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Diederik Roest: theoretical physicist and cosmologist

Diederik Roest’s office exudes the atmosphere you might expect of a physicist: crammed bookshelves, seminar announcements and lots of complicated-looking calculations on the whiteboard. And in the corridor, as well as more formulas, photos of excursions with colleagues and postcards from all corners of the globe. It’s obvious that the scientists here don’t conduct their research in solitude.

Diederik Roest
Diederik Roest

Heaps of talking

This is one of the first things that Roest says about his work. ‘We do heaps of talking here. The calculations on the whiteboards might give the impression that we’re always trying to work things out, but in reality we spend a lot of time talking and brainstorming. The culture of doing research is very much focused on interaction. Because you first need to work things through in conversation and only then do you test your theory with formulas. I am indebted to my supervisor for this: he taught me the importance of first spending time thinking and talking about the problem and only then doing the calculations. We had a very sociable group of PhD candidates and there was a great atmosphere. And now as well, I really enjoy working with so many young, motivated people.’

Not just physics

‘Another thing that makes my field so special is that people work together from so many disciplines. I routinely find myself brainstorming with astronomers, mathematicians and physicists. Everyone contributes from their own discipline and that’s very special. Funnily enough, maths and chemistry used to be my main interests. It wasn’t until later that I became especially fascinated by physics.’

Mini rubber bands

Asked about the main focus of his research, Roest says that he is in fact testing string theory against the universe. String theory works on the premise that the tiny elementary particles that make up the universe are strings, a kind of mini rubber band. Among other things, string theory can be used to describe quantum gravity, something that Einstein’s theory of relativity hasn’t fully succeeded in doing. ‘We’re using string theory to try to discover how nature works on a very small scale. This is because the universe was once small enough to be able to test this. If string theory is correct, it played a key role when our universe was first being created. And we should still be able to see that.’

Exciting time

‘The coming years will be very exciting because they’ll announce the results of two ongoing experiments, Planck and BICEP2, that are measuring the inflation of the universe. You can compare this inflation with blowing up a balloon – the first bit that’s so hard to blow up. We call this stage inflation. Both experiments are claiming different things, which naturally provokes lots of discussion about the observations and about who is right. The BICEP2 experiment, for instance, says that it has measured the gravitational waves from shortly after the big bang, but many scientists wonder whether this is strictly true. So in the coming years we’re going to learn a great deal about the universe, which I’m really looking forward to.’

Particle accelerators

Research is also being carried out at CERN, the Swiss institute for particle physics, into what matter is made up of, how nature works on a tiny scale. ‘To do this you have to make particles collide with one another at high speed. The higher the speeds, the bigger the accelerator has to be. I was impressed by the enormous size of the CERN accelerator. I was there to exchange knowledge and not to tinker, but I was given a tour of the accelerator. The tunnel is 100 metres below ground and is 27 kilometres long. It’s incredible to see. They’re now thinking about an even bigger accelerator, but it’ll be decades before that’s accomplished. Building something like that is also a political matter and politicians will ask whether such an accelerator will bring with it enough scientific benefits. Are the returns really in proportion to the costs? It’s getting tougher and tougher for the fundamental research that we are engaged in. Fundamental research does have invaluable spin-offs, but of course this isn’t until after the event.’

Young Academy

Diederik Roest has recently been appointed by the Royal Netherlands Academy of Arts and Sciences ( Koninklijke Nederlandse Akademie van Wetenschappen ; KNAW) to the Young Academy, an independent platform for top young scientists and scholars. Each year KNAW invites ten talented researchers to join its ranks and to organize various activities in the area of arts and science, science policy and society. This is something that Roest is very keen to do: ‘It involves working with young, motivated researchers, on everything to do with science and scholarship, outside your own discipline. Politicians often ask our advice and what we say is highly appreciated.’


For laypeople it is hard to imagine that our universe and earth are made up entirely of vibrating particles. To which quantum physicists would add that you can never know something for certain; you can only measure probabilities. ‘But that’s also difficult for quantum physicists’, says Roest. ‘Intuitively, I find this hard to conceptualize. But in this line of work you learn to let go of your everyday expectations. You learn to make hypotheses and then you start calculating using quantum theory. If your hypothesis proves correct, that doesn’t mean you can conceive of it intuitively.’


Asked whether he still thinks about work when looking at stars in the night sky, Roest replies: ‘Yes, actually I do. As with work, you’re preoccupied with very fundamental things. You ask yourself why we would be the only ones living in this vast universe. Why wouldn’t there be any other planets that are also inhabited?’

Typical working day

Returning to earth, what does Diederik Roest’s ‘typical working day’ look like? ‘Like many of my colleagues I begin the day by reading new articles published by peers around the world. They’re published on a kind of intranet and every morning I check to see if there’s anything interesting. After that I often give two hours of lectures in the morning. And the afternoons are mainly taken up with supervision, discussions with Master’s and PhD students. When do I get around to my own research? Well, not usually until the evening.

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Last modified:15 September 2017 3.15 p.m.
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