Distributed Consensus


In 1955, Isaac Asimov published a short story titled "Franchise", about a system that decides who should be elected president (in 2008) by picking a single voter to represent the whole population.

If a single voter is regularly selected at random then, over time, a larger, more representative sample of the population will build up. Any inconsistencies in single voters will be rejected by later consensus.

Distributed systems say "after a certain amount of time, enough votes will have been cast to be sure enough of a consensus".

Each voter must be selected at random, but if this selection is performed by a central machine, that machine must be trusted. To avoid this, everyone in the system is given a task that is guaranteed to give each participant an equal chance of completing first - a chance which is increased only by how much work they do.

As a reward for participating, anyone who casts a vote receives a monetary payment.

The system will, generally, consume energy up to the value of the reward for casting each vote.

To save energy, votes can instead be given to those who have purchased the most shares (stake) in the system (i.e. a single up-front payment, rather than an ongoing subscription).

Another alternative, valid for small populations, is to collect the sample in a single poll: invite all members to participate, and generate the consensus after a certain amount of time has passed. This works when most of the members are known to be good actors, so in order to avoid a small, good population being overwhelmed by new, bad actors, new members need to gradually build up reputation in order to vote.