maybe searching the forum for the thousands of topics on the subject. instead of making yet another one.

its not about fault with bitcoin code. its about a mining pool wanting to undo a block. after they have received goods or service. (undo some transaction) so that they can re-use that transaction value elsewhere

(its a double spend risk. not a break bitcoin code risk. as all network fullnode users have the same moral code. and changing block formations wont change the code. it only changes whats been a confirmed transaction)

the whole idea is
if it costs a block $200k every 10 minutes to be made.
to undo a block
say block 601
the moral mining pool(MMP) and the general network are already working on block 602
immoral pool(ImP) makes a new 601 minus his transactions

            0min   10min   20min   30min   40 min  50 min
MMP      601      602
ImP       601  601

for ImP to overtake MMP, ImP has to have more hashpower then the network.
            0min   10min   20min   30min   40 min  50 min
MMP      601      602      603       604
ImP       601  601  602  603  604

and maintain it
            0min   10min   20min   30min   40 min  50 min
MMP     601      602      603       604
ImP      601  601  602  603  604  605  606

thus at 605 everyone then follows his chain. thus ditching the mmp chain of 601-604
what he doesnt want to do is have the MMP overtaking him and re-establishing the 601 with the transaction
            0min   10min   20min   30min   40 min  50 min
MMP     601      602      603       604
ImP      601  601  602  603  604  605  606

anyway in stepping back to a scenario ImP was not re-overtaken
            0min   10min   20min   30min   40 min  50 min
MMP     601    602      603       604
ImP      601  601  602  603  604  605  606

this scenario now any/all transactions that were on mmp 601-604 are no longer confirmed.
and any transactions on ImP version are confirmed

however this cost ImP in this simple demo $1m of power to overtake with the 605 variant chain block
.
the premiss is.. unless people are going to want to undo a large transaction over $1m, they wont try to do this attack. as its not worth it otherwise

which is why as a more dis-incentive. anyone receiving a transaction will not release goods of $1m for 6 blocks(block cost $1.2m)

meaning if ImP buys something for $1m at block 601 he wont get the goods until 607
and then and only then can he try to break the 601 and start his undo of that transaction

           0min   10min   20min   30min   40 min   50 min   60 min   70 min   80 min
MMP     606      607       608       609      610       611       612       613        614
ImP      601  602  603  604  605  606  607  608  609  610  611  612  613  614  615

now its cost him 14 blocks ~$2.8mill
to undo a transaction of just $1m value

thus. he has lost money.. and would have been better off just being a moral miner

I don't think that if a 51% attack happens, then the coins in addition to Bitcoin will live, immediately a panic will start in the market and everyone will sell Bitcoin, because no mistakes should occur, and canceling transactions is quite the opposite of what Bitcoin was created for.

Of course, maybe in the future there will be a new coin that will be protected from such manipulations, but it will take at least 5 years to restore trust for people, I think so

51% is not unknown and the costs and complexity of executing it is how PoW solves the Byzantine general problem. If you think governments care about Bitcoin at all, to the extent that they're willing to spend billions on trying to harm the current Bitcoin, then you are wrong. You cannot prevent 51% attack but the opportunity costs that arises from this is immense. If it ever happens, then we roll back to before the attack and change the algorithm. By doing so, the government has effectively wasted billions of dollars for nothing.

51% attack is not a Bitcoin killer because the game theory behind it hasn't failed. The sheer energy required to execute the attack is equivalent to certain smaller countries. The land area required to house the ASICs and the manpower required to set it up would be fairly big as well. Without understanding the difficulty of executing an attack, and the benefits of doing so from the government's PoW, then you won't understand why this isn't a problem.

Well, before we talk about restoring trust, we should discuss whether it's possible to lose it in the first place. If there is a chance that an attack will happen, I'm pretty sure the community will prepare for the countermeasures. Your panic sell situation has been described and predicted multiple times but Bitcoin is still doing fine. Sure, everyone knows 51% is deadly, but it's not like anyone can pull the trigger and kill the network anytime.

Wrong, it's not about error in bitcoin code, Lol, it's about some entity controlling 51% of bitcoin's hashrate.


Yes, that is feasible, but what do they get in return? Nothing, there are no incentives and on the contrary, it might cause billions to attack bitcoin.


Again, there will be no profits in 51% attack, they are just going to waste a lot of their time and money out of nothing. It is not logical.

51% attack doesn't benefit anyone, even if the states who will support, collaborate and execute the attack won't get anything but just satisfaction that they did something plus bitcoin can recover from it even if in theory, it's a devastating attack. Also, with China out of the picture, it will be difficult to coerce every miner to participate in this one because not everyone will yield unless you use force which is going to be making noise and you don't want noise since people get nosy when there's noise.

The number of coins you own is irrelevant to a 51% attack. You can attack the network despite not owning any bitcoin.

No. You need a sustained minimum of 51% of the total hashrate to guarantee that your attack will be successful over a long enough time frame. You can have much more than this, but you could also try to attack the network with much less than this, although your chances of success exponentially decrease.

There are maybe two or three which I could see surviving, albeit after taking an enormous hit to their price. But if bitcoin dies, then the majority of the market dies with it.

51% attack is NOT some error in Bitcoin code and I don't know how you got that idea in the first place 
Taking over mining hashrate for Bitcoin is almost impossible task, some people tried to take over with various forks but they failed, this is most secured computer network in the whole world, and anyone willing to throw away many can try that again and se how it goes.

Exactly, if anyone or group of people had the hashpower/computing power to
attack the network it would be far more rewarding to actually help the network
and mine to earn a Bitcoin reward.

As franky1 mentioned this topic has been discussed many many times on the forum.
The question has been asked since 2011

https://bt.irlbtc.com/view/52388.20
https://bt.irlbtc.com/view/44078.0
https://bt.irlbtc.com/view/55394.0

How exactly will the capacity be transferred to other pools? Do they automatically do it or am I misunderstanding something?

The system is completely transparent and decentralized.