I was just wondering, in the hypothetical event that a global disaster leaves two or more networks of bitcoin nodes isolated from each other, but life manages to go on and both chains proceed, what would happen if they make contact again?
From what I know I would expect one chain to be discarded, is this correct?
When they reconnect it's longest chain according to protocol. You can read about "eclipse attack" - it's the same scenario if it's a disaster.
But you are right that it would be a shitshow because many transactions on one side would be undone and maybe a few individuals would have double spend.
In reality we assume that this would never happen because of how connected the internet is - especially with sattelites and stuff.
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but life manages to go on and both chains proceed,
Let's say that this hypothetical scenario were to happen today, and let's say the "cut" happened exactly where the western hemisphere (North & South America) had zero connectivity to the eastern hemisphere (Europe, Asia, Africa, Australia).
Then let's also assume hashrate is like 70% western hemisphere and 30% eastern hemisphere. Instantly blocks would start taking about 15 minutes each (western hemisphere) and more than 30 minutes each (eastern hemisphere).
So if this scenario lasted two hours, you still wouldn't likely have any transactions reach six confirmations on the eastern hemisphere.
But with that happening, once noticed, nobody should be accepting any further payments in bitcoin at all, without any other method for recourse should the spend end up being double spent once the eastern hemisphere side eventually rejoins the network from the western hemisphere.
Also, know that bitcoin transaction activity does not take that much bandwidth. If the data networks within each hemisphere were to still have connectivity, then a relay between the two hemispheres could be set up using just a single dialup connection even, if there were no other method, and both sides would be in sync.
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Bitcoin truly is a global currency, it's all or nothing.
Makes me wonder what it will look like if we end up with a Mars colony one day with the large communications delay.
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Well, since mining is a race and messages from mars arrive last, that eliminates that as a valid place to be mining -- all else being equal.
But for using the bitcoin blockchain, there's essentially no difference between using it on Mars versus on earth. Sure, it take you an hour and a half to see your transaction confirm (versus one hour for six confirmations here on earth), but other than that, there's not much of a difference.
As far as using a second layer (e.g., lighting network) or sidechain on mars, sure -- some of those would likely need mars-local versions to be useful in the same way. But even from mars, I could do a bitcoin spend on earth's Lightning network, if I am willing to use a node on earth -- it would just take 30+ minutes before I would know if the transaction succeeded.
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