> There are alternatives to hashing proof-of-work

Not really. Peercoin's security comes from the developer of the system signing every block. It attempts to use a "Proof of Stake" system where ownership of coins controls mining, but the problem with PoS is, ironically, that there is nothing at stake.

In PoW when you attempt to mine you must expend energy and so you should only mine on a consensus which is likely to be the surviving one if you want your work to not be wasted. In PoS the same is not true, and an optimally rational PoS miner will attempt to concurrently mine all forks which he does not hate.

Originally the signed blocks in PPC were supposed to be a bootstrap mechanism until most of the mining was PoS based, but then some clever miner started mining many possible histories and finding ones where he magically got lucky and his coins were the selected stake for all the blocks.

Primecoin's work isn't scientifically useful— no one had bothered describing it as interesting before it got pulled out as a PoW, and it's far less clear that its not trapdoored (that someone knows how to mine it much faster) than the one way function based proof of work.

You can convert basically any stochastic search into a PoW, but not necessarily a good one (e.g. it might have trapdoors).

More deeply, if your mining work has independent value that that dilutes your incentive to mine on the one true best consensus, since you'll still gain that value even if you mine on a losing consensus.

And ultimately the energy is _not_ wasted: It provides security for the system which is shared by all it's users. In Bitcoin you don't mint coins (with enormous energy costs) or print notes, you don't need bank vaults, or armored cars. You don't need to incarcerate counterfitters, fly around agents, or suffer counterfeiting losses. All currencies have operating costs, if Bitcoin's costs are comparatively good is a complicated analysis which I don't think anyone's done.

That's why the eventual value of bit-coin is supposed to be the value of the energy required to maintain it (because the cost of doing a transaction will be the transaction fees, which have to cover the miner spending the energy to process the transaction, but because anyone can compete in the market supply will always place the value at the cost of energy). Honestly in the long run bitcoin may be cheaper than credit cards or even cash in a pure energy sense. No matter what we do we'll have to spend energy to maintain our financial system.

* With cash we have to print and distribute cash, and move it around, and run hardware to validate it, and image scan it, and count it, and destroy it. Etc.

* Credit cards require servers, massive backups, authentication procedures, production of specialized hardware, and the same networked infrastructure as bitcoin, as well as server ops, bank managers, customer service. Etc.

* Bitcoin can use any machine, and the same internet as any other program. As chips get faster and more efficient the energy cost goes down.

> That's why the eventual value of bit-coin is supposed to be the value of the energy required to maintain it [...]

This is incorrect. The value of the sum total of fees over a certain period, will be equal (or slightly greater) than the cost of the energy required to maintain Bitcoin.

The value of Bitcoin itself is not limited to the amount of energy required to operate it. Confirming a 1M BTC transaction requires the same amount of energy as confirming a 1 BTC transaction, so the cost of the amount of energy expanded is not a limit to the value of Bitcoin.

Yes, but the (theoretical) only limiting factor on the market in a hundred years will be the cost of transaction fees. Which will be the cost of energy to maintain it. Theoretically a transaction fee will be the same regardless of amount of bitcoins in the transaction.

> a lot of energy is going to waste now.

Is it? How much does Bank of America spend in energy to keep up its servers? Backups? disaster-recovery setups? That's a significant energy cost, too.

I think a better example would be high speed trading and similar.

Of course any big corporation or administration is going to have a lot of underused ressources and redundancy but it doesn't mean they burn power "for the sake of it" as bitcoin does.

Also, bitcoin is not a bank, it's supposed to be a currency. If big banks were to switch to bitcoin I don't think they would spend less energy doing all you said. So no matter what you think of bitcoin it's fair to say it's not very "green" so far.

Greener than digging up precious metals to melt into blocks to be buried again in safes.

A better example than Bank of America would be a payment system like VISA.

That only accounts for a small fraction of the inefficient bloat of Big Banks

I completely agree that Peercoin had the opportunity to become a much more efficient virtual currency, but it seems that ship has sailed. However, Peercoin as it exists now is not a fully decentralized currency and so is and was vulnerable to government intervention (during the SR era, for example).

Primecoin is not calculating anything particularly useful from a scientific or medical point of view (Cunningham chains).