What puzzled me was this: I thought the mass of the Earth created a gravitational pull which was spread over its surface and thereby diluted but within the spherical chamber the surface area is relatively tiny and so the gravitational pull would be greatly concentrated. But I suppose I must be...
Suspend all disbelief and imagine digging to the center of the Earth, there you dig out a small spherical chamber, you sit in the middle, do you float or are you depatched violently to the wall around you instantaneously.