# Karl Schwarzschild

Karl Schwarzschild
Born9 October 1873
Died11 May 1916 (aged 42)[1]: xix
Potsdam, German Empire
NationalityGerman
Alma materLudwig Maximilian University of Munich University of Strasbourg
Scientific career
FieldsPhysics
Astronomy
InfluencedMartin Schwarzschild
Military career
Allegiance German Empire
Service/branchImperial German Army
Years of service1914–1916
RankLieutenant
Battles/warsWorld War I
Signature

Karl Schwarzschild (German: [kaʁl ˈʃvaʁtsʃɪlt] (); 9 October 1873 – 11 May 1916) was a German physicist and astronomer.

Schwarzschild provided the first exact solution to the Einstein field equations of general relativity, for the limited case of a single spherical non-rotating mass, which he accomplished in 1915, the same year that Einstein first introduced general relativity. The Schwarzschild solution, which makes use of Schwarzschild coordinates and the Schwarzschild metric, leads to a derivation of the Schwarzschild radius, which is the size of the event horizon of a non-rotating black hole.

Schwarzschild accomplished this while serving in the German army during World War I. He died the following year from the autoimmune disease pemphigus, which he developed while at the Russian front.[citation needed] Various forms of the disease particularly affect people of Ashkenazi Jewish origin.[citation needed]

Asteroid 837 Schwarzschilda is named in his honour, as is the large crater Schwarzschild, on the far side of the Moon.[2]

## Life

Karl Schwarzschild was born on the 9 October 1873 in Frankfurt on Main to Jewish parents. His father was active in the business community of the city, and the family had ancestors in the city dating back to the sixteenth century.[3] The family owned two fabric stores in Frankfurt. One of his brothers is the painter Alfred Schwarzschild.[4] He attended a Jewish primary school until 11 years of age[5] and then the Lessing-Gymnasium (as in secondary school). He received an all-encompassing education, including subjects like Latin, Ancient Greek, music and art, but developed a special interest in astronomy early on.[6] In fact he was something of a child prodigy, having two papers on binary orbits (celestial mechanics) published before he was sixteen.[7]

After Graduation in 1890 he attended the University of Strasbourg to study astronomy. After 2 years he transferred to the Ludwig Maximilian University of Munich where he obtained his doctorate in 1896 for a work on Henri Poincaré's theories.

From 1897, he worked as assistant at the Kuffner Observatory in Vienna. His work here was dedicated towards photometry of star clusters and laid the foundations for a formula linking the intensity of the star light, exposure time, and the resulting contrast on a photographic plate. An integral part of that theory is the Schwarzschild exponent (astrophotography). In 1899 he returned to Munich to complete his Habilitation.

From 1901 until 1909 he was a professor at the prestigious institute at Göttingen,[8] where he had the opportunity to work with some significant figures, including David Hilbert and Hermann Minkowski. Schwarzschild became the director of the observatory in Göttingen. He married Else Rosenbach, a great granddaughter of Friedrich Wöhler and daughter of a professor of surgery at Göttingen, in 1909. Later that year they moved to Potsdam, where he took up the post of director of the Astrophysical Observatory. This was then the most prestigious post available for an astronomer in Germany.[citation needed]

Karl Schwarzschild's grave at Stadtfriedhof (Göttingen)

From 1912, Schwarzschild was a member of the Prussian Academy of Sciences.

At the outbreak of World War I in 1914 Schwarzschild volunteered for service in the German army, despite being over 40 years old. He served on both the western and eastern fronts specifically helping with ballistic calculations.Thereby he rose to the rank of lieutenant in the artillery.[citation needed]

While serving on the front in Russia in 1915, he began to suffer from a rare and painful autoimmune skin disease called pemphigus. Nevertheless, he managed to write three outstanding papers, two on the theory of relativity and one on quantum theory. His papers on relativity produced the first exact solutions to the Einstein field equations, and a minor modification of these results gives the well-known solution that now bears his name — the Schwarzschild metric.

In March 1916 Schwarzschild was cleared from service due to his sickness and returned to Göttingen. Two months later, on May 11, 1916, Schwarzschild's struggle with pemphigus may have led to his death at the age of 42.[citation needed]

He rests in his family grave at the Stadtfriedhof Göttingen.

With his wife Else he had three children: Agathe Thornton (1910-2006) who emigrated to Great Britain in 1933. In 1946 she moved New Zealand where she became a Classics professor at the University of Otago in Dunedin; Martin who went on to become a professor of astronomy at Princeton University; and Alfred (1914-1944) who took his own life due to the persecution of Jews in the Holocaust.[citation needed]

## Work

Thousands of dissertations, articles, and books have since been devoted to the study of Schwarzschild's solutions to the Einstein field equations. However, although his best known work lies in the area of general relativity, his research interests were extremely broad, including work in celestial mechanics, observational stellar photometry, quantum mechanics, instrumental astronomy, stellar structure, stellar statistics, Halley's comet, and spectroscopy.[9]

Some of his particular achievements include measurements of variable stars, using photography, and the improvement of optical systems, through the perturbative investigation of geometrical aberrations.

### Physics of photography

While at Vienna in 1897, Schwarzschild developed a formula, now known as the Schwarzschild law, to calculate the optical density of photographic material. It involved an exponent now known as the Schwarzschild exponent, which is the ${\displaystyle p}$ in the formula:

${\displaystyle i=f(I\cdot t^{p})}$

(where ${\displaystyle i}$ is optical density of exposed photographic emulsion, a function of ${\displaystyle I}$, the intensity of the source being observed, and ${\displaystyle t}$, the exposure time, with ${\displaystyle p}$ a constant). This formula was important for enabling more accurate photographic measurements of the intensities of faint astronomical sources.

### Electrodynamics

According to Wolfgang Pauli (Theory of relativity), Schwarzschild is the first to introduce the correct Lagrangian formalism of the electromagnetic field [10] as

${\displaystyle S=(1/2)\int (H^{2}-E^{2})dV+\int \rho (\phi -{\vec {A}}\cdot {\vec {u}})dV}$

where ${\displaystyle {\vec {E}},{\vec {H}}}$ are the electric and applied magnetic fields, ${\displaystyle {\vec {A}}}$ is the vector potential and ${\displaystyle \phi }$ is the electric potential.

He also introduced a field free variational formulation of electrodynamics (also known as "action at distance" or "direct interparticle action") based only on the world line of particles as [11]

${\displaystyle S=\sum _{i}m_{i}\int _{C_{i}}ds_{i}+{\frac {1}{2}}\sum _{i,j}\iint _{C_{i},C_{j}}q_{i}q_{j}\delta \left(\left\Vert P_{i}P_{j}\right\Vert \right)d\mathbf {s} _{i}d\mathbf {s} _{j}}$

where ${\displaystyle C_{\alpha }}$ are the world lines of the particle, ${\displaystyle d\mathbf {s} _{\alpha }}$ the (vectorial) arc element along the world line. Two points on two world lines contribute to the Lagrangian (are coupled) only if they are a zero Minkowskian distance (connected by a light ray), hence the term ${\displaystyle \delta \left(\left\Vert P_{i}P_{j}\right\Vert \right)}$. The idea was further developed by Tetrode [12] and Fokker [13] in the 1920s and Wheeler and Feynman in the 1940s [14] and constitutes an alternative/equivalent formulation of electrodynamics.

### Relativity

The Kepler problem in general relativity, using the Schwarzschild metric

Einstein himself was pleasantly surprised to learn that the field equations admitted exact solutions, because of their prima facie complexity, and because he himself had produced only an approximate solution. Einstein's approximate solution was given in his famous 1915 article on the advance of the perihelion of Mercury. There, Einstein used rectangular coordinates to approximate the gravitational field around a spherically symmetric, non-rotating, non-charged mass. Schwarzschild, in contrast, chose a more elegant "polar-like" coordinate system and was able to produce an exact solution which he first set down in a letter to Einstein of 22 December 1915, written while he was serving in the war stationed on the Russian front. He concluded the letter by writing: "As you see, the war treated me kindly enough, in spite of the heavy gunfire, to allow me to get away from it all and take this walk in the land of your ideas."[15] In 1916, Einstein wrote to Schwarzschild on this result:

I have read your paper with the utmost interest. I had not expected that one could formulate the exact solution of the problem in such a simple way. I liked very much your mathematical treatment of the subject. Next Thursday I shall present the work to the Academy with a few words of explanation.

Boundary region of Schwarzschild interior and exterior solution

Schwarzschild's second paper, which gives what is now known as the "Inner Schwarzschild solution" (in German: "innere Schwarzschild-Lösung"), is valid within a sphere of homogeneous and isotropic distributed molecules within a shell of radius r=R. It is applicable to solids; incompressible fluids; the sun and stars viewed as a quasi-isotropic heated gas; and any homogeneous and isotropic distributed gas.

Schwarzschild's first (spherically symmetric) solution does not contain a coordinate singularity on a surface that is now named after him. In his coordinates, this singularity lies on the sphere of points at a particular radius, called the Schwarzschild radius:

${\displaystyle R_{s}={\frac {2GM}{c^{2}}}}$

where G is the gravitational constant, M is the mass of the central body, and c is the speed of light in a vacuum.[16] In cases where the radius of the central body is less than the Schwarzschild radius, ${\displaystyle R_{s}}$ represents the radius within which all massive bodies, and even photons, must inevitably fall into the central body (ignoring quantum tunnelling effects near the boundary). When the mass density of this central body exceeds a particular limit, it triggers a gravitational collapse which, if it occurs with spherical symmetry, produces what is known as a Schwarzschild black hole. This occurs, for example, when the mass of a neutron star exceeds the Tolman–Oppenheimer–Volkoff limit (about three solar masses).

## Cultural references

Karl Schwarzschild appears as a character in the science fiction short story "Schwarzschild Radius" (1987) by Connie Willis.

Schwarzschild's Cat is a comic on XKCD.com comparing the size and cuteness of cats.

## Works

The scientific estate of Karl Schwarzschild is stored in a special collection of the Lower Saxony National- and University Library of Göttingen.

Relativity
Other papers
English translations

## References

1. ^ Biography of Karl Schwarzschild by Indranu Suhendro, The Abraham Zelmanov Journal, 2008, Volume 1.
2. ^ "Crater Schwarzschild". Gazetteer of Planetary Nomenclature. USGS Astrogeology Research Program.
3. ^ "Nachforschung der Wahrheit" von der alten Lateinschule zum Lessing-Gymnasium in Frankfurt am Main : Festschrift zum 500-jährigen Jubiläum der Schule. Bernhard Mieles, Carolin Ritter, Christoph Wolf, Lessing-Gymnasium Frankfurt am Main, Frankfurter Societäts-Medien GmbH. Frankfurt am Main. 2020. ISBN 978-3-95542-379-7. OCLC 1244019080.CS1 maint: others (link)
4. ^ Schwarzschild, Karl (1992), "Karl Schwarzschild Lectures", Gesammelte Werke Collected Works, Berlin, Heidelberg: Springer Berlin Heidelberg, pp. 29–42, ISBN 978-3-642-63467-3, retrieved 2021-05-18
5. ^ "MacTutor History of Mathematics Archive". Reference Reviews. 30 (1): 27–28. 2016-01-18. doi:10.1108/rr-08-2015-0205. ISSN 0950-4125.
6. ^ Karl Schwarzschild (1873-1916) ein Pionier und Wegbereiter der Astrophysik. Klaus Reinsch, Axel Wittmann, Universitätsverlag Göttingen. Göttingen. 2017. ISBN 978-3-86395-295-2. OCLC 981916699.CS1 maint: others (link)
7. ^ Hertzsprung, Ejnar (June 1917). "Karl Schwarzschild". The Astrophysical Journal. 45: 285. doi:10.1086/142329. ISSN 0004-637X.
8. ^ Schwarzschild, Karl (1992), "Biography of Karl Schwarzschild (1873-1916)", Gesammelte Werke Collected Works, Berlin, Heidelberg: Springer Berlin Heidelberg, pp. 1–28, ISBN 978-3-642-63467-3, retrieved 2021-05-18
9. ^ a b Eisenstaedt, “The Early Interpretation of the Schwarzschild Solution,” in D. Howard and J. Stachel (eds), Einstein and the History of General Relativity: Einstein Studies, Vol. 1, pp. 213-234. Boston: Birkhauser, 1989.
10. ^ K. Schwarzschild, Nachr. ges. Wiss. Gottingen (1903) 125
11. ^ K. Schwarzschild, Nachr. ges. Wiss. Gottingen (1903) 128,132
12. ^ H. Tetrode, Zeitschrift für Physik 10:137, 1922
13. ^ A. D. Fokker, Zeitschrift für Physik 58:386, 1929
14. ^ Wheeler & Feynman, Rev. Mod. Phys. 21:425 (1949)
15. ^ Letter from K Schwarzschild to A Einstein dated 22 December 1915, in "The Collected Papers of Albert Einstein", vol.8a, doc.#169, (Transcript of Schwarzschild's letter to Einstein of 22 Dec. 1915) Archived 2012-09-04 at the Wayback Machine.
16. ^ Landau 1975.