As time goes on in 10, 15 or 20 years, bitcoin will get exponetially harder to mine and to recieve rewards.  I think this is an inherent design of bitcoin with a supply cap.  It will be reasonable to assume, miners will eventually go away to other easier to mine coins.  Who will then maintain the bitcoin network and keep it going?  How will bitcoin maintain its value? I appreciate any insight or articles/reseach to read.