Simulating the universe using Einstein’s theory of gravity may solve cosmic puzzles

Discussion in 'Astronomy, Exobiology, & Cosmology' started by paddoboy, Nov 27, 2017.

  1. paddoboy Valued Senior Member

    If the universe were a soup, it would be more of a chunky minestrone than a silky-smooth tomato bisque.

    Sprinkled with matter that clumps together due to the insatiable pull of gravity, the universe is a network of dense galaxy clusters and filaments — the hearty beans and vegetables of the cosmic stew. Meanwhile, relatively desolate pockets of the cosmos, known as voids, make up a thin, watery broth in between.

    Until recently, simulations of the cosmos’s history haven’t given the lumps their due. The physics of those lumps is described by general relativity, Albert Einstein’s theory of gravity. But that theory’s equations are devilishly complicated to solve. To simulate how the universe’s clumps grow and change, scientists have fallen back on approximations, such as the simpler but less accurate theory of gravity devised by Isaac Newton.

    Relying on such approximations, some physicists suggest, could be mucking with measurements, resulting in a not-quite-right inventory of the cosmos’s contents. A rogue band of physicists suggests that a proper accounting of the universe’s clumps could explain one of the deepest mysteries in physics: Why is the universe expanding at an increasingly rapid rate?

    The accepted explanation for that accelerating expansion is an invisible pressure called dark energy. In the standard theory of the universe, dark energy makes up about 70 percent of the universe’s “stuff” — its matter and energy. Yet scientists still aren’t sure what dark energy is, and finding its source is one of the most vexing problems of cosmology.

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  3. paddoboy Valued Senior Member


    General relativity and cosmic structure formation:


    Numerical simulations are a versatile tool for providing insight into the complicated process of structure formation in cosmology1. This process is mainly governed by gravity, which is the dominant force on large scales. At present, a century after the formulation of general relativity2, numerical codes for structure formation still employ Newton’s law of gravitation. This approximation relies on the two assumptions that gravitational fields are weak and that they originate from non-relativistic matter. Whereas the former seems well justified on cosmological scales, the latter imposes restrictions on the nature of the ‘dark’ components of the Universe (dark matter and dark energy), which are, however, poorly understood. Here we present the first simulations of cosmic structure formation using equations consistently derived from general relativity. We study in detail the small relativistic effects for a standard lambda cold dark matter cosmology that cannot be obtained within a purely Newtonian framework. Our particle-mesh N-body code computes all six degrees of freedom of the metric and consistently solves the geodesic equation for particles, taking into account the relativistic potentials and the frame-dragging force. This conceptually clean approach is very general and can be applied to various settings where the Newtonian approximation fails or becomes inaccurate, ranging from simulations of models with dynamical dark energy3 or warm/hot dark matter4 to core collapse supernova explosions.
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  5. river

    in einstein's theory gravity is not a force .
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