Programming the Universe: A Quantum Computer Scientist Takes on the Cosmos

by Seth Lloyd

Information can be created but it can’t be destroyed. Consider flipping a bit. Flipping a bit transforms information: 0 goes to 1 and vice versa. It also preserves information: if you knew that the bit was 0 before the flip, then you know that it is 1 after the flip. By contrast, erasure is a process that destroys information. During erasure, a bit that is initially 0 stays 0, and a bit that is initially 1 goes to 0. Erasure destroys the information in the bit. But the laws of physics do not allow processes that do nothing but erase a bit. Any process that erases a bit in one place must transfer that same amount of information somewhere else. This is known as Landauer’s principle, after Rolf Landauer, the pioneer of the physics of information, who discovered it in the early 1960s.