Well the title is a lie. Of course they can change and they already have changed in the past. But if this is bad news to you and you were lead to believe something else, don't fret, it's not all bad. Here, let me try and give you the bigger picture about rules in Bitcoin and who it is that you need to trust that they won't change to something you won't like.
First there's a myths that I want to address. I also want to make sure the community pays attention to this issue. Because as Ben Franklin told a woman the Americans got a republic if they can keep it (turns out they couldn't) so too I'm here to tell you that you have an excellent money system on your hands, if you can keep it.
Myth: Miners set the rules by voting
False. Miners do not vote, they validate. They check that transactions meet the rules and then they add them into a block and add it to the blockchain. If a subset of miners decide that a certain rule should be changed what happens ISN'T that all miners now validate transactions according to the new rule even if the subset has the majority of hashing power, instead a so called hard fork happens and some miners validate transactions that obey the new rules and those who stick with the old rules ignore them and by virtue of ignoring each other they split into two peer to peer networks.
But what if all miners suddenly switch to new rules? Can they do this? Is there something that stops them? Answer: YES, EVERY NON MINING FULL NODE
I mean this is critical for every Bitcoin user to understand. Bitcoin is a decentralized system, in which if you run a full node YOU HAVE A SAY in what rules are to be followed. Because once the miner adds a new block they send it around across the network and when it gets to you, your client also validates. It validates that the miner validated the transactions and added them into a block and into the blockchain following the right rules, rules that you gave your EXPLICIT consent to when you downloaded the Satoshi client. If all of the sudden all miners started validating according to some new rules, your client is coded to simply ignore them and as soon as just 1 miner following rules your client accepts as valid shows up, the network can continue to operate under these same rules.
The ONLY way for rules to ever change for you is if YOU PERSONALLY download a new client version with new rules. I cannot stress enough how important this is. This so important that it should be paramount for anyone who has any significant wealth in Bitcoin to run your own full node regardless of the costs that brings to you. I myself do it too even though I don't even use the client for anything else.
Now this doesn't mean you should never accept new rules in a new client. In fact you already did because those new rules solved a technical problem. But if you want to keep the Bitcoin money system running under the principles that it is built upon today (FINITENESS, TANGIBILITY, TRANSPARENCY, ANONYMITY, SECURITY, DECENTRALIZATION, SELF-OWNERSHIP, INTEGRITY, PRACTICALITY, RATIONALISM) it is paramount that any such rule changes do not immediately or down road preclude you from being able to run a full node. Because if you can't run a full node and you trust someone else to do it for you, then you have effectively given away your power to have say about what rules Bitcoin follows.
Right now you are a sovereign in Bitcoin. You should never give that up, under any circumstance.
What do I mean with sovereign? Well there's nothing anyone could possibly do that can make you accept rules you didn't agree with. Nothing. You yourself have to decide to consent to a rule change. But if running a full node becomes impossible for you then all that which you were told about Bitcoin, that rules virtually can't change, that it has a strict limit of 21million, ect, all these rules will then be left to be decided by a small number of super nodes and the people who control them. The second this becomes reality Bitcoin will be no different than simply a slightly more transparent Paypal. And if you don't want that you better make damn sure you can run a full node.
lesson for me
