When the hunt for new sources of energy had at one point got particularly frantic, one bright young chap suddenly spotted that one place which had never used up all its available energy was - the past. And with the sudden rush of blood to the head that such insights tend to induce, he invented a way of mining it that very same night, and within a year huge tracts of the past were being drained of all their energy and simply wasting away. Those who claimed that the past should be left unspoilt were accused of indulgingin an extremely expensive form of sentimentality.
Douglas Adams, The Ultimate Hitchhiker's Guide to the Galaxy
past, source-of-energy