A big leap in money's evolution came in the late Renaissance with the invention of the bank. The Rothschild family were the first to think of issuing letters of credit to traveling merchants that they could redeem at their destination, sparing them the inconvenience and danger of traveling the bandit-infested roads with their gold. Governments quickly picked up on this game as well and issued paper money. Its value lies in the universally held belief that it's worth a cup of coffee, a hamburger, a bus ride. Americans in the past 50 years have seen a movement away from cash.
Paychecks go directly to our bank accounts.
We pay our bills with checks or from an online account. We go shopping not with a wad of cash, but with a plastic card. We have gotten used to thinking of money as numbers on a screen or on a statement. At each step in its evolution, money has become more abstract - from something you could actually eat to a rare metal to a common piece of paper to a series of ones and zeroes on some bank's computer somewhere. The more meaningless the tokens we exchange, the greater our reliance on trust and on a shared sense of money's reality.