Ultimate fate of the universe Chronology of the universe

there several competing scenarios possible long-term evolution of universe. of them going happen depends on precise values of physical constants such cosmological constant, possibility of proton decay, , natural laws beyond standard model.

heat death: in case of indefinitely continuing metric expansion of space, energy density in universe decrease until, after estimated time of 10 years, reaches thermodynamic equilibrium , no more structure possible. happen after extremely long time because first, matter collapse black holes, evaporate extremely via hawking radiation. universe in scenario cease able support life earlier this, after 10 years or so, when star formation ceases. in grand unified theories, proton decay after @ least 10 years convert remaining interstellar gas , stellar remnants leptons (such positrons , electrons) , photons. positrons , electrons recombine photons. in case, universe has reached high-entropy state consisting of bath of particles , low-energy radiation. not known whether achieves thermodynamic equilibrium. hypothesis of universal heat death stems 1850s ideas of william thomson (lord kelvin) extrapolated theory of heat views of mechanical energy loss in nature, embodied in first 2 laws of thermodynamics, universal operation.
big rip: sufficiently large values dark energy content of universe, expansion rate of universe continue increase without limit. gravitationally bound systems, such clusters of galaxies, galaxies, , solar system torn apart. expansion rapid overcome electromagnetic forces holding molecules , atoms together. atomic nuclei torn apart , universe know end in unusual kind of gravitational singularity.
big crunch: in opposite of big rip scenario, metric expansion of space @ point reversed , universe contract towards hot, dense state. required element of oscillatory universe scenarios, such cyclic model, although big crunch not imply oscillatory universe. current observations suggest model of universe unlikely correct, , expansion continue or accelerate.
vacuum instability: cosmology traditionally has assumed stable or @ least metastable universe, possibility of false vacuum in quantum field theory implies universe @ point in spacetime might spontaneously collapse lower energy state (see bubble nucleation), more stable or true vacuum , expand outward point speed of light.




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