Einstein's Cosmological Constant (1917): A Static Universe

Einstein’s 1917 paper “Cosmological Considerations in the General Theory of Relativity” was the first attempt to describe the whole universe with general relativity. To keep his model universe static, Albert Einstein added a new term to his equations: the cosmological constant, which today is the simplest description of dark energy.

What the paper found

• A closed universe. Einstein assumed space is finite in volume but has no edge, like the surface of a sphere in one more dimension, and is evenly filled with matter.
• A new term, λ. A static universe of that kind did not fit his 1915 equations, so he added a term with a constant λ, now called the cosmological constant.
• A cautious justification. He wrote that the extension was not justified by actual knowledge of gravitation and that he needed it only to allow a nearly static distribution of matter, as the small velocities of the stars seemed to require.

How Einstein built the model

Einstein’s motivation was partly philosophical. In Newton’s theory, and in general relativity, a universe that goes on forever needs conditions set “at infinity”. Einstein wanted to avoid them, so he made space close on itself. He then asked which arrangement of matter could stay unchanged forever, and found that it worked only with the extra term balancing gravity on the largest scales. The paper was presented to the Prussian Academy of Sciences on 8 February 1917 and issued on 15 February, a little over a year after his field equations of 1915.

A centennial review in 2017 points out that Einstein did not test the model against astronomical observations and did not check whether it was stable. It is not: a static universe of this kind starts to expand or contract at the slightest disturbance.

Why it mattered

The paper founded relativistic cosmology. Within months Willem de Sitter found a different solution with the same constant. Alexander Friedmann (1922) and Georges Lemaître (1927) then showed that the equations naturally describe universes that change size, and Edwin Hubble’s 1929 velocity-distance relation showed that ours is expanding. In 1931 Einstein published a model of the universe without the constant.

The “biggest blunder” story

The famous line that the cosmological constant was Einstein’s “biggest blunder” comes from George Gamow’s recollection of a conversation. Historians have found no written record of Einstein using the phrase. In a 1947 letter to Lemaître he described the extra term as ugly, but the famous quotation itself rests on Gamow alone.

What we know now

The constant came back in 1998, when two supernova teams found that the expansion of the universe is accelerating. A positive cosmological constant is the simplest way to produce that acceleration, and it is built into the standard Lambda-CDM model fitted by the Planck satellite. Why its value is so small is one of the deepest open questions in physics, the cosmological constant problem. Since 2024 the DESI survey has found hints, at 2.8 to 4.2 sigma in its 2025 results, that dark energy may change over time rather than being a true constant (as of October 2026).

Who wrote it

Albert Einstein wrote the paper alone in Berlin, during the First World War, while corresponding with de Sitter about the structure of the universe.

Read the original

Einstein, A. (1917). “Kosmologische Betrachtungen zur allgemeinen Relativitätstheorie.” Sitzungsberichte der Königlich Preussischen Akademie der Wissenschaften (Berlin), pages 142-152. The German original is free to read as a scan on NASA ADS. The paper has no DOI. A detailed guided tour is in the 2017 centennial review on arXiv.