Blockchain

What is a blockchain?

A blockchain is a database maintained by a network of independent computers — called nodes — that agree on every update through a shared protocol, rather than relying on a single central authority [1]. Data is stored in blocks that are cryptographically linked to each other in sequence, making the history tamper-evident: changing one block would require changing every block after it, which the rest of the network would reject [2].

How it works

1. Transactions are submitted. A user sends a transaction — a transfer of value, a record update, a smart contract call — to the network.
2. Transactions are grouped into a block. Nodes collect pending transactions and assemble them into a candidate block.
3. The network reaches consensus. Using a consensus mechanism (such as proof-of-work or proof-of-stake), the network agrees on which block is valid and should be added next [1].
4. The block is linked and stored. Each block contains a cryptographic hash of the previous block, forming a chain. This link makes the history tamper-evident — altering a past block would change its hash, breaking every subsequent block [2].
5. Every node updates its copy. Once the network agrees, every node adds the new block to its local copy of the ledger. There is no single master copy — every node holds the full history.

Consensus mechanisms

Consensus mechanisms are the protocols that let distributed nodes agree on the state of the ledger without a central coordinator. The two most common:

• Proof of Work (PoW). Nodes compete to solve a computationally intensive puzzle. The winner proposes the next block and earns a reward. Bitcoin uses PoW, which provides strong security but consumes significant energy [3].
• Proof of Stake (PoS). Validators lock up cryptocurrency as collateral. The protocol selects validators to propose and attest to blocks; misbehavior is punished by slashing (destroying) their stake. Ethereum transitioned to PoS in 2022, reducing energy consumption by approximately 99.95% [1].

Other mechanisms — delegated proof-of-stake, proof-of-authority, proof-of-history — exist for specialized use cases, but PoW and PoS secure the vast majority of value on public blockchains.

Public vs. private blockchains

• Public (permissionless) blockchains — anyone can join the network, submit transactions, and participate in consensus. Bitcoin and Ethereum are public blockchains. They prioritize openness and censorship resistance.
• Private (permissioned) blockchains — a known set of organizations controls who can read, write, and validate. Hyperledger Fabric and R3 Corda are examples. They prioritize privacy and compliance for enterprise use cases [2].

The tradeoff: public blockchains offer stronger guarantees of neutrality and immutability but sacrifice privacy and throughput. Private blockchains offer faster settlement and access control but depend on trust among participants.

Smart contracts

A smart contract is a program stored on a blockchain that runs when predetermined conditions are met. Ethereum introduced smart contracts in 2015, enabling developers to build applications that execute automatically without intermediaries — financial services, supply chain tracking, digital identity, and more [1].

Smart contracts are the foundation for decentralized finance (DeFi), non-fungible tokens (NFTs), stablecoins, and the emerging agentic commerce ecosystem.

Why blockchain matters for the agentic economy

Blockchain provides the trust layer that autonomous AI agents need to transact without relying on a single platform or institution:

• Payments. Stablecoins on blockchain enable instant, programmable, cross-border payments that agents can initiate and verify without human intervention.
• Identity. Blockchain-based credentials let agents prove who they are and what they are authorized to do.
• Coordination. Smart contracts allow multiple agents to agree on terms, execute transactions, and settle disputes without a central mediator.
• Transparency. Every transaction is recorded on a shared ledger, providing an auditable trail for compliance and accountability [4].

The World Economic Forum projects that 10% of global GDP could be tokenized and stored on blockchain by 2027, with stablecoins as the critical enabling layer [4].

Common reader questions

Is blockchain the same as Bitcoin?

No. Bitcoin is a cryptocurrency that runs on a blockchain. Blockchain is the underlying technology — the distributed ledger and consensus mechanism — that Bitcoin was the first major application of. Thousands of other blockchains exist now, with different designs and purposes. Saying “blockchain” when you mean “Bitcoin” is like saying “internet” when you mean “email” [3].

Can blockchain data be changed?

In practice, no — and that is the point. Each block is cryptographically linked to the one before it, so altering a past transaction would require recalculating every subsequent block and convincing the majority of the network to accept the change. On large public blockchains like Bitcoin and Ethereum, this is computationally infeasible. This property is called immutability, and it is what makes blockchain useful for records that need to be trustworthy over time [2].

Is blockchain secure?

The blockchain protocol itself is highly secure — the cryptographic linking and consensus mechanisms make tampering extremely difficult. But the applications built on top of it can have vulnerabilities: smart contract bugs, compromised private keys, and social engineering attacks are real risks. Security depends on the quality of the code, the design of the system, and the practices of the people using it.

Why does blockchain use so much energy?

Proof-of-work blockchains (like Bitcoin) consume significant energy because nodes compete to solve computationally intensive puzzles. Proof-of-stake blockchains (like Ethereum since 2022) use a fundamentally different mechanism — validators stake collateral instead of burning energy — and consume roughly 99.95% less. The energy concern is specific to PoW, not to blockchain as a category [1].