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A key component of bitcoin is its decentralization (which effectively only exists with BTC and virtually nothing else). Part of this decentralization is the decentralization of the bitcoin nodes, which is owed to the fact that basically anybody can run a node (raspberry pi, bitcoin core software, a few other pieces, etc...) for a relatively cheap cost. I know this is why BCH hardforked off of BTC in 2017, since the latter refused to increase the block size to intentionally keep the chain small enough to be run by whomever. This makes a lot of sense to me.

However, what is going to happen when the bitcoin blockchain continues to increase in size over time? Even if the blocksize is kept constant, will the chain not eventually become unwieldy? Once it is the global base layer, will it not be too large of a chain for the everyday person to be able to download the chain and run the node? Will consensus allow for chopping off some portion of the earliest transactions that everyone has agreed upon? There are obvious downsides to this. What is the solution?

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    The claim that Bitcoin refused to increase the blocksize is BCH propaganda. Bitcoin did indeed double the block size in 2017. (This was a bad move, but it happened nonetheless)
    – Luke-Jr
    Oct 7, 2021 at 15:21

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There is a risk that the blockchain will continue to grow too quickly and become unwieldy, yes. However, if technology improvements continue at their current pace for several decades, and Bitcoin survives the intermediate turmoil, it will eventually start to get easier to run a node again.

"Chopping off some portion" significantly changes the security model, because not only are you no longer verifying the early blocks, but you are also now blindly trusting a "chain state" assigning coins to keys. There is no current known solution to avoid this blind trust - to verify the chainstate requires processing the old blocks.

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I don't think it will ever happen. In almost 12 years, size of bitcoin blockchain is around 400 GB. 500 GB hard disk is so cheap right now. Even 1 TB SSD comes under 100 USD, and HDD even for less. Think about 250 GB hard disk just 5 years earlier (blockchain size would have been around 200 GB then), it used to be so costly. I believe by time goes by, rate of increase in CPU & hard disc price (if it doesn't decrease) will be much slower than increase in size of Bitcoin blockchain. So comparatively, running Bitcoin node will become cheaper relative to the income in future even with increasing blockchain size.

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As the number of transactions increase, so called "layer 2" transactions will sprout up to keep lower level transactions off the blockchain--the tx fee will be too high to justify putting small transactions directly on. For example consider a credit card--people charge to the card for 30 days and then pay the card once from their bank account at the end of the month. It could work similarly with bitcoin, processing transactions all month on a credit card and then consumer paying the credit card bank at the end of the month from a wallet. Technically, the credit card bank could keep the direct purchase transactions on its own books and put only one tx on the bitcoin blockchain at the end of the month.

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