While US currency does change a little on occasional, the basic design of the notes has stayed fairly constant: green/black background, a portrait on one side and a pretty picture on the other. These concepts take that classic design and turn it on its head.
They're the work of designer Travis Purrington, and his philosophy was to create a currency that was forwards-looking, rather than reminiscent of the past. Rather than railroads and 19th-century landscape portraits, you get molecules, astronauts and silicon circuits. As Purrington explains:
This particular series plays on themes of human discovery and endeavours to connect achievement, theory and the fundamental properties of life.
This is of course not a conspiracy to trivialise or shun the great deeds of the past, but to communicate principle rather than effigy permeating through the spirit of industrial, organic and elemental systems.
Aesthetically, I also think he's nailed it. There's something strangely appealing about a portrait-oriented banknote. As far as I'm aware (although I'm sure a currency expert will be along to correct me post-haste), every country uses landscape-oriented money, so to see a portrait design is decidedly refreshing. The pastel colours and monochrome contrast definitely gives a modern look, which chimes well with his overall design philosophy.
Purrington says that he was inspired by Switzerland, which holds a contest every 20 years or so to redesign the franc. If there was a competition to replace the US' bills tomorrow, these would definitely get my vote. [Travis Purrington]