So what happens to lost bit coins?

[MacDschie]

It doesn't matter how many coins there are on an address. Nobody will 'guess' or 'hack' the corresponding private key, not within a million billion trillion years.

Not quite. Only until somebody builds a quantum computer...  

[Domrada]

Please don't flame me, I'm just spit-balling here.

Could the blockchain size problem and the lost coins problem both be solved by the following solution?

Change the protocol so that the client nodes only keep the last x years of blockchain history.  As blocks with coins that haven't been moved in x years fall off the back of the chain, those coins are added to the next new block's mining rewards.

I don't really understand the protocol well enough to know whether a change like this would even be possible. Comments?

[Jutarul]

Please don't flame me, I'm just spit-balling here.

Could the blockchain size problem and the lost coins problem both be solved by the following solution?

Change the protocol so that the client nodes only keep the last x years of blockchain history.  As blocks with coins that haven't been moved in x years fall off the back of the chain, those coins are added to the next new block's mining rewards.

I don't really understand the protocol well enough to know whether a change like this would even be possible. Comments?

yes. if you can convince a significant portion of the network to include the change anything is possible. That's how the bitcoin protocol evolves: proposals are made, discussed, coded - but then it's up to the transaction validation nodes to download the source and agree to any changes.

[DannyHamilton]

Please don't flame me, I'm just spit-balling here.

Could the blockchain size problem and the lost coins problem both be solved by the following solution?

Change the protocol so that the client nodes only keep the last x years of blockchain history.  As blocks with coins that haven't been moved in x years fall off the back of the chain, those coins are added to the next new block's mining rewards.

I don't really understand the protocol well enough to know whether a change like this would even be possible. Comments?

How many years?  Who gets to choose?  I vote for 10,000,000 years.  I'd hate for someone to choose a number like 40 years.  Just think, a 20 year old sets aside a bunch of bitcoin for retirement today and stops paying attention to bitcoin.  A year later the system is changed to re-issue coins more than 40 years old. When he is 62, he goes to access his coins and they are gone!

[Jutarul]

Please don't flame me, I'm just spit-balling here.

Could the blockchain size problem and the lost coins problem both be solved by the following solution?

Change the protocol so that the client nodes only keep the last x years of blockchain history.  As blocks with coins that haven't been moved in x years fall off the back of the chain, those coins are added to the next new block's mining rewards.

I don't really understand the protocol well enough to know whether a change like this would even be possible. Comments?

How many years?  Who gets to choose?  I vote for 10,000,000 years.  I'd hate for someone to choose a number like 40 years.  Just think, a 20 year old sets aside a bunch of bitcoin for retirement today and stops paying attention to bitcoin.  A year later the system is changed to re-issue coins more than 40 years old. When he is 62, he goes to access his coins and they are gone!

This has been discussed before. You can keep your coins alive my moving them within your own wallet. But I agree - recovering lost coins by means of a maximum life of an unspent transaction serves no purpose. Just add digits, or start another blockchain.

[JoelKatz]

It doesn't matter how many coins there are on an address. Nobody will 'guess' or 'hack' the corresponding private key, not within a million billion trillion years.

Not quite. Only until somebody builds a quantum computer...  

Indeed. We probably have at least 50 years before it's practical. And we'll probably be able to see it coming at least 10 years in advance.

http://arxiv.org/pdf/quant-ph/0301141v2.pdf