University Professor of Physics Renata Kallosh received an honorary doctorate from the University of Groningen on 13 June. A day earlier, she and her husband Andrei Linde, also a physics professor, talked to Science LinX and gave a Masterclass on fundamental physics and cosmology.
A conversation in the private dining room of the Prinsenhof Hotel marks the start of a busy day. Kallosh and Linde show no signs of jetlag, despite having just flown in from the States. Linde is quick in his replies and tends to step in with broad statements and plenty of humour. Kallosh is more pensive, carefully formulating her answers.
Both were born and educated in the Soviet Union, and spent their early careers in relative isolation. Only in 1988 were they given permission to work at CERN in Geneva, where they met a young Dutch scientist, Eric Bergshoeff. Kallosh and Bergshoeff began to collaborate, and have done so ever since. Bergshoeff now holds the De Sitter Chair in Theoretical Physics at the University of Groningen, and is the one who nominated Kallosh for the honorary doctorate.
The conversation starts with a general question: why a career in physics? Kallosh: ‘I started out studying mathematics, but I wanted to use my knowledge to describe nature, to be able to solve problems in the real world.’ She therefore chose cosmology, focusing on the mathematical description of the birth and evolution of the universe.
Cosmology has an added advantage: you can use the universe as a giant experiment for high-energy physics. ‘The energy in the early universe is many times higher than what you can get in the biggest accelerators.’ The angle Kallosh took in cosmology was to investigate high-energy physics using string theory.
This particular branch of physics describes the building blocks of matter not as particles, but as tiny strings (or even membranes) that extend into more than three dimensions. In reality we observe only three of these spatial dimensions (time is the fourth), as the others are rolled up and not visible.
String theory has been around for a long time, but for years it was hard to show that it was more than a mathematical construct. However, Kallosh has shown that string theory does help describe the real universe, and can answer questions other physical theories cannot. ‘When cosmologists discovered that vacuum energy was not zero, only string theory could explain this’, she says. ‘And then dark energy was discovered, a force that causes the universe to expand in an accelerating way, and again, string theory was needed to explain this.’ Her paper on this topic (‘Andrei served as consultant cosmologist’) is highly influential and has been cited over 2000 times.
Kallosh has also contributed to a theory that her husband co-formulated: inflation. This describes how, only a fraction of a second after it came into being, the universe expanded from the size of an atom to the size of a football. It explains why the universe is as homogenous as it is, but it also suggests there is not just the universe we observe but that a huge number of different universes may have expanded, each forming a bubble. Together these are called the multiverse.
Alan Guth laid the foundations of the theory. ‘He had a great idea, but got important parts wrong’, says Linde. Indeed, Guth quickly published a paper in which he claimed that no further progress could be made in inflation theory. ‘But as the mail to the Soviet Union was notoriously slow, I only received the paper a few months after he published it, and by that time, I’d already improved his theory’, Linde says with a broad smile.
Kallosh and Linde have worked together a lot, although their approach differs. ‘Andrei has intuitive ideas’, says Kallosh, ‘while I like constructing things.’
‘And when she does, it sometimes makes no sense to me’, adds Linde. ‘But I’m proved wrong often enough.’ He mentions Kallosh’s working habits: ‘She gets a fax with raw ideas, mulls it over and will then wake at 5 a.m. with a clear solution. So she slips out of bed, writes it down and goes back to sleep. Really strange!’
Both scientists have won their share of prizes. Only the other week, Linde was awarded the Kavli Prize for Cosmology. But they still dream about what they would like to discover. Kallosh: ‘I’d like to know the level of intensity of gravity waves.’ These ripples of spacetime were reputedly observed recently, but the results are now in some doubt. More conclusive data will become available in the next few years. ‘This will tell us something about the energy level of the early universe.’
Linde has a more philosophical dream. ‘We study the development of the universe, but I’d like to know how it was born. For me, that’s closely linked to questions about life and death, not just of the universe but also of us. When we study the universe, it’s like studying a person by looking around in his house. Then there’s the question of whether the universe exists if it’s not populated. Are we just actors, passing through, or do we play a bigger part?’ He smiles. ‘It’s more metaphysics than physics, and I don’t expect much progress here. But it’s big questions like these that keep me going as a physicist!’
As we leave for the Masterclass the two are to give at the Zernike campus, Kallosh turns and says: ‘Don’t forget to mention how wonderful our collaboration with the University of Groningen has been. I’ve enjoyed working with Erik Bergshoeff, and with Diederik Roest. And I’m thrilled to receive an honorary doctorate.'
Read more about the honorary doctorate on the University of Groningen website.
A small group of young scientists and half a dozen fifth-year pupils from the Praedinius Gymnasium were invited to the two-hour masterclass. Andrei Linde took up most of the time explaining how inflation theory helps us understand the universe.
Renata Kallosh took the stage briefly (she was giving a science seminar later that day) to share some exciting new results. University of Groningen physicist Diederik Roest published a paper in December 2013, which expanded upon a paper by Kallosh from 2003. ‘We were stuck with that work’, Kallosh explains, ‘And the paper by Roest and colleagues showed us the way forward. We’ve now finished a paper building on their findings, which is to be published in a few days’ time.’
So how did the Praedinius pupils digest all this fundamental physics? ‘I really enjoyed it’, says Cas Versluijs. ‘It’s not the sort of physics we learn at school, but I’ve been reading up on it myself.’
‘So have I’, adds Leonora Verveld. ‘And it’s really cool to meet people like this.’
Both intend to study physics, combined with Astronomy (Cas) or Philosophy (Leonora). Why? ‘To learn how everything is made’, says Cas.
‘It’s so awesome to realize the infinite size of everything’, adds Leonora.
‘Yes, and we’re part of it all’, Cas responds. But they do admit the masterclass was a bit difficult.
Leonora: ‘It’s like I’m missing about three years’ worth of background information.’
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