You might say it all started with a spot of hay fever. In June 1925, a young physicist named Werner Heisenberg retreated to the barren island of Helgoland in the North Sea, seeking respite from his allergies. There, he scribbled down equations that would light an intellectual fire in Europe, eventually forming the basis of an idea that shook our view of how reality works to the core. That idea was quantum theory.

In recognition of the quantum centenary, the United Nations has designated 2025 as the International Year of Quantum Science and Technology. There will be celebrations, exhibitions and conferences all over the world.

If you know only one thing about quantum theory, it is probably that it is “weird”. Indeed, the idea that the quantum world is too strange to fully understand has infected our culture. There are even products or described as “quantum”, a tacit signal that they have powers beyond our comprehension.

The idea that the quantum world is too strange to fully understand has infected our culture

It is true that quantum theory paints a strange picture of the subatomic world – but to stop there would be to miss its true importance. In this centenary year, we should be celebrating the theory for its power and provocation – as we do in a trio of articles in this special issue.

Physicist Carlo Rovelli gives us his take on the origins of quantum mechanics and introduces its bold claims. We see how these ideas have revolutionised technology – and how they will continue to do so. And we explore the profound questions quantum theory forces us to ask about what “real” really means. The fact that it paints such an uneasy picture of the subatomic world hints that we are missing something about the workings of the universe – but new interpretations and experiments are inching us towards a fresh understanding.

Quantum theory has been wildly successful, too. Few other scientific ideas have passed so many experimental tests. Its origins may hinge on a bout of hay fever, but it is a legacy not to be sniffed at.