What is a Blockchain?
A blockchain is a distributed ledger where data is written in blocks, chained with cryptographic hashes, and replicated across many computers.
Who Is This For?
- •New learners who have never used a blockchain
- •Anyone curious how crypto assets are recorded and verified
Learning Objectives
- 01Describe how blocks link to form an immutable ledger
- 02Explain why decentralization removes single points of failure
- 03Identify real-world scenarios where transparency matters
Decentralization Basics
Traditional systems rely on a central authority—a bank, a company, a government. Blockchains flip this model by distributing control across a network of independent computers.
Traditional (Centralized)
Single point of failure. Bank controls everything.
Blockchain (Decentralized)
No single point of failure. Everyone has a copy.
Networks of Nodes
Blockchains run on thousands of computers (nodes) that all maintain identical copies of the ledger. Bitcoin has ~15,000 nodes worldwide.
Censorship Resistant
No single operator can block transactions or shut the system down—there's no 'off switch' anyone can flip.
Always Online
Even if half the nodes go offline, the network keeps running. Compare that to a bank website that crashes during high traffic.
💡 Think of it like this: If Wikipedia was a blockchain, instead of trusting Wikimedia servers, every reader would have a complete copy. Edits would need consensus from the network, not permission from admins.
Immutability & Hashing
Once data is written to a blockchain, it cannot be changed without detection. This is achieved through cryptographic hashes that link each block to the previous one.
#️⃣ What's a Hash?
A hash is a fixed-size “fingerprint” of data. Feed in any input and you get a unique output. Even tiny changes produce completely different results.
⛓️ The Chain Effect
Each block contains the previous block's hash. Changing any historical data breaks all links that follow—making tampering obvious to everyone.
Interactive Blockchain Simulator
Click "Try to Tamper" on any block to see what happens when someone changes historical data.
000000a7f3b2a7f3b2c9d4e1c9d4e1f2a8c6📔 The Public Notebook Analogy
Imagine a notebook written in permanent ink. Every new page includes a code calculated from the previous page. Thousands of people have exact copies.
If anyone changes an old page, their code won't match everyone else's—the tampering is immediately obvious.
Transparency & Use Cases
Every transaction on a public blockchain is visible to anyone. This radical transparency enables new forms of trust, verification, and analysis.
Public but Pseudonymous
Key insight: Anyone can see the transaction, but addresses are just strings. Without additional information, sender/receiver remain pseudonymous—not anonymous.
Why Transparency Matters
Payments & Settlement
Track stablecoin flows, verify settlements instantly, audit treasury movements without waiting for bank statements
NFT Provenance
Prove authentic ownership, verify an NFT's complete history, and confirm it came from the real creator
DAO Governance
Verify vote counts are accurate, see who delegated to whom, ensure decisions reflect actual community consensus
📊 The Analytics Advantage
Because blockchain data is public, analysts can track whale movements, monitor DeFi protocol health, and measure network activity—all without needing permission from anyone.
Common Mistakes & Gotchas
These misconceptions trip up most beginners. Understanding them now will save you confusion later.
⚠️ Pro tip: Before interacting with any blockchain, assume that transaction will be visible forever. This is a feature for accountability—but it requires a different mental model than traditional finance.
Knowledge Check
Let's see how well you understood the material. Answer all 5 questions below.
What links one block to the next in a blockchain?
Why is decentralization important for resilience?
Are blockchain transactions private by default?
What happens if someone tries to change data in an old block?
Which of these is a common misconception about blockchains?