>>10781452The force of gravity is proportional to the product of two masses and inversely proportional to the square of the distance between them.
If the center of the earth were hypothetically hollow and you could go there then yes gravity would be flipped, sort of.
The Earth's mass is not distributed perfectly, and you still have gravity perturbation from the sun, moon, planets, etc. So if you were floating in the very center you would inevitably, fall in a preferred direction back to the "floor" of the inner hollow space. Gravity would be lower there than on the outer surface of the Earth though.
In space there exists areas called Lagrange points between celestial bodies. Pic related, not to scale obviously. The L1 point for example is where the Sun's and the Earth's gravity cancel each other out. If you get a spacecraft there you can essentially park it and remain there. Though realistically there are minor perturbations from other celestial bodies that require the spacecraft to make small thrust corrections in order to hold it's position. Typically a "Halo" orbit is used, where the spacecraft orbits around the point rather than attempting to stay right in the center. That's what the upcoming Lunar Gateway space station will be doing.
We know about the molten iron core because we can measure the Earth's mass by it's gravitational pull on other planets/etc, by measuring seismic waves that travel through the planet, and by the fact that the Earth generates it's own magnetic field.
