Big Crunch

Big Crunch
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Name	Big Crunch
Caption	Artistic depiction of a collapsing universe
Status	hypothetical
Field	Cosmology

Big Crunch The Big Crunch is a hypothetical cosmological end-state in which an expanding universe reverses and collapses into a high-density state. Proposed in classical cosmological discussions by proponents of closed-universe models such as Albert Einstein and Georges Lemaître, it contrasts with perpetual-expansion scenarios advanced in the contexts of work by Edwin Hubble, Alan Guth, and Stephen Hawking. The concept has influenced debates among researchers at institutions like Princeton University, Cambridge University, and California Institute of Technology.

Overview

The proposal envisions a cosmic contraction that would terminate the epoch initiated by the Big Bang and potentially culminate in a singularity comparable to the initial high-density state associated with models studied by Roger Penrose, Kip Thorne, and John Wheeler. Early proponents used solutions to the Friedmann equations derived from Albert Einstein's General relativity and considered boundary conditions discussed at conferences such as the Solvay Conference. The idea appears alongside competing end-state proposals from researchers at Harvard University and Massachusetts Institute of Technology who explored heat-death and vacuum-decay alternatives.

Theoretical Background

Classical derivations employ the Friedmann–Lemaître–Robertson–Walker metric and the Friedmann equations formulated by Alexander Friedmann and refined by Georges Lemaître to relate scale factor evolution to energy content described in terms of components like matter (baryonic and dark), radiation, and cosmological-constant-like terms associated with Albert Einstein's lambda. Early analytical studies referenced work by George Gamow and Hermann Bondi, while later quantum cosmology treatments invoked techniques advanced by Stephen Hawking and James Hartle. Theoretical dependence on parameters measured by Arno Penzias and Robert Wilson in cosmic microwave background studies, and density estimates influenced by surveys from Sloan Digital Sky Survey teams, grounds the condition for collapse in the critical density formulation linked to Fritz Zwicky's dark-matter inferences.

Dynamics and Mathematical Models

Mathematical models of a contracting phase use scale factor a(t) solutions to the Friedmann equations with positive curvature (K > 0) historically associated with closed models studied by Carl Friedrich Gauss-era geometry and modernized in texts by George F. R. Ellis. Dynamical behavior includes recollapse times computed in frameworks influenced by Andrei Linde's inflationary scenarios, perturbation evolution analyzed with formalisms from Vladimir Belinskii, Isaak Khalatnikov, and Evgeny Lifshitz, and singularity theorems by Stephen Hawking and Roger Penrose that predict geodesic incompleteness under energy-condition assumptions. Numerical relativity simulations carried out on supercomputers at centers like Los Alamos National Laboratory and CERN incorporate equations of state derived from particle-physics models developed at Fermi National Accelerator Laboratory and Brookhaven National Laboratory.

Observational Constraints and Evidence

Empirical constraints derive from redshift surveys pioneered by Edwin Hubble and modern missions including Hubble Space Telescope, Planck, and WMAP that measure expansion history, microwave-background anisotropies, and parameters such as the Hubble constant debated between teams from Carnegie Institution and SH0ES Project. Observations of accelerated expansion attributed to dark energy were reported by groups at Lawrence Berkeley National Laboratory and the Supernova Cosmology Project and the High-Z Supernova Search Team, invoking a cosmological constant consistent with Einstein's lambda and reducing the likelihood of recollapse. Large-scale structure measurements from Two-degree Field Galaxy Redshift Survey and Sloan Digital Sky Survey provide matter-density estimates, while gravitational-lensing studies by teams at European Southern Observatory and Keck Observatory probe dark-matter distributions relevant to collapse criteria.

Implications for Cosmology and Physics

A confirmed collapse would have profound implications for theories developed at Institute for Advanced Study and explored by theorists like Edward Witten and Juan Maldacena, affecting ideas about entropy evolution discussed by Ludwig Boltzmann's heirs, time's arrow debated by Arthur Eddington, and the applicability of quantum gravity approaches such as loop quantum gravity advanced by Carlo Rovelli and string theory advanced at CERN and Perimeter Institute. A recollapse could motivate cyclic proposals associated with researchers including Paul Steinhardt and Neil Turok, and would influence scenarios of baryogenesis and reheating studied in particle-physics programs at CERN and SLAC National Accelerator Laboratory.

Alternatives and Related Scenarios

Alternative end-state scenarios considered by communities at Princeton University and University of Maryland include eternal expansion (heat death) articulated by proponents following Friedrich Engels-era thermodynamic tradition, vacuum metastability and false-vacuum decay analyzed by Sidney Coleman and Frank Wilczek, Big Rip models linked to phantom energy investigated by groups at University of California, Berkeley and University of Chicago, and cyclic or ekpyrotic models developed by Paul Steinhardt and Neil Turok. Observational programs led by collaborations at European Space Agency and National Aeronautics and Space Administration continue to discriminate among these via precision cosmology missions such as Euclid and James Webb Space Telescope.

Category:Cosmology