The big ideaNot one trusted keeper, but many copies that agree: that was the new idea.
How it works
In the made-up village of Kettle Hollow, Mira kept one notebook of who owned how many tokens. One keeper's notebook can be lost, soaked or changed.
So the village tried something new: everyone kept their own copy of every payment.
If one copy is changed, the other copies still agree, and the village follows the most copies.
Pages linked in a chain, each with the seal of the page before, make a changed old page easy to spot.
Leo changes one copy. Four copies still agree, so his change is ignored.One keeper or many copies.The idea in real life. The spacing is even, not to scale.
Example 1: One copy is changed
Five villagers each keep a copy.
Leo changes his copy, and the other four do not.
Four copies agree and one differs: 4 + 1 = 5.
The village follows the most copies, so Leo's change is ignored.
Example 2: How many copies must a cheat change?
There are five copies.
Change 1 or 2 copies, and 4 or 3 copies still agree on the true story.
To win, a cheat must change most of them, 3 of the 5 or more.
Everyone is watching, so that is very hard to do in secret.
Example 3: Sealed pages in a chain
Page 1 has its seal.
Page 2 carries the seal of page 1, and page 3 carries the seal of page 2.
Someone changes page 1.
Its seal no longer fits, so every seal after it breaks.
The change is easy to see.
A changed old page breaks the seals after it.
Example 4: The limit
Only twenty-one million coins can ever exist.
Printing too many notes makes each note buy less.
Here nobody can print more, because there is no bank in the middle to print them.
Words to know
copy
A record that each villager keeps of every payment.
seal
A mark that links a page to the page before it.
keeper
The one person who writes down the record.
chain
Pages linked one after another, each with the seal of the one before.
limit
Only twenty-one million coins can ever exist.
Watch out
Nobody owns the record. Many copies keep each other honest.
A cheat has to change most copies at once, not just one.
There is no bank in the middle of this system. Banks still work well, and most money still lives there.
Nothing is guaranteed to be safe. People disagree, many places have rules, and it has risks to learn about with a grown-up.
Try it
Four copies agree and Leo's copy is different. Which story does the village follow?
A page in the chain is changed. What happens to the seals after it?
There are 5 copies and 3 are changed. How many are still true?
What year was the idea described?
Answers: 1. The story the four copies agree on · 2. They all break · 3. 2 · 4. 2008
Try at homeWith a grown-up, find a trusted source and read about the risks of any new kind of money. What questions would you ask?
For grown-upsThis is history and a big idea, not advice about any money. Talk about why many copies that agree are harder to cheat than one notebook, and if your child wants to know more, look up the risks of any new kind of money together.
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