Bitcoin mining is very concentrated, so if one or more of the major miners is robbed, it's entirely plausible that similarly situated entities would collaborate and just undo the transaction.
That being said, I do think patio11 is technically correct, given his unconventionally strict definition of "finality".
Probability is at the core of Bitcoin's proof of work security mechanism. There is a non zero probability that I could rewrite the whole Bitcoin transaction history in the next 15 minutes, if my miner gets really, really, really lucky. The chances of that happening are of course abysmally small and not worth considering. For all practical purposes, Bitcoin transactions are final past a few confirmations.
I estimate the probability of a similar Bitcoin action to be small, but much larger than the "miner gets really, really, really lucky" scenario you propose. Do you disagree?
> I estimate the probability of a similar Bitcoin action to be small, but much larger than the "miner gets really, really, really lucky" scenario you propose. Do you disagree?
Of course, I agree. That being said, I'd still put the probability in the vanishingly small category, especially for any individual transaction that isn't an exploit, and not worth considering in the context of "finality", as the term is commonly used (and not as patio11 defines it).
The payment was still never actually reversed on Ethereum Classic. And that blockchain exists to this day. Sure, the amount of the not-actually-reversed transaction has lost value in $ at mark-to-market but it’s still the same amount of ether on the same blockchain as it’s always been.
In that sense a better term is that the payment was rejected by the community, or routed around, rather than reversed IMO.
Anyway, I just find this a really bad example in general because it’s 1 an exceptional case, most other hard forks haven’t been done just for transactions 2 it required almost the entire community to choose to follow the hard fork (which is the only thing that actually destroys value). Yes, it does show that you can do something like a payment reversal in crypto but it’s very hard and unlikely. In this case the exception proves the rule
In particular, Bitcoin mining is concentrated into a small number of pools, but the amount of actual power they hold is very questionable. Because nobody censors transactions, we can't know if miners would flee or not if they began to.
English banknotes are printed by De La Rue plc, but it's not like they have a stranglehold on the English economy. If they began to act up, their 'power' would dry up very quickly.
Also, even with 100% of miners cooperating, reversing a two week old transaction would still take two weeks. There are some technical issues with this, since new transaction would grind to a halt and it would generally be a mess.
Note how Ethereum wasn't miners collaborating (soft fork), it was a hard fork, which required no miner cooperation at all.
A hard fork of Bitcoin in this way is indeed possible, but would require the consent of a lot of entities. Ethereum is much more 'socially' centralized in terms of its governance process, and it was very obvious that if they didn't go along with it, then the big, centralized entity that held all the proceeds from the ICO would stop paying the developers, and the PR goons, and and and...
I'm not going to draw any conclusions about the future based on this, but we can observe that big players (Binance) have lost money, publicly considered 51% attacks, then backed down. We can also observe the fate of Marathon's OFAC pool - he didn't fly so good, who wants to try next?