DW: CERN is celebrating its 60th birthday. What does it mean to you - not just from a scientific but also from a political point of view?

Rolf-Dieter Heuer: A lot has changed in world politics over the past 60 years. During CERN's youngest years, some states closed themselves off to other countries. We had the Iron Curtain. Relations between Beijing and Taipei were difficult, and those between China and the USA, or the USA and Russia. At CERN, we could ignore all these difficulties. People from all over the world have cooperated here, throughout our 60 years.

This is what CERN stands for: friendship and cooperation between people. When you working at CERN, you may not even know where another person comes from. Everyone's focused on a common goal. And it's important to note that those who work at CERN overcome their prejudices. They learn that their colleagues are just people like themselves. For example, we had a student summer party, organized jointly by Israeli and Palestinian students, and they noticed how much they had in common culturally. It was a real eye-opener.

The Large Hadron Collider (LHC) has been on a break since last year. Has it been a creative break?

Not so much creative, because we already knew what we had to do: we had to refurbish the LHC and we had to open the 27 kilometer ring every 20 meters in order to do something. We knew all that before. Our collaborators [the universities and institutes] have also had a chance review their experiments. They've been evaluating data, and they're still doing that, whilst preparing for the new data that will come. So it was a little bit creative, but it was also a lot of hard work.

What do you expect to find when you restart the LHC next year?

First, I expect to find a working machine. After all this work, it's almost a new machine. So we will have to be very careful when we switch it back on. And then we'll be taking it to a higher energy. This will open a door to higher mass and perhaps to particles that will form dark matter. But what we already know is that we have to investigate the properties of the Higgs boson in detail, because there may be a lot of new physics in the properties of the Higgs boson. But for that we need: collisions, collisions, collisions.

Which are the main questions, you have not yet answered?

One question is: why isn't there any more antimatter in the universe? How did the differences in the properties of matter and antimatter come about? This question touches us in the sense that if there were no differences between the properties, we wouldn't exist. So we have to answer that question. Ninety-five percent of the universe is the dark universe: dark matter and dark energy. We do not understand that. We have only described five percent [of the universe]. So there is a lot of work to do. And we also need to better understand the properties of the hot dense matter roughly one microsecond after the Big Bang. Basically, how did this strong force behave?

Rolf-Dieter Heuer has been the Director-General of the European Organization for Nuclear Research (CERN) in Geneva since 2009. He has worked as a physicist there since 1984. Before that he conducted research at the German Electron-Synchrotron and at the Universities of Heidelberg and Stuttgart.