# Walter Noll

**Walter Noll** (January 7, 1925 – June 6, 2017) was a mathematician, and Professor Emeritus at Carnegie Mellon University. He is best known for developing mathematical tools of classical mechanics, thermodynamics, and continuum mechanics.^{[1]}

Born in Berlin, Germany, Noll had his school education in a suburb of Berlin. In 1954, Noll earned a Ph.D. in Applied Mathematics from Indiana University under Clifford Truesdell.^{[2]}

His thesis "On the Continuity of the Solid and Fluid States" was published both in *Journal of Rational Mechanics and Analysis* and in one of Truesdell's books.^{[3]} Noll thanks Jerald Ericksen for his critical input to the thesis.

Noll has served as a visiting professor at the Johns Hopkins University, the University of Karlsruhe, the Israel Institute of Technology, the Institut National Polytechnique de Lorraine in Nancy, the University of Pisa, the University of Pavia, and the University of Oxford.^{[2]}

In 2012 he became a fellow of the American Mathematical Society.^{[4]} Noll died on June 6, 2017 at the age of 92.^{[5]}

In continuum mechanics, Noll introduced the so-called **principle of material objectivity**,^{[6]} which states that the constitutive laws governing the internal conditions of a physical system and the interactions between its parts should not depend on whatever external frame of reference is used to describe them.

"Principle of material objectivity" is now an obsolete term that has been replaced by **principle of material frame-indifference**.^{[7]}