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  2. Flatness problem - Wikipedia

    en.wikipedia.org/wiki/Flatness_problem

    The flatness problem (also known as the oldness problem) is a cosmological fine-tuning problem within the Big Bang model of the universe. Such problems arise from the observation that some of the initial conditions of the universe appear to be fine-tuned to very 'special' values, and that small deviations from these values would have extreme ...

  3. Horizon problem - Wikipedia

    en.wikipedia.org/wiki/Horizon_problem

    The horizon problem (also known as the homogeneity problem) is a cosmological fine-tuning problem within the Big Bang model of the universe. It arises due to the difficulty in explaining the observed homogeneity of causally disconnected regions of space in the absence of a mechanism that sets the same initial conditions everywhere.

  4. Bentley's paradox - Wikipedia

    en.wikipedia.org/wiki/Bentley's_paradox

    Bentley's paradox (named after Richard Bentley) is a cosmological paradox pointing to a problem occurring when Newton's theory of gravitation is applied to cosmology. Namely, if all the stars are drawn to each other by gravitation, they should collapse into a single point.

  5. Big Bang - Wikipedia

    en.wikipedia.org/wiki/Big_Bang

    The Big Bang is a physical theory that describes how the universe expanded from an initial state of high density and temperature. [1] The notion of an expanding universe was first scientifically originated by physicist Alexander Friedmann in 1922 with the mathematical derivation of the Friedmann equations.

  6. Penrose–Hawking singularity theorems - Wikipedia

    en.wikipedia.org/wiki/Penrose–Hawking...

    The Hawking singularity theorem is based on the Penrose theorem and it is interpreted as a gravitational singularity in the Big Bang situation. Penrose shared half of the Nobel Prize in Physics in 2020 "for the discovery that black hole formation is a robust prediction of the general theory of relativity". [1]

  7. Cosmological perturbation theory - Wikipedia

    en.wikipedia.org/wiki/Cosmological_perturbation...

    Both cases apply only to situations where the universe is predominantly homogeneous, such as during cosmic inflation and large parts of the Big Bang. The universe is believed to still be homogeneous enough that the theory is a good approximation on the largest scales, but on smaller scales more involved techniques, such as N-body simulations ...

  8. Equation of state (cosmology) - Wikipedia

    en.wikipedia.org/wiki/Equation_of_state_(cosmology)

    These problems are solved by cosmic inflation which has . Measuring the equation of state of dark energy is one of the largest efforts of observational cosmology . By accurately measuring w {\displaystyle w} , it is hoped that the cosmological constant could be distinguished from quintessence which has w ≠ − 1 {\displaystyle w\neq -1} .

  9. Brief Answers to the Big Questions - Wikipedia

    en.wikipedia.org/wiki/Brief_Answers_to_the_Big...

    Brief Answers to the Big Questions is a popular science book written by physicist Stephen Hawking, and published by Hodder & Stoughton (hardcover) and Bantam Books (paperback) on 16 October 2018. The book examines some of the universe 's greatest mysteries, and promotes the view that science is very important in helping to solve problems on ...