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zk-SNARK is “Zero-Knowledge Succinct Non-Interactive Argument of Knowledge’s “certificate’ whose size just <1kb. The block size of bitcoin is increasing because the numbers of transactions are increasing which causing the system to become slower, expensive, and less scalable. To make bitcoin more decentralized, we need to create more nodes means we need more independent miners. The number of miners are decreasing then only big farms will control whole bitcoin mining, hence they will control the bitcoin network.