Double spending is a potential issue in digital currencies, including Bitcoin, where the same digital token can be spent more than once. This is because digital tokens do not have the same physical attributes as cash or other physical forms of currency, and it can be easily copied and spent multiple times.
In a traditional, centralized system, a central authority is responsible for keeping track of the validity of each transaction and preventing double spending. However, in a decentralized system like Bitcoin, where there is no central authority, a mechanism must be put in place to prevent double spending.
Bitcoin uses a distributed ledger technology called the blockchain to keep track of all transactions. Each transaction is grouped with others into a block and added to the blockchain. Once a block is added to the blockchain, it is very difficult to alter or remove.
Bitcoin’s consensus mechanism, called proof of work, ensures that only valid transactions are added to the blockchain and that double spending is prevented. In summary, double spending in Bitcoin happens when a user tries to spend the same bitcoin in multiple transactions, it is prevented by the consensus mechanism of the blockchain which ensures that only valid transactions are added to it and that the same coin cannot be spent twice.