What Bitcoin is and how it moves between people
Bitcoin is a digital currency that exists only as data on computers and networks, not as physical coins or bills. When you own bitcoin, you hold a private key — a long string of characters that only you know — that proves you control a specific amount of bitcoin. To send bitcoin to someone else, you use your private key to sign a transaction, which is then broadcast to thousands of computers running the Bitcoin network.
Those computers verify that you actually own the bitcoin you are trying to send by checking the entire history of transactions. Once verified, the transaction gets bundled with other transactions into a block. That block is added to a chain of previous blocks — hence the term blockchain — and the bitcoin moves to the recipient's address. The recipient now holds the private key that controls that bitcoin, and the cycle repeats.
No bank, payment processor, or company sits in the middle. The network itself does the work of confirming ownership and recording the transfer. This is why bitcoin is called decentralized — no single entity controls it.
Key Takeaways
- Bitcoin transactions are verified by a network of thousands of computers rather than by a bank or payment company.
- A private key is a secret string of characters that proves you own your bitcoin and is required to send it to someone else.
- Transactions are bundled into blocks and added to a permanent, unchangeable record called the blockchain.
- Mining is the process by which new bitcoin is created and transactions are verified, and miners are rewarded with newly created bitcoin and transaction fees.
- Bitcoin's supply is capped at 21 million coins, and the rate at which new bitcoin enters circulation is programmed to slow over time.
Mining: how transactions get verified and new bitcoin is created
When you send bitcoin, your transaction does not when ready appear on the blockchain. Instead, it sits in a mempool — a waiting area where unconfirmed transactions gather. Miners pick transactions from this pool, bundle them together, and compete to solve a difficult mathematical puzzle. The first miner to solve the puzzle gets to add a new block to the blockchain and receives a reward: newly created bitcoin plus the transaction fees from all the transactions in that block.
This process is called proof of work. The puzzle is hard enough that it takes significant computing power to solve, but straightforward for the network to verify once solved. This design makes it extremely expensive and impractical for someone to fake transactions or rewrite history — they would need to control more computing power than the rest of the network combined.
The puzzle difficulty adjusts automatically every two weeks so that a new block is added roughly every 10 minutes, regardless of how many miners are competing. If more miners join and computing power increases, the puzzle gets harder. If miners leave, it gets easier. This keeps the pace of block creation steady.
How the blockchain records and protects transaction history
Each block contains a unique fingerprint called a hash, which is generated from the data inside that block. Each new block also contains the hash of the previous block, creating a chain. If someone tries to change even one transaction in an old block, that block's hash changes, which breaks the chain and alerts the network that something is wrong.
To successfully alter the blockchain, an attacker would have to recalculate not just one block but every block that came after it — and do so faster than the network is adding new blocks. With thousands of miners working around the clock, this is computationally impossible for any single actor or group. The longer ago a transaction occurred, the more blocks have been added after it, and the more find it becomes.
This immutability is why the blockchain is useful for recording ownership. Once a transaction is confirmed and buried under several new blocks, it is essentially permanent. You cannot reverse it, and no one can claim they sent you bitcoin if the transaction is not on the chain.
Private keys, public addresses, and wallet security
Your private key is a random number that only you should ever know. From this private key, a mathematical function generates your public address — a shorter string of characters that anyone can see and use to send you bitcoin. The relationship is one-way: someone who knows your public address cannot work backward to discover your private key.
Think of it like a mailbox. Your public address is the mailbox number that anyone can use to send you mail. Your private key is the only key that opens the mailbox and lets you take the mail out. If someone gets your private key, they can send your bitcoin anywhere, and there is no way to reverse it or recover it.
A wallet is software or hardware that stores your private keys and helps you sign transactions. When you use a wallet to send bitcoin, the wallet uses your private key to create a digital signature that proves you authorized the transaction. The signature is included in the transaction data, and the network verifies it using your public address. This proves you sent the bitcoin without ever revealing your private key.
The supply cap and the halving schedule
Bitcoin's code includes a hard limit: only 21 million bitcoin will ever exist. This is not a policy that could change — it is built into the protocol itself. New bitcoin is created only through mining, and the amount created per block is programmed to decrease over time.
When Bitcoin launched in 2009, miners received 50 bitcoin per block. Every 210,000 blocks — roughly every four years — this reward is cut in half. This event is called a halving. After the first halving, the reward became 25 bitcoin per block. After the second, it became 12.5. After the third, 6.25. This pattern continues until the reward becomes so small it rounds to zero, at which point no new bitcoin will be created.
Because the reward decreases and the supply is capped, bitcoin becomes scarcer over time. Miners will eventually earn income only from transaction fees, not from newly created bitcoin. This design is intentional: it creates predictable scarcity, unlike government currencies that central banks can print in unlimited quantities.
How transaction fees work and why they vary
When you send bitcoin, you can choose how much fee to include. The fee is not a fixed percentage — it is a per-byte cost that depends on how large your transaction is in data size and how busy the network is at that moment. A straightforward transaction sending bitcoin to one address might be 200 bytes. A transaction sending to multiple addresses might be 500 bytes.
Miners prioritize transactions with higher fees because they earn those fees as income. When the network is congested and many transactions are waiting, fees rise because people compete to get their transaction included in the next block. When the network is quiet, fees drop because miners will include low-fee transactions just to fill blocks.
You set the fee yourself when you send bitcoin. If you set it too low, your transaction might wait hours or days to be confirmed, or it might be dropped from the mempool entirely. If you set it higher than necessary, you pay more than you had to. Most wallets estimate a reasonable fee based on current network conditions, but you can override that estimate.
Consensus and why the network agrees on one version of truth
Bitcoin has no central authority — no company, government, or person decides which transactions are valid. Instead, the network reaches consensus through the rules built into the software that every node (computer running Bitcoin) follows.
When a miner creates a new block, every other node checks it against these rules. Is every transaction in the block valid? Does the miner have the right to create this block? Does the block's hash meet the difficulty requirement? If the block breaks any rule, nodes reject it and ignore it. Only blocks that follow all the rules are added to each node's copy of the blockchain.
Because all nodes follow the same rules, they all end up with the same blockchain. If someone tries to broadcast a fraudulent block or a block that violates the rules, the network straightforward rejects it. This is why Bitcoin does not need a central authority — the rules themselves enforce honesty.
Frequently Asked Questions
Can bitcoin transactions be reversed?
No. Once a transaction is confirmed and added to the blockchain, it cannot be reversed or undone. This is by design. If you send bitcoin to the wrong address or to a scammer, there is no refund mechanism and no customer service to call. This is why it is critical to double-check addresses before sending.
How long does it take for a bitcoin transaction to confirm?
A transaction is typically considered confirmed after it has been included in one block and several more blocks have been added after it. Since blocks are added roughly every 10 minutes, one confirmation takes about 10 minutes. Most exchanges and services wait for 3 to 6 confirmations, which takes 30 to 60 minutes. Transactions with very high fees may confirm faster; those with low fees may take hours or days.
What happens if two miners solve the puzzle at the same time?
Occasionally, two miners solve the puzzle nearly simultaneously and broadcast two different blocks. The network temporarily splits, with some nodes following one block and others following the other. This fork is resolved when the next block is mined — the chain that grows longer becomes the valid chain, and nodes on the shorter chain switch over. Transactions on the abandoned block are returned to the mempool and included in future blocks.
Is bitcoin anonymous?
Bitcoin is pseudonymous, not anonymous. Transactions are linked to public addresses, not to names, so you can send bitcoin without revealing your identity. However, every transaction is permanently recorded on the blockchain and visible to anyone. If someone connects your public address to your real identity, they can see all your transaction history. Law enforcement and blockchain analysis companies have tools to trace transactions and link addresses to people.
What stops someone from creating fake bitcoin?
The network verifies every transaction by checking the entire history of the bitcoin being sent. If you try to send bitcoin you do not own or send the same bitcoin twice, the network rejects the transaction. The blockchain is the source of truth — it records who owns what, and that record is maintained by thousands of independent computers that all follow the same rules.