Caroline Jonas

PhD student in the independent research group “Theoretical Cosmology”

What is your current position at our institute?

I'm a PhD student in the Independent Research Group Theoretical Cosmology.

What is your academic education?

  • Bachelor in Physics at Université Libre de Bruxelles
  • 1 year erasmus at EPFL (Switzerland) for the first year of Master of Science in Physics
  • last year of Master of Science in Physics at Université Libre de Bruxelles

Can you please describe your research in general terms?

My thesis focuses on the study of quantum effects in the early Universe. Using different approaches within quantum cosmology, we aim at describing the beginning of our Universe in a formalism that is consistent with quantum mechanics. This is tricky because the best theory describing our Universe, general relativity, is known to be inconsistent with quantum mechanics. We thus have to go beyond general relativity.

What's your favourite figure from a paper you co-authored?

This figure, taken from, represents the evolution of the Universe in a regime called “eternal inflation”. Inflation is a phase of very rapid expansion of the Universe, that is often assumed to have occurred at very early times. This phase of expansion helps cosmologists explain why our Universe is observed to be extremely homogeneous and isotropic (similar in all directions and all positions, see e.g. the CMB). However, it also brings along additional puzzles, and is not unanimously supported. One of the point of controversy is precisely eternal inflation. Because of quantum fluctuations, inflation sometimes reach a regime where it can never stop. In this figure, we represent the transition from an initial state (in green), where inflation happens, into a final state (in orange), where inflation should stop. However, we compute that quantum effects imply that there are always some regions of the newly expanded spacetime that will continue to expand indefinitely. Therefore, inflation never ends and we talk about “eternal inflation”. In our paper, we showed that if the Universe did enter this phase, the transition amplitude (i.e. “probability”) between the early and current state of the Universe, would become infinite. We argued that theories with such infinite amplitudes might be ruled out by a physical principle that we called “finite amplitude principle”. In the case of inflation, such a principle would thus constrain the type of allowed expansion, in order to avoid the “eternal inflation” regime.

What was the reason you chose the Max Planck Institute for Gravitational Physics for your research?

Because I had heard of the Max Planck Institute and I was interested in Theoretical Cosmology, especially because this kind of research was not undertaken in my previous university.

Caroline Jonas' AEI homepage can be found at

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