This to me is one of the most interesting aspects of bitcoin. Some have speculated that if bitcoin is widely adopted in the global economy, then a certain perc

This to me is one of the most interesting aspects of bitcoin. Some have speculated that if bitcoin is widely adopted in the global economy, then a certain percentage of all energy produced on the planet will have to be spent doing proof of work to secure the blockchain. It's pretty easy for me to see a swing back to centralised currencies in that situation, it's only worth all the energy needed if you really don't trust the central authority. There are a number of suggested solutions to this problem, one of which is proof-of-stake and there is already a client based on bitcoin called ppcoin which uses it. Currently ppcoin is a hybrid of proof-of-work and proof-of-stake but potentially could be a low energy version of bitcoin. I have often thought that if bitcoin is really successful it will be worthless, because it will have forced the central authorities to be more fiscally responsible, removing the reason for bitcoins existence. But I can't also help thinking that maybe we just need several competing global centrallly printed currencies, and you can pay or be paid in whichever you choose. As long as a cartel doesn't form competition should keep the central authorities honest.