At the heart of all the natural sciences is measurement – assigning a number to a physical property. Just how accurately we can measure, however, has long been an open question. Can we just keep building better and better devices to make more and more accurate measurements?
What appears to be true for standard technology breaks down as things get smaller. In the quantum world there are fundamental limits to what you can know about a system. This crucial feature of quantum mechanics was discovered by German physicist Werner Heisenberg in 1927 and named the Heisenberg Uncertainty Principle after him.
Only now, almost a century later, we understand the full scope of its implications and have experimental evidence for the ultimate limits of uncertainty.
What Are We Uncertain About?
Heisenberg’s principle may have shattered the dream of perfect measurements, but it doesn’t mean that we cannot know anything for sure. In particular, there are pairs of properties of quantum systems that are incompatible, which means that they cannot be measured with arbitrary accuracy at the same time on the same system.
One such pair is position and velocity. Take an atom, for example. To measure its position one would take a picture of it. To measure its velocity one would compare two successive pictures. Increasing the resolution of the first picture...
