Plenty of Room at the Bottom

Two Thousand-Dollar Wagers and the Blueprint for Nanotechnology

Shrink every printed page of the twenty-four volumes of the Encyclopaedia Britannica by a linear factor of $25{,}000$, and the entire encyclopedia fits comfortably on the flat head of a single bronze pin 1.6 millimeters in diameter. Even after that twenty-five-thousand-fold reduction, the resolution limit of the human eye (roughly 0.2 millimeters) translates to 80 angstroms on the pinhead. Each individual halftone printing dot still measures 320 angstroms across. That dot leaves room enough for roughly one thousand metal atoms arranged in a square grid.

On the evening of December 29, 1959, Feynman presented that arithmetic at the annual banquet of the American Physical Society at the Huntington-Sheraton Hotel in Pasadena. Under the title There's Plenty of Room at the Bottom, he asked why human engineering had stopped at the millimeter scale. Living cells routinely packed the entire genetic blueprint of a human being into DNA strands just 20 angstroms wide. Suppose physicists could write information at the scale of 100 atoms per bit. Then every book ever printed in the world—twenty-four million volumes across the British Museum, the Library of Congress, and the Bibliothèque Nationale—could be etched inside a tiny cube. That cube would measure just one-two-hundredth of an inch wide, barely visible as a single speck of dust.

The barrier to building microscopic computers, swallowable surgical micro-robots, and atomic-scale chemical synthesizers was not Heisenberg's uncertainty principle. It was simply that human beings had not yet built fine-fingered tools. Feynman argued that the fundamental laws of physics place no barrier whatsoever against manipulating and arranging matter atom by individual atom.

To design working machines at the micrometer and nanometer scales, Feynman warned that engineers could not merely scale down a Detroit automobile engine without accounting for three physical scaling shifts:

• * Surface adhesion over gravity: As linear dimensions $L$ shrink by $10^{-4}$, mass and inertia scale as $L^3$ ($10^{-12}$) while surface area scales as $L^2$ ($10^{-8}$) and van der Waals molecular attraction grows dominant, meaning microscopic gears will stick together unless designed for surface forces.
• * Instantaneous thermal dissipation: Because heat capacity scales with volume while thermal conduction scales with area, a microscopic solenoid or transistor radiates waste heat almost instantly, allowing much higher current densities without melting.
• * Reversed electron-microscope lithography: By reversing the magnetic lenses of an electron microscope to demagnify an electron beam instead of magnifying an image, engineers could write sub-micron circuit wires and evaporate metal layers directly onto substrates.

To prove that extreme miniaturization was an immediate laboratory challenge rather than distant science fiction, Feynman closed his banquet talk by offering two personal prizes of $1,000 each from his own wallet. The first $1,000 check would go to the first person who constructed a rotating electric motor, controlled from the outside and excluding lead-in wires. The entire motor had to fit inside a cube $1/64$ of an inch (0.4 millimeters) on each side. The second $1,000 check would go to the first person who reduced a page of printed book text by a linear factor of $25{,}000$ so that it could be read only through an electron microscope.

Feynman assumed both prizes would sit unclaimed for decades until new lithography beams were invented. Instead, a Caltech alumnus and instrumentation craftsman named William McLellan spent his lunch breaks over five months building the motor by hand. He used a watchmaker's lathe, a wooden toothpick, and a single-hair paintbrush to wind four microscopic stator coils with copper wire 0.00008 inches thick. The second prize held out for twenty-six years until November 1985. That autumn, Stanford graduate student Tom Newman used electron-beam lithography to etch the opening page of Charles Dickens's A Tale of Two Cities inside a square 5.9 micrometers wide. When William McLellan brought his wooden box with a microscope to Caltech in November 1960 to claim the first thousand-dollar check, his working two-thousand-part electric motor was smaller than the period at the end of a printed sentence.