In the first article, we explained what a blockchain is.

A shared record.
Kept by many computers.
Very hard to change.

Now comes the next question.

If many computers share the same record, who decides what gets added next?

That decision process is one of the most important parts of any blockchain.

It is called validation.

The Core Problem Blockchains Must Solve

Imagine a shared notebook.

Many people can write in it.
Everyone wants their entry included.

But:

• some people may lie
• some may make mistakes
• some may try to cheat

A blockchain needs a way to decide:

• which entries are valid
• which ones are ignored

This decision process must work without a boss.

That is the hard part.

Different blockchains solve this problem in different ways.

Proof of Work

Security Through Effort

Proof of Work was the first major solution.

It is used by Bitcoin.

In Proof of Work, computers compete to add the next entry to the record.

They do this by solving difficult puzzles.

These puzzles:

• take real effort
• use electricity
• cannot be easily faked

The first computer to solve the puzzle earns the right to add the next block.

Because solving the puzzle is costly, cheating becomes expensive.

To attack the system, you would need huge amounts of power.

That is why Proof of Work is considered very secure.

The downside is simple.

It is slow.
It uses a lot of energy.

This is a deliberate tradeoff.

Proof of Stake

Security Through Ownership

Proof of Stake solves the same problem in a different way.

Instead of using energy, it uses ownership.

Computers that help run the network must lock up some of the blockchain’s currency. This is called staking.

The system then chooses who gets to add the next block based on:

• how much they have staked
• and other rules

If someone tries to cheat, they can lose what they staked.

This creates a strong incentive to behave honestly.

Proof of Stake uses far less energy than Proof of Work.

It is faster.
It is cheaper to run.

Ethereum switched to Proof of Stake in 2022 for this reason.

The tradeoff is that the system relies more on participants who already hold value in the network.

Proof of History

Ordering Events in Time

Some blockchains add another idea on top.

Proof of History is one example.

It does not replace other systems.
It works alongside them.

The problem it solves is ordering.

In fast systems, many actions happen at once.
It can be hard to agree on what happened first.

Proof of History creates a shared timeline.

It provides a way to prove that:

• event A happened before event B
• without constant communication

This helps the network move faster.

Solana uses Proof of History together with Proof of Stake to increase speed.

Proof of Authority

Trusting Known Participants

Proof of Authority takes a very different approach.

Instead of being open to anyone, the network is run by approved participants.

These participants are known in advance.

They may be:

• companies
• institutions
• or trusted entities

Because participants are known, the system can be very fast and efficient.

This design is often used in:

• private blockchains
• enterprise systems
• internal networks

The tradeoff is clear.

It is less decentralized.
It relies on trust in specific actors.

Why There Is No “Best” Method

Each validation method solves the same problem.

Who gets to write the next entry?

They just make different choices.

Proof of Work prioritizes security through effort.
Proof of Stake prioritizes efficiency through ownership.
Proof of History helps systems move faster.
Proof of Authority prioritizes speed through trust.

None of these is perfect.

Each one fits a different purpose.

Why This Matters

People often argue about which blockchain is better.

Those arguments usually ignore one thing.

Different blockchains are designed for different goals.

A system built for maximum security will not feel fast.

A system built for speed will make other tradeoffs.

Once you understand how validation works, these differences make sense.

They are design choices, not accidents.

The Takeaway

Every blockchain needs a way to decide what gets written down.

That decision process shapes everything else:

• speed
• cost
• security
• who participates

When you understand how a blockchain validates information, you understand what it is built to do.

And once you see that, crypto stops feeling random.

It starts to feel designed.