> This leads to the selection of a hybrid design that composes digital hashing with low precision vector-matrix multiplication (intended for photonic acceleration) to produce HeavyHash. HeavyHash is an iterated composition of an existing hash function, i.e. SHA256, and a weighting function such that the cost of evaluation of HeavyHash is dominated by the computing of the weighting function.
What is the weighting function? How do we verify that the result is valid? There have been other attempts to make proof of work more capex sensitive (especially memory-hard variants, like birthday paradox) but they all end up suffering from the fact that the very fact that you can verify the result means that you can brute force the outcome, and often that's a tradeoff that works.
Without knowing specifics it's very hard to say whether this particular proof of work algorithm does not permit an energy-inefficient brute force solution that will end up making the energy problems just as bad -- my intuition is that of course this won't work, as a matter of "no free lunch" -- the cost to secure a coin will be equal to the value of keeping it secure.
I guess we'll have to wait:
> Beyond these intuitions, the specifics of the algorithm and a detailed proof of its security will be published in a separate manuscript. [54]
> [54] Michael Dubrovsky and Marshall Ball. Towards optical proof of work; oPoW. Unpublished Manuscript, 2019.