Telegraph Hill

No, I am not referring to the famous hill in San Francisco or the one in London, also known as Plowed Garlic Hill, but to Potsdam's Telegrafenberg, a 96-meter hill. Red Baron has visited Potsdam several times, but I always missed one attraction and, for a physicist, a must: The expressionist Einstein Tower (Einsteinturm) in Potsdam's Albert Einstein Science Park. Erich Mendelssohn built this astrophysical observatory on Telegrafenberg from 1919 to 1922.

During my last trip to Berlin, I took the S-Bahn to Potsdam Hauptbahnhof, intending to take the uphill bus to Telegrafenberg. However, the line only operates in the morning and late afternoon, transporting the science institutes' employees up and down the hill. Eventually, I took a taxi to the Science Park's guarded entrance. 

I told the man behind the counter that I wanted to visit the monument dedicated to my famous physics colleague. He smiled, stood up, and handed me a pound of paper with information. Well documented, I started my uphill walk, passing various information panels and institute buildings.

The Telegrafenberg got its name from the mechanical telegraph that the Prussian government implemented in the first half of the 19th century. After Napoleon's defeat and the Congress of Vienna in 1814/15, most of Europe's old borders were restored, with some noteworthy exceptions. 

Austria cleverly gave up its possessions on the Upper Rhine - note that, on Napoleon's order, the Breisgau, with its capital Freiburg, had already become "badisch" in 1806 - thus avoiding any future confrontation with France, while Prussia acquired territories on the Lower Rhine, including the coal-rich Ruhr district as well as the cities of Cologne and Coblenz. Thus, the Prussians assumed the Wacht am Rhein (The watch over the Rhine River) concerning France.

Königlich-Preußische Optische Telegrafenlinie from Berlin to Koblenz

With such a vast territory spanning from Königsberg in East Prussia to Aachen at the Belgian border, fast information transmission in the kingdom was a challenge. Messengers on horseback took three to four days to cover the distance between Berlin and Coblenz. Thus, Prussia began constructing an optical-mechanical telegraph line in 1833, with 62 relay stations covering 550 kilometers between Berlin and Coblenz.

Reconstructed Prussian optical-mechanical telegraph station in
 Cologne-Flittard. The many signal arms enabled the transmission
of information-rich messages (©Superbass/Wikipedia)

The line started at Dorotheenstraße in Berlin, joined the Saint Anna Church in Dahlem, passed the miserable hill of the Schäferberg (shepherd's mountain!), went to the Telegrafenberg at Potsdam, and continued to Magdeburg's Saint-Jean Church. 

After many more relay stations, the line crossed regions belonging to the Duchy of Brunswick, regained Prussian territory in Westphalia at Paderborn, and eventually reached Coblenz via the Cologne-Flittard relay. With the new installation, a telegram took 1.5 hours to transmit.

On my way to the Einstein Tower, I passed the street sign Schwarzschildweg honoring Karl Schwarzschild, the German astronomer. He directed Potsdam's Astrophysical Observatory from 1906 until his early death in 1916. In 1897, while in Vienna, he derived a formula to calculate the optical density of a photographic emulsion. Photographic measurements could now calculate the intensity of faint stellar light sources with high precision.

Whereas Einstein gave only an approximate solution to his field equations of general relativity around a single spherical, non-rotating mass, Schwarzschild calculated the exact solution while serving with the Prussian Army in Russia in 1915. He wrote to Einstein: As you see, the war treated me kindly enough, despite the heavy gunfire, to allow me to get away from it all and take this walk in the land of your ideas. 

Needless to say, Einstein was impressed. Schwarzschild's calculations produced the famous Schwarzschild radius, the size of the event horizon of a non-rotating black hole. Karl's son Martin became a distinguished professor of astronomy at Princeton University.

The Michelsonhaus

The first impressive landmark on my way to the Einstein Tower was the former astrophysical observatory built in the late 1870s. The building has three observation towers with rotating domes initially equipped with telescopes. Later, the building became known as Michelsonhaus because, in 1881, Nobel Prize winner Albert A. Michelson (1907) performed his key experiments in its basement, proving that the velocity of light is always constant. His discovery was the basis for Einstein's theory of relativity. In 2000, the Institute for Climate Impact Research (PIK) moved into the building after major renovations.

Großer Refraktor

Another impressive sight is the Big Refractor Building. The Großer Refraktor features two telescopes in parallel, one for the observer and one for the camera. The installation was built in 1899, used until 1968, and completely refitted in 2006.

The Einsteinturm was built on the summit to house a solar telescope designed by the astronomer Erwin Finlay-Freundlich. The telescope supports experiments and observations to validate (or disprove) Einstein's theory of relativity.

The Einstein Tower, as seen from the front.

Here the building is seen from the back with the Big Refractor in the background.

On my way back to the gate, I passed a nostalgic monument. The GDR was proud of having sent, with Russian help, the first German cosmonaut - the name distinct from NASA's astronauts - into space. Sigmund Werner Paul Jähn returned from space station Salyut 6 to Earth together with Russian Commander Valery Fyodorovich Bykovsky on the Soyuz 29 mission. They both became Heros of the German Democratic Republic. In 1983, Jähn received a doctorate from the Zentralinstitut für Physik der Erde (Central Institute for the Physics of the Earth), specializing in remote sensing of the Earth and located on Potsdam's Telegrafenberg.

Together on Earth and in space

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