Once PoS and Casper is reached, what stops block times from dropping into the millisecond range?

Question

After reading through Vlad's Casper Post, I am under the impression that Casper consensus will be reached when the validators all agree on a bit (more or less). If this is the case, why can the 'voting' not be done every 1 second or less? Given global information transfer times, we can include 250ms latency for intercontinental data transfer (being very lenient).From what I understand, consensus will go as follows:

@1ms - "Everyone agree on 1 (as opposed to 0)?"

@250ms - "Yes."

@500ms - "Consensus reached. Start over."

With this model, it takes 0.5s to reach consensus.

I read here that it will drop to 2-7.5s, not millisecond range. Given my statements above, how is it not faster?

Answer 1

I think the answer is basically latency, plus giving enough of the nodes enough of a reasonable amount of time to validate. Millisecond blocks would only really get responses from a minority of nodes, it depends on how much of a consensus you want to build. Millisecond blocks would likely not allow for enough time for a majority consensus to form.

Perhaps in the future there could be suitable conditions for millisecond block times.