What Is Bitcoin, Anyway — and Why Does It Exist?

How something scarce can emerge from data that can be copied — and what that has to do with our money.

You send a friend a photo. They receive it, and you still have it. They can forward it; you can send it again. That is precisely what makes digital communication so useful: information can be reproduced almost without limit.

With money, that would be a problem. If you could send the same ten euros to a baker, a neighbour and an online shop at the same time, nobody would accept them as payment. Money must be transferable without the sender being able to spend it again afterwards.

Bitcoin addresses exactly this question: how can value be transferred over the internet without the same funds being spent more than once — and without a central authority keeping the books?

Understanding that brings you closer to the heart of Bitcoin than looking at any price chart.

Why digital money usually needs a bank

When you transfer ten euros, no digital banknote travels down a wire. Banks change entries in their books: your balance falls and the recipient’s rises. The institutions arrange settlement and ensure that you cannot spend your available balance more than once.

This works because we trust those institutions and because they operate within a legal and technical framework. We rely on them to keep accurate records, remain available and carry out our instructions.

With cash, the process is more immediate. When you give someone a ten-euro note, it is then in their possession. You cannot spend that same note again because you no longer have it.

Bitcoin brings one property of cash into the digital world: value can pass directly between people without a bank keeping the books for them. That requires a different way to agree on which payments are valid.

Why would anyone want that if banks already perform this task? Because it creates an alternative: a monetary system that does not require an account with a company and in which new units are issued under rules that participants can verify together. How useful that is depends on the situation. The ability to hold money yourself and transfer it over the internet gives you another option.

Shared records without a central authority

Bitcoin is an open network and also the name of its monetary unit. The idea was published in 2008 under the name Satoshi Nakamoto; the network launched in 2009.

Instead of a central account system, there is a publicly verifiable transaction history — the blockchain. New transactions are grouped into blocks. Each block refers to its predecessor, linking the history together.

Imagine a ledger whose entries many participants can check independently. Simply writing something in it is not enough. A payment must comply with the rules: anyone spending bitcoin must demonstrate that they are authorised to do so. Funds that have already been spent cannot be used again.

Technically, Bitcoin does not maintain ordinary bank accounts. It tracks unspent amounts from previous transactions. A wallet — the software used to receive and spend bitcoin — calculates the displayed balance from those amounts.

The essential point is that a digital signature demonstrates the authority to spend. The shared transaction history makes it possible to establish which funds have already been spent.

What miners and nodes do

An open ledger needs a way to put new entries in order. Otherwise, someone could broadcast two conflicting payments at once, leaving different participants with different versions.

This is where mining comes in. Miners assemble candidate blocks and use specialised hardware to search for a cryptographic result that meets the required conditions. Finding one involves a great many attempts. This evidence of computational work is called proof of work.

The search consumes computing power and electricity and costs money. A successful result, however, is quick to check. If a valid block becomes part of the accepted chain, its miner can claim the newly issued bitcoin permitted by the rules, along with the transaction fees.

On average, a new block arrives roughly every ten minutes. Individual intervals can vary considerably.

Full nodes are computers running software that independently checks transactions and blocks. A miner can propose a block, but a node accepts it only if it complies with that node’s rules. More computing power does not make an invalid block valid.

Among valid chains, nodes follow the one with the greatest accumulated proof of work. Anyone seeking to replace a confirmed payment with a conflicting history must therefore build an alternative, equally valid chain with sufficient work behind it. As long as honest miners collectively have more computing power than an attacker, the attacker’s chance of success falls as further confirmations accumulate.

The network makes manipulation costly. It does not assume that every participant is honest. This protection does require energy, so both its benefits and its costs belong in any assessment of Bitcoin.

Not every user needs to run a full node. If you leave verification to your wallet or its provider, you rely on others at that point. Running your own full node allows you to check independently that the rules are being followed. A Bitcoin app alone does not guarantee that independence.

Who decides the rules

If Bitcoin is software, surely someone could just change the code. Why, then, should its supply really be limited?

Anyone can indeed copy and modify the code. It does not follow that others will adopt those changes.

Developers can propose improvements. Miners can produce blocks. Users and node operators decide which software to run and which rules to accept. No single person or institution can impose a new monetary system on the entire network.

Nor is this a vote in which the largest number of computers automatically wins. Starting a thousand additional nodes does not give someone the right to override other participants’ rules.

Changes require technical work and agreement among people. Fundamental disagreements can produce incompatible networks. Which rules people continue to recognise as Bitcoin cannot be settled by a single software download.

The difference from state-issued money is not simply that the rules are public — laws and central bank rules can be read too. The distinctive feature is that no central authority can make new Bitcoin rules binding on every participant. Others actually have to adopt the changed rules.

Why people talk about 21 million bitcoin

Under the current rules, the total amount of bitcoin that can be issued approaches an upper limit of 21 million. Because the calculation works in the smallest whole units, the maximum possible issuance falls slightly below that figure.

New bitcoin are issued according to a predetermined schedule. The permitted issuance per block halves every 210,000 blocks — roughly every four years. It is expected to reach zero around the year 2140. Miners would then rely on transaction fees for revenue. Whether those revenues will finance sufficient security over the long term depends, among other things, on future demand for transactions.

The limit does not mean that only 21 million people could own bitcoin. One bitcoin consists of 100 million satoshis, or sats. You do not need to acquire or transfer a whole bitcoin — just as you do not need an entire gold bar to own a small amount of gold.

This scarcity is a property of supply. It does not guarantee a price. People assign value to bitcoin when they find its properties useful and are willing to exchange something else for it. A limited quantity alone is not enough: even a scarce asset can lose substantial value if demand falls.

What a wallet actually holds

The word wallet suggests that digital coins are stored inside it. In reality, a self-custodial wallet primarily manages the secret keys that let you authorise spending.

Bitcoin do not sit on your phone or a hardware device in the way that photos do. The network’s records establish which funds can be spent under which conditions. Your keys allow you to spend the corresponding amounts.

To receive a payment, you have your wallet generate an address, often displayed as a QR code. To make a payment, the wallet creates a transaction and signs it with the appropriate private key. The signature can be verified without revealing that secret key.

Many wallets can be restored using a recovery phrase, usually consisting of twelve or 24 words. This is not an ordinary customer-service password. For typical wallets, the phrase is enough to spend the associated bitcoin; some arrangements also require an additional passphrase or further keys. These words belong neither in an email nor in the hands of someone claiming to provide support. If all the necessary keys and backups are lost, access can be lost permanently too.

Self-custody means both freedom and responsibility. No account provider has to approve your payment. But there is also no central authority that can simply issue replacement access credentials.

A balance held with an exchange is different. If the provider controls the keys, you depend on it for access and withdrawals. An app displaying a bitcoin balance does not, by itself, prove self-custody.

What Bitcoin can do — and where its limits lie

Bitcoin makes it possible to transfer value over the internet and hold it yourself without necessarily using a bank account or central custodian. That can be useful for people who live, work or make payments across borders.

It does not make Bitcoin trouble-free money for every situation. Its exchange rate can fluctuate sharply. Transactions take up space on the blockchain, fees vary, and confirmation does not follow a guaranteed timetable. There is no central authority that will reverse a confirmed payment on request.

Bitcoin is not automatically anonymous, either. The blockchain is public. Addresses do not have names built into them, but they can be linked to people.

The security of the network and the security of an individual user are also different things. A functioning protocol will not stop you from installing a fraudulent app or giving your recovery words to a scammer.

Anyone seeking to understand Bitcoin should know these limits as well as its possibilities.

Why understanding Bitcoin is worthwhile

You do not have to buy bitcoin to learn about it. Nor do you have to agree with every criticism of the current monetary system.

Simply exploring it raises questions that often remain invisible in everyday life: who keeps the records of our money? Who is allowed to create new units? What role do custodians play? And how much responsibility do we want to take on ourselves?

Bitcoin offers a way to hold and transfer digital money under jointly verifiable rules without necessarily relying on a central account provider.

Whether that has practical value for you is a separate question. Understanding comes first. Anyone who sees only a fluctuating number on a trading platform misses the heart of the idea: people can agree on a shared ledger without handing control of it to a single authority.

Questions about Bitcoin? I am happy to explain the basics personally, with room for your questions. Email me at kontakt@andyzyklisch.de. You can find out more on Understand Bitcoin.

This article is for educational purposes. It does not provide individual investment advice or a recommendation to buy.

Sources and further reading

• Satoshi Nakamoto: Bitcoin: A Peer-to-Peer Electronic Cash System, 2008. The original proposal for digital payments without a central trusted intermediary.
• Bitcoin Developer Guide: Block Chain, Transactions and Mining. The technical foundations of transaction records, validation and proof of work.
• Bitcoin.org: Frequently Asked Questions. The network’s origins, open development and basic principles.
• Blockstream: Why is the Bitcoin supply limited?. The issuance limit and halving schedule. Also see Bitcoin Core, amount.h for satoshis and amount limits.
• Bitcoin Developer Guide and Bitcoin.org: Wallets and Securing your wallet. Key management, backups and custody risks.
• Bitcoin.org: Some things you need to know and Protect your privacy. Price risks, payments and public transaction data.