## Hendrik KramersDutch theoretical physicist.
Date of Birth:
17.12.1894Country: Netherlands |

**Content:**

## Biography of Hendrik Kramers

## Early Life and Education

Hendrik Kramers was born on December 17, 1894, in Rotterdam, in a family of a doctor. After graduating from high school in 1912, he enrolled at Leiden University, where he studied theoretical physics under the guidance of P. Ehrenfest. In 1916, he completed his studies at the university and traveled to Copenhagen, where he became one of Niels Bohr's closest collaborators. In 1919, Kramers defended his doctoral dissertation in Leiden, which focused on the mathematical formulation of various aspects of spectral theory. He also conducted a detailed calculation of the hydrogen atom spectrum in an external electric field.

## Contributions to Physics

In 1920, Kramers started working at the Institute of Theoretical Physics in Copenhagen. Using Bohr's correspondence principle, Kramers developed a relativistic theory of the Stark effect (1920) and described the continuous X-ray spectrum of hydrogen (1923). He also provided a mathematical description of the quantization of molecular rotational motion (1923). In his attempt to describe the helium atom in a similar way to the hydrogen atom, Kramers showed that the quantization of classical orbits leads to underestimated values of nuclear binding energy. Kramers was one of the co-authors of a groundbreaking paper (Bohr, Kramers, Slater, 1924) where the assumption that momentum and energy are statistically conserved in elementary processes was first proposed (although this idea was later recognized as incorrect). The paper also introduced the concept of virtual oscillators associated with quantum transitions, which formed the basis of Kramers' developed theory of dispersion. He later refined this theory in collaboration with W. Heisenberg (1925).

In 1926, Kramers was offered the position of chair of theoretical physics at Utrecht University. Here, independently of L. Brillouin and G. Wentzel, he developed an approximate solution method for the one-dimensional Schrödinger equation, which is now known as the BVK equation (Brillouin – Wentzel – Kramers equation). In 1927, he derived (independently of R. Kronig) the relationship between the real and imaginary parts of the polarizability (Kramers-Kronig relation). In 1929, he formulated one of the theorems that had significant importance in the theory of magnetism (Kramers theorem). In 1930, he developed a mathematical framework for describing the multiplet structure of spectra.

## Later Life and Legacy

In 1934, Kramers returned to Leiden as a professor of theoretical physics, where he remained until the end of his life. With his later works, Kramers made significant contributions to various fields of theoretical physics, including quantum mechanics, optics, thermodynamics, magnetism, and the theory of strong electrolytes. In 1946, Kramers was elected chairman of the Scientific and Technical Committee of the United Nations' Atomic Energy Commission. From 1946 to 1950, he served as the president of the International Union of Pure and Applied Physics (IUPAP). He was awarded the Lorentz Medal in 1948 and the Hughes Medal in 1951. The universities of Oslo, Lund, Stockholm, and Sorbonne bestowed upon him the honorary doctorate.

Kramers passed away on April 24, 1952, in Oegstgeest, the Netherlands.