[ml/nj]

The crushing pressures and intense temperatures in Earth's deep interior squeeze atoms and electrons so closely together that they interact very differently.

I still want to know where these crushing pressures come from. If you're 1000 feet under water, the crushing pressure comes from the weight of the water column directly above you, and that weight comes from the attraction of that mass of that water column to the mass of the earth. But if you're in a cave 1000 feet deep there is no crushing pressure.

And when you get to the center of the earth there is no weight at all. Any mass there is surrounded by a uniform field of terrestrial mass and all the terrestrial gravitational forces cancel out. (Just as all the gravitational forces due to the mass of the earth to your left are canceled out by the gravitational forces of the mass of the earth to your right.)

ML/NJ

[Strategerist]

If there’s a cave the pressure is being routed around the opening to the rock on either side (hopefully, or the cave collapses.)

This isn’t talking about the center of the Earth; it’s the lower mantle, anyway.

[Yardstick]

Well let’s say you’re not quite at the center but maybe a few hundred or a thousand miles out and the metals there are all liquified. In that case you would expect great pressures, wouldn’t you?

[CodeToad]

Water is heavier than air. :)

[thackney]

I still want to know where these crushing pressures come from.

Some deep underground oil/gas fields are at +10,000 psi pressure.

[BitWielder1]

Rock is much heavier than water.
Pressure increases as you go down, at some point I'd guess caves are no longer possible, the rock can no longer sustain empty spaces.
Even deeper, the rock is so hot it's soft or melted.
There is no gravity at the center, yes, but you still have the accumulated inward pressure from columns of 3,947 miles of rock and nickel-iron.
Even with diminished gravity, "It's heavy, man".

[GonzoGOP]

I still want to know where these crushing pressures come from.

Look at it this way. Because the core is a liquid each square cm of your surface is supporting a column of mostly iron and nickle 6,378 kilometers tall. That column contains 437800000 cubic centimeters of material at a density of 5.52 g/cm^3. That is a mass of 2,416 metric tons. Sure the bottom few millimeters experience minimal gravitation effect, but the top few thousand kilometers are in full 1g. And the effect is not linear, it increases exponentially with distance from the center. So you are still looking at thousands of tons of material pushing down of every square centimeters.

This actually understates the force by quite a bit. Since it isn't a column but a complex curved wedge due to the spherical shape of the planet. But you get the picture and I didn't want to work the math for a simple blog post.

Then there is expansion. When you heat materials they expand. And they expand in all directions. So you have the very hot core trying to expand. However it can't because there is all of the other material stacked on top of it. So even if you open a chamber at the exact center of the core in addition to the gravitational column effect you also get smashed by the expansion of all the liquid iron and nickle around you.