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Consensus on a decentralized basis
Why is this so important? Within one integrated function, miners validate history, clear transactions and get paid for security on a trustless basis; the integrity of bitcoin’s fixed supply is embedded in its security function, and because the rest of the network independently validates the work, consensus can be reached on a decentralized basis. If a miner completes valid work, it can rely on the fact that it will be paid on a trustless basis. Conversely, if a miner completes invalid work, the rest of the network enforces the rules, essentially withholding payment until valid work is completed. And supply of the currency is baked into validity; if a miner wants to be paid, it must also enforce the fixed supply of the currency, further aligning the entire network. The incentive structure of the currency is so strong that everyone is forced to adhere to the rules, which is the chief facilitator of decentralized consensus.

If a miner solves and proposes an invalid block, specifically one that either includes invalid transactions or an invalid coinbase reward, the rest of the network will reject it as invalid. Separately, if a miner builds off a version of history that does not represent the longest chain with the greatest proof of work, any proposed block would also be considered invalid. Essentially, as soon as a miner sees a new valid block proposed in the network, it must immediately begin to work on top of that block or risk falling behind and performing invalid work at a sunk cost. As a consequence, in either scenario, if a miner were to produce invalid work, it would incur real cost but would be compensated nothing in return.

Through this mechanism, miners are maximally incentivized to produce honest, valid work and to work within the consensus of the chain at all times; it is either be paid or receive nothing. It is also why the higher the cost to perform the work, the more secure the network becomes. The more energy required to write or rewrite bitcoin’s transaction history, the lower the probability that any single miner could (or would) undermine the network. The incentive to cooperate increases as it becomes more costly to produce work which would otherwise be considered invalid by the rest of the network. As network security increases, bitcoin becomes more valuable. As the value of bitcoin rises and as the costs to solve blocks increases, the incentive to produce valid work increases (more revenue but more cost) and the penalty for invalid work becomes more punitive (no revenue and more cost).

Why don’t the miners collude? First, they can’t. Second, they tried. But third, the fundamental reason is that as the network grows, the network becomes more fragmented and the economic value compensated to miners in aggregate increases; from a game theory perspective, more competition and greater opportunity cost makes it harder to collude and all network nodes validate the work performed by miners which is a constant check and balance. Miners are merely paid to perform a service and the more miners there are, the greater the incentive to cooperate because the probability that a miner is penalized for invalid work increases as more competition exists. And recall that random nonce value; it seemed extraneous at the time but it is core to the function that requires energy resources be expended. It is this tangible cost (skin in the game) combined with the value of the currency which incentivizes valid work and which allows the network to reach consensus.

Because all network nodes independently validate blocks and because miners are maximally penalized for invalid work, the network is able to form a consensus as to the accurate state of the chain without relying on any single source of knowledge or truth. None of this decentralized coordination would be possible without bitcoin, the currency; all the bitcoin network has to compensate miners in return for security is its native currency, whether that is largely in the form of newly issued bitcoin today or exclusively in the form of transaction fees in the future. If the compensation paid to miners were not reasonably considered to be a reliable form of money, the incentive to make the investments to perform the work would not exist.

The role of money in a blockchain
Recall from Bitcoin Can’t Be Copied, if an asset’s primary (if not sole) utility is the exchange for other goods and services, and if it does not have a claim on the income stream of a productive asset (such as a stock or bond), it must compete as a form of money and will only store value if it possesses credible monetary properties. Bitcoin is a bearer asset, and it has no utility other than the exchange for other goods or services. It also has no claim on the income stream of a productive asset. As such, bitcoin is only valuable as a form of money and it only holds value because it has credible monetary properties (read The Bitcoin Standard, chapter 1). By definition, this is true of any blockchain; all any blockchain can offer in return for security is a monetary asset native to the network, without any enforceable claims outside the network, which is why a blockchain can only be useful in connection to the application of money.

Without a native currency, a blockchain must rely on trust for security which eliminates the need for a blockchain in the first place. In practice, the security function of bitcoin (mining), which protects the validity of the chain on a trustless basis, requires significant upfront capital investment in addition to high marginal cost (energy consumption). In order to recoup that investment and a rate of return in the future, the payment in the form of bitcoin must more than offset the aggregate costs, otherwise the investments would not be made. Essentially, what the miners are paid to protect (bitcoin) must be a reliable form of money in order to incentivize security investments in the first place.

This is also fundamental to the incentive structure that aligns the network; miners have an embedded incentive to not undermine the network because it would directly undermine the value of the currency in which miners are compensated. If bitcoin were not valued as money, there would be no miners, and without miners, there would be no chain worth protecting. The validity of the chain is ultimately what miners are paid to protect; if the network could not reasonably come to a consensus and if ownership were subject to change, no one could reasonably rely on bitcoin as a value transfer mechanism. The value of the currency ultimately protects the chain, and the immutability of the chain is foundational to the currency having value. It’s an inherently self-reinforcing relationship.

Immutability is an emergent property
Immutability is an emergent property in bitcoin, not a trait of a blockchain. A global, decentralized monetary network with no central authority could not function without an immutable ledger (i.e. if the history of the blockchain were insecure and subject to change). If settlement of the unit of value (bitcoin) could not reliably be considered final, no one would reasonably trade real world value in return. As an example, consider a scenario in which one party purchased a car from another in return for bitcoin. Assume the title for the car transfers, and the individual that purchased the car takes physical possession. If bitcoin’s record of ownership could easily be re-written or altered (i.e. changing the history of the blockchain), the party that originally transferred the bitcoin in return for the car could wind up in possession of both the bitcoin and the car, while the other party could end up with neither. This is why immutability and final settlement is critical to bitcoin’s function.

Remember that bitcoin has no knowledge of the outside world; all bitcoin knows how to do is issue and validate currency (whether a bitcoin is a bitcoin). Bitcoin is not capable of enforcing anything that exists outside the network (nor is any blockchain); it is an entirely self-contained system and the bitcoin network can only ever validate one side of a two-sided value transfer. If bitcoin transfers could not reliably be considered final, it would be functionally impossible to ever trade anything of value in return for bitcoin. This is why the immutability of bitcoin’s blockchain is inextricably linked to the value of bitcoin as a currency. Final settlement in bitcoin is possible but only because its ledger is reliably immutable. And its ledger is only reliably immutable because its currency is valuable. The more valuable bitcoin becomes, the more security it can afford; the greater the security, the more reliable and trusted the ledger.

Ultimately, immutability is an emergent property, but it is dependent on other emergent network properties. As bitcoin becomes more decentralized, it becomes increasingly difficult to alter the network’s consensus rules and increasingly difficult to invalidate or prevent otherwise valid transactions (often referred to as censorship-resistance). As bitcoin proves to be increasingly censorship-resistant, confidence in the network grows, which fuels adoption, which further decentralizes the network, including its mining function. In essence, bitcoin becomes more decentralized and more censorship-resistant as it grows, which reinforces the immutability of its blockchain. It becomes increasingly difficult to change the history of the blockchain because each participant gradually represents a smaller and smaller share of the network; regardless of how concentrated ownership of the network and mining may be at any point in time, both decentralize over time so long as value increases, which causes bitcoin to become more and more immutable.

Bitcoin, not blockchain
This multi-dimensional incentive structure is complicated but it is critical to understanding how bitcoin works and why bitcoin and its blockchain are dependent on each other. Why each is a tool that relies on the other. Without one, the other is effectively meaningless. And this symbiotic relationship only works for money. Bitcoin as an economic good is only valuable as a form of money because it has no other utility. This is true of any asset native to a blockchain. The only value bitcoin can ultimately provide is through present or future exchange. And the network is only capable of a single aggregate function: validating whether a bitcoin is a bitcoin and recording ownership.

The bitcoin network is a closed loop and an entirely independent system; its only connection to the physical world is through its security and clearing function. The blockchain maintains a record of ownership and the currency is used to pay for the security of those records. It is through the function of its currency that the network can afford a level of security to ensure immutability of the blockchain, which allows network participants to more easily and consistently reach consensus without the need for trust in any third-parties. The cumulative effect is a decentralized and trustless monetary system with a fixed supply that is global in reach and accessible on a permissionless basis.

Every other fiat currency, commodity money or cryptocurrency is competing for the exact same use case as bitcoin whether it is understood or not, and monetary systems tend to a single medium because their utility is liquidity rather than consumption or production. When evaluating monetary networks, it would be irrational to store value in a smaller, less liquid and less secure network if a larger, more liquid and more secure network existed as an attainable option. Bitcoin is valuable, not because of a particular feature, but instead, because it achieved finite, digital scarcity. This is the backbone of why bitcoin is secure as a monetary network and it is a property that is dependent on many other emergent properties.

A blockchain on the other hand is simply an invention native to bitcoin that enables the removal of trusted third parties. It serves no other purpose. It is only valuable in bitcoin as a piece to a larger puzzle and it would be useless if not functioning in concert with the currency. The integrity of bitcoin’s scarcity and the immutability of its blockchain are ultimately dependent on the value of the currency itself. Confidence in the aggregate function drives incremental adoption and liquidity which reinforces and strengthens the value of the bitcoin network as a whole. As individuals opt in to bitcoin, they are at the same time, opting out of inferior monetary networks. This is fundamentally why the emergent properties in bitcoin are next to impossible to replicate and why its monetary properties become stronger over time (and with greater scale), while also at the direct expense of inferior monetary networks.

“I don’t believe we shall ever have a good money again before we take the thing out of the hands of government, that is, we can’t take them violently out of the hands of government, all we can do is by some sly roundabout way introduce something that they can’t stop.” -F. A. Hayek

Ultimately, a blockchain is only useful in the application of money because it is dependent on a native currency for security. Bitcoin represents the most secure blockchain by orders of magnitude. Because all other blockchains are competing for the same fundamental use case of money and because bitcoin’s network effects only continue to increase its security and liquidity advantage over the field, no other digital currency can compete with bitcoin. Liquidity begets liquidity and monetary systems tend to one medium as a derivative function. Bitcoin’s security and liquidity obsoleted any other cryptocurrencies before they left the proverbial gates. Find me a cryptocurrency that comes close to bitcoin relative to security, liquidity or the credibility of its monetary properties, and I will find you a unicorn.

The real competition for bitcoin has and will remain the legacy monetary networks, principally the dollar, euro, yen and gold. Think about bitcoin relative to these legacy monetary assets as part of your education. Bitcoin does not exist in a vacuum; it represents a choice relative to other forms of money. Evaluate it based on the relative strengths of its monetary properties and once a baseline is established between bitcoin and the legacy systems, this will then provide a strong foundation to more easily evaluate any other blockchain related project.