its probably one of those theoretical machines like a perpetual motion device, it can never exist in our understanding of engineering because there can never be perfection
if i understand these are basically self-replicating 'naninites', tiny little robots able to manipulate matter at the atomic level (atom by atom) and reproduce themselves by rearranging (or modifying in some way) materials at the atomic level. E.g. if it was made entirely of carbon it would just move a bunch of carbon atoms around until it was another of itself, which could then create another and another ad infinitum
If each was created only out of the elements of the earth, then each could reproduce themselves by eating up more of the earths elements, the net result being all the earths elements becoming squillions of little robots instead of the raw materials they are supposed to be