Where is the longest chain of Bitcoin? The 'longest chain' of Bitcoin is like a person's' self ', it must exist but cannot be seen or touched, and it is a dynamic and complex adaptive growth. The longest chain has the following characteristics: -1. The longest chain is complete and conforms to the completeness of G ö del's first-order predicates. -2. The longest chain is dynamic and constantly changing, and at a certain moment it will stop at a distributed miner block node. The logic of distributed ledger is similar to Git, but unlike Git, Git has an absolute reference frame (such as the absolute reference frame branch displayed on the web server in GitHub), while Bitcoin's longest chain is relative. At a certain moment, whoever has the highest difficulty level is the longest chain. -3. The longest chain only solves the existence notarization of UTXO, which is the theoretical basis for the operation of lightning network state channels. Namely, the assets of Bitcoin's account system are independently controlled by distributed UTXO accounts. Assuming that Bitcoin no longer generates new blocks, the BTC transfer of the entire Bitcoin network still holds true on the basis of honesty among everyone. And the longest chain only solves conflict notarization (i.e. solves the double spending problem caused by malicious actors). -4. The attention of the Bitcoin network is entirely focused on the longest chain, which maintains the existence of UTXOs (the generation and destruction of UTXOs are achieved through asymmetric interactions based on asymmetric encryption algorithms), while the longest chain is maintained through P/NP asymmetric interactions between distributed miners and blockchain structures. We use the category of Complex Adaptive Systems (CAS) to extract Satoshi Nakamoto's expertise in designing Bitcoin, and then use CAS's expertise to construct a truly complex adaptive cryptocurrency system.