Introduction to Emergent Consensus

The principles of emergence in nature can be applied in the Bitcoin network to enable emergent consensus for block-size limiting, referred to as “EC”

Emergence — Fundamental to Nature

Emergence is everywhere in nature. From crystals and snowflakes to the spiralling shape of galaxies, macroscopic properties of liquids to weather patterns, ant-hills and living organisms. Yet this is a Cinderella science because the phenomenon of emergence is difficult to predict, except in simple cases. This field is the study of complexity, and therefore includes complex adaptive systems. Such systems have many individuals interacting according to simple rules and thereby producing 2nd-order or system-wide effects.

Fig 2. Interaction at peer-to-peer level produces emergent phenomena with top-down feedback

This graphic by the anthropologist Richard Seel breaks down the process of emergence.

In begins at (A) with discrete entities such as molecules, insects, or humans. At (B) there is interaction. A construct emerges in (C) transcending the entities. It could be a vortex, beehive, or a market price. Finally in (D) there is top-down causation shaping how the individual entities behave. Causation takes varied forms like natural selection or adaptive information control. Emergence drives self-organization, and it can be hierarchical with many layers such as in multicellular biology. Reductionism fails at first base because not even all the layers are known. An emergent property is simultaneously part of a system and also external to it. Emergence depends upon a system to become manifest but also transcends it at the same time.

Emergent Consensus — Decentralized Block Size Limiting

Bitcoin can harness emergence to achieve problem-solving benefits. The reason is that its global network comprises thousands of independent nodes which are usually owned by different people. Bitcoin nodes also communicate to each other via peer-to-peer message interaction. These features mean that the addition of simple rules allows complex network-wide behaviour to develop outside the messaging layer.

There is already emergent consensus from the Bitcoin network: the market price of BTC. This is determined on exchanges by buyers and sellers. Although the market price is outside the network it would vanish if the network itself vanished.

Bitcoin nodes which participate in EC simply need to allow flexiblity in determining a block size limit — flexibility where full node owners set the maximum sizes for blocks that they will make and accept, also the delay for acceptance of oversized blocks. This capability for delayed acceptance effectively makes nodes become fork tolerant where forks exist due to block size limit disagreement. Because of this the forks will always be transient.

Bitcoin full nodes interact during block propagation. The differences in EC settings have a holistic effect on participating nodes and once critical mass occurs then emergence results effecting a varying block size limit on the entire network by top-down feedback. A top-down block size limit is an irrational number that oscillates as node owners change their settings. it can never be known exactly, only approximated.

Security aspects for Bitcoin businesses can be handled in an EC implementation. Consider the case of a peer-to-peer exchange, which treats transactions as final after three confirmations. In this case the addition of software which detects a fork situation can provide an automatic stop on treating transactions as final, until the temporary fork is resolved completely. Such a safety-net would rarely inconvenience users.

Bitcoin Implementations — EC enabled

One of the features of EC is that development teams can choose different methodologies for nodes to converge on an EC-driven block size limit. In this situation the actual prevailing limit becomes a meta-consensus, or a second layer of consensus which is an optimal synthesis of the lower-layers, weighted by the number of nodes which use the different flavors of EC.

Links are provided for detailed explanations about how EC is used in different Bitcoin implementations:

Bitcoin Classic

Bitcoin Unlimited

Bitcoin XT

Further reading:

Emergence Nova ScienceNOW
http://www.pbs.org/wgbh/nova/nature/emergence.html

Types and Forms of Emergence by Jochen Fromm
https://arxiv.org/pdf/nlin/0506028.pdf