[bdonlan]

The problem with this is that mining isn't just about reporting hash rates, it's a critical part of the Byzantine failure tolerant consensus algorithm that was bitcoin's key contribution. If miners had a lower duty cycle as you suggest, any dishonest miner could execute a majority attack with little resistance, absent some other kind of mitigation.

While proofs of work are wasteful, the only alternative I know of is simply entrusting some third party with control of the network.

[joosters]

You could keep the blockchain and run with vastly reduced difficulty, but with one alteration: the next block needs to include a specific magic secret number. This magic key is unknowable in advance of a specific time, preventing workers from doing the hash work until the key is 'published'. This forces the miners to pause and not do any hashing for a set time.

Now, this gets to the real issue: We need a source for these magic numbers, it needs to be trusted and available and verifiable by everyone, and it needs to be unpredictable and unknowable until a specific time.

What possible sources are there? You could imagine a centralized system, where some computer on the internet spits out a random number for the next 'magic key' every minute. But of course, you have to trust the owner of this computer and so we'd lose all the decentralized features of Bitcoin.

Another possibility: Tie the magic key to some public knowledge, e.g. the value of the NASDAQ at a specific time. Again, this still has problems as 1) there's a limited range of possible values, so miners could pre-compute various versions, and 2) the value could be gamed by market traders.

Anyway, I don't have an answer for the ideal source of these 'magic keys', but if someone could come up with one, you could keep all of bitcoin's mechanisms while vastly reducing its energy waste

[dllthomas]

You could require some other kind of block interleaved between proof-of-work blocks. For instance, imagine you do proof-of-stake as follows: Any account with more than X btc (as of the previous block in the chain) can mint a block by including as the nonce the previous hash value signed with their private key, constraining the rest of the block such that the only thing to vary in the new block is the time value, adding a rule that between two chains with equal difficulty the one with the earlier most recent POS block wins, and forbidding acceptance of blocks "from the future".

This would seem to lead to a situation where, after a proof-of-work block is minted, those minting POW blocks relax and those minting POS blocks march things forward for each of their accounts until they find the earliest time that satisfies any of them - at which point they simply wait until that time arrives (for themselves or anyone else playing).

[im3w1l]

Very interesting idea!

I have a suggestion for how to deal with these magic numbers. Make 9 out of 10 blocks duds (and it should be known in advance which), that contain very little reward. This means that, most mining power will switch of for these blocks, and only be active for the other 1 of 10 blocks.

[ozgung]

Or you can use a hash generated from multiple market values around the world. That way it will also work 7/24.

[glomph]

Wouldn't that mean you could only have new transactions when the next magic number comes out?

[joosters]

Currently, all bitcoin transactions have to wait until they get into the next mined block, which is about every 10 minutes (I think?)

[glomph]

But that time serves a purpose for security. So for the proposed solution the time would have to increase from 10 minutes to 10 minutes + how ever much time we want to save hashing energy for.