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4 years ago in Astrophysics By Akshatha Patel
On what basis is the Big Crunch hypothesis proposed as the fate of the universe?
In modern cosmology, accelerated expansion driven by dark energy is the consensus. But reading older textbooks, the Big Crunch was a major contender. What was the reasoning? Was it purely based on the Friedmann equations with a high density parameter (Ω>1), or were there specific observational hints that made it a compelling idea before the late-1990s supernova results?
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By Deeksha S Answered 3 years ago
The hypothesis arose naturally from the simplest solutions to Einstein's equations in a homogeneous universe the Friedmann models. If the average mass-energy density (Ω_m) exceeded the critical density, gravity would win. Before the 1990s, estimates of Ω_m from galaxies and clusters suggested it might be close to, or even exceed, the critical value. Furthermore, the philosophical appeal of a cyclic universe held sway. The clinching evidence against it came only with precise measurements of the cosmic microwave background and, decisively, the 1998 supernova observations showing accelerated expansion. This required introducing a dominant dark energy component (Ω_Λ), which makes a simple gravitational crunch exceedingly unlikely.
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