Molecular computing is the science of using individual molecules to build computer programs. Instead of running software on a traditional computer, some scientists are now trying to replace the silicon chip with test tubes, liquids, and even living cells due to a concern about the limits of miniaturization—a real and pressing problem that threatens the future advancement of computers.

To get an idea of how small computers have already become, think of a standard processor chip and imagine this: if the chip circuit were magnified such that the individual components were the size of office buildings, and the interconnections between them were the size of streets and avenues, then the entire circuit at this scale would stretch from London to San Francisco. Very impressive, but can it continue? The answer is "no."

When it comes to creating smaller and smaller computers, existing technology...