Einstein–de Sitter universe

• 1. The 1932 Collaboration

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  Albert Einstein and Willem de Sitter met in 1932 to discuss the nature of space. They had just learned that Edwin Hubble found a linear relation between galaxy redshifts and their distance. This discovery forced Einstein to set his cosmological constant to zero within the Friedmann equations. The result was a model known as the Friedmann, Einstein universe. Later that same year, the two men proposed an even simpler cosmic model. They assumed both spatial curvature and the cosmological constant vanished completely. Modern physics describes this construction as a flat matter-only Friedmann, Lemaître, Robertson, Walker metric. It represented a bold step toward understanding an expanding cosmos without extra parameters.

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• 2. Density And Expansion Rates

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  Einstein and de Sitter derived a specific mathematical relation for average density. Their formula linked the expansion rate directly to the amount of matter present. The equation stated that H0 squared equals k times rho divided by three. Here H0 represents the Hubble constant while rho denotes average matter density. K stands for the Einstein gravitational constant. Under these rules, the size of the universe evolves with time according to a simple power law. This evolution makes the current age exactly two-thirds of the Hubble time. The model described a universe of critical matter density poised at the limit of eventual contraction. Einstein later clarified he saw this only as one possibility among many for the expanding universe.

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• 3. Standard Model For Decades

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  The Einstein, de Sitter universe became the standard model for many years after its proposal. Its popularity stemmed from extreme simplicity compared to other competing theories. Scientists lacked empirical evidence for either spatial curvature or a cosmological constant during that era. The absence of contradictory data allowed the model to dominate cosmological thought. It served as a theoretical case where the universe sat precisely on the edge between eternal expansion and future collapse. Researchers used it as a baseline for understanding cosmic history without complex variables. This dominance persisted until new observations began to challenge its core assumptions about reality.

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• 4. Inflation And Zero Curvature

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  Cosmic inflation theory emerged in the 1980s to explain early universe conditions. This theory predicted that the curvature of space should be very close to zero. Such a prediction naturally revived interest in models like the Einstein, de Sitter universe. A case with zero cosmological constant implies the specific structure proposed by Einstein and de Sitter. During this period, scientists developed the theory of cold dark matter. Initial estimates placed the cosmic matter budget at roughly 95 percent cold dark matter and 5 percent baryons. These developments aligned well with the flat geometry required by inflationary scenarios. The model gained renewed attention as a plausible description of the cosmos.

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• 5. Accelerating Expansion Discovery

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  Observations from the 1990s created increasingly serious problems for the standard model. Galaxy clustering studies and measurements of the Hubble constant contradicted earlier predictions. The situation changed dramatically following the discovery of accelerating universe expansion in 1998. Subsequent observations of the cosmic microwave background occurred between 2000 and 2003. Redshift surveys provided further evidence against the original framework. It is now generally accepted that dark energy makes up around 70 percent of present energy density. Cold dark matter contributes approximately 25 percent according to modern Lambda-CDM models. The simple matter-only version could no longer describe reality accurately.

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• 6. High Redshift Approximation

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  The Einstein, de Sitter model remains useful for describing the distant past. It serves as a good approximation during redshifts between 300 and 2. This period occurs well after the radiation-dominated era but before dark energy became important. Scientists use this range to study early structure formation without complex corrections. The simplicity of the model allows researchers to isolate specific physical processes. While it fails at low redshifts, its utility persists in high-redshift regimes. Modern cosmology retains the model as a tool for understanding the early universe's evolution.

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