'Quantum leap.' We often invoke the term to describe sudden breakthroughs, as one era dramatically shifts to the next. But as Trygve Ulf Helgaker, professor of theoretical chemistry at the University of Oslo, explains, quantum leaps occur all around us at all times – even when reading the words in this article.

In this first edition of the Centre for Advanced Study’s (CAS Oslo) lunch seminar series this autumn, Helgaker walks listeners through the basic structure of atoms, and then explains how atoms, molecules, and systems can exist in different energy states. The jump from one state to another – caused by either absorbing or emitting energy – is a quantum leap.

‘A quantum leap completely changes the system instantaneously,’ Helgaker says.

The signal your eye sends to the brain when it detects light, for example, is the result of a quantum leap. So is a sunburn, which is a visible sign of DNA damage caused by invisible ultraviolet radiation.

‘[The radiation] goes in and destroys bonds and destroys molecules, because the UV radiation is sufficiently strong to do these jumps, whereas visible light is not,’ Helgaker says. ‘Otherwise we wouldn’t be alive.’

Helgaker is this year leading the research group Molecules in Extreme Environments at CAS Oslo. Read more about his project here.