## Jan Pieter van der Schaar, Ph.D.

I am a theoretical physicist working in the area of quantum gravity, string theory and cosmology. Currently I am an associate professor in the Korteweg-de Vries Institute for Mathematics and also a member of the String Theory Group at the University of Amsterdam. I received my master's and Ph.D. at the University of Groningen, after which I held postdoctoral research positions at the University of Michigan, CERN's Theory Division and the Institute for Strings, Cosmology and Astroparticle Physics (ISCAP) at Columbia University, before arriving at the University of Amsterdam in January 2006. Links to my Ph.D. thesis and a (popular) HTML version of my master's thesis entitled "Stringy Black Holes" can be found in the menu on your left.

### Quantum Gravity, String Theory and Cosmology

One of the biggest challenges in theoretical physics is the construction of a consistent theory of quantum gravity. Although the quantum effects such a theory should describe are incredibly small in ordinary situations, they are expected to be crucial when trying to understand the extraordinary circumstances inside black holes, or moments after the conception of our universe, approximately 13,7 billion years ago. On a more conceptual level, a theory of quantum gravity should elucidate the microscopic structure of space-time, and perhaps `explain' the origin and properties of our current universe.

String theory is a fundamental theoretical framework based on the existence of tiny vibrating string-like objects, allowing for a unified description of all matter and forces in nature by identifying different matter and force particles with the different vibrational modes of the string. One of the vibrating modes of this string can be shown to behave just like a graviton, the messenger particle of the gravitational force, and therefore string theory automatically incorporates gravity. Even better, there is suggestive evidence that string theory is a consistent quantum theory not leading to non-sensical results (infinities), leaving us with a consistent theory of quantum gravity. Of course, for this unified theoretical framework to become true science, at some point string theory needs to be confronted with experiment. Because of the incredibly tiny size of fundamental strings, this has turned out to be a serious problem.

This is where cosmology comes in. My research is concentrated on trying to embed cosmological theory, the physics of the universe as a whole, into string theory and study its consequences. The ultimate hope is that this will someday lead to the discovery of clean string theoretical signatures in cosmological experiments. At the same time I am also motivated to obtain theoretical results that will either enhance our understanding of cosmology through string theory, or vice-versa. Among other things, one topic that I have been actively pursuing is the study of string scale signatures in the observable Cosmic Microwave Background anisotropies, which can be thought of as a snapshot of the early universe as it existed 300 thousand years after the Big Bang. The good news is that this might be possible under some (special) circumstances, the bad news is that it is less clear at this moment whether these circumstances are present in string theory. To find out more about this and related stuff, please check out some of the links on this page.

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