Answering the biggest questions with the tiniest particles
From lectures by Robbert Dijkgraaf to a telescope on the ocean floor: during his double bachelor’s in Physics and Astronomy, Jelle Oonk discovered that the path to big cosmic answers sometimes runs through the smallest, hardest-to-catch particles—neutrinos.
Why did you choose this programme?
‘I found choosing a degree quite difficult because I have broad interests and considered many directions. In the end, I looked back at what fascinated me as a child. I devoured Robbert Dijkgraaf’s DWDD University lectures and could spend evenings staring at the stars from my bedroom window. That brought me to Physics and Astronomy—and in Leiden, I could combine the two as a double bachelor. That extra bit of challenge appealed to me straight away.’
How did you choose your thesis topic?
‘I wanted to find a topic that combined my interests in the biggest questions of cosmology and the smallest building blocks of nature. I found exactly that in KM3NeT, a telescope currently under construction the size of a cubic kilometre of seawater. Together with my supervisor, Dorothea Samtleben, I came up with the idea of studying how accurately the telescopes are aligned. That alignment is crucial to determine where the neutrinos are coming from.’
What did you investigate, and what did you discover?
‘The moon plays a surprising role: it blocks some of the particles, which means fewer signals are detected in its direction. Because the moon’s position is known with extreme precision, you can use this “moon shadow” to calibrate the alignment of the detector. I developed a method that determines and corrects the alignment in all three rotational directions, whereas previous studies only considered two. After analysing millions of observations, I showed that the directional accuracy is already below one degree.’
What was the most memorable moment during your thesis?
‘The method I developed is likely one of the few ways to reconstruct its origin once more data become available.’
‘Shortly after starting my project, I was able to attend the international presentation of a Nature paper on the detection of the most energetic neutrino ever recorded. At that time, however, the telescope wasn’t aligned accurately enough to pinpoint exactly where that neutrino came from. That made the moment even more special: the method I developed is likely one of the few ways to reconstruct its origin once more data become available.’
What did you learn from your studies and your thesis?
‘A discussion within the research group about a possible collaboration with a party linked to a foreign Ministry of Defence made a deep impression on me. It showed how science and societal issues can intersect. I also found it inspiring to see how ideas build on one another within a research group. The most important insight I gained is that my early interests are deeply connected: to understand the biggest questions about the universe, you have to study the tiniest particles.’
What are your plans for the future?
‘I’ve started the Research in Physics: Cosmology master’s programme. Ultimately, I see myself working at the intersection of science and society. But if research keeps fascinating me as much as it did during my thesis, I certainly won’t rule out a PhD.’