It’s more complicated, right? How do you know that I didn’t send that apple to Uncle Tommy as an email attachment first? Or your friend Joe? Or my friend Lisa too?

Maybe I made a couple of copies of that digital apple on my computer. Maybe I put it up on the internet and one million people downloaded it.

As you see, this digital exchange is a bit of a problem. Sending digital apples doesn’t look like sending physical apples.

Some brainy computer scientists actually have a name for this problem: it’s called the double-spending problem. But don’t worry about it. All you need to know is that, it’s confused them for quite some time and they’ve never solved it.

Until now.

But let’s try to think of a solution on our own.

Ledgers

Maybe these digital apples need to be tracked in a ledger. It’s basically a book where you track all transactions — an accounting book.

This ledger, since it’s digital, needs to live in its own world and have someone in charge of it.

Say, just like World of Warcraft. Blizzard