No, a majority of miners cannot decide to change some aspect of the protocol. If they do, they will be mining on their own fork. Not only would the majority of miners have to agree, but so would all the users and businesses have to agree to use that fork.

You misunderstood.

Bitcoin is not a democracy. Bitcoin is a zero trust system. Each full node is autonomous, it validates the entirety of the rules on its own— trusting only its source code (which you or anyone else can audit).  Only through autonomy can you have independence and the assurance that the majority of wolves won't vote to have you for supper.

Unfortunately, to resolve to double spending a digital cash system must have a way of agreeing what order the transactions happened in.  Its is not possible to have a decentralized antonymous system where everyone agrees on the same order of events— because the apparent temporal ordering of events depends on the relative position of the events and the observers in space— this is a consequence of relativity.  So before Bitcoin many people believed that this sort of system was fundamentally impossible.

Bitcoin solves the fundamental impossibility by relaxing the autonomy by the minimum amount necessary:  We use a majority of computational power to decide on the ordering of transactions.  But _ONLY_ the ordering. Nothing else. That one compromise makes all the rest possible.

Of course, controlling the ordering of transactions is a powerful thing— because a transactions validity depends on its order relative to possible conflicting transactions penned by the same author.   This is why it's important that the majority of the Bitcoin computing power is well distributed,  that we don't let it consolidate into the hands of a few service providers (like mining pools or exchanges).  The use of computing power makes the the system not only resistant to attack, but it makes the attacks have a clear and fairly consistent real monetary cost— so people can reason about the risks, and the economics of the system make it so that it should hopefully be more profitable to cooperate than to attack it.

The state currencies of democratic nations is theoretically democratic money, unhappiness of the current state of affairs is part of the motivation behind Bitcoin. Democracy is not a good method of making decisions— it's often just the least bad option.  But Bitcoin is something stronger than democracy, ... though not quite as strong as the laws of nature.

Of course— the rules of the system can be changed, but it requires basically everyone to agree to the change because the old system and change system won't talk to each other, it's basically like replacing Bitcoin with something else.   This has actually happened, for example, there was once a bug in the rules of the system where the values of transactions could overflow and someone exploited the bug to create a billion bitcoins for himself.  People noticed this right away and published a fixed version of bitcoin which rejected the block containing that transaction and all blocks after it... and everyone applied the fix, because it was obviously in everyone's interest except the attacker's, and life went on.

But if people are afraid of e.g. the supply of Bitcoin being changed they really shouldn't be.  Yes, almost all the Bitcoin users could switch to some fork of bitcoin that had different rules— but with the same effort they could just switch to paypal.  There is always the risk that someone will use something else. But Bitcoin itself isn't subject to petty majority rule.


(I wrote basically the same thing at https://bitcointalk.org/index.php?topic=61922.msg723476#msg723476  too ... couldn't find it at first because the only quote I could think of from it is all over the internet now )

So it can be done. Despite the fact that it would create a rift in the network, a change can be made part way through the mining of a Bitcoin chain.


What say do they have? Their transactions are broadcast only, no? It's just a matter of whether the coins they spend exist in the chain they broadcast to.


Guess that's what I was going for. As much as I would like to see the pandemonium of such an event, like a bad train wreck, I also understand that politically, it would end up doing more harm than good.

I edited what I said a bit to make it more accurate.  It's not a simple majority to fork; it's you have to convince the world that your new system is the new chain is BitCoin and that the old system should be ignored.

Well why not—  if you abandon a privileged position, a reasonable thing to abandon if you're stipulating _decenteralized_, it's makes perfectly reasonable example.  If you use things like finite processing speed as examples as to why attack resistant decentralized autonomous agreement isn't possible people will just argue what IFs involving faster computers and other such spherical bovine.   Going to a more fundamental argument, even if its totally wanky makes it clear that the goal is really autonomy but its simply not achievable, and so we instead take majority ordering with eventual consistency.


I can't believe it. I completely agree with a statement of yours. I'm flabbergasted.

Well, it takes a big, tall, handsome, wise and intelligent man to admit when he's wrong...

In Bitcoin everyone broadcasts everything which is valid.  It uses a lightweight inventory exchange to avoid sending a bunch of data redundantly. This is part of how Bitcoin, as Satoshi wrote, "takes advantage of the nature of information being easy to spread but hard to stifle". The fact that everyone passes on all the good information makes it so someone can't disrupt the system with a few misbehaving nodes.

Miners broadcast blocks they mine to other nodes, who then broadcast those blocks to other nodes, and so on in that fashion until all the nodes have all the blocks (that's how P2P networks work). The only difference between mining nodes and non-mining nodes is that miners occasionally generate new blocks in addition to passing on blocks received from other nodes.

Miners can't force users to download and run new versions of the client software that would allow the new rules (which violate the established Bitcoin protocol) to be supported.

Users won't support changes that bring them negative economic consequences (e.g., actions like issuing currency faster, which debases their holdings).

If there ever were a chance of disruptions, commercial mining operations being built and run as protection would probably be the response.

Actually, in 1978, computer scientist Leslie Lamport wrote an extremely influential paper linking the order of events in distributed systems to relativity. In my opinion, Lamport is one of the most important computer scientists, though he hasn't won a Turing Award yet.

You can read about the paper here:
http://www.podc.org/influential/2000.html

You can read the actual paper (relativity comes up within in the first 2 pages) here:
http://research.microsoft.com/en-us/um/people/lamport/pubs/time-clocks.pdf

Personally, I'm very interested in how Bitcoin's proof-of-work system relates to the classical "consensus" problem in distributed systems. I suspect some compter scientists have already talked about this somewhere, but I haven't bothered to look it up yet