Skeptical question

[pesci]

If a nefarious miner tries to reward herself 10000 bitcoins after finding a correct PoW for her copy of the block, what is to prevent her from doing so ?

Is there some central place where the current correct reward is to be found so that everyone knows for certain what it is e.g. https://somewebsite.com/current_reward.xml ?

When a reward values changes, but not everyone hears about it, there are bound to be miners who submit valid PoW and blocks whose reward is out of sync with the larger consensus. How is that discrepancy dealt with?

E.g. a miner submits a valid PoW for their block but rewards herself 25 BTC instead of 12.5. Does that miner get a chance to fix her mistake?

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[Upgrade00]

If a nefarious miner tries to reward herself 10000 bitcoins after finding a correct PoW for her copy of the block, what is to prevent her from doing so ?

Consensus and protocol. Such a transaction would not be verified.

When a reward values changes, but not everyone hears about it, there are bound to be miners who submit valid PoW and blocks whose reward is out of sync with the larger consensus. How is that discrepancy dealt with?

The consensus rule, nodes verify everything to make sure the network is functioning smoothly, if someone requests something which is not in the current protocol, it would be promptly rejected by the nodes.
Halving events are very much anticipated and it's unlikely majority of nodes would forget when it occurs.

[hatshepsut93]

E.g. a miner submits a valid PoW for their block but rewards herself 25 BTC instead of 12.5. Does that miner get a chance to fix her mistake?

A block with reward different from the current correct reward can not be valid. Doesn't matter if it's 1 Bitcoin more or even 1 satoshi less, if it's not precisely what it needs to be, such block is invalid. When a node tries to send invalid block to peers, they reject it and don't propagate it any further. This is why it's important to have a big decentralized network of nodes. If miners controlled all the nodes, like in a scenario that emerges from big block forks, then they could change the rules as they want, and users would only have 2 options - accept the rules or stop using Bitcoin at all.

[BlackHatCoiner]

E.g. a miner submits a valid PoW for their block but rewards herself 25 BTC instead of 12.5. Does that miner get a chance to fix her mistake?

If they reward themselves an invalid amount of Bitcoins, then it's not a valid proof of work, because it does not satisfy the conditions that are agreed. In your case, if a miner chose to reward himself 25 BTC instead of 12.5, he'd have to redo the proof of work in order for the block to be considered valid. (assuming 12.5 BTC is currently the correct reward)

Doesn't matter if it's 1 Bitcoin more or even 1 satoshi less, if it's not precisely what it needs to be, such block is invalid.

Actually, it can be less than the standard block reward. One could simply choose to be rewarded with 5.25 BTC and bring that 1 BTC out of circulation. It's their decision as it's their money; it really doesn't differ much from the OP_RETURN.

For more information: https://bitcointalk.org/index.php?topic=5342114.msg57215743#msg57215743

[pooya87]

You have to first realize that everything in bitcoin is decentralized and is enforced by the nodes. So when an individual (like you) runs a node they are enforcing certain rules known as consensus rules. When they receive a transaction in their mempool or a new block that a miner has mined they verify everything about them with these rules. If they break any of those rules (like having a reward more than what is allowed) they simply reject that block or transaction as invalid.

When a reward values changes, but not everyone hears about it,

Again things are decentralized, everyone computes the block reward on their own with the same rules. The rule is that block reward starts from 50 and is cut in half every 210000 blocks. So for example when a node receives block #1534 they know its reward is 50BTC and when they receive block #697123 they know its reward is 6.25BTC and so on.

E.g. a miner submits a valid PoW for their block but rewards herself 25 BTC instead of 12.5. Does that miner get a chance to fix her mistake?

Reward is claimed as the output of the first transaction in each block which is known as coinbase transaction. This tx (and anything else about the block) can not change after the hash (that is used in PoW) was computed otherwise the hash will change.

[o_e_l_e_o]

A block with reward different from the current correct reward can not be valid. Doesn't matter if it's 1 Bitcoin more or even 1 satoshi less, if it's not precisely what it needs to be, such block is invalid.

This is not accurate.

The constraint set by the protocol is that if you sum all the outputs in a block (including the coinbase transaction), that number must be less than or equal to the sum of all the inputs in a block plus the block reward. This effectively sets an upper limit on how much a miner can reward themselves for finding a block, being the block reward plus the total fees. However, there is no lower limit. Miners are free to claim 1 satoshi less, 1 bitcoin less, or indeed, no reward at all, if they so choose. This has happened many times in the past, usually by mistake, but has resulted in the irreversible loss of a few dozen bitcoin.