PoW doesn't run on "power" in general, but on electricity. It can be trivial to convert some forms of power into electricity, but not all. One particular form of power which could seen as "wasteful" is that of burning fuels to create heat. A mining chip is a 100% efficient electricity to heat converter. If the cost of useful mining chips could become small enough, it would never make sense to use a traditional burner for heating a space, but using mining equipment would be preferable because you could recover some of the cost of the energy used to heat the space in potential mining rewards.
This is the goal we should aim for: As we're approaching the upper limit of Moore's Law, mining equipment will have a much longer lifetime and focus on reducing the cost of production could turn households and other buildings into data furnaces. It may not even be necessary for mining to be profitable - as long as there is there is a large enough ROI for users of such data furnace to cover its initial cost and eventually reduce their heating bill.
> 0: and it is a definite article, like the internet. There by definition can't be more than one at any given time.
Technically multiple chains can and do exist at any time because there is no "given time" - time is relative. Two miners at two ends of the earth may both produce a valid block at a given time (say, in UTC), but the nodes in proximity to them will receive their blocks at different times, due to distance and the fundamental speed limit of information transmission. The multiple chain conflict lasts until the next block is produced. Such conflicts could last for multiple blocks in a row, but with a probability which rapidly declines with number of blocks.
