Content
Preventing 51% attacks can be viewed from two aspects.
On the one hand, this situation itself only exists in theory.
The vast majority of miners will maintain the entire Bitcoin system through honest mining
This is not guaranteed by the character of the miners, but maximized from their perspective. First of all, there are bitcoin rewards for miners for mining. Early calculation of a block can get 50 bitcoins. The latter rewards will become less and less, but transaction fees are a new reward method.
If they falsify transactions collectively, users lose confidence in Bitcoin and no one is using Bitcoin. Then the miners falsified the transaction and stole the bitcoins and it would be meaningless.
On the other hand, if there is such a 51% attack, it is recommended that the payee wait until 6 confirmations on the entire network before delivering the goods. At the rate of one block in 10 minutes, it only takes one hour to ensure that your money is basically received.
Note that the basic affirmation is used here, but the longer you wait, the safer the transaction is.
The principle is actually very simple. For Alice, assuming that the block he wants to forge is the last one, he only needs to calculate the success once, but if there are six blocks behind the block where he wants to tamper the transaction, he has to recalculate six. This block is much more difficult.