Illustrating the origin of galaxies and other structures with negative gravity, No. 17 in series
FUNDAMENTAL UNSOLVED PROBLEMS IN PHYSICS AND ASTROPHYSICS 2.17 The Origin of Galaxies and Other Structure. There are two commonly-discussed theories of galaxy formation, neither of which works very well. In the gravitational instability picture, small statistical perturbations in the early universe grow through gravity in an expanding fluid. However, the growth rate is too slow to produce galaxies as observed in a reasonable time. This problem can be overcome in principle by assuming the presence of larger-than-random seed perturbations. These could have been a preGalactic generation of stars (population III), black holes, defects from an early phase when a scalar field was important, or quantum fluctuations. In the adiabatic or pancake picture, galaxies form from the anisotropic collapse of large clouds of gas with masses of the order of clusters or superclusters. However, this should have led to the formation of spirals with disks aligned preferentially, for which there is some but not convincing evidence (Wesson 1982). This problem could be overcome in principle by a strong relaxation (randomizing) process early on, but this is poorly understood, and in any case this theory merely pushes the origin of structure backwards in time. Both of the standard theories of galaxy formation clearly contain ad hoc elements, as do theories of the origin of larger-scale structure. -- Paul S. Wesson Department of Physics University of Waterloo Waterloo, Ontario N2L 3G1 Canada prepared for California Institute for Physics and Astrophysics 366 Cambridge Avenue Palo Alto, California 94306 U.S.A. Email: [email protected]
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In the above introduction gravity serves to slow down the initial event in the Big Bang theory, in that gravity is assumed fundamentally attractive. However, when a repulsive gravity is introduced into computer simulations, structure like that in the universe at present is apparent (videos). *
The problem has been to reconcile this evidence with present understanding of gravity as fundamentally attractive, and introduction of the ad hoc "cosmological constant" to account for repulsion; also, to label the observed large-scale repulsion of the universe as due to "dark energy." Despite common usage, all this is hypothetical. It has been shown in earlier articles in this series that a fundamentally repulsive gravity on the large scale can be reconciled with apparently attractive gravity below the scale of galactic superclusters, and with the quantum scale.
* {{ https://www.youtube.com/watch?v=Pci9ScvpQ6I (copy and paste to search box)
Simulation of 4 * 2048 particles of equal mass under the influence of Newtonian-like gravity, which is attractive between particles of the same color and repulsive otherwise.
The simulation involved 100000 evolution steps and took 3 days of CPU time. The position of the particles was recorded every 100 steps.
This video shows the first 10000 steps of the simulation. One can see small areas in which particles of only one color begin to form structures. }}