What Are the Limits of Computing?

What’s the Latest Development?

A computation, whether it is performed by electronic machinery or an abacus or in the brain, is a physical process. It is therefore subject to physical laws, but what are the physical limits of computation? And what do quantum computations imply? “Even in quantum mechanics extremely fast events can take place without any loss of energy. Our confidence that quantum mechanics allows computing without any minimum expenditure is bolstered when we remember that Benioff and others have developed models of reversible quantum-mechanical computers, which dissipate no energy and obey the laws of quantum mechanics.”

What’s the Big Idea?

What did computational theory look like in 1985? Many old questions are still perplexing computer scientists today: “How much energy must be expended to perform a particular computation? How long must it take? How large must the computing device be? In other words, what are the physical limits of the process of computation? So far it has been easier to ask these questions than to answer them. To the extent that we have found limits, they are terribly far away from the real limits of modern technology. … We are looking for general laws that must govern all information processing, no matter how it is accomplished.”