It is a pleasure for me to thank my advisor Professor Lorenz Kramer for providing me with many insightful ideas for my thesis work, for leaving me much freedom, and, not at the least, for having encouraged me to tackle this long-time unresolved problem. I thank him also for giving me the possibility to flee some of the grueling Bayreuth winters which I spent in Santa Barbara and Tucson.

I also would like to thank Prof. G. Ahlers in Santa Barbara and Prof. A. Newell in Tucson for their hospitality. I am also indebted to Gunther Ahlers for providing me with some experimental results prior to publication and giving me a careful overview of the experimental situation of thermal fluctuations and to Ingo Rehberg for helpful discussions.

I thank Armin Hertrich for providing me with a fortran code for the nontrivial basic state; he also showed me some tricks in using computers.

I thank M. Schm{\"o}gner for showing me the ropes of the drawing program "topdraw". I was always able to get help at once, whenever I encountered a computer problem.

Special thanks to my parents Hanskarl and Christine Treiber for encouraging and supporting me in any aspect. I can not imagine better parents.