Can Bitcoin survive on fees alone after block subsidy dies?

[Synchronice]

OP, Bitcoin should survive on fees alone because when we reach the moment when all the blocks will be mined, there should be at least 100x more transactions daily than we have today. Also, we have to increase Bitcoin block size to accept more transactions. To my mind, it's stupid to keep the current block size as it is and expect any survival on fees or to even expect the existence of Bitcoin transactions. Over growing popularity, we will have to increase the block size, it will benefit every Bitcoin user and miners too.

Bitcoin has only been around for about 17 years.  And look how much it changed.  How many Forks we had.  It adapted to the current times and if it can not survive on Fees alone, some thing will have to change.

Satoshi has obviously thought about what will happen in 2140.  I would personally say it is going to survive on Fees alone but that depends on many factors.  Including whether in the following 114 years there is going to be a Bitcoin competitor that ultimately proves to be superior and takes over.  I would say living the moment and not caring about the future is not the best way to approach this question either but it is not the end of the World.  If the survival had such a small chance, none of us would be here because why support some thing that has an expiration date.

In terms of code, functionality, features, innovation, privacy and so on, there are superior coins but still, none of them beats Bitcoin because there is a different reason. Bitcoin is the number one because it has the most credible monetary story. From the 2010s, Bitcoin was the currency that most people, exchanges, miners, businesses and other entities were focused on and prioritized, so it becomes harder every day for another coin to replace Bitcoin.

[d5000]

Worse yet, the value that Bitcoin fees have to protect is 2 orders of magnitude higher than for Doge.

The attack target value is not related directly to market cap. It is related to the potential the attacker can double spend.

I believe that number to be more related to the average value in purchasing parity that is transferred in each block.

Let's look at such an attack and how it would be peformed:

- The attacker buys the Bitcoins he wants to steal (and probably mixes them a bit)
- He spends the transactions in a single block, to different merchants and exchanges.
- He begins to mine in secret.
- He waits until the confirmation period at all merchants and exchanges is over and all orders are confirmed. Probably most of the time he'll try to swap the coins for altcoins.
- He takes over the chain and "rewinds" all his transactions.

The merchants and exchanges would all have some kind of maximum value he can deposit. This maximum value, however, depends on purchasing power and not BTC probably. Let's say he tries to spend 100,000 BTC (6 billion USD) on 1000 different platforms, 1 BTC on each platform. This would not be a problem with 60,000 $ per BTC. But it would be probably a problem with 600,000 $ per BTC, because only a few platforms would allow such big deposits. He would then have to try to scam a lot more platforms, which makes the attack more complex.

So I believe there is some relation between market cap and double spend potential but the relation is not linear. It would even be somewhat detectable: blocks with an unnatural spike in transacted BTC could rise the alarms in merchants and exchanges, and make them rise the confirmation requirement. That's why I think the attacker would try to stay inside the normal limits, and thus be bound to the average transaction volume.

Another source of income for the attacker are short sales but this is way more difficult to predict, it is probably more related to market cap, but also related to the number of BTC (and their value in USD/purchasing power) available for lending and the security measures of the trading platforms. Most trading platforms would probably stop trading as a security measure when they detect a long reorg, and thus the attacker may have severe difficulties in re-buying the coins without having to go through some sort of scrunity for the sources of funds.