user32364: So I was reading this discussion today and came across this concept:

Monero, Litecoin, Ethereum ... will be Bitcoin sidechains before long, and
  as there's no additional value to having standalone blockchains, the
  sidechain implementations will naturally persevere and prosper due to
  the network effect.

I vaguely grasp the idea of implementing a sidechain. I don't grasp how an entirely different blockchain, such as Ethereum, could possibly be implemented as a Bitcoin sidechain. Is this a real thing that could happen? How?

user30017: Practically speaking to transfer an existing chain to a sidechain would be nearly impossible. You would have to transfer all the value of the altcoin to Bitcoin and then to the sidechain. This means that somehow people would sell their altcoin for bitcoin to transfer it onto a sidechain. But how would that work? If an alt-coin was "moving" to a sidechain no one would be willing to buy it. The particular alt-coin community could devise some kind of a scheme to transfer the value, but there would always be unforeseen consequences. (look at the Ethereum DAO-hard-fork fiasco for an example)   
Think about it like this: what if a country A decided to get rid of its currency, lets call it A-dollar and instead start using USD. In this case you would tender your A-dollars to the central bank and they would issue and equivalent amount of USD to you. This is only possible (in theory btw) because there is a central authority. How would this work with a decentralized currency?  
These are just some high level thoughts, as usual the 'devil' is in the details.

user24974: The idea is that Bitcoin is agnostic when it comes to any sidechains derived from it.  When some coins are brought in from Bitcoin to the sidechain, Bitcoin only sees what it always sees: transaction outputs locked up by an encumbrance script.  The other chain must be aware of Bitcoin's blockchain, and from there, the sidechain's rules will see that the coins have been encumbered such that the coins are now issued on the sidechain's blockchain.
So let's say that Ethereum does not issue ether via mining reward, but rather requires you to lock up bitcoin on Bitcoin's blockchain, thus "moving" that bitcoin from the main chain to the sidechain.  Now the ether can be traded, payed to a smart contract, or anything else that ether can do on the Ethereum block chain.  You can even trade it back to the main chain, thus claiming the bitcoin that was "moved" to the Ethereum chain.  The fact that the two blockchains are fundamentally different doesn't matter, as long as the sidechain is aware of the parent, and can handle moving coins back and forth.
You may want to check out this answer for a more in-depth explanation to sidechains.

32364: <p>So I was reading <a href="https://www.reddit.com/r/Bitcoin/comments/4tebwl/jpmorgan_lost_two_leaders_on_its_blockchain/" rel="nofollow">this</a> discussion today and came across this concept:</p>

<blockquote>
  <p>Monero, Litecoin, Ethereum ... will be Bitcoin sidechains before long, and
  as there's no additional value to having standalone blockchains, the
  sidechain implementations will naturally persevere and prosper due to
  the network effect.</p>
</blockquote>

<p>I vaguely grasp the idea of implementing a sidechain. I don't grasp how an entirely different blockchain, such as Ethereum, could possibly be implemented as a Bitcoin sidechain. Is this a real thing that could happen? How?</p>
 30017: <p>Practically speaking to transfer an existing chain to a sidechain would be nearly impossible. You would have to transfer all the value of the altcoin to Bitcoin and then to the sidechain. This means that somehow people would sell their altcoin for bitcoin to transfer it onto a sidechain. But how would that work? If an alt-coin was "moving" to a sidechain no one would be willing to buy it. The particular alt-coin community could devise some kind of a scheme to transfer the value, but there would always be unforeseen consequences. (look at the Ethereum DAO-hard-fork fiasco for an example)   </p>

<p>Think about it like this: what if a country A decided to get rid of its currency, lets call it A-dollar and instead start using USD. In this case you would tender your A-dollars to the central bank and they would issue and equivalent amount of USD to you. This is only possible (in theory btw) because there is a central authority. How would this work with a decentralized currency?  </p>

<p>These are just some high level thoughts, as usual the 'devil' is in the details.</p>
 24974: <p>The idea is that Bitcoin is agnostic when it comes to any sidechains derived from it.  When some coins are brought in from Bitcoin to the sidechain, Bitcoin only sees what it always sees: transaction outputs locked up by an encumbrance script.  The other chain must be aware of Bitcoin's blockchain, and from there, the sidechain's rules will see that the coins have been encumbered such that the coins are now issued on the sidechain's blockchain.</p>

<p>So let's say that Ethereum does not issue ether via mining reward, but rather requires you to lock up bitcoin on Bitcoin's blockchain, thus "moving" that bitcoin from the main chain to the sidechain.  Now the ether can be traded, payed to a smart contract, or anything else that ether can do on the Ethereum block chain.  You can even trade it back to the main chain, thus claiming the bitcoin that was "moved" to the Ethereum chain.  The fact that the two blockchains are fundamentally different doesn't matter, as long as the sidechain is aware of the parent, and can handle moving coins back and forth.</p>

<p>You may want to check out <a href="https://bitcoin.stackexchange.com/a/25550/24974">this answer</a> for a more in-depth explanation to sidechains.</p>
