text: can we dig the land in at a place till it reaches to another side of the world.? if we make the hollow place for travelling like trains. if we out 1 time a train into it. then it would oscillates and we can  make more profit in travel areas. you forget that we will accelerate towards the mean point and then slow down as we go the other extreme. also oscillations such as those will be impeded by a lot of problems, the chief among them would be friction.  the cost of digging the tunnel would shadow all the profits incurred. if a mishap occurs in the tunnel, the people are done for.  consider the eurotunnel between england and france.