Explain Ethereum like I'm five

Assuming you already know bitcoin.

Ethereum is like Bitcoin, but more flexible, you can write full programs for it to automate money dependent things. The programs are called smart contracts and the can hold money like people or banks can. The money they work with are called Ether.

For example, You could write one that says, when two people paid 1000 into it wait a month and check how the weather was every day. After the month give one of them all the money if it was mostly warm and the other one if it rained much. Like a automatic insurance for farmers.

I'm continuing the "magic book" analogy:

Imagine that you have this magic book, which everyone can write something in (Ethereum's case, pograms also, not just monetary transactions) and nobody can delete anything from it. Everyone have the same physical copy of this book on their hard drives and everyone need to sync it. Some books (well almost everyone), have the option to ditch this book from your HDDs, becuse you will trust a third-party (another guy's HDD) to store this book for you. But you don't want to do that, because rather you trust only yourself, when it comes to money.

This book will grow, some will faster, some slower. One day, this book will be terabytes of data. One day, countries will use this book as their official currency. And when Bob from grocery store will jump on it, you bet this book will grow faster.

One day you wake up and thinking, this sh*t is downloading 200GB of transaction data into my local blockchain DB from midnight and I still have 6 other cryptocurrencies where I store my money in.

Than you screwed, you don't want to invest in another hard drives, you just enter in some other dudes blockchain DB address and basically you just gave up the decentralization of the whole thing.

This will happen with every-single-blockchain-technology!

One day, people start to give up specific blockchain technologies and start to use a fresh one, because they want a smaller sized DB.

Or storage prices become marginally lower and technology become better. But what do you do with your smartphones? How do you want to store petabytes of data? Maybe the next 10-20-30 years it will be possible. But what I afraid is that it will grow so fast (the blockchain technologies) that people just start to give up using the local copy of this book. And with this decision they give up the purpose of the whole thing: decentralised independence from oligarchs. With this decision the whole thing become just the "ECoin" from Mr. Robot and sh*theads like *P Morgan and another oligarchs will control the entire thing, because they have the server capacity to STORE the whole thing. From this day, the whole database will be just another bank's internal DB which you can't afford to look inside.

I hope I just looking a bad outcome and this never gonna happen. You already gave up the sovereignty of the technology with mobile phone wallets. And just to tell the truth, I gave up mine also, because I use a local copy of myetherwallet from git (because I trust a third-party independent dude, which I don't really know who the heck is).

Blockchain is internet's answer for money, but certainly not perfect (just like the internet).

I'm downloading the Monero blockchain file since 3 days. It's 18GB now.

It took me a few hours of solid research to understand blockchain. I know the question is about Ethereum, but I'll explain Bitcoin here and hopefully that will get you most of the way.

Imagine that you want to buy your little sister's toy truck. Your parents give you a monthly allowance, but not in cash -- they tell you how much money you've been allotted and allow you to request cash from your balance whenever you need it to buy something. You want to spend $5 of your allowance to buy the toy truck, but your little sister would just add the money to her own allowance, so there's no point dealing in cash. You decide to create a transaction record: you write out the amount of money you're giving her and what she's giving you in return on a piece of paper. It's like a receipt at the store.

You would each sign the transaction with your name, but you want this transaction to be secret so that your friends don't know you own the toy truck (they would want to borrow it all the time). So you sign with a big word that your sister doesn't know how to spell, and she signs with a big word that you don't know how to spell. It takes each of you so long to learn to spell new words that you aren't worried these signatures will be compromised. You take this paper to the copy machine and copy it once. This way you each have a record of the transaction. The next time she wants to spend her allowance, she can use the transaction record to get the $5.

There's one problem left to solve: sibling rivalry. You don't want her to claim that she never got paid and the truck is still hers. And she doesn't want you to claim that she made up the transaction and you still have that $5. (Either of you could do this by pretending you can't spell the big word you signed with.) So you each take your copy of the transaction record, make two copies from it, and put them on your parents' bedroom table.

Each of your parents has a box where they keep transaction records. They add the new records, checking with each other to make sure the records are identical and placed in the boxes in the exact same order, and they go on their way.

When your sister wants to spend the $5 she earned, all she has to do is write the big word she signed with on a piece of paper, put it in a sealed envelope, and slide it under the closed door of your parents' bedroom. In return, they'll slide a sealed envelope with a $5 bill in it back under the door.

But wait! How do they know which allowance to deduct the $5 from? Well, we'll need to reimagine the allowances a little. Suppose they don't track allowances by your real name, but by a nickname--and they don't know whose nickname is whose. In addition, they have a list of big words that you provided at the same time as the nickname, so when you sign something by spelling a big word, they can associate it with the correct nickname.

By this system, your parents could have thousands of children, each with their own allowance, and keep a perfect record of how much money each child's balance has even though they don't know which balance belongs to which kid. The children can trade money back and forth all the time and not a cent will get misplaced. But by this point, the workload of managing all those transactions is pretty enormous, so they invite their friends to live at your house and help them out. Your parents set aside some of the money they earn at their jobs and give it to each other and to their friends based on how many transactions they verify each day. And the copy machine is running all the time, because everyone has to have a box that has every transaction ever in it, all in the exact same order.

In Bitcoin, your computer is the box. You have a copy of literally every Bitcoin transaction that has ever happened, and so does every other Bitcoin user (there are no parents, or in other words, no central authority). When you want to create a new transaction, you do so anonymously, but you and the other participant in the transaction both use math to generate a public key (kind of like a big word only you can spell) which proves that the money in question was owned by the computer sending it and is now owned by the computer receiving it. And everyone who does the math necessary to verify the transactions gets paid a small amount of Bitcoin for doing it. Once the transactions are verified, they propagate outward to the entire Bitcoin network.

This is the way I understand it. If I got anything wrong, feel free to correct me.

Here is a nice collection on reddit, and this is my favorite:

Imagine you would have a magic book. There are people around the world who also have a copy of the magic book. Now, everyone can write into that book; if you write something into the book, it appears in all other copies of the book, around the world, pretty much instantly. Nobody, not even you, can erase what you wrote into that book or what someone else wrote into that book. That's basically blockchain technology, on which Bitcoin, Ethereum, and all other cryptocurrencies are based.

Bitcoin, for example, uses the magic book to log transactions of the virtual currency "Bitcoin". You'd basically write into the magic book "I give Cathy 1 Bitcoin". The book then checks through all the entries of any entries of me having Bitcoin in the first place and if so, send the intended 1 to Cathy. Now Cathy has an entry in the magic book and now it knows she has some Bitcoin too, so if she tries to send one, the magic book can confirm.

Ethereum goes further, here you can basically write small "self-executing" programs that can't be deleted. So with our book analogy, you could write into the book "I bet 1 ETH with Amy that the weather on May the 2nd is sunny and nice", and include a data link to Google Weather or similar which the program can check. You pay a small fee to deploy the program. The code then keeps getting executed on thousands of computers worldwide. If it actually rains on May the 2nd, the program sends 1 ETH from you to Amy's wallet. Since anyone can check the code of the program, Amy doesn't have to trust me, the creator of the program, she can check my code for herself. Also, the program can't be suddenly deleted (so I can't just quit the bet after looking at the forecast on May the 1st).

So Ethereum is basically a giant, coordinated decentralized swarm of individual's computers connected to each other on the web where anybody can deploy his mini-programs (called smart contracts) for a small fee.

whatthefuckisethereum.com

This is a great explanation but I'm going to be pedantic - I have a five year old and there's absolutely no way in hell he would understand beyond "I'm getting a truck!"

I don't have a ready-set-go answer for ethereum specifically. I do have one however for crypto-currencies so here it is:

Ethereum is a crypto-currency. Crypto-currencies are alternative digital currencies. Alternative as they do not have a state, country or union to back them up trough its traditional financial enstablishment (USD US, GBP GB, EUR EU). Digital as they rely solely on digital means for traditional currency activities (Issuing, Pricing, Trading) and finaly Crypto as they make heavy use of cryptography technologies to validate and secure their various activities (Issuing and trading mostly).

Here's an awesome article that finally made me understand what the Blockchain actually is.

hackernoon.com/wtf-is-the-blockcha...

Excellent video by the YouTube channel 3Blue1Brown explaining cryptocurrencies and the blockchain in general.

Explain Blockchain like I'm five