The key is that the computation required is a strictly serial computation: each step has to be completed in a series, one after another.
Since clock speeds aren't increasing, we know that the minimum time the computation can be computed isn't going to be much lower than the time anyone can compute it with off the shelf hardware. Furthermore, in my scheme, if you do have a particularly fast computer you have an incentive (via Bitcoin txout bounties) to reveal that capability to the world.
Exactly.
The key is that the computation required is a strictly serial computation: each step has to be completed in a series, one after another.
Since clock speeds aren't increasing, we know that the minimum time the computation can be computed isn't going to be much lower than the time anyone can compute it with off the shelf hardware. Furthermore, in my scheme, if you do have a particularly fast computer you have an incentive (via Bitcoin txout bounties) to reveal that capability to the world.