First model of the Universe according to the theory of relativityAlbert Einstein and Willem de Sitter

What is the most important question that humanity can ever ask itself? How about: ‘How did it all begin?’ This is precisely the fundamental question that is answered by Einstein’s new general theory of relativity, a fact that Leiden Professor of Astronomy Willem de Sitter was the first to understand.

From 1917 onwards, De Sitter published a series of articles describing such phenomena as the continuous expansion of the Universe. In these articles, he describes the Universe shortly after what later researchers would come to refer to as the Big Bang. This period is now called the ‘inflation period’, because according to current models the Universe then expanded rapidly in a very short period of time – faster than the speed of light.

World War I

Einstein and De Sitter had already had extensive contact with one another during World War I. Through De Sitter, who lived in the neutral Netherlands, Einstein was able to submit his theoretical ideas to the British astronomer Sir Arthur Eddington. Shortly after the war, Eddington confirmed Einstein’s theory on the curvature of space and time with a detailed analysis of a solar eclipse.

After the publication of the general theory of relativity, Einstein and De Sitter collaborated more closely than ever. This ultimately led to the Einstein-De Sitter model of the Universe, with which the two scientists laid the foundation for our current understanding of the evolution of the Universe.

Livening things up

De Sitter was appointed Professor of Astronomy in Leiden in 1908, at a time when Leiden astronomy was in something of a lull following its first Golden Age. De Sitter immediately proceeded to liven things up. In Leiden he further expanded on his Groningen PhD research, in which he studied the moons of Jupiter, an important topic in astronomy at the time.