Poll: What happens when the blockchain size gets too big?

[jjc326]

At some point wouldn't it make sense to cull some of the very old data in the blockchain?  Why not get rid of transactions that are like 100 transactions ago?  I'm not saying to use a time based limit (because people could have BTC stored and not use it for years) but transactions that were hundreds of transactions ago, why not?

[TimS]

At some point wouldn't it make sense to cull some of the very old data in the blockchain?  Why not get rid of transactions that are like 100 transactions ago?  I'm not saying to use a time based limit (because people could have BTC stored and not use it for years) but transactions that were hundreds of transactions ago, why not?

First of all, there are on the order of 500 transactions in a typical block (currently at https://blockchain.info/), so "hundreds of transactions" is not nearly old enough - maybe instead, you can store the balance of ~3 million (current) addresses with their balances in a ledger.
Second, it reduces the security. E.g. what if someone created a ledger (via 51% attack) that says that they have every bitcoin in circulation? How would we know that's the true result of the chain of transactions, and not fictional? The cryptographic signatures authorizing each transaction are the only thing preventing a 51% attack from stealing all bitcoins (instead of just doing other disruptive things).

[Nagle]

It looked like this was going to be a problem in 2012-2013, when growth in transaction volume was expected.  Then the growth in transaction rate slowed down..  The current system can handle about 600K transactions per day, and the current rate is around 75K per day. We're years away from problems. Bitcoin will probably be over before this becomes a problem.