The hollow earth theory stems from legend, myth, fabrication, and superstition. Check it out on the net. The earth is a series of mantles and pockets which are filled in. It isn't compressed, either as that would stifle all life and natural science processes. Vibration isn't an indicator. Bells do vibrate but not shaken apart nor their form integrity altered. Everything is in balance. By forces and phenomena science could explain as soon as it divests itself of it's pet fallacies. It is the height of presumptuousness to say we know it all. A hundred or so years ago you could be ruined if you were a surgeon who believed sterilizing of everything in surgery and post op care were critical. Less than fifty years ago, they were cutting out the frontal lobe of people's brains considering it therapeutic. What the scientific community has to say is not, to me, sacrosanct.