Ya, If the area was hollowed out and you were at the center of the planet the gravity would pull from every area around you canceling out its self with the right way, real effects of gravity, And if you were to dig to the middle of the planet and pass the middle you would have your gravity pull on you depending on your distance to the sides, And plus, There should be a core which is hot and slowly takes 1 hp bar per minute one your 4 blocks near it, And also the core should increase in gravity depending on mass and the mass of the planet and gravity+mass is affected per block, Which would be slightly werid, and buggy.