Bitcoin is a digital currency which operates free of any central control or the oversight of banks or governments. Instead it relies on peer-to-peer software and cryptography.

A public ledger records all bitcoin transactions and copies are held on servers around the world. Anyone with a spare computer can set up one of these servers, known as a node. Consensus on who owns which coins is reached cryptographically across these nodes rather than relying on a central source of trust like a bank.

Every transaction is publicly broadcast to the network and shared from node to node. Every ten minutes or so these transactions are collected together by miners into a group called a block and added permanently to the blockchain. This is the definitive account book of bitcoin.

In much the same way you would keep traditional coins in a physical wallet, virtual currencies are held in digital wallets and can be accessed from client software or a range of online and hardware tools.

Bitcoins can currently be subdivided by seven decimal places: a thousandth of a bitcoin is known as a milli and a hundred millionth of a bitcoin is known as a satoshi.

In truth there is no such thing as a bitcoin or a wallet, just agreement among the network about ownership of a coin. A private key is used to prove ownership of funds to the network when making a transaction. A person could simply memorise their private key and need nothing else to retrieve or spend their virtual cash, a concept which is known as a “brain wallet”.

Can bitcoin be converted to cash?

Bitcoin can be exchanged for cash just like any asset. There are numerous cryptocurrency exchanges online where people can do this but transactions can also be carried out in person or over any communications platform, allowing even small businesses to accept bitcoin. There is no official mechanism built into bitcoin to convert to another currency.

Nothing inherently valuable underpins the bitcoin network. But this is true for many of the world’s most stable national currencies since leaving the gold standard, such as the US dollar and UK pound.

What is the purpose of bitcoin?

Bitcoin was created as a way for people to send money over the internet. The digital currency was intended to provide an alternative payment system that would operate free of central control but otherwise be used just like traditional currencies.

Are bitcoins safe?

The cryptography behind bitcoin is based on the SHA-256 algorithm designed by the US National Security Agency. Cracking this is, for all intents and purposes, impossible as there are more possible private keys that would have to be tested (22⁵⁶) than there are atoms in the universe (estimated to be somewhere between 10⁷⁸ to 10⁸²).

There have been several high profile cases of bitcoin exchanges being hacked and funds being stolen, but these services invariably stored the digital currency on behalf of customers. What was hacked in these cases was the website and not the bitcoin network.

In theory if an attacker could control more than half of all the bitcoin nodes in existence then they could create a consensus that they owned all bitcoin, and embed that into the blockchain. But as the number of nodes grows this becomes less practical.

A realistic problem is that bitcoin operates without any central authority. Because of this, anyone making an error with a transaction on their wallet has no recourse. If you accidentally send bitcoins to the wrong person or lose your password there is nobody to turn to.

Of course, the eventual arrival of practical quantum computing could break it all. Much cryptography relies on mathematical calculations that are extremely hard for current computers to do, but quantum computers work very differently and may be able to execute them in a fraction of a second.

What is bitcoin mining?

Mining is the process that maintains the bitcoin network and also how new coins are brought into existence.

All transactions are publicly broadcast on the network and miners bundle large collections of transactions together into blocks by completing a cryptographic calculation that’s extremely hard to generate but very easy to verify. The first miner to solve the next block broadcasts it to the network and if proven correct is added to the blockchain. That miner is then rewarded with an amount of newly created bitcoin.

Inherent in the bitcoin software is a hard limit of 21 million coins. There will never be more than that in existence. The total number of coins will be in circulation by 2140. Roughly every four years the software makes it twice as hard to mine bitcoin by reducing the size of the rewards.

When bitcoin was first launched it was possible to almost instantaneously mine a coin using even a basic computer. Now it requires rooms full of powerful equipment, often high-end graphics cards that are adept at crunching through the calculations, which when combined with a volatile bitcoin price can sometimes make mining more expensive than it is worth.

Miners also choose which transactions to bundle into a block, so fees of a varying amount are added by the sender as an incentive. Once all coins have been mined, these fees will continue as an incentive for mining to continue. This is needed as it provides the infrastructure of the Bitcoin network.

Who invented bitcoin?

In 2008 the domain name .org was bought and an academic white paper titled Bitcoin: A Peer-to-Peer Electronic Cash System was uploaded. It set out the theory and design of a system for a digital currency free of control from any organisation or government.

The author, going by the name Satoshi Nakamoto, wrote: “The root problem with conventional currencies is all the trust that’s required to make it work. The central bank must be trusted not to debase the currency, but the history of fiat currencies is full of breaches of that trust.”

The following year the software described in the paper was finished and released publicly, launching the bitcoin network on 9 January 2009.

Nakamoto continued working on the project with various developers until 2010 when he or she withdrew from the project and left it to its own devices. The real identity of Nakamoto has never been revealed and they have not made any public statement in years.

Now the software is open source, meaning that anyone can view, use or contribute to the code for free. Many companies and organisations work to improve the software, including MIT.

What are the problems with bitcoin?

There have been several criticisms of bitcoin, including that the mining system is enormously energy hungry. The University of Cambridge has an online calculator that tracks energy consumption and at the beginning of 2021 it was estimated to use over 100 terawatt hours annually. For perspective, in 2016 the United Kingdom used 304 terawatt hours in total.

The cryptocurrency has also been linked to criminality, with critics pointing out to it being a perfect way to make black market transactions. In reality, cash has provided this function for centuries, and the public ledger of bitcoin may actually be a tool for law enforcement.