Cosmologist Uroš Seljak developing methods to detect exoplanets

A professor at Berkeley since 2008 and one of two directors of the Berkeley Center For Cosmological Physics, Seljak was awarded a honorary doctorate from his alma mater, the University of Ljubljana, earlier this week, which he says means a lot to him.

Talking with the STA, he says he is extremely grateful to Ljubljana university, which was the start of his scientific career that he continued at the Massachusetts Institute of Technology. He sees the title as a further confirmation of his successful research work.

At Berkeley, Seljak is concerned with fundamental questions about the evolution of the universe, about how it began, what it is made of and what the future of the universe will look like.

"Over the last few decades, we have made remarkable progress in understanding the evolution of the universe. We have a standard model that says the universe started with a Big Bang and then, we believe, expanded very rapidly," says Seljak.

The theory of the very rapid expansion of the universe is called inflation theory, which is also directly linked to the formation of stars, galaxies and planets. Ultimately, it can explain everything in the universe. "It is a very attractive theory, but the question is how to prove or disprove it," he says.

Gruber Prize for contribution to understanding of early universe

It was Seljak, along with fellow theoretical physicists Marc Kamionowski of Johns Hopkins University and Matias Zaldarriga of the Institute for Advanced Study, who made a major contribution to the methods that are key to studying the origins of the universe. The trio won the prestigious Gruber Prize in Cosmology from the Gruber Foundation at Yale University in 2021.

Their work has focused on studying the polarisation of the Cosmic Microwave Background (CMB), a remnant of radiation that dates back to the formation of the universe. They worked out the mathematical meaning of the use of CMB radiation back to the first fraction of a second of the universe's existence and identified a feature in the polarisation of the CMB, the so-called B-polarisation.

This determines the existence of primordial gravitational waves, which is a key part of the inflation theory, the theory of the exponential expansion of space in the early universe.

Seljak says that if B-polarisation and thus gravitational waves could be measured directly, this could be a confirmation of the inflation theory.

"Although we have more and more precise experiments, we have not yet measured gravitational waves. The inflation theory has very vague predictions about what the size of these waves should be. It's quite possible that the size is too small to be detected by experiments."

However, this would not, in his view, invalidate the inflation theory. There are still many other models within the theory that can be tested.

Developing methods to detect new planets

Seljak has recently been working on developing machine learning methods for applications in cosmology and astronomy. "We are developing generative methods that allow us to improve the precision and results of cosmology experiments," he says.

At the same time, he is also working on developing methods that would make it possible to have faster and more accurate statistical data processing and could ultimately be used to look for exoplanets or planets outside our solar system.

"With an optimal method, we could detect undiscovered planets that otherwise have a weak signal," he explains. Ultimately, this could increase the likelihood of detecting possible planets that are in the so-called habitable zone, i.e. planets where life can form. "These are usually planets somewhere between Venus and Mars, and they also have a very weak signal," he says.

"There is a lot of potential in developing these kinds of methods. In fact, NASA is planning a very large telescope to try to find life on other planets in space. But first we obviously need to locate these planets and direct the telescope to where to look for them in the first place. I hope we will make a breakthrough in this field," he says.

Apart from Seljak, the University of Ljubljana also awarded a honorary doctorate on Tuesday to Jean Greisch of the Institut Catholique de Paris, one of the leading representatives of contemporary hermeneutic philosophy and philosophy of religion.