What is Blockchain

What Problem Does Blockchain Solve?

Imagine you send $100 to a friend online. How does your bank know you actually have $100 and haven’t already spent it?

The answer — your bank keeps a ledger. A record of every transaction. You trust the bank to keep this record honest.

But what if you didn’t need to trust a bank? What if thousands of computers around the world all kept the same record simultaneously — and they all had to agree before any transaction was approved?

That is exactly what blockchain does.

What is a Blockchain?

A blockchain is a digital ledger — a record of transactions — that is shared across thousands of computers simultaneously.

Think of it like this:

Imagine a Google Doc that thousands of people can read — but nobody can edit or delete anything. Every new entry is permanent and visible to everyone forever.

Every time a transaction happens on Bitcoin:

• It is grouped with other transactions into a block
• That block is verified by thousands of computers
• Once verified — the block is added to the chain of previous blocks
• It can never be changed or deleted

How Are Blocks Connected?

Each block contains three things:

1. Transaction data
A list of all transactions in that block — who sent what to whom.

2. A timestamp
The exact time the block was created.

3. A hash
A unique digital fingerprint of that block. If anyone tries to change even one letter in the block — the hash changes completely — and the entire chain breaks.

This is what makes blockchain tamper proof.

Why Can’t Blockchain Be Hacked?

To hack a blockchain — you would need to:

• Control more than 50% of all computers running the network simultaneously
• Redo all the mathematical calculations for every block ever created
• Do this faster than thousands of honest computers are adding new blocks

On the Bitcoin network — this would require more computing power than all the world’s supercomputers combined. It is practically impossible.

Types of Blockchain

Public Blockchain
Open to everyone. Anyone can read, write and participate.
Example: Bitcoin, Ethereum

Private Blockchain
Controlled by one organization. Used by businesses internally.
Example: Hyperledger

Hybrid Blockchain
Mix of public and private. Some data is public, some is restricted.

Blockchain Beyond Crypto

Blockchain is not just for cryptocurrency. It is being used for:

• Supply chain — tracking products from factory to store
• Healthcare — secure sharing of medical records
• Voting — tamper proof digital elections
• NFTs — proving ownership of digital assets
• Smart contracts — automatic agreements without lawyers

The Key Insight

The genius of blockchain is this — it replaces trust in institutions with trust in mathematics.

You don’t need to trust a bank, government or company. You trust the code — and the code is open for anyone to verify.

“Don’t trust. Verify.” — the motto of the Bitcoin community.

In the next topic we will learn what altcoins are and why thousands of cryptocurrencies exist.