-kshully : i can totally see a hillsized pendulum with elephants, there's nothign tekwise stopping that from happening , you get free fertilizer probably along the way but the impact on the environment might be less than extracting lithium from seawater or digging holes for that extra-speed erosion.
Though ... in gedanken ... if you were to build a stirling engine that size wouldnt you have a free space elevator as a bonus ?
With no additives needed from external sources as long as the payloads dont exceed the force of the upward pressure ... but can sapients build a structure 10km high ? - it seems indeed unlikely that, though its not perpetuum and it would end when the core stops moving , it might last some time and the chances of deep or closeby space suffering from galactic warming to the point where the heat difference is too small to keep moving is
euh
unlikely

what was i saying

o yea

well, can they build something that high ?