<p>I think this question has a faulty premise. What usually gets elected in POS systems is the <em>author of the next block</em>. The author of the next block is not the only validator of the blockchain. Every single full node validates the entire chain, so an invalid block will be rejected by all other participants.</p>
<p>Whether or not there is a possibility of a fork depends on the nature of the authorship election. If there is actually just a single participant that can author the next block, there would obviously be no possibility of a fork, but that would come at the cost of the blockchain grinding to a halt when the sole author does not issue a block. Systems I have investigated had some form of backoff strategy to allow multiple authors with different priority to issue blocks, or made it just magnitudes easier for the elected author to find a block.</p>

CC BY-SA 4.0
2020-09-17T16:04:29.490Z
I added an "Edit" to the question. I'd like to know your opinion. Thanks.
Questioner
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2020-09-17T16:15:08.400Z
So, do you in each round, multiple authors will be elected? Thank you if you could confirm.
Questioner
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2020-09-17T16:15:39.613Z
That edit is just doubling down on the tautology of your question: under the premise that there is only a single author creating a single next block, there is no fork. Obviously true but also completely uninteresting as that's not a workable system (except as a permissioned blockchain with a single central author) because it would suffer liveness issues immediately and would be trivially DOSable.
Murch
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2020-09-17T21:28:48.410Z
Concerning a part of your answer: **_"If there is actually just a single participant that can author the next block, there would obviously be no possibility of a fork, but that would come at the cost of the blockchain grinding to a halt when the sole author does not issue a block."_** We have a similar situation in Bitcoin, when **a single** miner is the **only winner** of PoW (in most of the case) to be the **single author** of the next block. This block then will be broadcast to all the miners. If PoW's answer is correct, the block is accepted.
Questioner
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2020-09-17T22:15:06.147Z
That is a false equivalency. In Bitcoin all miners are eligible to find the next block and it is the discovery of the block that determines the author. The way you phrase it, you make it sound as if the author is determined first and then they craft the block which is not the case.
Murch
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2020-09-17T22:35:49.500Z
From my point of view, although all miners pick up some transactions and insert in their block, nevertheless, only one of them will eventually be the legitimate author of the next block: one who has solved PoW to become the winner of a lottery. This lottery can be another mechanism, such as randomness or ... (but in that case, in my opinion, chaining blocks or transactions no longer make sense.) The difference of such a lottery with PoW is that no external resource is consumed. (That's why I said chiang transactions no longer make sense ...)
Questioner
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2020-09-17T22:36:05.633Z
Of course, PoW is more secure against DoS or Sybil attacks, but in the sense of "decentralization" **if randomness process is performed de-centrally**, it could be decentralized too.
Questioner
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2020-09-17T23:27:59.963Z
If the "decentralized randomness" is something the network needs to agree upon, the "decentralized randomness" requires a consensus protocol. That's a catch-22 when you want to build a consensus protocol such as POS.
Murch
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2020-09-18T00:02:07.087Z
I believe neither PoW nor PoS are consensus technique. PoW is only a Sybil attack prevention mechanism and PoS tries to play the same role ... How it is successful depends on many parameters. Of course, use of PoS for blockchain is not effective, as chaining blocks is meaningful when the nodes are forced to solve a heavy PoW (in proportion to total power of the network.)
Questioner
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2020-09-18T00:02:21.253Z
So, there are two different terms: "blockchain" (a tree-like data structure that can be useful only by using PoW in an open network) and "decentralization" that can be implemented without blockchain. In both cases of PoW and PoS, there is no consensus, but the rest of the network accepts the winner's block, because the protocol says such a rule: If PoW's answer is correct, then accept the new block ! If there is another chain at the same time, then accept the longest one (more difficult); otherwise you are interpreted as a malicious node !
Questioner
CC BY-SA 4.0
2020-09-17T15:18:59.957Z
2020-09-17T15:18:59.957Z
Murch
<p>Regarding the fact that in Proof-of-Stake, a stakeholder will be elected randomly as the next validator in each epoch (or each round), logically, in each round there is only a single validator, and so a single proposed block. With these conditions, is there still the possibility of occurring a fork in each round? </p>
<p><strong>Edit:</strong> According to the answer by @Murch , we can say &quot;author of the new block&quot; rather than &quot;validator&quot;. Nevertheless, if in each round, only a single author is elected to write the next block (as a winner), whether this block will be validated by the rest of network or not, in this round, only a single block has been created and so no fork occurs. Is n't it?</p>
<p>Concerning a part of @Murc's answer: <strong><em>&quot;If there is actually just a single participant that can author the next block, there would obviously be no possibility of a fork, but that would come at the cost of the blockchain grinding to a halt when the sole author does not issue a block.&quot;</em></strong></p>
<p>But, we have a similar situation in Bitcoin, when <strong>a single</strong> miner is the <strong>only winner</strong> of PoW (in most of the case) to be the <strong>single author</strong> of the next block. This block then will be broadcast to all the miners. If PoW's answer is correct, the block is accepted.</p>
<p><strong>Related question:</strong> <a href="https://bitcoin.stackexchange.com/q/99068/41513">Proof-of-Stake: How to prevent someone from being always selected as an author of block?</a></p>

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2022-08-04T03:00:07.847Z
https://ethereum.stackexchange.com/q/87553/19041
D.W.
<blockchain-fork><proof-of-stake>
Possibility of occurring Fork in case of using Proof-of-Stake?
Questioner
# Possibility of occurring Fork in case of using Proof-of-Stake?

(Asked by: username_0 on 2020-09-17)

Regarding the fact that in Proof-of-Stake, a stakeholder will be elected randomly as the next validator in each epoch (or each round), logically, in each round there is only a single validator, and so a single proposed block. With these conditions, is there still the possibility of occurring a fork in each round?

**Edit:** According to the answer by @username_2 , we can say "author of the new block" rather than "validator". Nevertheless, if in each round, only a single author is elected to write the next block (as a winner), whether this block will be validated by the rest of network or not, in this round, only a single block has been created and so no fork occurs. Is n't it?

Concerning a part of @Murc's answer: ***"If there is actually just a single participant that can author the next block, there would obviously be no possibility of a fork, but that would come at the cost of the blockchain grinding to a halt when the sole author does not issue a block."***

But, we have a similar situation in Bitcoin, when **a single** miner is the **only winner** of PoW (in most of the case) to be the **single author** of the next block. This block then will be broadcast to all the miners. If PoW's answer is correct, the block is accepted.

**Related question:** [Proof-of-Stake: How to prevent someone from being always selected as an author of block?](https://bitcoin.stackexchange.com/q/99068/41513)

**Tags:** blockchain-fork, proof-of-stake

> **Comments:**
> **username_1**: https://ethereum.stackexchange.com/q/87553/19041  

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## 1 answers

### Answer by username_2 on 2020-09-17. Score: 0

I think this question has a faulty premise. What usually gets elected in POS systems is the *author of the next block*. The author of the next block is not the only validator of the blockchain. Every single full node validates the entire chain, so an invalid block will be rejected by all other participants.

Whether or not there is a possibility of a fork depends on the nature of the authorship election. If there is actually just a single participant that can author the next block, there would obviously be no possibility of a fork, but that would come at the cost of the blockchain grinding to a halt when the sole author does not issue a block. Systems I have investigated had some form of backoff strategy to allow multiple authors with different priority to issue blocks, or made it just magnitudes easier for the elected author to find a block.

> **Comments:**
> **username_0**: I added an "Edit" to the question. I'd like to know your opinion. Thanks.  
> **username_0**: So, do you in each round, multiple authors will be elected? Thank you if you could confirm.  
> **username_2**: That edit is just doubling down on the tautology of your question: under the premise that there is only a single author creating a single next block, there is no fork. Obviously true but also completely uninteresting as that's not a workable system (except as a permissioned blockchain with a single central author) because it would suffer liveness issues immediately and would be trivially DOSable.  
> **username_0**: Concerning a part of your answer: **_"If there is actually just a single participant that can author the next block, there would obviously be no possibility of a fork, but that would come at the cost of the blockchain grinding to a halt when the sole author does not issue a block."_** We have a similar situation in Bitcoin, when **a single** miner is the **only winner** of PoW (in most of the case) to be the **single author** of the next block. This block then will be broadcast to all the miners. If PoW's answer is correct, the block is accepted.  
> **username_2**: That is a false equivalency. In Bitcoin all miners are eligible to find the next block and it is the discovery of the block that determines the author. The way you phrase it, you make it sound as if the author is determined first and then they craft the block which is not the case.  
> **username_0**: From my point of view, although all miners pick up some transactions and insert in their block, nevertheless, only one of them will eventually be the legitimate author of the next block: one who has solved PoW to become the winner of a lottery. This lottery can be another mechanism, such as randomness or ... (but in that case, in my opinion, chaining blocks or transactions no longer make sense.) The difference of such a lottery with PoW is that no external resource is consumed. (That's why I said chiang transactions no longer make sense ...)  
> **username_0**: Of course, PoW is more secure against DoS or Sybil attacks, but in the sense of "decentralization" **if randomness process is performed de-centrally**, it could be decentralized too.  
> **username_2**: If the "decentralized randomness" is something the network needs to agree upon, the "decentralized randomness" requires a consensus protocol. That's a catch-22 when you want to build a consensus protocol such as POS.  
> **username_0**: I believe neither PoW nor PoS are consensus technique. PoW is only a Sybil attack prevention mechanism and PoS tries to play the same role ... How it is successful depends on many parameters. Of course, use of PoS for blockchain is not effective, as chaining blocks is meaningful when the nodes are forced to solve a heavy PoW (in proportion to total power of the network.)  
> **username_0**: So, there are two different terms: "blockchain" (a tree-like data structure that can be useful only by using PoW in an open network) and "decentralization" that can be implemented without blockchain. In both cases of PoW and PoS, there is no consensus, but the rest of the network accepts the winner's block, because the protocol says such a rule: If PoW's answer is correct, then accept the new block ! If there is another chain at the same time, then accept the longest one (more difficult); otherwise you are interpreted as a malicious node !  

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