> When I see a hash that satisfies the difficulty, I know it must have taken time. The method by which the delay is accomplished is “work”, but the hash is a proof of time, not work.<p>I disagree with this characterization.<p>Mostly because there actually is a more proper concept of Proof-of-Time, that doesn't depend on Bitcoin's dynamic difficulty adjustment to space puzzle solutions a certain time apart on average.<p>It is what Bram Cohen is trying to use in conjunction with Proof-of-Space to make [1] a greener alternative to Bitcoin.<p>One candidate problem for proving time is modular square roots. In a group of order 2^k-1, we can square element x (k-1) times to obtain x^(2^(k-1)), which is the square root of x^(2^k)=x. Since the k squarings cannot be parallellized, this takes time proportional to k.<p>[1] <a href="https://chia.net/" rel="nofollow">https://chia.net/</a>
>> If the stated problem is to find a conforming hash, all you have to do is to try it once, and bingo, you’ve affected the global hash rate, and for that one attempt you were a participant helping others solve the problem. You did not need to tell others that you did it (unless you actually found a solution), others didn’t need to know about it, but your attempt did affect the outcome. For the whole universe, no less.<p>>> It is noteworthy that since SHA is progress-free, each attempt could be thought of as a participant joining the effort and immediately leaving. Thus miners join and leave, trillions of times per second.<p>Is the value of pooled mining that participants in the pool share the nounce they’re calculating, to avoid duplicating work within the pool?