What backs up digital money?

[Alan Horowitz]

I will put forth the proposition that Federal Reserve "Notes" are not 
notes.

A note is a promise to (a) pay
                       (b) a certain amount
                       (c) at a certain time
                       (d) to a certain person.

As in the phrase that *used to* appear on United States Currency:  "will 
pay the Bearer One Dollar in Silver upon Demand".  The only extant legal 
definition of a dollar is a Federal statute of 1792, defining it as a 
certain weight of pure silver.