Assuming we stick with silicon chips (i.e. there's no immediate commercialised breakthroughs in optical and quantum computing), increases in mining difficulty will have to taper back from 75% per month...
But if the difficulty were to continue rising at 75% per month (i.e. exponentially), then we'd reach a total bitcoin network hashrate of:
- 1 PetaHash/s (10^15) by October 2013
- 1 ExaHash/s (10^18) by November 2014
- 1 ZettaHash/s (10^21) by December 2015
- 1 YottaHash/s (10^24) by January 2017
The only thing likely is 1 PetaHash/s around the end of this year or early next. The rest is insane.
To put this in perspective, at continuing 75% monthly difficultly increases, in less than 18 short months (around end 2015) we'd be looking at
- 1 ZettaHash/s, or equivalent to almost 13 YottaFLOPS of processing power in the network (if you make some voodoo math FLOP/Hash assumptions akin to the Genesis block calculator).
- China now has the World's fastest supercomputer (Tianhe-2) at 24 PetaFLOPS. 13 YottaFLOPS would equal 288 BILLION of these suckers.
- This is equivalent to 7 TRILLION Playstation 3's, or, 1000 PS3's for every single person currently on the planet.
Granted ASICs void this FLOP comparison, but it's just a comparison to put things in context.
Then there's the rare earth metal resources, manufacturing, electricity, etc needed for so much compute power...
We know ASIC manufacturers will be deploying up to 1 PetaHash/s each in product over the next year.
Once we get to around 10 PetaHash/s in the entire network early 2014, I personally think the monthly increases in network difficulty will taper off very significantly.
But until then, better factor in some heavy increases in monthly difficulty, perhaps doubling or more in the coming months....