Bitcoin miners basically utilize powerful computers in order to verify the transactions. Usually, there are mining pools which have groups of miners to combine their mining power and be more efficient. However, if someone gets more than 50 percent of networks mining power, they can use it to manipulate the system as per their personal needs.
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https://coingape.com/what-is-51-attack-in-bitcoin-blockchain/as far as i know yes.. thats make it more centralized right? but some other project counter this with different methods..