> In fact if you reduce your energy expenditure below some unspecified threshold it becomes utterly worthless. This is not really true--it's not like lowering

> In fact if you reduce your energy expenditure below some unspecified threshold it becomes utterly worthless. This is not really true--it's not like lowering the security budget means all the old blocks can be rewritten at will. Roughly speaking, the cost of rewriting a block is the cumulative PoW cost of that block and all the blocks after it, although this amount typically decreases over time as better mining equipment lowers the present cost of hashrate. For current transactions, if the security budget relative to the transacted value gets low, all it means is that one must wait longer to achieve the same level of confidence in transaction finality. It doesn't abruptly render the currency "utterly worthless".