Hi guys I was wondering wether that how much price would be after 100 years and also what could be mining difficulty of a Bitcoin.
The fact that you are old enough to sign up for the form and ask such a question suggests that you need to be a supercentenarian to witness it, out of the nearly 8B population we have right now, studies show that there is between 300 and 350 supercentenarian, in other terms, 1 in 1000 centenarians (people who live up to 100 years) will get to 110, and to be centenarians the chances are 1 in 1000, so it's extremely unlikely for any of us to be there in a 100 years from now.
Now that we got the human race life span stuff out of the way, the answer to your question is "nobody knows", everything will be determined by the VALUE extracted by miners, even the comment above that says
it will likely become very low considering that competition to mine for block rewards will no longer be necessary when 21million bitcoins have been mined
could be wrong, when all the 21M BTC are mined, BTC could very well be trading at say 100M dollars each, if we were to assume that transaction fees are 5% of the total block reward, today it's 0.3125 which is about $5000 + $100,000 for the block reward = $105,000. in 2123 the total fees could be 0.1
BTC per block so at 100M that's 10,000,000$ per block, which even after accounting for inflation still beats the now "105,000", even with BTC trading at 10M still beats it.
We also don't know how adopted BTC will be, if the protocol is changed and BTC becomes a means of payment for daily usage, maybe the block size will increase and we would have millions of transactions that all add up to make a large sum of fees, maybe it just becomes a store of value that doesn't move much and the total fees won't add up to a fraction of what they are now and thus only 1-2% of the total hashrate is sustained, you can't even imagine what is going to happen next year when the rewards drop by 50%, let alone predict difficulty in 100 years.
But one thing to keep in mind is that there will always be someone willing to mine BTC, even if the block reward was only enough to buy a bottle of milk, 2 folks with their old CPUs would be mining it, in fact, even if power bill exceeds the rewards people would still mine it just to sustain the blockchain which they invested in, we could even have on-demand mining, say nobody broadcasts any transaction for 24 hours, nobody mines no blocks, miners see pending transactions, they turn their gears on, just to mine that transaction into a block and turn off their rigs again, some difficulty rules will need to be adjusted if we get to that stage, but sure thing is, anything is possible when a 100 years had passed.
And since we don't know how things are going to be in 100 years from now, it's best to assume that the young generation then will figure out what to do to the protocol to keep it in the best shape and adjust their environment, one thing I know for sure is, it's not our problem to worry about.
