Well, is quite sure that prices at cex.io are in real bubble:
I used mining calculator at
http://mining.thegenesisblock.com/ with buying 100GHS at current price from cex.io for 4BTC (1GHS=0.04BTC), and I couldn't break even with higher monthly increase of difficulty than 32% per month, see
http://mining.thegenesisblock.com/a/7908fc0daaIf used more appropriate increase in difficulty of 100% per month, I can break even after 6 months when I buy 100GHS for 2BTC (1GHS=0.02BTC) and after next 6 month the profit will be 0.04 BTC, see
http://mining.thegenesisblock.com/a/2be83da502 I guess that market participants at cex. io dont use math. Any comments?
Fixed percentage difficulty increase month over month over month.
Maybe in 2020 the total surface area of Earth would not be enough for all the asic chips, needed to sustain that difficulty.