dig a hole all the way through the earth, through the center, and jumped

• in?

• Well, Michael, you probably would't make it very far - that's because of the Coriolis

• effect (which is why a ball curves weirdly when you toss it while riding a merry go round

• and why hurricanes always spin counterclockwise in the northern hemisphere). At the equator,

• the earth (and you on it) is rotating eastwards at 1670 km/hr. As you go deeper, the bits

• of earth around you are still spinning around once per day, but they don't have as far to

• travel so they're going at slower and slower speeds. If you jumped into a vertical shaft,

• you'd soon be traveling east faster than the rock around you so that after falling only

• a few kilometers, you'd crash into the eastern wall. It might not be a disaster, but some

• miners near Lake Superior tried to test this by dropping cannon balls down a mile-long

• shaft - and the balls never reached the bottom.

• OK, so what if the tunnel went from pole to pole, so the Coriolis effect didn't apply,

• and let's also assume that there's no air resistance, or friction

• Ok. Since the earth's mass is more concentrated close to the middle, gravity would pull you

• down with roughly the same amount of force for the first 3000 km, or halfway to the center

• of the earth - this familiar, constant force would accelerate you until you were falling

• 8km every second, and the trip halfway to the middle of the earth would only take 13

• minutes. Soon after, you'd reach the earth's outer core, and this is the point in your

• journey where the pull of gravity would be strongest - but only slightly stronger than

• the force we're used to on the surface.

• As you continued to fall closer to the center, so much of the earth's mass would now be above

• you that it would begin to seriously cancel out the attraction of the mass below, and

• the pull would weaken until you reached the center. Here, you'd experience no gravitational

• pull at all - or rather, the earth would be pulling on you the same amount in all directions,

• so you could float freely around with no sense of "up" or "down". Except, remember, that

• you'd be speeding past at 22,000 miles per hour, or 6 miles a second.

• Once you passed the center, the whole process would reverse and you'd gradually slow, pulled

• down (or is it up?) weakly at first and then more strongly, until when you got to the other

• side, you'd stop moving and could step out on the surface, a mere 37 minutes, or one

• dryer cycle, later.

• Of course, the deepest we've ever been able to dig is the Kola Superdeep borehole in Russia.

• But it only went down 12km, which is only two thirds the length of Manhattan. They had

• to stop because it got too hot: 180°C. And this is sort of the problem with digging a

• hole through earth - earth is hot, and molten in the middle. You can't just dig a hole through

• it with shovels. But here's a question: wasn't the middle of earth wasn't all "liquidy",

• what if earth was hollow, but weighed the same?

• Well, with its entire mass concentrated in a thin shell right under our feet, the earth

• wouldn't have a magnetic field any more, because that comes from the molten iron core. So we'd

• be totally vulnerable to radiation from the solar wind and storms, and this means we'd

• see the aurora EVERYWHERE. Look! The NorthernSouthernEastern lights!

• And if you jumped inside the hollow earth to escape the solar storm? Well, gravity from

• the different parts of the spherical earth-shell would perfectly cancel out and you'd float

• freely about inside as if the earth weren't there at all! Of course, you'd better bring

• a space suit, because there's not nearly enough air ON earth to fill up the entire INSIDE

• of earth. But what if the entire inside of the hollow earth were covered with mirrors?

• Henry, that's ridiculousfor now

• Ok, so back outside of the earth, we wouldn't really notice much difference from a gravitational

• perspective - falling things would still accelerate at 9.8 m/s^2, a baseball would follow the

• same trajectory, and the moon would follow the same orbit around the earth.

• Hey Henry, let's go to outer space, right now. Bring your gun - this'll all make sense

• later. C'mon.

• Oh, and you're coming too. Click this annotation to head over to my channel, Vsauce, to see

• the rest of our adventures. I'll see you over there.

Flying in a 747 from one side of the earth to the exact opposite side would take about

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# What if the Earth were Hollow?

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Why Why posted on 2013/03/29
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