If a Miner Finds a Bitcoin Block, Who Decides If It Is Valid?

[Sammysmart001]

Let imagine a miner found a Bitcoin block and the miner decide to broadcast it to the whole network, does this means that the block accepted it automatically ?
What if the miners give themselves extra BTC? What if they add an invalid transaction and who do says that Yes this block is valid ?
Surprising the answer is no, the network don’t just accept it.

What does the miner actually do ?

The miner job is just as simple, what the miner does is to collet transaction, build a Candidate block, Search on for a valid proof of work and then broadcast the block if they succeed. But having to find a block doesn’t mean that you are the boss. Block still have to pass a test, that’s the network validation rule

The full node is the checker                  

Let veiw it from this aspect: The Miner submits an application while the Full Node checks the application. Let imagine the miner will say I found a block then node at the other hand saying, that cool let me check if it follows the rules. And the node don’t just trust the miner, it verify.
Most users may ask , what if the block is invalid ?
Even if the block has a valid proof of work other validating nodes is going to reject it,if it break any of the consensus rules. Proof of work doesn’t make an invalid block valid .

What if two valid blocks show up ?

Sometimes two minners can find valid block at nearly the same time. Sometimes different nodes do see different valid blocks as the new one, but all nodes do follow the chain with the most cumulative proof of work. This how network do get all nodes to agree to settle on one chain.

The big takeaway is that miners produce blocks while full node at the other hand independently validate them. Bitcoin is working today because participate is following same consensus rules.

So Let me leave this technical questions for the community
1. If a miner finds a block with valid proof of work  but a transaction breaks the rules what will happen when full node receives it ?
2. Can A miner with huge amount of mining power force an invalid transaction into accepted Bitcoin blockchain?   
3. And lastly we’re does the miner job end and then a node validation begins ?

[Livingleged]

Let imagine a miner found a Bitcoin block and the miner decide to broadcast it to the whole network, does this means that the block accepted it automatically ?
What if the miners give themselves extra BTC? What if they add an invalid transaction and who do says that Yes this block is valid ?
Surprising the answer is no, the network don’t just accept it.

The thing is that a miner finding a block does not automatically make that block valid. Proof of work only prove that the miner have performed the required computation work, but it doesn’t override the main bitcoin consensus rule. So when other full nodes receive the block they will independently verify the header, proof of work, UTXO, transaction, spending script, coinbase rewards and other consensus rule. That is why if a miner decides to give him self more bitcoin than permitted, the node will reject that enter block and will eventually not build on that particular block. However there isn’t any central authority that decides whether a block is valid, the node just enforces the same consensus rules independently.

[Ambatman]

If a miner finds a block with valid proof of work  but a transaction breaks the rules what will happen when full node receives it ?

The node rejects it. Like not just the transaction but the block itself.

Can A miner with huge amount of mining power force an invalid transaction into accepted Bitcoin blockchain?

Nope
Hashrate determines a miner ability to produce blocks and influence  which valid chain wins
Not change the consensus rules followed by validating nodes.

And lastly we’re does the miner job end and then a node validation begins ?

I would say there's an overlap
Even Satoshi original design consider mining as something performed by network nodes.
Miners propose a block
Full node users verify if it sticks to the consensus rules.

[Antidote47k]

Miners and full nodes aren’t necessarily two completely separate participants. Miners themselves also run validating nodes when constructing its candidate block, so the distinction is more likely between proposing a block and having other nodes accept it as part of a valid chain. Miners themselves can produce a block that its own node would reject if its mining software constructed something invalid.
Essentially, miners searches for PoW on a candidate block, while nodes independently verify if that block is in line with the consensus rules. Those nodes can include miners themselves since most typically run validating nodes. So miners can’t make other validating nodes accept a block that violates consensus rules even if it has enormous hashrate.
In that sense, PoW gives the miner influence over which valid chain can be extended, but the nodes would still determine what they consider valid.

[Mia Chloe]

~snip

Miners can actually rely a fake block but the consensus rule actually compels other miners to verify first before they can accept it and proceed to relay it to other nodes too. The security feature here is every transaction has a chain connection or in simple terms an origin.

This is basically one of the major reasons why the Merkel tree is very important in transactions and confirmations. Before another node can accept and verify the transaction most definitely has to have a Merkel root that can be used to identify the identity of that transaction else they can't relay because it's gonna be invalid.

[promise444c5]

1. If a miner finds a block with valid proof of work  but a transaction breaks the rules what will happen when full node receives it ?

On a normal day nodes should reject every invalid transaction, so they shouldn’t even include in their memory pool talk more of adding it to a.block.. But that can happen if node(s) are behind  and running with old consensus rules. 

It will definitely be valid to them  and if a miner is running such, they produce a valid block under the old rule(s) while  the up-to-date node rejects them because it fails to meet up with the newer consensus rule(s), therefore invalid to them .

[Sammysmart001]

And lastly we’re does the miner job end and then a node validation begins ?

I would say there's an overlap
Even Satoshi original design consider mining as something performed by network nodes.
Miners propose a block
Full node users verify if it sticks to the consensus rules.

Yea that an intresting point being overlap, i was actually looking at it more as the miner do proposes the block while full node verifies it. But you are right on point that the roles are not completely separated.

So now will it be correct to say that a miner can also be running a full node and still be doing it own validation before having to build on the chain ?

[Nathrixxx]

1. If a miner finds a block with valid proof of work  but a transaction breaks the rules what will happen when full node receives it ?
2. Can A miner with huge amount of mining power force an invalid transaction into accepted Bitcoin blockchain?   
3. And lastly we’re does the miner job end and then a node validation begins ?

Remember their protocols that guide the blockchain technology upon every bitcoin transaction on the mempool, a block got rejected by the node once not in consensus.

Secondly, the answer to this is very simple and it talks about harsh rate, this is where you discover that there is a global distribution of the hashrate as this is not only constituted upon a particular mining pool.

The answer to your third question still falls back at the first answer I have provided for the first question.

[L E G E N D A R Y]

Okay, the very important distinction here is that, the process of finding a block and having that block accepted are basically two different things. What the PoW does is to prove that the miner actually expended computational work, not to give the miners permission to somehow alter or rewrite Bitcoin’s rules.

If a block contains an invalid transaction, validating nodes will have to reject that block and won’t build on it, and it doesn’t matter whether the PoW is valid or not. In the end, what the miner have succeeded to do is to waste the work spent producing that block.

Again, it doesn’t matter how much enormous the hash power of a miner is, it’ll still be impossible to unilaterally change an invalid transaction to become valid, and this is because consensus rules are enforced independently by nodes and no amount of hash power can change that rule.

[Ambatman]

So now will it be correct to say that a miner can also be running a full node and still be doing it own validation before having to build on the chain ?

Yes
Like I said before from design Satoshi expected miners to also be network nodes.
If another miner say Mark finds a block and Alice could verify that it's valid
And adds it while trying to find a block after it.