<p><em>Immutable transactions</em> are a consequence of blockchain-based systems when the following are true:</p>

<ol>
<li>There is a <strong>cost</strong> (in currency and in acquiring materials) of producing a block consistent with the rules of the protocol, and this cost cannot be circumvented</li>
<li>The cost is great enough where incurring this cost to increase the length of the blockchain is more profitable than incurring this cost to fork the blockchain</li>
<li>As part of the rules of the protocol, past transactions cannot be altered by future additional data</li>
</ol>

<p>Proof of work fits into this because <strong>it is provably costly</strong>. It requires energy, and it also requires development time and materials to create machines that use this energy efficiently. This cost prevents forks from being supported, as you have limited energy and you can only use that energy once.</p>

<p>This contrasts with Proof of Stake, or an IP based voting system because a lack of energy requirement means that there an incentive to support <em>all</em> forks. This is referred to as the <a href="https://ethereum.stackexchange.com/questions/2402/what-exactly-is-the-nothing-at-stake-problem">Nothing-at-stake problem</a>.</p>

CC BY-SA 4.0
2019-12-18T18:50:34.637Z
2019-12-18T18:50:34.637Z
hedgedandlevered
<p>I have a disagreement with a person: I believe that the primary and most important goal of including proof-of-work (and therefore the nonce) in a block is to make it hard for an attacker to change that block (and since we are talking about a chain the next ones) without committing enough resources to recalculate not only the current but also all the blocks after that. Without it the attacker could simply create forks of the blockchain without any problems (free).</p>

<p>He claims that it is a mechanism is there to solve the problem of determining representation in majority decision making. If the majority were based on one-IP-address-one-vote, it could be subverted by anyone able to allocate many IPs. Proof-of-work is essentially one-CPU-one-vote.</p>

<p>Who is more right?</p>

CC BY-SA 3.0
2017-04-19T20:26:54.707Z
They both seem right to me. If votes are expensive, it's hard for anyone to change the majority vote.
David Schwartz
<blockchain><proof-of-work>
Is the purpose of proof-of-work the immutability of the blockchain?
dr.doom
# Is the purpose of proof-of-work the immutability of the blockchain?

(Asked by: username_0 on 2017-04-19)

I have a disagreement with a person: I believe that the primary and most important goal of including proof-of-work (and therefore the nonce) in a block is to make it hard for an attacker to change that block (and since we are talking about a chain the next ones) without committing enough resources to recalculate not only the current but also all the blocks after that. Without it the attacker could simply create forks of the blockchain without any problems (free).

He claims that it is a mechanism is there to solve the problem of determining representation in majority decision making. If the majority were based on one-IP-address-one-vote, it could be subverted by anyone able to allocate many IPs. Proof-of-work is essentially one-CPU-one-vote.

Who is more right?

**Tags:** blockchain, proof-of-work

> **Comments:**
> **username_1**: They both seem right to me. If votes are expensive, it's hard for anyone to change the majority vote.  

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## 1 answers

### Answer by username_2 on 2019-12-18. Score: 1

*Immutable transactions* are a consequence of blockchain-based systems when the following are true:

1. There is a **cost** (in currency and in acquiring materials) of producing a block consistent with the rules of the protocol, and this cost cannot be circumvented
2. The cost is great enough where incurring this cost to increase the length of the blockchain is more profitable than incurring this cost to fork the blockchain
3. As part of the rules of the protocol, past transactions cannot be altered by future additional data

Proof of work fits into this because **it is provably costly**. It requires energy, and it also requires development time and materials to create machines that use this energy efficiently. This cost prevents forks from being supported, as you have limited energy and you can only use that energy once.

This contrasts with Proof of Stake, or an IP based voting system because a lack of energy requirement means that there an incentive to support *all* forks. This is referred to as the [Nothing-at-stake problem](https://ethereum.stackexchange.com/questions/2402/what-exactly-is-the-nothing-at-stake-problem).


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